Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept to work at all.
I'm aware that a single package containing two op amps could probably do a much better job.
Open the file in notepad++ (which you do use don't you?) and under encoding select Convert to ANSI. Save the file.
That will fix issues with u symbols.
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TEXT -424 800 Left 2 !.tran 100
TEXT 632 -200 Left 3 ;Edward Rawde's weird sinewave oscillator. October 2024
On 16/10/2024 9:55 pm, Edward Rawde wrote:
Is the reason why this doesn't produce a better looking sinewave
because the amplifier slew rate is faster going down than it is
going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept
to work at all.
I'm aware that a single package containing two op amps could probably
do a much better job.
Open the file in notepad++ (which you do use don't you?) and under
encoding select Convert to ANSI. Save the file.
That will fix issues with u symbols.
Version 4
SHEET 1 2772 1280
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WIRE 640 -144 352 -144
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SYMATTR InstName R27
SYMATTR Value 22k
SYMBOL res 2048 -112 R0
SYMATTR InstName R28
SYMATTR Value 22k
SYMBOL polcap 2160 64 R0
SYMATTR InstName C18
SYMATTR Value 220ľ
SYMBOL res 1616 576 R0
SYMATTR InstName R29
SYMATTR Value 22k
SYMBOL res 1872 576 R0
SYMATTR InstName R30
SYMATTR Value 22k
SYMBOL cap 2176 544 R0
SYMATTR InstName C19
SYMATTR Value 1ľ
SYMBOL res 1440 -80 R0
SYMATTR InstName R31
SYMATTR Value 220k
SYMBOL cap 1376 240 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C21
SYMATTR Value 10ľ
TEXT -424 800 Left 2 !.tran 100
TEXT 632 -200 Left 3 ;Edward Rawde's weird sinewave oscillator.
October 2024
I assume this is an intellectual challenge and not a real project? I
suspect the jfet gate-channel is forward biased so the amplitude control section is my first place to look?
piglet
On 17/10/2024 12:32 pm, piglet wrote:...
On 16/10/2024 9:55 pm, Edward Rawde wrote:
Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
I assume this is an intellectual challenge and not a real project?
I suspect the jfet gate-channel is forward biased so the amplitude control section is my first place to look?
piglet
Hmm, that forward biased gate only happens during startup. Some other ideas:
The amp input bias R6 loads the Wien network too much - try lowering the Wien network impedance?
Replace R7 with constant current sink if you think slew rate is the issue?
Rectifier load is too heavy on the follower - increase R22?
Q5 base reference is not stiff enough - lower R26-27-28?
Q4 base current flows through rectifier - reference D1 instead to +12 rail?
Maybe later I will find time to explore...
piglet
Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept to work at all.
I'm aware that a single package containing two op amps could probably do a much better job.
On 17/10/2024 7:55 am, Edward Rawde wrote:
Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept to work at all.
I'm aware that a single package containing two op amps could probably do a much better job.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
has a pretty good example of a sine wave oscillator. I've speculated that a four quadrant analogue multiplier could offer a better
gain control mechanism.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD734.pdf
though it is hideously expensive. The simulation I worked up used two with the second one controlling a quadrature input to give
you smooth control of the frequency of oscillation in addition to its amplitude.
I thought about building one, but there's no obvious application.
--
Bill Sloman, Sydney
Is the reason why this doesn't produce a better looking sinewave because
the amplifier slew rate is faster going down than it is going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept to
work at all.
I'm aware that a single package containing two op amps could probably do a much better job.
Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept to work at all.
I'm aware that a single package containing two op amps could probably do a much better job.
Open the file in notepad++ (which you do use don't you?) and under encoding select Convert to ANSI. Save the file.
That will fix issues with u symbols.
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the amplifier in use is not ideal for this.
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the
amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due to
too much gain.
--
piglet
Edward Rawde <invalid@invalid.invalid> wrote:
Is the reason why this doesn't produce a better looking sinewave because
the amplifier slew rate is faster going down than it is going up or some
other reason?
Ignore the wild decoupling, it took me long enough to get the concept to
work at all.
I'm aware that a single package containing two op amps could probably do a >> much better job.
if noise is more important than waveform, I found amplitude control by >clipping gave the lowest noise. The oscillators in this...
<http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
...are amplitude stabilised by clipping.
