Wednesday, May 14, 2008

Volume Mod

My tremolo pedal has a sickening issue. It boosts the volume significantly when engaged. In the vast plains of Utopia, a tremolo should not do that. At the waveform's peak, it should be unity volume. The idea of a volume mod to counter the issue cropped up. That way, I could expand the use of my tremolo, both as a normal 'unity volume' tremolo with the option of a 'clean boost' when the speed and depth knobs dailed to minimum and the volume pot adjusted to taste.

Circled in red is the output jack. I removed it first. The idea of a volume mod is to connect the circuit output to lug 1 of a pot, and then lug 2 of the pot to the output jack. Lug 3 and the ring of the output jack would be connected to the circuit's ground.
As usual, de-soldering was a pain in the ass. I should remind myself to get a de-soldering flux/wick soon, because my de-soldering pump is pretty much useless. Nevertheless, I soldiered on and finally removed the output jack.

Circled in red is where the cheap black plastic jack once was. Circled in yellow is a 100k pot. People normally use 5k pots for volume control, but I felt that using a 100k would bump my 'awesome quotient' a few steps higher. Circled in blue is a spare mono jack I ripped out from my failed dual-transistor fuzz circuit.
So I plugged my guitar in and turned on the pedal. Volume control did what it was supposed to do, but it did a little more too. It was also active when the pedal is bypassed!! I didn't know why it was doing that!! Could it be that I soldered the pot somewhere in the the middle of the circuit? Did I accidentally short out a pcb trace while soldering and de-soldering? Did the pedal's 'non true-bypass' nature contribute to this problem?

Then i figured out the reason. Either on or off, true-bypass or not, the last remaining thing before the output jack is the pot. So even if the effect is bypassed, the signal would still go through the pot. This means that although I was able to achieve unity volume when the tremolo is on, the signal level would reduce once I turn the effect off. A cut in volume when in 'engaged' mode would lead to the same thing in bypass mode. So, unity volume was never achieved in the end!! I just ruined the resale value of a $115 pedal!! Kudos to me!!

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