BillH2121 Posted August 28, 2007 Share Posted August 28, 2007 First, my system consists of Mac 2102 tube amp. C41 preamp, Mac CD205, and turntable. Everything is plugged into a Monster power strip except the amp which is plugged directly into wall socket. No problems with hum until last night. I turn on the system and hear what sounds like a ground loop hum. I unplugged the sub and hum remained - turned off cd player and still a hum. When I move output cables from output 1 to outpput 2 on the preamp, the hum still exists. Turntable is grounded to preamp. Why all the sudden would a hum appear and what's the first step for troubleshooting? Thanks Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 28, 2007 Share Posted August 28, 2007 You should disconnect all feeds to the power amp and see if the hum is still there. This will prove it is a problem with the amp. If so, the next question is whether both channels have the hum. If so, it might be a power supply filter cap gone bad. I'm stealing some of this from an earlier thread by someone more experienced than I am. Smile. Gil Quote Link to comment Share on other sites More sharing options...
BillH2121 Posted August 28, 2007 Author Share Posted August 28, 2007 I'll try that - Jeez, it better not be the amp, I just spent 5 months without it waiting for warranty work to be done. Supposedly, McIntosh went through it and made it like new. Thanks for the suggestion. Quote Link to comment Share on other sites More sharing options...
BillH2121 Posted August 28, 2007 Author Share Posted August 28, 2007 Alright - I disconnected the output innerconnects to the amp and no hum. Replaced the output innerconnects with different ones and still a hum. Looks like the amp is the culprit? I don't know if I can bear to send it back to McIntosh knowing how far behind they are on warranty work. Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 28, 2007 Share Posted August 28, 2007 Maybe we're miscommunicating. Let's assume the power amp is indeed powered up and the speakers are attached. But there are no interconnects attached feeding a signal, and thus there is no hum input possible. If it is quiet, then the power amp is not creating the hum. Is this the case? Gil Quote Link to comment Share on other sites More sharing options...
jacksonbart Posted August 28, 2007 Share Posted August 28, 2007 its something else. Quote Link to comment Share on other sites More sharing options...
BillH2121 Posted August 28, 2007 Author Share Posted August 28, 2007 Maybe we're miscommunicating. Let's assume the power amp is indeed powered up and the speakers are attached. But there are no interconnects attached feeding a signal, and thus there is no hum input possible. If it is quiet, then the power amp is not creating the hum. Is this the case? Gil Gotcha - when the innerconnects are removed from preamp to the amp, there is no hum. Yeah,I was confused at first, but now I see what you mean and I'm greatly relieved its not the amp. Ok, I guess I move up the chain now and consider the preamp? I've checked all the connections to speakers and amp/preamp/cd and still the hum is there. Quote Link to comment Share on other sites More sharing options...
vluuv Posted August 28, 2007 Share Posted August 28, 2007 I just posted a similar question in the Aragon forums -- in my case, the problem appears to be coming from the amp. A bad power supply filter cap was mentioned here earlier. Can you explain? Thx. Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 29, 2007 Share Posted August 29, 2007 Going back to Bill's issue. Does the C-41 have a monitor speaker output? I see the C-40 does. Try connecting a speaker to that. If the preamp has an internal issue causing the hum it might very well show up on the monitor speaker output. Of course try with and without any cables feeding an input to the C-41. I'll get to vluuv 's question when I can put up some diagrams. Essentially, the cap acts as a filter or integrator, you are really charging it up and slightly discharging it in normal operation. The output of power supply is d.c. like from a battery. Also, we are really listening to the power supply. The transistors or tubes act a valves to connect the power supply to the speakers in accord to the input (which twists the handle on the valve). So you need clean d.c. from the power supply. People are asked, is the hum in both channels. This is because typically the power supply (even with several d.c. outputs) feeds power to both channels. It is one of the few things common to both channels. The only other thing is the chassis voltage, so therefore sometimes a ground loop effects both channels. We try to eliminate that in testing by disconnecting all the feeds. Gil Gil Quote Link to comment Share on other sites More sharing options...
BillH2121 Posted August 29, 2007 Author Share Posted August 29, 2007 Thanks Gil for the advice - I'm off work Friday and I plan to go through all the connecting and unconnecting as needed for diagnosis. Plus, I plan to hook up my C-26 in place of the C-41 and see if that answers the question. Thanks again. Quote Link to comment Share on other sites More sharing options...
Arkytype Posted August 30, 2007 Share Posted August 30, 2007 Gil, You have a PM. Quote Link to comment Share on other sites More sharing options...
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