"piglet" <erichpwagner@hotmail.com> wrote in message news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the
amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the amplifier >> by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
"piglet" <erichpwagner@hotmail.com> wrote in message news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the
amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due
to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in response to Bill to produce a sine wave no matter what I do with the
control loop gain.
It either grows to clipping or dies.
On Fri, 18 Oct 2024 09:48:17 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Edward Rawde <invalid@invalid.invalid> wrote:
Is the reason why this doesn't produce a better looking sinewave
because the amplifier slew rate is faster going down than it is going
up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept
to work at all.
I'm aware that a single package containing two op amps could probably
do a much better job.
if noise is more important than waveform, I found amplitude control by >>clipping gave the lowest noise. The oscillators in this...
<http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
...are amplitude stabilised by clipping.
If the gain of an oscillator loop is close to 1.00, say 0.98 to 1.02,
one can add in a small tweak, a crude multiplier or even a clipper, to
make up the difference.
Of course, with many-bit DACs being cheap nowadays, it's easier to do a
DDS sine wave generator, and get super-precise frequency and amplitude.
A 70 cent uP can do that, and even use PWM to eliminate the DAC.
All sorts of elegant analog circuits are blown away by cheap digital
junk. Sigh.
On Fri, 18 Oct 2024 08:36:15 -0700, john larkin wrote:
On Fri, 18 Oct 2024 09:48:17 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Edward Rawde <invalid@invalid.invalid> wrote:
Is the reason why this doesn't produce a better looking sinewave
because the amplifier slew rate is faster going down than it is going
up or some other reason?
Ignore the wild decoupling, it took me long enough to get the concept
to work at all.
I'm aware that a single package containing two op amps could probably
do a much better job.
if noise is more important than waveform, I found amplitude control by >>>clipping gave the lowest noise. The oscillators in this...
<http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
...are amplitude stabilised by clipping.
If the gain of an oscillator loop is close to 1.00, say 0.98 to 1.02,
one can add in a small tweak, a crude multiplier or even a clipper, to
make up the difference.
Of course, with many-bit DACs being cheap nowadays, it's easier to do a
DDS sine wave generator, and get super-precise frequency and amplitude.
A 70 cent uP can do that, and even use PWM to eliminate the DAC.
All sorts of elegant analog circuits are blown away by cheap digital
junk. Sigh.
Put the output you get from that through a spectrum analyzer and it won't >look quite so super-duper.
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the
amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due
to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do with the
control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb in the f/b path.
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the
rise time still seems to be slower than the fall time. It may be
that the amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due
to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do with the
control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb in
the f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your
equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have them
now.
I'm trying to make a low cost oscillator which produces the cleanest 1K
Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation is
hard to say.
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the
rise time still seems to be slower than the fall time. It may be
that the amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due >>>>> to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do with the
control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb in
the f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your
equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have them
now.
I'm trying to make a low cost oscillator which produces the cleanest 1K
Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation is
hard to say.
A real-world oscillator needs some kind of stimulus to start up.
This could be a voltage 'shock' at switch-on or just inherent noise in the circuitry. JL informs me LTSpice doesn't have such a stimulus unless you provide it yourself. I suspect that's the main reason you will find oscillators difficult to get started in simulation.
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the >>>>>>> rise time still seems to be slower than the fall time. It may be >>>>>>> that the amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs. >>>>>>
Elsewhere I think your amplitude control problems could be simply
due to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted
in response to Bill to produce a sine wave no matter what I do with
the control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb
in the f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your
equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have them
now.
I'm trying to make a low cost oscillator which produces the cleanest
1K Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation
is hard to say.
A real-world oscillator needs some kind of stimulus to start up.
I don't seem to be having startup problems, startup is fine but then it
goes up to clipping or dies to nothing.
I don't find this surprising and I'm wondering whether a real circuit
would do the same.
This could be a voltage 'shock' at switch-on or just inherent noise in
the circuitry. JL informs me LTSpice doesn't have such a stimulus
unless you provide it yourself. I suspect that's the main reason you
will find oscillators difficult to get started in simulation.
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the >>>>>>> amplifier by uncoupling the Wien network and injecting test inputs. >>>>>>>
The circuit below produces a reasonable looking sinewave but the >>>>>>>> rise time still seems to be slower than the fall time. It may be >>>>>>>> that the amplifier in use is not ideal for this.
Elsewhere I think your amplitude control problems could be simply >>>>>>> due to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted >>>>>> in response to Bill to produce a sine wave no matter what I do with >>>>>> the control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb
in the f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your
equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have them
now.
