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Had a friend ask me to take a look at his Ashdown Mag 300 EVO II amp. It has loud buzz on the D.I (xlr plug) output. Sounds like a bad ground loop to me. The buzz is only on this output. Everything else seems to be fine. The 1/4" outputs work. We tried a couple of known good cables and had the same problem. I pulled the chassis and took a look at the board thinking that I would find a bad solder joint on the plug. You can see the back side of the board without pulling it. All of the joints looked good. I checked continuity on each plug pin to the solder joint on the back of the board and all checked good. I have not pulled the board yet to look at the front side. Not sure what to look for there. I do not have a schematic for this amp. Any direction as what to look for now would be greatly appreciated. Thanks.
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schematic attached
Check the LINE OUT signal for buzz, if that is good, we are only looking at IC2 which is the DI driver, check its power supplies are smooth DC without too much ripple. Check the output of each op amp, do you get the buzz there. If you remove the ground wire from the DI out socket, do you still get the buzz (it could just be an earth loop in your test setup.
There are a few electrolytics here, we could just replace them, in case one of them is the culprit, also if IC2 is socketed, try another one.... -
Mozwell mentioned lifting the ground in case it was a ground loop, I was thinking the same, or perhaps the opposite, a blown ground trace due to interconnection with some ground fault.Originally posted by Enzo
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