G'day Folks,
I have what I assume is a v1(?) Organ Donor PCB(built and working fine) without the internal Level control.
I only noticed the difference while referencing the current build doc for the control names, so I thought I'd have a crack at adding this trimpot to my board, using the schematic for reference.
Testing after installation, the trimpot is definitely not doing anything to the signal, that I can hear.
I ran the 10k resistor from the + side of c16 to pin 2 of IC4, pin1 of the trimpot joined between resistor body and IC pin. Joined pin 2 & 3 of the trimpot and ran that to pin 1 of IC4.
Have I done this correctly?
Why C16 ? it looks like it's in the power section. Unless C16 on your version is C14 here above ?
Not sure what are the differences between your version and this one, but i would try replacing R15 by a trimmer, or a pot wired as a variable resistor ?
I'm not sure i understand the blue symbols on your pic, under IC4, and why you would need an internal volume trimmer ?
https://docs.pedalpcb.com/project/OrganDonor-PedalPCB.pdf This is the current build doc(Revised 3/1/24) linked on the Organ Donor PCB page. This schematic is the one I’m referencing. The revision addresses the well documented volume drop of the Organ Donor effect.
If you zoom in on IC4.1 you can see the revision, disconnecting pins 1 & 2 of the IC and replacing that connection with the resistor and trimpot. This is what I have added. I did forget to say that I severed the connection between ic4 pins 1 $ 2 then added the other components.
So if you did exactly as per the schematics, maybe you can try to add a piece of cardboard or plastic under your jumpers and resistor, to prevent them from shorting with a trace on the pcb.
If it still doesn't work i would check for shorts in this aera with a multimeter, and check the extra resistor and trimmer values, just in case.
You "severed the connection" between pin 1 and 2, i guess you used your multimeter to check if there isn't continuity ?
eh là bas ma has got it covered in regards to checking for shorts and values with a multi-meter, but I still have questions & suggestions.
Took me a hot minute to figure out what the blue squiggles were — IC pins "1-" and "2-"
I've looked at both the old and new schematics; what you've done in theory should be working so I'd do like eh là bas ma says and double-check for continuity where there should AND should NOT be. Especially test around IC4's 1,2,3,4 and C11, R11, R8, R4 — hard to tell with reflections off the flux, but there may be a short there.
BTW, you can edit your first post to include the fact that you severed the connection between pins 1&2 of IC4;
which brings me to the question: HOW did you do this disconnect?
It's a multi-tiered PCB, so depending on how you severed the trace you may have inadvertently cut another trace, OR as I suspect not actually made the full cut between pins 1&2 (which would explain why the trimmer does nothing when you turn it). Test for continuity between pins 1&2 with the trimpot fully off (or better, trimpot disconnected).
Suggestions:
- Rewire on top (component-side) of the PCB instead of having wires cross from a trimpot on the underside. It will be easier to see & control short-prevention of the mod. Lots of shorting-potential underneath.
- SIMPLIFY the wiring — you can pull VREF from one side of R8 or R4 which are much closer to IC4 Pin2 than C16:
You could put VREF direct to IC4-pin 2, and ONLY there, because
You then run a trimpot from IC4's pin 2 to pin 1 (Short the trimmer's lugs 2&3)
You could still do everything underneath, but just run the VREF to pin 2, then trimmer between pin 2 > pin 1.
or
Half & Half: You could put the trimmer on top (component side), and the 10k from VREF to pin 2 underneath.
After looking at the board some more, here's how I'd do it — everything underneath simplified and pulling VREF from R4 (after ensuring that PCB's trace between IC4 Pins 1 & 2 is severed w/o damaging anything else):
Nothing crosses.
You could even do it top side and put the trimmer right on the PCB instead of floating it in mid-air, it'd be more stable, and run jacketed wires instead of bare ones underneath the IC socket:
BTW — I've drilled holes in PCBs, cut slots in from the side and other hackage to sever traces, AFTER checking to make sure I wasn't damaging other traces.
Even have had to chop corners off a board, one time, to fit it in a smaller enclosure.
Hard to check traces and ground-planes with the PedalPCB boards, 'cause you can't shine light through them.
Pic from the Net
Lastly — did you consider adding a separate boost between the Organ Donor's output and the 3PDT?
Could be a simple LP-1, or GPCB's Afterblaster (JFET boost, or wait for PPCB's version), Enchanted, Black Tiger, Amentum...
Thanks, yeah I found that out. There is no continuity between pins 1 & 2. Reattached the resistor/trimpot using r4 as suggested above. The effect works perfectly but still the trimmer does nothing. Dud trimmer?