I'm trying to make a low cost oscillator which produces the cleanest
1K Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation
is hard to say.
A real-world oscillator needs some kind of stimulus to start up.
I don't seem to be having startup problems, startup is fine but then it
goes up to clipping or dies to nothing.
I don't find this surprising and I'm wondering whether a real circuit
would do the same.
Yes, it's just what they do without some kind of dynamic gain control. The overall loop gain needs to be 1.
few seconds, but when something warms up, you're either damped or through
the rails.
This could be a voltage 'shock' at switch-on or just inherent noise in
the circuitry. JL informs me LTSpice doesn't have such a stimulus
unless you provide it yourself. I suspect that's the main reason you
will find oscillators difficult to get started in simulation.
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the >>>>>>>> amplifier by uncoupling the Wien network and injecting test
The circuit below produces a reasonable looking sinewave but the >>>>>>>>> rise time still seems to be slower than the fall time. It may be >>>>>>>>> that the amplifier in use is not ideal for this.
inputs.
Elsewhere I think your amplitude control problems could be simply >>>>>>>> due to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted >>>>>>> in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb >>>>>> in the f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your
equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have
them now.
I'm trying to make a low cost oscillator which produces the cleanest >>>>> 1K Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation >>>>> is hard to say.
A real-world oscillator needs some kind of stimulus to start up.
I don't seem to be having startup problems, startup is fine but then
it goes up to clipping or dies to nothing.
I don't find this surprising and I'm wondering whether a real circuit
would do the same.
Yes, it's just what they do without some kind of dynamic gain control.
The overall loop gain needs to be 1.
Yes. That's why I have a control loop which in theory should do that.
Any calculator will show that repeated multiplication of a number
slightly greater than 1 increases without limit.
In practice an amplifier will limit at or near the supply rail.
And if the number it slightly less than 1 it will reduce to 0.
A Wien bridge has an overall voltage gain of 1/3 so the circuit needs to
be held at a gain of 3.
As long as it starts up then the gain control loop should be able to
hold the gain at whatever is needed for a specific output level.
I'm still working on that.
Fixed resistors might give you that for a
few seconds, but when something warms up, you're either damped or
through the rails.
This could be a voltage 'shock' at switch-on or just inherent noise
in the circuitry. JL informs me LTSpice doesn't have such a stimulus
unless you provide it yourself. I suspect that's the main reason you
will find oscillators difficult to get started in simulation.
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able though. Let us know how you get on.
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...the-amplitude-of-a-wien-bridge-oscillator
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Ok. This simple circuit is based on the circuit you can find here.
Without doubt, it's the trickiest aspect of the design. Definitely
do-able though. Let us know how you get on.
https://electronics.stackexchange.com/questions/697687/how-to-control-
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4 SHEET 1 2196 916 WIRE -160 -160 -256 -160 WIRE -16 -160 -160
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >>> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >>> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Jeroen Belleman
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >>> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Jeroen Belleman
On Sat, 19 Oct 2024 00:19:35 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >>>> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Jeroen Belleman
But tricky to Spice.
And a thermal device of course makes the amplitude temperature
sensitive, especially when the heating goes directly as the square of
the sine amplitude.
It would be better to have the native loop gain very close to 1.00 and
give the AGC mechanism a small influence, like +- a few per cent
maybe.
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able >>>> though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain.
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain.
That's why I added R3 in this circuit.
It does not seem to be safe to reduce R3 below 1k.
R4 helps a lot too for reasons I don't fully understand.
It may be moving the FET to a better part of its operating characteristics.
A single rail version also works with another op amp producing 6V for R4 and two 20k resistors for R2 between 12V and 0V.
As expected, this produces twice the output voltage and I've not found a way to reduce it.
This will probably be my final offering for a 1KHz sinewave oscillator unless anyone can suggest improvements without using light
dependent resistors.
From the LTSpice plot, I can't discern any impurity in the signal this circuit produces.
It would be interesting to see what a real circuit and a spectrum analyzer says but I probably won't be building it.
I haven't used an LDR since playing with an ORP12 around age 10.
I seem to remember that they can degrade over time but maybe that only happens in sunlight.
There are plenty of examples online, but some of them don't seem to >>>>> simulate.
Whether that's because they do work in reality but not in simulation >>>>> is hard to say.
A real-world oscillator needs some kind of stimulus to start up.
I don't seem to be having startup problems, startup is fine but then
it goes up to clipping or dies to nothing.
