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

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.
 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.
 I've now dug a bit deeper. Here is a five transistor version of John May's four transistor version.

Out of curiousity, 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.
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