SOLVED Tellurian Trouble (no overdrive)

[slowpogo]

I'm a little embarrassed to ask for help because this is such a simple build and I haven't had such basic trouble in a long while.

Essentially, the pedal does not overdrive. LED turns on and the volume and tone knobs work, but the drive knob does almost nothing. From min to max, the drive knob increases the level by about 3db but there is no clipping. I'm using the Philips OA9 Ge diodes suggested by @MichaelW but also tried a few other types with no difference. The carbon comp resistors are new Arcols (not NOS).

Double checked part values, all seem correct. I tested all the diodes before installing. Everything seems to be oriented correctly. Solder joints all look fine but I reflowed most of them for good measure. Tried a different JRC4558D, same result. I checked continuity of the visible traces on the board, all good. Would love to check all continuity but there is no build doc/no schematic.

I'm hoping someone spots something obvious I missed. Or if there are "usual suspects" for this result (no gain from a gain pedal) please let me know.



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[MichaelW]

I don’t think we have a schematic for this one yet. @Robert any chance we can get that?

@slowpogo, not sure if the diode orientation makes a difference or not without a schematic but did you check the anode/cathode orientation on the GE’s?

 

[Robert]

https://docs.pedalpcb.com/project/Schematic-TellurianDrive.png

 

[jimilee]

Did you check your pots to make sure they’re in the right spot? I can’t tell you how many times I’ve done that, even when I check them first.

 

[slowpogo]

not sure if the diode orientation makes a difference or not without a schematic but did you check the anode/cathode orientation on the GE’s?

Yes. I also checked that the red dot on the diode actually indicates the cathode (with some old diodes it's the opposite) -- it does in this case and they are correctly oriented on the board.

Did you check your pots to make sure they’re in the right spot? I can’t tell you how many times I’ve done that, even when I check them first.

I did check that, thanks.

I'll work through the schematic and see if anything's funky. Thanks @Robert

 

[Robert]

Try jumping the two Ge diodes and see if you get clipping with just the 1N914's in circuit.

 

[slowpogo]

I figured it out. Earlier during the build I had accidentally used a 22nf instead of 220nf, I caught it right away and desoldered the 22nf. Turns out one of the C3 pads (VREF side) had gotten ripped out while desoldering and I didn't even know. So C3 was not receiving any voltage.

I ran a jumper wire to the VREF side of C101, and that was all it took! It's working and sounding great. Now to experiment with Ge diodes.

Thanks all for the ideas and help, having the schematic cleared it up pretty quickly.

EDIT: Just realized that the PCB graphic on the product page shows the traces better than I could see on the populated board. That probably would eventually have helped me figure it out too. Good to know for next time

 

[MichaelW]

@slowpogo
Glad to you got it solved and I saw your build report. Pretty interesting where you landed on the diodes. I think I have some 1N60P's and never thought to try them. Now I with I hadn't soldered mine in hahaha.....

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