# Amp humming need help



## wjs1820 (Mar 5, 2010)

I've got an older Rotel receiver (rsx-1057) that I was trying to get some more power from, so I picked up a used B&K amplifier It's an av125.5. The amp sounds great when on and does a better job of feeding my B&W 703's. My problem with it is, after turning the receiver off, the amp goes in to bypass mode and after about 2 hours it develops a hum through my center channel speaker. I've experimented with turning the amp off completely and that resulted in a slight pop followed by the hum when I turned it back on, this is prior to the receiver coming on. Once the receiver is on no hum. I'm curious if anyone else has this issue or is familiar with the problem. My concern is if it's a filtering capacitor, will it eventually let go and blow the amp and or speakers. Is it worth repairing, as I can still send it back? Thanks for the help.


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## tonyvdb (Sep 5, 2007)

If its only the centre channel thats humming and not the other 4 channels of the B&K I suspect something is wrong with the amp. I would return it if you can.


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## Wayne A. Pflughaupt (Apr 13, 2006)

It’s not unusual for an amp to generate some hum when the source component is shut off, but still connected to the amp. Rather than leave the amps on all the time, get a power sequencer like the old Adcom ACE-515 that turns on the amps after the receiver is turned on, then on power-down shuts the amps off first. You can find them on eBay pretty cheap. Panamax, Carvin and Furman also make similar devices.

Regards, 
Wayne


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## Wardsweb (Apr 2, 2010)

Yes, the sequence should always be receiver or preamp on first and then the amp(s). Reverse when shutting down; amp(s) off first and then the receiver/pre. Many amps do not like having an open input.


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## wjs1820 (Mar 5, 2010)

the amp has bypass mode and a 12v trigger which I was using. What really got me worried was after going away for the weekend the hum was much louder than the 2hr tests. This leads me to believe that a capacitor is leaking. I was considering repairing it but decided instead to pack it up and save for a 200 watt option.


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## 8086 (Aug 4, 2009)

Check or test the inputs on the amp. Make sure the signal going in isn't being tainted by some external source like a power cord or a bad RCA plug. Try swapping the center input/output for one of the left or right inputs. This may also help rule out a bad center on your pre-amp.


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## MagnusAtom (Oct 23, 2012)

Are all your plugs from the same power socket? If not, try to have them all on the same line. Let me know how it goes. 

Alternatively, if you don't use the same power source, try insulating the ground of the power cord of the component going into the separate power supply. You can try a temporary insulation by just taping it with scotch, or black tape/ insulation tape, just to check.


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## wjs1820 (Mar 5, 2010)

Thanks for the info guys, I do appreciate it but I figured my best solution was sending it back. I didn't try swapping inputs but I was using the same power supply. I actually thought the power supply could've been causing it. Unfortunately I'm not in the position to pay $5000 for a new amp so the info will be helpful on my next one.


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## MagnusAtom (Oct 23, 2012)

Lets hope the problem is with the amp then!


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## 8086 (Aug 4, 2009)

wjs1820 said:


> Thanks for the info guys, I do appreciate it but I figured my best solution was sending it back. I didn't try swapping inputs but I was using the same power supply. I actually thought the power supply could've been causing it.  Unfortunately I'm not in the position to pay $5000 for a new amp so the info will be helpful on my next one.


I think that is where Emotiva comes in to play. Champagne at rock bottom beer prices.


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## Zeitgeist (Apr 4, 2009)

It's gotta be the amp...

"and after about 2 hours it develops a hum through my center channel speaker."

The key being it just starts happening after sitting there..


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## MagnusAtom (Oct 23, 2012)

Any updates? Did the swap solve the problem?


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## wjs1820 (Mar 5, 2010)

Well, after a few days trying to investigate the hum problem, I finally fixed it, I packed it up and returned it. I then found a used B&K Reference 7250 for a couple dollars more. The 7250 is a monstrous beast by comparison with 5x200wpc. It doesn't have balanced inputs, which doesn't effect me anyway, but wow what a difference in sound quality. The Av125.5 was good but more in a subtle nuance way. The 7250 is dead quiet with no humming at all and truly makes music come alive. The Dave Matthews/ Tim Reynolds concert from Radio City on Blu-ray, is simply amazing. 

Thanks to all for your comments and support. I'm happy again, at least for now...


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## derwin424 (Jan 31, 2013)

i am running a B&K AVR505s2. When i use the off button on the remote (i.e. put the B&K into standby), i hear a low buzzing sound from my center channel speaker and if i unplug and replug the banana plugs into the speaker there is static. Anyone else experiencing this?


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