I don't find this surprising and I'm wondering whether a real circuit
would do the same.
Yes, it's just what they do without some kind of dynamic gain control.
The overall loop gain needs to be 1.
Yes. That's why I have a control loop which in theory should do that.
Any calculator will show that repeated multiplication of a number
slightly greater than 1 increases without limit.
In practice an amplifier will limit at or near the supply rail.
And if the number it slightly less than 1 it will reduce to 0.
A Wien bridge has an overall voltage gain of 1/3 so the circuit needs to
be held at a gain of 3.
As long as it starts up then the gain control loop should be able to
hold the gain at whatever is needed for a specific output level.
I'm still working on that.
Without doubt, it's the trickiest aspect of the design. Definitely do-able though. Let us know how you get on.
Fixed resistors might give you that for a
few seconds, but when something warms up, you're either damped or
through the rails.
This could be a voltage 'shock' at switch-on or just inherent noise
in the circuitry. JL informs me LTSpice doesn't have such a stimulus >>>> unless you provide it yourself. I suspect that's the main reason you >>>> will find oscillators difficult to get started in simulation.
A Wien bridge has an overall voltage gain of 1/3 ...
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here.
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain.
That's why I added R3 in this circuit.
It does not seem to be safe to reduce R3 below 1k.
R4 helps a lot too for reasons I don't fully understand.
It may be moving the FET to a better part of its operating characteristics.
A single rail version also works with another op amp producing 6V for R4 and two 20k resistors for R2 between 12V and 0V.
As expected, this produces twice the output voltage and I've not found a way to reduce it.
This will probably be my final offering for a 1KHz sinewave oscillator unless anyone can suggest improvements without using light
dependent resistors.
From the LTSpice plot, I can't discern any impurity in the signal this circuit produces.
It would be interesting to see what a real circuit and a spectrum analyzer says but I probably won't be building it.
I haven't used an LDR since playing with an ORP12 around age 10.
I seem to remember that they can degrade over time but maybe that only happens in sunlight.
Edward Rawde <invalid@invalid.invalid> wrote:
[...]
A Wien bridge has an overall voltage gain of 1/3 ...
If all the components are perfect and correctly matched.
In a practical oscillator where the resistors are switched or the
capacitors ganged, there will be slight mis-matches due to tolerances
and the loss will be greater (and unpredictable).
On Fri, 18 Oct 2024 09:48:17 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
Edward Rawde <invalid@invalid.invalid> wrote:
Is the reason why this doesn't produce a better looking sinewave because >>> the amplifier slew rate is faster going down than it is going up or some >>> other reason?
Ignore the wild decoupling, it took me long enough to get the concept to >>> work at all.
I'm aware that a single package containing two op amps could probably do a >>> much better job.
if noise is more important than waveform, I found amplitude control by
clipping gave the lowest noise. The oscillators in this...
<http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
...are amplitude stabilised by clipping.
If the gain of an oscillator loop is close to 1.00, say 0.98 to 1.02,
one can add in a small tweak, a crude multiplier or even a clipper, to
make up the difference.
Of course, with many-bit DACs being cheap nowadays, it's easier to do
a DDS sine wave generator, and get super-precise frequency and
amplitude. A 70 cent uP can do that, and even use PWM to eliminate the
DAC.
All sorts of elegant analog circuits are blown away by cheap digital
junk. Sigh.
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here. >>>>>>
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the
top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill
Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain.
That's why I added R3 in this circuit.
It does not seem to be safe to reduce R3 below 1k.
R4 helps a lot too for reasons I don't fully understand.
It may be moving the FET to a better part of its operating characteristics. >>
A single rail version also works with another op amp producing 6V for R4 and two 20k resistors for R2 between 12V and 0V.
As expected, this produces twice the output voltage and I've not found a way to reduce it.
This will probably be my final offering for a 1KHz sinewave oscillator unless anyone can suggest improvements without using light
dependent resistors.
From the LTSpice plot, I can't discern any impurity in the signal this circuit produces.
It would be interesting to see what a real circuit and a spectrum analyzer says but I probably won't be building it.
I haven't used an LDR since playing with an ORP12 around age 10.
I seem to remember that they can degrade over time but maybe that only happens in sunlight.
I got your earlier circuit to work a lot better simply by increasing R7 to 5.6k. If you use the View option on the trace viewing
panel to pull out an FFT of the output (I use Blackmann-Harris windowing) from 10sec to 20 sec, you can see that second harmonic
distortion is about 20dB below the primary - not great but better than it was.
