4558 and 072 work but 5532 and 833 do NOT [solved]

[DrAlx]

Regarding impedances, its the DC resistances that count for the offset voltage calc, so the first opamp has just the 1M feedback contributing at the inverting input.  The non-inverting has (1M + 10k||10k). EDIT (1M + 10k) EDIT2 (1M + 10k||10k) .  Got the battery symbol confused for a cap.

The resistance matching idea works on the assumption that the two input bias currents will be in the same ballpark.  That might not be the case in practice.  So it's not something that lets you increase the resistor values to as large as you like.  Plus the larger you make the resistors the more the tolerances on the actual resistances matter.

[DrAlx]

I've never yet completely understood the +input bias resistor calculation. Given that R1 is AC coupled, I don't see how it can affect bias current on the -input. Surely there is only the feedback R2? That happens to be 1M.

BTW, you can see the loading effect of your meters input impedance on pin 3 with the 1M fitted. If you had 2 meters and measure the output at the same time, you would see that also drop.

Meter impedance. Of course.  I didn't look at the voltages properly. 
The bias levels are OK.
The bias on the output from the first opamp matches the bias on the +terminal of the second.

[j_flanders]

Regarding impedances, its the DC resistances that count for the offset voltage calc, so the first opamp has just the 1M feedback contributing at the inverting input. 

Thanks Jim and Alex. That definitely explains it.

It would also answer this question earlier on:

case1:
R1=100k R2=1M: 10x gain: sounds ok(ish) but chords and notes don't ring out, when the input signal gets too low, it simply cuts out
case2:
R1=1M R2 100K: 10x attenuation: sounds ok,chords and notes fully ring out, still even mild some distortion
I'm surprised why that last case works and the before last doesn't.

I was still using 100k's in the voltage divider for Vb then, so the difference would have been  50k / 1M (not working case1) vs 50k /100k (working case2)

Not trying to derail the thread but since this circuit started out as a Muff Fuzz I have two questions about most schematics found online:
What's up with C2, or why is it connected from Vcc to vB instead of ground?





Could this perhaps be the only correct version of the original Muff fuzz?
Based on the (somewhat gating) sound, I doubt that the original only had diodes in the feedback loop.
At least it sounds nothing like my transistor version Muff Fuzz nor anything like the single muff in my Double Muff.

[bluebunny]

What's up with C2, or why is it connected from Vcc to vB instead of ground?

"Ground" is just as much a power rail as "9V", so I guess it really doesn't matter: the function is the same.  Just habit, perhaps?