Add Verb build (very) low output issue

[Anonymous]

Hi guys, after some days now of troubleshooting and searching bits of answers about an Add Verb build I am direclty asking you for help.. It’s my second pedal build so I’m a kind of a noob. I managed to get it working in bypass mode, made the led light on (couldn’t do that with the 3pdt switch pcb provided and moved on with the switch wiring but leaving the pcb unused on) and it even works when the pedal is switched on but I get very low volume.

I have the 100k resistor as R2 (lost the spare 27k but I will get another one if that’s the problem). As i said i get an very faint audio out signal witch also has reverb working but i barely hear it. I tested with an audio probe and I get good audio at pin 2 of IC1 and very low at pin 1.. at pin 3 and 5 of the brick i get it also very low up until the jack tip out.. I am thinking that a resistor has a bad value but I tested each one and they match the build docs (from musikding.de)..

What can I do next as I even switched the IC1 with another one from another pedal (comaptible model) and I gat the same problem (with the pin 1 output).

Thank you for your time!

[Cybercow]

George – yes! R2 MUST be 27K. If you put in a 100K at R2, the resultant volume will be very low. I know it’s going to be a PITA to change because the reverb brick is in the way. However, it may easier to strap a 37K resistor in parallel with existing 100K resistor at R2.  That would drop the input resistance to the opamp from 100K to 27,007Ω and resolve the issue. You should be able to do that from the component side of the PCB and not have bend (and risk breaking any legs of) the reverb brick. It may not be a pretty fix, but it should work a treat.

But if you can carefully extract that 100K from the R2 position and get in the correct resistor value of 27K in place, all the better.

Good luck!

[Anonymous]

Thank you! I thought about adding a resistor in parallel in order to get to 27k but I wasn’t sure thatwould fix it. Thank you for the quick answer, I will report back.

[Anonymous]

I managed to cleanly remove the 100k resistor and replace it with a 27k but the low output didn’t change a bit.. I migh have a faulty component but I don’t know where to look.

The audio probe procedure is the one below? (I found it in another older post)

IC1A pin 2>pin1>Brick pin 3>pin 5, pin 6>Reverb pot lug3>IC1B pin 6>pin 7> board OUT.

 

Thanks.

[Anonymous]

So in order to close this thread.. I solved the issue by replacing the TL072 IC.. I managed to get another TL072 and it works perfectly now. Thank you for your time.

[Cybercow]

Glad you solved it. Happy building!

[Author]

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