And the waveform looks like a sine wave.
The less influence the FET has on the gain of the circuit, the better the sine wave.
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the
amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the amplifier >>> by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due to >>> too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize amplitude.
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
Could that just be second harmonic distortion? You could test the
The circuit below produces a reasonable looking sinewave but the rise >>>>> time still seems to be slower than the fall time. It may be that the >>>>> amplifier in use is not ideal for this.
amplifier by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due
to too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do with the
control loop gain.
It either grows to clipping or dies.
That's the main purpose behind having a thermistor or filament bulb in the >> f/b path.
Sure, but why use thermistors or filaments if you don't have to?
Filaments don't last forever, particularly not if you drop your equipment, and filaments make me think of something like a 5U4.
I forget when I last saw a filament. House lamps don't even have them now.
I'm trying to make a low cost oscillator which produces the cleanest 1K Hz sinewave I can get, using only resistors, capacitors and
semiconductors.
There are plenty of examples online, but some of them don't seem to simulate. Whether that's because they do work in reality but not in simulation is hard to say.
On 18/10/2024 4:46 pm, john larkin wrote:
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>> time still seems to be slower than the fall time. It may be that the >>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due to >>>> too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active
stage - it has no voltage gain so some people say it cannot work - they
are wrong of course.
On 18/10/2024 4:46 pm, john larkin wrote:
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>> time still seems to be slower than the fall time. It may be that the >>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the
amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply
due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active
stage - it has no voltage gain so some people say it cannot work - they
are wrong of course.
piglet
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>>> time still seems to be slower than the fall time. It may be that the >>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the
amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply
due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in
response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active
stage - it has no voltage gain so some people say it cannot work - they
are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the
power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an inverting amplifier via a 3-stage RC network.
kw
On 18/10/2024 4:46 pm, john larkin wrote:
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>> time still seems to be slower than the fall time. It may be that the >>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply due to >>>> too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active
stage - it has no voltage gain so some people say it cannot work - they
are wrong of course.
Amplitude grows to power rail limits and non-linearities creep in.
Version 4
SHEET 1 1132 680
WIRE 640 -272 400 -272
WIRE 784 -272 640 -272
WIRE 928 -272 784 -272
WIRE 1072 -272 928 -272
WIRE 640 -224 640 -272
WIRE 400 -144 400 -272
WIRE 784 -144 784 -272
WIRE 640 -96 640 -144
WIRE 720 -96 640 -96
WIRE 640 -64 640 -96
WIRE 928 -48 928 -272
WIRE 1072 -48 1072 -272
WIRE 272 -16 64 -16
WIRE 400 -16 400 -64
WIRE 400 -16 336 -16
WIRE 432 -16 400 -16
WIRE 576 -16 432 -16
WIRE 784 0 784 -48
WIRE 864 0 784 0
WIRE 432 32 432 -16
WIRE 784 48 784 0
WIRE 64 96 64 -16
WIRE 160 96 64 96
WIRE 304 96 240 96
WIRE 1072 112 1072 32
WIRE 64 128 64 96
WIRE 432 160 432 112
WIRE 784 176 784 128
WIRE 64 224 64 192
WIRE 160 224 64 224
WIRE 304 224 304 96
WIRE 304 224 240 224
WIRE 640 224 640 32
WIRE 880 224 640 224
WIRE 928 224 928 48
WIRE 928 224 880 224
WIRE 64 256 64 224
WIRE 928 304 928 224
WIRE 64 352 64 320
WIRE 160 352 64 352
WIRE 304 352 304 224
WIRE 304 352 240 352
WIRE 640 352 640 224
WIRE 640 352 304 352
WIRE 64 384 64 352
WIRE 928 464 928 384
WIRE 64 480 64 448
FLAG 432 160 0
FLAG 928 464 0
FLAG 64 480 0
FLAG 1072 112 0
FLAG 784 176 0
FLAG 880 224 OUT
SYMBOL res 256 368 M270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R1
SYMATTR Value 470
SYMBOL res 256 240 M270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R2
SYMATTR Value 4700
SYMBOL res 256 112 M270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R3
SYMATTR Value 47k
SYMBOL cap 80 384 M0
SYMATTR InstName C1
SYMATTR Value 100n
SYMBOL cap 80 128 M0
SYMATTR InstName C3
SYMATTR Value 1n
SYMBOL cap 80 256 M0
SYMATTR InstName C2
SYMATTR Value 10n
SYMBOL npn 720 -144 R0
SYMATTR InstName Q2
SYMATTR Value 2N2222
SYMBOL voltage 1072 -64 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 20
SYMBOL res 416 16 R0
SYMATTR InstName R5
SYMATTR Value 470k
SYMBOL pnp 576 32 M180
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL npn 864 -48 R0
