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I traced my Exar OD-02 OverDrive from series 2. Initially, I hoped that it will have the same circuit as OD-1, because most of the Exar series 1 and 2 pedals share the same PCBs, but it wasn't the case.
PCB is single-sided and was easy to see all the tracks on a light. My unit seems to be produced in 1996 or later according to the date code on the gain potentiometer.
It appeared that it is definitely not a TS variation, but a discrete op-amp OD. Definitely inspired by Boss discrete op-amp designs but less complicated. The signal chain consists of: an input buffer, discrete op-amp gain stage with diodes in the feedback loop, simple lowpass filter tone stack, and output buffer.
As the result, it's a pretty nice-sounding OD circuit, small and easy to build. Attaching the schematic to the post. I stripped out everything related to buffered bypass switching, so it is a true bypass version.

Thanks for sharing the schematic, what are the dimensions of the board?

Manfred wrote: ↑07 Nov 2022, 10:23 Thanks for sharing the schematic, what are the dimensions of the board?

about 52x70mm

Drew a vero layout for this circuit as i find it rather interesting. Somewhat bare bones discrete opamp OD. Not yet verified, but i'm planning to build one. Seems like a nice base for some mods as well.


//edit. - Built it and it works. Sounds pretty damn good to my ears. There were one mistake on the gain pot label. Also. Check the comments below - Pots are log.
So yeah. Consider this layout verified.

@mirosol - that's great, thanks for the layout! It sound nice, try it.

From what I remember - with TELPOD brand potentiometers, B taper means log (audio) and A taper is linear.
I have OD-02 on a breadbard now and log (A) is a way to go

ps. I've just measured Telpod 47k A - linear taper.

temol wrote: ↑13 Nov 2022, 11:36 From what I remember - with TELPOD brand potentiometers, B taper means log (audio) and A taper is linear.
I have OD-02 on a breadbard now and log (A) is a way to go :)

ps. I've just measured Telpod 47k A - linear taper.

Yup. That sounds about right. Thanks Temol!
Just finished building the layout and swapped erroneus gain pot label for pin 3 - and taper for gain+tone pots. Log works way better. I left the volume as linear, as that felt right. I'll update the layout in a sec.

I went with J112s and a BC550/BC560. This thing sounds pretty damn good. Slow boiling overdrive with very nice crunch texture. Straight forward discrete opamp driver.

temol wrote: ↑13 Nov 2022, 11:36 From what I remember - with TELPOD brand potentiometers, B taper means log (audio) and A taper is linear.
I have OD-02 on a breadbard now and log (A) is a way to go

ps. I've just measured Telpod 47k A - linear taper.

Ok, so they used Soviet letters for pots, didn't know that - thanks

mirosol wrote: ↑13 Nov 2022, 17:42

temol wrote: ↑13 Nov 2022, 11:36 From what I remember - with TELPOD brand potentiometers, B taper means log (audio) and A taper is linear.
I have OD-02 on a breadbard now and log (A) is a way to go

ps. I've just measured Telpod 47k A - linear taper.

Yup. That sounds about right. Thanks Temol!
Just finished building the layout and swapped erroneus gain pot label for pin 3 - and taper for gain+tone pots. Log works way better. I left the volume as linear, as that felt right. I'll update the layout in a sec.

I went with J112s and a BC550/BC560. This thing sounds pretty damn good. Slow boiling overdrive with very nice crunch texture. Straight forward discrete opamp driver.

Just designed PCBs for it, will make some as well - probably in December. It's funny, I got 200 J113 about month ago and didn't know where to used them .

VitaliiBobrov wrote: ↑14 Nov 2022, 22:00 Ok, so they used Soviet letters for pots,

No.
Just different marking for log/linear tapers. Polish company Telpod taper codes:
- linear: A; M+N,
- non-linear: B; C; S.

mirosol wrote: I went with J112s and a BC550/BC560. This thing sounds pretty damn good. Slow boiling overdrive with very nice crunch texture. Straight forward discrete opamp driver.

I've just tested J113, MMBF5457, MMBFJ201, MMBF5485, MMBF5458. Differences are rather suble, at least to my ears.
Here's quick comparison: https://www.dropbox.com/s/itflyz0712mtmyr/od02mg.wav
Gain set to 11 o'clock, tone 14 o'clock. Guitar -> breadboard -> audio interface -> daw. I only added speaker cab impulse response (4x12 V30 Mesa Boogie)

I created a GitHub repo with KiCad files, Gerbers, schematic, and Interactive BOM for a modified version I did as a part of the Pedal Drop series: https://github.com/vitaliy-bobrov/kropy ... -overdrive

It has additional clipping options on the toggle and Fat switch.

This looks like an discrete Timmy

Neurobasher wrote: ↑20 Jun 2023, 15:01 This looks like an discrete Timmy

Timmy didn't exist when this thing was released

Hmm intresting, so maybe Paul's inspiration??
Thanks for sharing your nice work!