Re: Five transistor version of the low distortion sine-wave oscillator

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vtihob$sfdm$1@dont-email.me...

On 12/04/2025 6:27 pm, Bill Sloman wrote:

Edward Rawde posted an eight-transistor low distortion sine wave oscillator circuit recently, and John May pointed out that you
could leave out half the transistors.
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I couldn't immediately see exactly how either of the circuits worked, though I could get the simulations to run under LTSpice and
see roughly what was going on.
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I've now dug a bit deeper. Here is a five transistor version of John May's four transistor version.

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Out of curiousity,

Is that allowed Bill? I thought that making component changes to see if the circuit works better was design by evolution?

Did you mean R20? I don't see R27.

I think the only way forward with this circuit would be to build and test it.

I'd do a first prototype with everything through hole except LT1679 and NSS40301MDR2G.

I'd also put four more resistors in series with each 68k (maybe reduce them to 56k) for the four diodes so I can make the current
pulses in the four diodes exactly equal.
And add a capacitor (100n min) to ground where the resistors join.

And use the remaining LT4167 (two quad packs) as an output buffer so that whatever is connected to the output doesn't disturb the
operation of D10.

I upped the currents through Q1A and Q1B by about an order of magnitude (R27 down to 27k, R17 down to 22kk and R28 down to 68k)
and the worst case harmonic became the second at 2kHz, 155dB below the the fundamental. The fourth was close behind at at about
157dB down.
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Essentially, their incremental resistance has dropped by an order of magnitude, and the ripple on the gain-control signal produces
less voltage excursion.
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--
Bill Sloman, sydney