SYMATTR InstName Q3
SYMATTR Value 2N2222
SYMBOL res 624 -240 R0
SYMATTR InstName R6
SYMATTR Value 220k
SYMBOL res 768 32 R0
SYMATTR InstName R7
SYMATTR Value 4700
SYMBOL res 912 288 R0
SYMATTR InstName R8
SYMATTR Value 1000
SYMBOL res 384 -160 R0
SYMATTR InstName R4
SYMATTR Value 470k
SYMBOL cap 336 -32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 100n
TEXT 728 480 Left 2 !.tran 100m
TEXT 400 432 Left 2 ;EPW SED OCT 2024
TEXT 304 480 Left 2 ;VOLTAGE FOLLOWER RC OSC
piglet
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>>> time still seems to be slower than the fall time. It may be that the >>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the
amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply
due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted
in response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the
active stage - it has no voltage gain so some people say it cannot
work - they are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the
power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an inverting amplifier via a 3-stage RC network.
kw
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>>>> time still seems to be slower than the fall time. It may be that the >>>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the
amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply
due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in >>>>> response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active
stage - it has no voltage gain so some people say it cannot work - they
are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the
power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an
inverting amplifier via a 3-stage RC network.
kw
What do you do with the cold end of C1 in that scenario?
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message
news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote: >>>>>>>>>>>>>>>>>
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here. >>>>>>>
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the >>>>>> top of the wave. In that region the dynamic resistance of the FET
is very large, and therefore the gain of the opamp drops to about
one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so
great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is
really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill
Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain.
That's why I added R3 in this circuit.
It does not seem to be safe to reduce R3 below 1k.
R4 helps a lot too for reasons I don't fully understand.
It may be moving the FET to a better part of its operating characteristics. >>>
A single rail version also works with another op amp producing 6V for R4 and two 20k resistors for R2 between 12V and 0V.
As expected, this produces twice the output voltage and I've not found a way to reduce it.
This will probably be my final offering for a 1KHz sinewave oscillator unless anyone can suggest improvements without using light
dependent resistors.
From the LTSpice plot, I can't discern any impurity in the signal this circuit produces.
It would be interesting to see what a real circuit and a spectrum analyzer says but I probably won't be building it.
I haven't used an LDR since playing with an ORP12 around age 10.
I seem to remember that they can degrade over time but maybe that only happens in sunlight.
I got your earlier circuit to work a lot better simply by increasing R7 to 5.6k. If you use the View option on the trace viewing
panel to pull out an FFT of the output (I use Blackmann-Harris windowing) from 10sec to 20 sec, you can see that second harmonic
distortion is about 20dB below the primary - not great but better than it was.
And the waveform looks like a sine wave.
The less influence the FET has on the gain of the circuit, the better the sine wave.
If you run this circuit then View, FFT, Use current zoom extent, Ok
It implies that unwanted harmonics are 40dB down.
I'm not sure I believe that but if true then it's not bad for a very low cost circuit.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote: >>>>>>>>>>>>>>>>>>>
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote: >>>>>>>>>>>>>>>>>>>
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...[Snip...]
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:...
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote: >>>>>>>>>>>>>>>>>>
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
Ok. This simple circuit is based on the circuit you can find here. >>>>>>>>
https://electronics.stackexchange.com/questions/697687/how-to-control-the-amplitude-of-a-wien-bridge-oscillator
It produces a something wave.
I wouldn't call it sine but at least it's not clipping.
What's going on here?
Version 4
You're hitting the flat portion of the Id vs. Vds curve around the >>>>>>> top of the wave. In that region the dynamic resistance of the FET >>>>>>> is very large, and therefore the gain of the opamp drops to about >>>>>>> one. As a result, the positive tip of the output gets sort-of
squashed.
There are probably ways to fix this, for example by feeding a
portion of the output signal to the FET gate, but a quick
attempt I made didn't work very well. This is why FETs aren't so >>>>>>> great as gain setting elements.
