Tremolo issues, loud pop in a buffered pedal

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Hanky-
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Post by Hanky- »

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I have narrowed down the issue to the two P-Channel Jfets Q1 & Q2.
These are PMBFJ175.

These serve as a switch to provide quiet pop free switching but mine has developed a huge pop when switching. Plus there is an issue of the gain being higher than normal when the effect is turned on which is introducing a bunch of hiss.

Heat seemed to affect the problem but not fix it, at first I thought it was a damaged trace but its these. Getting replacement for these is proving tricky, I have found substitues but it will be weeks till I'll receive any.

I have removed these from the board & hard wired the drain and source terminals of Q1 and wired up Q2 source to connect to C6 +ve terminal via footswitch. However I get a drop in the volume of the effect when turned on, depth knob & wave knob has to be maxed to get a lot of tremolo fx happening.

Is there anything else I could do to fix the gain drop when the fx is on. My troubleshooting knowledge is limited :oops:
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Hanky-
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Post by Hanky- »

I found a solution, sort of.

The problem is definitely with these p channel jfets Q1 & Q2.

One of them is bad, giving ton of hiss, sometimes static and possibly the pop.

These work as electronic switches here. Based on the cd4049ub, either Q1 receives ~8V at its gate terminal while Q2 receives 0V at its gate terminal or Q2 receives ~6.5V at its gate terminal while Q1 reveives 0V. Thus at a given instance Q1 is on and Q2 is off or Q2 is off and Q1 is on.

So I removed both of these. Connected one wire from the source terminal of Q1, another to the source of Q2, and wired the dpdt switch half side to toggle between which source wire is connected in circuit to Q1 drain terminal point to complete the circuit.

Results: No hiss, no static pops & perfectly functioning.

I'm still waiting from my regular local online supplier to find the replacement Q1&2 jfets, till then this solution is working for time being.
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