Troubleshooting PedalPCB Blue Breaker build.

[ctelecaster]

Hi there,

Having some issues with my Blue Breaker build. Technically my second one - I built one as a trial run to get my soldering technique down. I put it all together and I got sound in bypass, and power/LED when on but weak signal. I get about unity gain with the volume and gain controls both fully up, and the signal is being colored somewhat by the circuit compared to bypass. No crunch or distortion to be heard. The tone control behaved as expected. It almost seemed to a layman like the signal wasn't being amplified, just passed through the circuit.

I decided to start from scratch on a second PCB with all fresh components since my soldering on the first go was less than stellar, and it behaves exactly the same as the first. I'm assuming there's some kind of common issue with both boards I built because they both behaved exactly the same: colored clean signal at approx. unity gain with volume and gain pots up full. I am at a bit of a loss as to what it could be.

Things I've tried:

• Measured every resistor for correct value and every diode for shorts one by one when populating board - everything checked out.
• Since it sounded to me like the signal was being passed through without amplification, I suspected the op amp. I tried several different TL072s with no change. Thinking I may have gotten a dodgy batch of TL072s from Amazon, I swapped in both a 4480 and a 1458 both sourced from stompboxparts, also with no change.
• Reflowed everything in between tests.

Any guidance is appreciated. Attached should be a couple of board shots. Thanks!

[bluebunny]

There's a couple of joints that look like they have little or no solder, and one "blobby" one that I can spot.  You might want to try re-doing those.  But since there's an op amp in there and it's quieter than you expect, then I would check the resistors around the op amp which set its gain.

[duck_arse]

https://docs.pedalpcb.com/project/BlueBreaker.pdf





first thing I'd do is link to the circuit diagram, parts layout, build docs, such that members would not ...... etc ....

and the second thing would be, I'd check the value you have at R10 - 1k, and the value you have at R8 - 1M. the build docs in front of me says R8 should be 1k, and R10 should be 1M.

no, the second thing would be I'd ask for voltages - but in this case they would should all show correct. it's your in-series with the output and your pulldown values is swapped, badly pinching off your probably otherwise good signal.

[ctelecaster]

https://docs.pedalpcb.com/project/BlueBreaker.pdf





first thing I'd do is link to the circuit diagram, parts layout, build docs, such that members would not ...... etc ....

and the second thing would be, I'd check the value you have at R10 - 1k, and the value you have at R8 - 1M. the build docs in front of me says R8 should be 1k, and R10 should be 1M.

no, the second thing would be I'd ask for voltages - but in this case they would should all show correct. it's your in-series with the output and your pulldown values is swapped, badly pinching off your probably otherwise good signal.

I noticed this discrepancy between the build docs and the board printing too - they seem to have revised the board without changing the build doc. I did swap these two just as a Hail Mary and got no sound at all - weak sound came back when putting them back in the position indicated on the board.

Here's a shot of what the board indicates for those two resistors, in contradiction to the build doc (this is a picture of an identical board leftover from my first attempt)



Here's some voltages measured a minute ago on the pins of the IC:

1: 4.55v
2: 4.55v
3: 2.27v
4: 0v
5: 4.46v
6: 4.54v
7: 4.54v
8: 9.09v

[Locrian99]

Your voltage at pin 3 looks off to me.

Check your soldering joints and values here. 




I'd guess the 1m resistor myself but I'm making a very half educated guess

[antonis]

Your voltage at pin 3 looks off to me.

It strongly depends on OP's DMM impedance..

As long as DC voltages on pins 2 and 1 are equal to V_REF, bias configuration should be OK..

[antonis]

I'd check (via continuity test) the correct placement of R8 and R10 on PCB, according to schematic..

[duck_arse]

as my colleague antonis sez - consult the circuit daigram. of the four pads below the IC, when looking for correct spots for correct values, your output pulldown needs to be high value, and one end is hard-to ground. so, power off, meter to resistance, one probe to ground, probe the pads for 0 ohms. the other end of that resistor goes to OUT/C7, so that's another easy find.

same goes for the 1k resistor, which needs to be a lowish value because it is in series with  the audio output by the IC. one end of that resistor is hard-to the output pin, so put one probe on the IC socket pin 7, and probe the four pads till 0 ohms appears. and the other end of that resistor goes straight to the tone pot, so probe for that connection next.

and when you have sorted the resistor placements out, fire of a strongly worded email to the pedalpcb.com people, and tell them their product is not documented well enough to trouble-free build.

if you build the signal tracer probe thing audio probe, you can prove your two opamp sections are passing good signal, at least up to the tone section.