Using a lightbulb --or more generally a PTC resistor-- for R7 is >>>>>>> really hard to beat.
Ok thanks Jeroen.
It looks like the best approach for the gain control is either a filament or something like that used in the document Bill
Sloman
posted.
https://www.analog.com/media/en/technical-documentation/application-notes/AN132f.pdf
Note that the LDR has a very small influence range on the loop gain. >>>>>
That's why I added R3 in this circuit.
It does not seem to be safe to reduce R3 below 1k.
R4 helps a lot too for reasons I don't fully understand.
It may be moving the FET to a better part of its operating characteristics.
A single rail version also works with another op amp producing 6V for R4 and two 20k resistors for R2 between 12V and 0V.
As expected, this produces twice the output voltage and I've not found a way to reduce it.
This will probably be my final offering for a 1KHz sinewave oscillator unless anyone can suggest improvements without using
light
dependent resistors.
From the LTSpice plot, I can't discern any impurity in the signal this circuit produces.
It would be interesting to see what a real circuit and a spectrum analyzer says but I probably won't be building it.
I haven't used an LDR since playing with an ORP12 around age 10.
I seem to remember that they can degrade over time but maybe that only happens in sunlight.
I got your earlier circuit to work a lot better simply by increasing R7 to 5.6k. If you use the View option on the trace viewing
panel to pull out an FFT of the output (I use Blackmann-Harris windowing) from 10sec to 20 sec, you can see that second harmonic
distortion is about 20dB below the primary - not great but better than it was.
And the waveform looks like a sine wave.
The less influence the FET has on the gain of the circuit, the better the sine wave.
If you run this circuit then View, FFT, Use current zoom extent, Ok
It implies that unwanted harmonics are 40dB down.
I'm not sure I believe that but if true then it's not bad for a very low cost circuit.
<snipped .asc file>
The revised .asc file is a bit of a mess. You've added R11 to get the output frequency close to 1KHz.
What you should have done is to have used 0.1% 10.5k resistors -it's an E96 value and you can buy them off the shelf - at R1 and
R2.
That got me to 1.001kHz.
Since the capacitors at C1 and C2 can at best only be +/-1% tolerance parts - you can't buy anything better off the shelf - this
is quite close enough.
You can use a trimming potentiometer to get closer to the target frequency, but that does have its downsides.
R4 certainly does make the circuit settle faster - how is a bit of a mystery
but you've created a total mess with R5,R7, R8, and R10. It's not clear what you were trying to do.
I found that I could get by without R4 provided that I stuck with sensible resistance values at R7 and R8 - R7 went up to 6.2k and
I put 330R across J1.
On 10/19/24 12:57 PM, piglet wrote:
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>>>>> time still seems to be slower than the fall time. It may be that the >>>>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the >>>>>>> amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply >>>>>>> due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in >>>>>> response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize
amplitude.
Here is an amusing oscillator that has a voltage follower as the active >>>> stage - it has no voltage gain so some people say it cannot work - they >>>> are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the
power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an
inverting amplifier via a 3-stage RC network.
kw
What do you do with the cold end of C1 in that scenario?
That connects to the collector, as it is now and forms the first section
of the RC network. (voltage sources are zero impedance from the point of
view of AC). C4 is a coupling capacitor - its value and the high
impedance of R4,R5 and Q1 mean it has little effect on the phase shift.
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:57 PM, piglet wrote:
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise >>>>>>>>> time still seems to be slower than the fall time. It may be that the >>>>>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the >>>>>>>> amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply >>>>>>>> due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in >>>>>>> response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize >>>>>> amplitude.
Here is an amusing oscillator that has a voltage follower as the active >>>>> stage - it has no voltage gain so some people say it cannot work - they >>>>> are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the
power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an >>>> inverting amplifier via a 3-stage RC network.
kw
What do you do with the cold end of C1 in that scenario?
That connects to the collector, as it is now and forms the first section
of the RC network. (voltage sources are zero impedance from the point of
view of AC). C4 is a coupling capacitor - its value and the high
impedance of R4,R5 and Q1 mean it has little effect on the phase shift.
It still works if I replace the transistors with an op amp non inverting follower - no inversion in sight. How would you re-describe that?
On 10/20/24 2:55 AM, piglet wrote:
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:57 PM, piglet wrote:
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 10/19/24 12:13 PM, piglet wrote:
On 18/10/2024 4:46 pm, john larkin wrote:<...>
On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"piglet" <erichpwagner@hotmail.com> wrote in message
news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
The circuit below produces a reasonable looking sinewave but the rise
time still seems to be slower than the fall time. It may be that the >>>>>>>>>> amplifier in use is not ideal for this.
