Gentlemen,
How critical is the choice of thermistor for a WB oscillator? Stability is desired; we know that much (along with minimal distortion of course). The usual problem with WB oscillators is they are not amplitude stable and
either die out or saturate. However, by means of a non-linear negative f/b arrangement, they *can* be made stable. One common solution is to use a thermistor, usually one with a positive temperature coefficient. The issue is, that it must be 'nimble' enough to regulate the output level without being *so* 'nimble' as to respond to peaks and troughs of the output
signal's cycles. I'm going to call this 'nimbleness' "tau" for the time being. I know it's not the right Greek letter, but no doubt some helpful
soul will point out the correct one.
So the question is, how the hell do you select a thermistor with the
optimum 'tau' for any given wideband WB oscillator?
Your pal,
CD.
Cursitor Doom <cd999666@notformail.com> wrote:
Gentlemen,
How critical is the choice of thermistor for a WB oscillator? Stability is desired; we know that much (along with minimal distortion of course). The usual problem with WB oscillators is they are not amplitude stable and either die out or saturate. However, by means of a non-linear negative f/b arrangement, they *can* be made stable. One common solution is to use a thermistor, usually one with a positive temperature coefficient. The issue is, that it must be 'nimble' enough to regulate the output level without being *so* 'nimble' as to respond to peaks and troughs of the output signal's cycles. I'm going to call this 'nimbleness' "tau" for the time being. I know it's not the right Greek letter, but no doubt some helpful soul will point out the correct one.
So the question is, how the hell do you select a thermistor with the optimum 'tau' for any given wideband WB oscillator?
Your pal,
CD.
I think they should all get there in the end but a longer tau thermistor
will take longer to settle.
piglet <erichpwagner@hotmail.com> wrote:
Cursitor Doom <cd999666@notformail.com> wrote:
Gentlemen,
How critical is the choice of thermistor for a WB oscillator? Stability is >> > desired; we know that much (along with minimal distortion of course). The >> > usual problem with WB oscillators is they are not amplitude stable and
either die out or saturate. However, by means of a non-linear negative f/b >> > arrangement, they *can* be made stable. One common solution is to use a
thermistor, usually one with a positive temperature coefficient. The issue >> > is, that it must be 'nimble' enough to regulate the output level without >> > being *so* 'nimble' as to respond to peaks and troughs of the output
signal's cycles. I'm going to call this 'nimbleness' "tau" for the time
being. I know it's not the right Greek letter, but no doubt some helpful >> > soul will point out the correct one.
So the question is, how the hell do you select a thermistor with the
optimum 'tau' for any given wideband WB oscillator?
Your pal,
CD.
I think they should all get there in the end but a longer tau thermistor
will take longer to settle.
You could always use a large bulky thermistor which does not self-heat
and then heat it with a resistor fed from a power amplifier. That would >trade off distortion against settling time.
On a sunny day (Sun, 20 Oct 2024 20:17:58 +0100) it happened liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in <1r1qtlq.zz9rd16lqyaiN%liz@poppyrecords.invalid.invalid>:
piglet <erichpwagner@hotmail.com> wrote:
Cursitor Doom <cd999666@notformail.com> wrote:
Gentlemen,
How critical is the choice of thermistor for a WB oscillator?
Stability is desired; we know that much (along with minimal
distortion of course). The usual problem with WB oscillators is they
are not amplitude stable and either die out or saturate. However, by
means of a non-linear negative f/b arrangement, they *can* be made
stable. One common solution is to use a thermistor, usually one with
a positive temperature coefficient. The issue is, that it must be
'nimble' enough to regulate the output level without being *so*
'nimble' as to respond to peaks and troughs of the output signal's
cycles. I'm going to call this 'nimbleness' "tau" for the time being.
I know it's not the right Greek letter, but no doubt some helpful
soul will point out the correct one. So the question is, how the hell
do you select a thermistor with the optimum 'tau' for any given
wideband WB oscillator?
Your pal,
CD.
I think they should all get there in the end but a longer tau thermistor >> will take longer to settle.
You could always use a large bulky thermistor which does not self-heat
and then heat it with a resistor fed from a power amplifier. That would >trade off distortion against settling time.
Servo controlled potmeter?
Jan Panteltje <alien@comet.invalid> wrote:
On a sunny day (Sun, 20 Oct 2024 20:17:58 +0100) it happened
liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
<1r1qtlq.zz9rd16lqyaiN%liz@poppyrecords.invalid.invalid>:
piglet <erichpwagner@hotmail.com> wrote:
Cursitor Doom <cd999666@notformail.com> wrote:
Gentlemen,
How critical is the choice of thermistor for a WB oscillator?
Stability is desired; we know that much (along with minimal
distortion of course). The usual problem with WB oscillators is they
are not amplitude stable and either die out or saturate. However, by
means of a non-linear negative f/b arrangement, they *can* be made
stable. One common solution is to use a thermistor, usually one with
a positive temperature coefficient. The issue is, that it must be
'nimble' enough to regulate the output level without being *so*
'nimble' as to respond to peaks and troughs of the output signal's
cycles. I'm going to call this 'nimbleness' "tau" for the time being. >> >> > I know it's not the right Greek letter, but no doubt some helpful
soul will point out the correct one. So the question is, how the hell >> >> > do you select a thermistor with the optimum 'tau' for any given
wideband WB oscillator?
Your pal,
CD.
I think they should all get there in the end but a longer tau thermistor >> >> will take longer to settle.
You could always use a large bulky thermistor which does not self-heat
and then heat it with a resistor fed from a power amplifier. That would
trade off distortion against settling time.
Servo controlled potmeter?
It would be constantly hunting unless the resolution was infinely small
and there was absolutely no mechanical backlash..
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