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But you know you have to set 6V on a test points, right? And only when Sag does not limit the voltage?

First let's make sure you're doing everything correctly. 1. Set the maximum voltage on the pin 1 of the Sag knob. Sag should be probably at zero (max CCW) but it's better to measure the voltage than stare at the knob. From now on - do not adjust Sag. You want max voltage.. like there's no Sag...

Do not rely on the Sag knob position. Measure voltage in the circuit - you want max possible voltage on pin 1 of the Sag.

Because audio signal can affect the bias voltage.

No, I haven't even started yet. I would prefer to use the full schematic rather than with some modules omitted.

@Robert - any update on this?

Thank you for your offer. I think I already have everything I need to design a pcb. I like this part of the build and I like to lay a board in my own way :) I'll post an update here. Thanks again.

@Paul.Ruby thanks for the schematic and explanations. Now I have to find some time to process it and probably design a board for the O2.

I had a similar "issue" with fake 072s. https://forum.pedalpcb.com/threads/tl072-vs-tl072.12830/

Is the schematic similar to this one?

@Paul.Ruby - do you use a buffer between output of your AMT preamps and next pedal? Btw - O2 schematic omitts input buffer.

Vp 0.6–0.63V and Idss 0.5–0.52mA

Gain @ noon. Bat41 Bat46 Bat42 Bat48 Bat85 1N4148 Ge diode

Some oscilloscope shots from the O2 on a breadboard. Testing different diodes. Cyan trace - second stage output, yellow trace - third stage output. 1kHz sinewave, 200mv p-p Gain @ max. Bat41 Bat46 Bat42 Bat48 Bat85 1N4148 Ge diode

For me O2 is ok, but not amazing. Maybe because I connected it only to the audio interface instead of the power amplifier. I'll give it another chance in some time. Btw - I recommend Crunch channel of the AMT Bulava SS30. Schematic available here One comment about the diode in O2. Schematic...

Just tested O2 on a breadboard. Seems to be ok.

@Paul.Ruby - O2 schematic appeared today on freestompboxes

99% yes. Why?

1.4.3. Parts 1, 2 and 3 - different gain and MID settings. In each part MID at min, noon, max. Part 4 - hm.. I played with MID and PUSH pot. Probably... :) https://www.dropbox.com/scl/fi/kn1xcaboxl9wg2lz8qxhm/push5.wav?rlkey=6f1nk8x4jw4wcsoxwnuh6y47n&st=oi7o7srq&dl=0

Layout 1.3.2 is still on breadboard so I will soon convert it to 1.4.3 and upload a recording.