BIAS Problems??

[anrandroll]

Hi, I'm new to the Forum and I have a technical doubt regarding an EA tremolo clone that I am putting together based on the Runoffgroove Mods. The thing is that the 100k trimpot of BIAS is set at approximately 4.5 - 5.0 V and the circuit goes out of point. We came to think that it could be the trimpot but no, there is something that remains loaded or unloaded and is increasing or decreasing the voltage at certain times and the BIAS goes off point and the pedal can either distort, or turn off. First we thought that the problem was the trimpot that was moving by itself, but when we measure with the multimeter the truth that the voltage doesn't move.

A friend has a booster that behaves similarly by placing a switch to add more bass and try to change the trimpot for a fixed resistance, but it does not work either. It only works if you disconnect the switch and leave it in stock.

Greetings and many thanks for sharing so much knowledge!

Here's the link to schematics: http://home-wrecker.com/eatremolo.html

[ElectricDruid]

If the bias voltage is where it's supposed to be and doesn't move, what makes you think it's anything to do with the bias or the trimpot?

My bet would be that the LFO is faulty somehow. That's everything from Q2 rightwards.

HTH,
Tom

[duck_arse]

when you set the bias on that circuit, you measure the voltage at the drain of the mosfet, NOT at the gate, as your meter will tell you lies. 4V5 is a good drain voltage for a 9V supply, which is why we always ask for the voltages around the circuit. we also ask for photos of what you have built so we can see things, and we always say welcome to the forum.

[ElectricDruid]

we always say welcome to the forum.

Indeed we do. Sorry to have not spotted that.

Welcome!

[anrandroll]

Hi, thanks for yours answer! the problem was grownd in the box with the jacks. Design problem