[bralack42]

Hello

The CMoy amp I built about two weeks ago has a problem. When I turn the thing on, it plays beautifully for about thirty seconds to a minute, and then the volume seems to dip a little and the sound becomes distorted and "clipped" even when listening at normal levels. I replaced the opamp (OPA2132PA) and this still doesn't help.

If it helps any, the amplifier is set to a gain of about 3.5 because I feed it at line-level. The capacitors are the ones specified in Tangent's tutorial (220uF electrolytics and 0.1uF metal film boxes) The resistors are Vishay/Dale RN55D's. I'm using a pair of Switchcraft jacks for IN/OUT and a Panasonic 10K pot.

 

[tangent]

I suspect a high-resistance short to ground somewhere. The major suspects are the jacks. You may have melted something inside, such that you have a thin but electrically permeable insulation layer between two contacts, or you're using a metal case and your insulation on your jacks isn't quite up to snuff...something like that. The problem could also be down on the board. Check your soldering job, especially everything that connects to the ground bus and everything that's near that ground bus.

 

[bralack42]

Thanks a lot for the help....

I'm using a switchcraft jack, and on one of them it kinda "cracks" when I wiggle it. I'm thinking this could be the suspect jack. It could also be the pot: it was really difficult wiring it up, with the lugs being so close together.

 

[tangent]

To eliminate the jacks from suspicion, desolder the wires from them and use alligator jumpers to tie them directly to your mini cables as I show in the CMoy tutorial. If that clears up the problem, replace the jack.

 

[bralack42]

Thanks a lot for your help Tangent. Unfortunately, you can't account for all the bozos who don't realize their battery is dead! I went and got a new one and it sounded perfect!