Could that just be second harmonic distortion? You could test the >>>>>>>>> amplifier
by uncoupling the Wien network and injecting test inputs.
Elsewhere I think your amplitude control problems could be simply >>>>>>>>> due to
too much gain.
Perhaps, but I've not so far been able to get the circuit I posted in >>>>>>>> response to Bill to produce a sine wave no matter what I do
with the control loop gain.
It either grows to clipping or dies.
--
piglet
I do a lot of instant-start LC oscillators as the timebase of
triggered delay generators. I let them clip just a bit to stabilize >>>>>>> amplitude.
Here is an amusing oscillator that has a voltage follower as the active >>>>>> stage - it has no voltage gain so some people say it cannot work - they >>>>>> are wrong of course.
piglet
If you move the ground to the emitter of Q3 and slide R8 through the >>>>> power supply to the collector of Q3 you can see that it is a
conventional phase shift oscillator with feedback from the output of an >>>>> inverting amplifier via a 3-stage RC network.
kw
What do you do with the cold end of C1 in that scenario?
That connects to the collector, as it is now and forms the first section >>> of the RC network. (voltage sources are zero impedance from the point of >>> view of AC). C4 is a coupling capacitor - its value and the high
impedance of R4,R5 and Q1 mean it has little effect on the phase shift.
It still works if I replace the transistors with an op amp non inverting
follower - no inversion in sight. How would you re-describe that?
Exactly the same argument applies - any current coming out of the opamp
must come from the power supplies and so goes through R8. The gain to
the PS pin can be much more than unity.
Some circuit designs exploit this feature - I think I have seen John
Larkin describing one. There are also designs in The Art of Electronics
using it.
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vf2569$2f0q$1@nnrp.usenet.blueworldhosting.com...
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
On 20/10/2024 4:52 pm, Edward Rawde wrote:
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vf2569$2f0q$1@nnrp.usenet.blueworldhosting.com...
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
<snip>
This will probably mess up the thread structure, but here's another variation. It struck me that the current spike being pulled
from the amp through D1 is probably messing up the op amp's output stage, so I decided to buffer the op amp output with a PNP to
minimise this.
The 4th harmonic is now almost 50dB below the fundamental.
On 20/10/2024 4:52 pm, Edward Rawde wrote:
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vf2569$2f0q$1@nnrp.usenet.blueworldhosting.com...
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
<snip>
This will probably mess up the thread structure, but here's another variation. It struck me that the current spike being pulled
from the amp through D1 is probably messing up the op amp's output stage, so I decided to buffer the op amp output with a PNP to
minimise this.
The 4th harmonic is now almost 50dB below the fundamental.
On 20/10/2024 4:52 pm, Edward Rawde wrote:
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vf2569$2f0q$1@nnrp.usenet.blueworldhosting.com...
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vf20si$96u8$1@dont-email.me...
On 20/10/2024 3:36 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vevqip$3q3dn$1@dont-email.me...
On 19/10/2024 2:03 pm, Edward Rawde wrote:
"john larkin" <JL@gct.com> wrote in message news:j656hjp1rq659uh61k3q75bipaf386qqh1@4ax.com...
On Fri, 18 Oct 2024 18:58:43 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Jeroen Belleman" <jeroen@nospam.please> wrote in message news:veumn5$3fbqu$1@dont-email.me...
On 10/18/24 23:19, Edward Rawde wrote:
"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veuirv$3cmo3$10@dont-email.me...
On Fri, 18 Oct 2024 15:59:09 -0400, Edward Rawde wrote: >>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>> news:veucs2$3cmo3$9@dont-email.me...
On Fri, 18 Oct 2024 14:20:48 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>> news:veu7kt$3cmo3$8@dont-email.me...
On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>
"Cursitor Doom" <cd999666@notformail.com> wrote in message >>>>>>>>>>>>>>>>> news:veu45s$3cmo3$5@dont-email.me...
On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote: >>>>>>>>>>>>>>>>>>
"piglet" <erichpwagner@hotmail.com> wrote in message >>>>>>>>>>>>>>>>>>> news:vetde5$38sbk$1@dont-email.me...
Edward Rawde <invalid@invalid.invalid> wrote:
<snip>
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