• The Wien Bridge Oscillator problem (your Sunday ruined part1)

    From Cursitor Doom@21:1/5 to All on Sun Oct 20 16:36:10 2024
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to Cursitor Doom on Sun Oct 20 17:26:01 2024
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to piglet on Sun Oct 20 20:17:58 2024
    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.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to Liz Tuddenham on Mon Oct 21 06:09:53 2024
    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?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to Jan Panteltje on Mon Oct 21 09:38:21 2024
    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..


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to Liz Tuddenham on Mon Oct 21 09:41:29 2024
    On a sunny day (Mon, 21 Oct 2024 09:38:21 +0100) it happened liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in <1r1rup0.62nful1573k8wN%liz@poppyrecords.invalid.invalid>:

    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..

    Yes, I should have written 'resistor' perhaps
    Imagine a temperature controlled wire pulling on the arm of a pot:


    power amp -->- heated_wire -> ground

    |
    [ ]
    ------0----------------------->[ ] resistence element
    ( bearing [ ]
    ) |
    ( heated wire on power amp


    Thing will point up and down at the resistor element as the wire cools or heats up, contracts or expands..
    Or perhaps modify an old moving coil volt meter to point at some resistor element from an old potmeter?
    Plenty space for playing / experimenting.
    Not sure it will work or is very practicle.

    So I will stay with Linux and 'sox' on my Rapberry Pi for now ofr audio.
    or with that on my big PC that has 2 good soundcards.

    Or for higher frequencies the FPGA and DAC I have.
    Or all the other stuff I already mentioned.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)