Exar OD-02 OverDrive
- VitaliiBobrov
- Breadboard Brother
Information
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.
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.
- Attachments
-
- exar-od-02-schematic.pdf
- Exar OD-02 OverDrive schematic
- (68.14 KiB) Downloaded 1028 times
- Manfred
- Tube Twister
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Thanks for sharing the schematic, what are the dimensions of the board?
- VitaliiBobrov
- Breadboard Brother
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- mirosol
- Resistor Ronker
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.
//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.
Last edited by mirosol on 13 Nov 2022, 18:02, edited 3 times in total.
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"No such thing as innocence" -Iron Chic
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"No such thing as innocence" -Iron Chic
- VitaliiBobrov
- Breadboard Brother
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@mirosol - that's great, thanks for the layout! It sound nice, try it.
- temol
- Solder Soldier
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.
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.
- mirosol
- Resistor Ronker
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.
http://tagboardeffects.blogspot.com/
http://mirosol.kapsi.fi/
"No such thing as innocence" -Iron Chic
http://mirosol.kapsi.fi/
"No such thing as innocence" -Iron Chic
- VitaliiBobrov
- Breadboard Brother
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Ok, so they used Soviet letters for pots, didn't know that - thanks
- VitaliiBobrov
- Breadboard Brother
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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 .mirosol wrote: ↑13 Nov 2022, 17:42Yup. 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
- Solder Soldier
No.
Just different marking for log/linear tapers. Polish company Telpod taper codes:
- linear: A; M+N,
- non-linear: B; C; S.
- temol
- Solder Soldier
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)
- VitaliiBobrov
- Breadboard Brother
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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.
It has additional clipping options on the toggle and Fat switch.
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- my favorite amplifier: Tube Amps
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This looks like an discrete Timmy
- VitaliiBobrov
- Breadboard Brother
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Timmy didn't exist when this thing was released
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- Posts: 2
- Joined: 13 Feb 2021, 15:43
- my favorite amplifier: Tube Amps
- Completed builds: J Dunlop JH Fuzz
ZVEX Fuzz factory
MXR Dyna-comp
Emma Transmorgrifier
Keeley Compressor plus
Walrus audio V3 Deep six
Solo Dallas Storm
Keeley Mag echo
MXR Phase 90
Voodoo labs Micro vibe
Dead astronaut Tremshifter
misc. Tremolo
MXR dist+
Paul cochrane Timmy
Fulltone OCD
Jackson Audio amp mode
Peter Cornish SS-2, SS-3, G-2, buffer
Suhr Rufus
Throbak strange master
Xotic BB-preamp, EP-booster
Way Huge pork-loin
Bearfoot FX pink purple fuzz
Wampler pantheon, pinnacle, sovereign
Greer lightspeed
Basic audio Scarab de luxe
etc.etc.etc. (all strickly for own use)
Hmm intresting, so maybe Paul's inspiration??
Thanks for sharing your nice work!
Thanks for sharing your nice work!
I built today based on Miro’s layout and it sounds great. I dig these discrete circuits. Built the Discrete Distortion + yesterday and really like it. I think that old school type of OD/Dist just appeals to me most. Thanks to all of you for helping newbies like me learn how to make all these fabulous circuits. The tones coming out of my studio these days are unbelievable. Thank you!
- VitaliiBobrov
- Breadboard Brother
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I've opened Exar OD-3 recently, and it appeared to be the same circuit - they changed transistors (probably just what was available at the time) and improved power supply filtering a bit. Schematic is in the attachments.
- Attachments
-
- exar-od-3-schematic.pdf
- Exar OD-3 schematic
- (48.73 KiB) Downloaded 64 times