The Sweat Box is an octave up fuzz pedal, which is a design I honed in on years ago. I recreated this design on a breadboard and added in some additional filtering and diode selection switches. It sounds awesome, works great. So, I decided to turn the design into a product. Easy, right?
6/28- I built two prototypes, one for me and one for the band Milk for the Angry. These prototypes consisted of hybrid perf/pcb. Once finished, one of the prototypes was not operating properly. The gain was scaled down less than the original guitar signal. First session of troubleshooting. (4 hours)
- Visually inspected all components and boards side by side. Check!
- Isolated the PCB from the perf board, there I find the PCB was operating properly on its own. That directed my problem to somewhere on the additional perf board.
- Second visual inspection, with a double check and confirm ohms with volt meter. Check!
- Measured all voltages, the supply voltage was sitting lower than the breadboard at around 8.3V, but shouldn’t make a difference and was expected due to the voltage drop of the protection diode. (Make note to deprecate this protection diode)
- Next, started following the signal path, with a quarter jack audio probe, desoldering/isolating components one by one, until I found that the signal was not making it through the audio transformer.
- After that, I measure the resistance on the primary and secondary, then between the primary and secondary of the operating and non-operating. The non-operating measured in Meg ohms while the operational unit read 800K ohm. This is odd. It couldn’t be the transformer, audio is still going through it, and transformers are pretty dang tough.
- Continue to dissect the signal path, I shunted the primary winding to the secondary, in which case the signal would be at the correct volume, but had too much noise for me to be happy to call good.
- This has got be an impedance issue, but how? There’s no way the tolerances could be that far off? Right? What else could it be….
- The issue was left unsolved, I was happy to have one operational unit, so I put this unit on the shelf.
7/19- The artwork was completed for The Milk for the Angry unit. This unit was a little different it had an additional footswitch and LED for the voltage doubler portion of the circuit as opposed to having it as a toggle. Neither of which would make a difference in sound quality with the non-operational unit which was a direct clone of the breadboard. The Milk for the Angry circuit worked until the entire unit was closed up, where it would intermittently had the same issue as the non-operational. “Well good,” I thought, “this is something I can get to the bottom of.” So I began to test on the MFTA board. (2 hours)
- First step was to take everything out of the enclosure. I did that and everything worked as it should. Phew! what a relief.
- I started placing components in the enclosure one at a time and testing. Foot switches first, then the quarter inch plugs, followed by the toggle switches then it stopped working….
- So, I took out all three toggles and placed them in one at a time, I was able to place all three in and the pedal was still working. Okay!
- Now it was time to move forward to the potentiometers…. still good. Lastly I placed the PCB and perf board. The issue then surfaced again. Great, I’ve isolated it to these boards getting shorted out on another component inside, since the build was already kind of a squeeze….
- After, going back and forth between operational and non-operational, trying to get the enclosure closed and resurfacing the issue, the circuit stopped working, with the same symptoms as the non-operational unit.
- I removed the circuit completely out of the enclosure, and still not working.
- Feeling defeated, I put this on the shelf
7/26- Being Sunday, I have a meeting with Bucket List Guitars on Tuesday. They are an online shop based out of Morro Bay, who is interested in checking out my products to sell. I want bring my finished and unreleased products along with some of my prototypes for sampling. (6 hours)
- Testing, testing, testing, all the same as the above, aside from cutting traces and probing
- Aha! I found the issue, there is a 1K ohm in place of a 200 ohm on the PCB right before the amplifier. This has to be the issue….
- I placed the 1K in the breadboard, and there was a slight volume drop, not a lot, but enough for me to swap out the resistor on the PCB, still no change
- I shunted the protection diode, with no change.
- Well the only choice now is to replace the perf board portion piece by piece and omitting all the toggles. This all works.
- Time to replace the transformer, after removal I instantly metered the transformer with instant satisfaction to see the secondary coil had an open circuit. After replacement the circuit is now operational.
It seems as if I broke a transformer with one MFTA circuit while the other was dead on arrival. Both of these circuits had wrong value resistors. I have been dialing in this circuit on my test bench for the last 4 months doesn’t make sense for these transformers to fail so quickly. I was able to put this pedal together, but still not happy with the sound.
7/28- After doing some listening at Bucket List Guitars, it was a clear disappointment. The pedal was breaking up and oscillating on the signal path while turned off. The breaking up sound I realized was due to the audio interface clipping(not the pedals fault), but there was a hissing now that bled into the signal path while off. There are a couple initial things I know I need to change, and I hope this clears everything up.