What Makes An Audio Op Amp An Audio Op Amp?

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Yes!

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B-E resistors on the optos increase their breakdown voltage and make them faster, but reduce CTR. Yes, the opamp Iq gets involved.

A cool config would be to use low-voltage optoisolators but cascode them into depletion fets, like a Supertex LND150 maybe. That sould be faster and get this up to 500 volts and more power.

John

I've wanted something like that too - I keep thinking it should be possible to make something much better and much cheaper with modern parts. I have a Advantest R9211C FFT servo / dynamic signal analyzer, it has an amazing range of functions, but is quite clunky to use and the processor is slow by modern standards. I still wouldn't part with it.

(It does 100kHz simultaneously on both channels and has an arb generator built in too).

On 13 Jul., 20:21, Phil Hobbs wrote: ...

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Thanks for the answer.

Can you remedy the VCO pitfall by clamping the VCO tuning voltage with a 1N4448 to some minimum voltage?

Glenn

Sure, you can bandage it like that, or just make sure your loop is simple enough that if the oscillator quits, it always increases the control voltage. Straight loops using the phase-frequency detector (PD II), with or without frequency dividers, do this reliably. If you use the XOR phase detector (PD I), it'll recover some percentage of the time, depending. More complicated loops, e.g. ones using LSB frequency conversion, can lock up when that happens, and never recover.

Usually if I'm building a PLL of higher frequency than the metal-gate

Cheers

Phil Hobbs