Cupcake developed a tremolo?

[casssax]

Hi,

I built the Cupcake pedal and I've had a few problems I had to fix.

I had a solder bridge on the drain and source of Q1. The only way to get at it was to remove the trimmer pot and the Q1 transistor (it was on the component side of the board under the body of the transistor). I put in a new transistor and a new trimmer pot (I destroyed both trying to de-solder them).

Since then everything seems to be working but I've noticed a strange modulation or tremolo effect that is just barely noticeable when notes ring out.

I'm wondering what the most likely cause of this is?

I'm guessing that it can only be a transistor or the IC. 

[heathxx]

or Sorcery!

[midwayfair]

Since then everything seems to be working but I've noticed a strange modulation or tremolo effect that is just barely noticeable when notes ring out.

Sounds like pumping (basically, voltage building up and discharging in the envelope section at an unsteady rate), and you might have just not noticed it before. Double check the 100K and 4.7uF cap after the diode to ensure they're the right value; you could try increasing the decay (increase the resistor to, say, 120K or 150K) to help cure it, or possibly replace the cap to make sure it wasn't bad. But you should first adjust the bias carefully and see if that does anything to help.

[casssax]

Cool, Thanks.

I'll check those out.

I might just order a new pcb and start over with this pedal. Seems like every time I use it something else strange happens.