[sdiy] The TL074 has changed!

[Mike Beauchamp]

On 2025-08-04 08:11, mskala at northcoastsynthesis.com wrote:
> I don't think there is really any phase reversal going on, because the op
> amp (either version) can surely go at least as far as about -12V output,
> at which point under the described circuit input conditions the op amp
> inputs will still be within a couple of volts of zero, nowhere near the
> point where they'd trigger phase reversal.  I think the real issue is
> clipping:  the newer version can drive its output closer to the rails, and
> so the circuit which depends on clipping behaviour, ends up clipping
> differently.
>


Hi Matthew, thanks I always appreciate your detailed explanations.

I've modified a PCB with the old TL074 so I can measure the current 
between Q14 and the LM13700. The saturation (or as I call it my 
intentional "squish") of the circuit is noticeable. With the knob at 
100%, the current is 32mA. If I add a 5V CV to resonance-CV the current 
only goes up to 37mA.

With the new TL074H, the current drops immediately to 0mA as soon as the 
resonance-CV goes over 1V with the knob at 100%. So I don't think it's 
clipping, I think it's doing something entirely different.

Mike




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