Tremulus Lune - BIG Switch Pop

Slade · April 27, 2009, 12:01:45 AM

Hello.
Well, I've been debugging for a long time a BIG switch pop on a Tremulus Lune that I made. I'm using a vactec VTL5C3, TL072 Opamps for LFO and Audio Path. One thing I've noticed is that I'm getting 0.3v at the IN of the circuit when it's on.
I have changed the IN and OUT resistors from 1M to 510k and to 4M and the problem persists equally.
Also I wanted to ask how important is the voltaje of the electrolytic caps in this project?

Thank you very much for your answers

Greetings.

tempus · April 27, 2009, 12:11:27 PM

The voltage of the caps needs to be at least as high as the voltage they will be blocking or passing. So if there's 4.5v that needs to be blocked you need at least a 5v cap to do the job. 300mv sitting at the in of the circuit (I'm assuming this is the guitar in) is going to cause a pretty big pop. I would check to make sure the cap is OK.

Slade · April 27, 2009, 01:30:10 PM

Thanks,
I'm using 25v caps, so I figured that "the excess" of voltage could be a bad factor with this problem.

tempus · April 27, 2009, 01:47:51 PM

I wouldnt think so. All the 25v rating means is that if you hit it with more than 25v it can fail (or blow up). It's probably not a bad idea to overspec your caps a little bit anyway, to give a bit of a safety margin.

Slade · April 27, 2009, 02:21:57 PM

So, I can't figure out this problem, it's driving me crazy!!!!!!!

tempus · April 27, 2009, 11:18:05 PM

If you've got 300mv sitting on your input, it would make sense that that cap is leaky. Have you tried substituting another?

Slade · April 27, 2009, 11:58:03 PM

Thanks, tempus.
Yes, I have.. I tried other values there too, but nothing works

I had this problem once before and it was solved by simply changing the opamps to low noise opamps.. Now it doesn't work

R.G. · April 28, 2009, 09:29:13 AM

Mother Nature is whispering in your ear.

If you have 300mv on the input, the voltage is coming from somewhere. Try taking your input capacitor OUT. Measure now. Is the 300mV still there?

If not, then the current to make that 300mV was coming through the cap. That means that the cap is faulty or put in the circuit backwards.

If the 300mVis still there, then the cap is OK and something else is leaking.

Slade · April 28, 2009, 11:02:34 AM

Thanks, R.G., I'll try that now.

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Tremulus Lune - BIG Switch Pop