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Quasar Crackle/Pop in Treble Control (not dirty pot!)

Started by idy, October 24, 2012, 03:19:11 AM

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idy

I have built the Quasar several times on Madbean pcb pattern, using RC values. Also have done the AC/RC on vero. On the PCB versions I had a strange crackle or pop on the treble control. BOth times. And even after swapping out pots several times. The one I have now has two loud "pops", both close to the counter-clockwise extreme. I have swapped the pots out (alpha, 50k linear) and the replacements do the exact same thing in the same place!

The earlier version got a nasty distortion on this same point in the pot travel, a sudden extreme fizziness that went away after I subbed the pots. The new circuit had the fizz on the first pot, just the pop on the second and third.

Any ideas? Whole baggy of pots with identical defect? I took one apart and there is no visible damage, no huge splash of solder or anything.

madbean


idy

Good question. Thank you!
I was using a mosfet, CA3260. When you asked I put in a 4558 and the problem went away. What was it?

madbean

Maybe the high input impedance of the the CA3260....? Dunno.

idy

So we still like the sound of the ca3260e better.
A little more on the pops: they only happen when volume is on maximum, at two points on the "cut" side of the treble control. I can also park the treble in the danger zone and get the pop by sweeping the volume back to full.

I have found out that the pedal only does this when it is plugged into another high impedance pedal: BYOC reverb,  Boss reverb/delay (even bypassed the buffer makes the popping happen)  FA-1 clone, a tremulous lune clone etc. My ampeg scrambler also pops with it, and it has a 1M input impedence.
The popping does not happen when the pedal goes into a fuzz face, or a rangemaster or a LPB or a simple MOSFET booster. (I thought that was high Z, maybe I added a too-small pull down resistor...)

Maybe next step is to breadboard a different kind of output buffer. I really like the OD with Baxandall tone control.