Hackomatic wrote:Following byacey's line of reasoning . . It appears the Carvin amp is balanced input only via XLRs or 1/4" TRS jacks. Without a schematic to verify, I'll assume it's an active balanced circuit via a 2 section opamp. You could eliminate half the opamp's section by rigging up an unbalanced connector and feeding only pin 2 of the XLR or the tip of the 1/4" with the grounds attached to pin 1 & 3 on the XLR or the ring and sleeve on the 1/4". You will loose some level overall, but it will help determine if it's in the input stage of the amp. If it passes that test and both channels perform equally, then move the input signal to pin 3 of the XLR with ground to pin 1 & 2 or ring of the TRS with ground tied to tip and sleeve and try it again.
Most common is a dual opamp input like a TL072 or a 5532, 1 opamp section for each channel input. One balanced input would drive pin 2 and 3 of the 1st. opamp, and pin 5 and 6 of the 2nd. opamp section driven from the channel 2 input. Typically the output of the opamps would then be terminated on the high end of the respective input level controls.
If this is the topology, then driving either pin 2 or 3 would yield the same problem if that particular opamp section is defective. If you get signal driving one pin of 2 or 3 the XLR and none on the other pin, then it could be an input connector problem or bad solder joints, coupling cap, etc.
However, the original poster indicated the problem changed states after moving the parallel mono / bridging switches. These switches would be generally be located after the input balancing opamp outputs but before the level controls. Because he indicated the HF was rolled off on one channel, I think it's something more than just an open input pin.
If cleaning the switches doesn't clear up the problem and you don't have any experience, I would suggest you get it in to a technician to have a look.
