Oscillator Distortion

Cursitor Doom · 2024-10-13T17:10:30+00:00

Gentlemen,Last week I got an old (1968) pulse generator out of mothballs and managed to get it fully functional again. However, before replacing the case, I (true to form) dropped it on the bench and something on the PCB must have shorted out against the metal tools it fell on, because it no longer works properly. I've found an issue with the principal oscillator. It's generating distorted sine waves. It's a wien bridge type using BJTs as the gain element and fine tungsten filaments as thermistors, so should produce near perfect sine waves before they're chopped and shaped by subsequent circuitry, but since the fall, it's not.Here's the oscillator output: found some weird periodic spikes on the power supply rails in the oscillator stage. They are actually present on the rail, not just picked up by the ground lead of the scope out of the ether, as I used a short ground clip in this instance. I'm not sure if these could cause the distortion or not.'m out of ideas. What could cause such distortion if the PS rail isn't responsible?Your pal,CD.

Oct 13, 2024 Last reply: 1 year ago 43 Replies

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Phil Hobbs 1 year ago

Yup.

Vernier adjustments to a nearly perfect basic platform are Good Medicine, very generally.

Cheers

Phil Hobbs

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chuck 1 year ago

Phil with respect, again you make false assumptions and conclusions. There is no distortion above -40dB with 5mV of gate modulation and less than -60 dB with 0.5mV of gate ripple with a 1s gate time constant.

The JET is very linear over a small voltage range of 0.5 mV and current range when the Vin+ node is ground referenced so the JFET modulates the inverting gain limited by a series R.

Get it?

Tony

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john larkin 1 year ago

Yeah, we all know what a doofus Phil is.

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Can't see that. It wants me to sign up or something.

Download limit? Expiry date?

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ehsjr 1 year ago

Wait. What? Do you disagree with Phil's statement, which was: "Vernier adjustments to a nearly perfect basic platform are Good Medicine, very generally." ???

Or (based on the rest of your post) did you mean to reply to a different post?

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