I was adding a switch to my brother's NewClassD amp, but am having a curious situation. The switch was to go between SE->bal (4PDT), wired up basically like what Kerry did with the relays on the mini ss DYnalo:

Everything ohms out correctly, but when I went to test it, the R channel works perfectly (in either position), but no sound from the L channel. I took it all apart tonight (not the switch and input wiring), but disconnected from the amp boards, etc. Everything once again ohms out perfectly, no shorts. L- and R- shorted to gnd when switch is in SE position, straight thru then not.

The XLRs are the metal Neutriks like the NC3MD-LX-HE, etc. The only thing odd that I noticed is the shell of the XLRs to pin 1 or the panel ohms out at ~10 ohms. This is with nothing connected (like the schematic above... the connections to the amp are open). The RCAs are isolated from the panel, and the shell grounds aren't connected to anything, though they are touching the panel. Otherwise, all the grounds are isolated, and the ground wires (pin 1 on the XLRs and the sleeves on the RCAs) are not connected to anything. Perplexing, and not sure why or if that could cause the L channel not to work.

I know when my brother built the amp a few years ago, he could not get the balanced connections to work, but not sure exactly what symptoms he found then. Any thoughts?

Try reversing the cables going into the switch to see if the problem follows the cables. 
 

Also, have you tested both channels of the app to make sure they are working correctly.

I wired up a pair of RCAs and reinstalled the jumpers to set the amp to SE input last night. Running a signal from my mAudio FW into it, the R channel was working but the L was not, so it appears it is an amp problem and there probably isn’t anything wrong with the switch and input wiring. Although why, with nothing connected to the back panel, and the back panel off of the amp, so not touching anything, am I seeing 10 ohms from the XLR pin 1s to the back panel and XLR shells? Odd unless it has to do with the particular Neutrik jacks.


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