Cause for HUM in an amplifier/ AVR

kcoc321
kcoc321 Posts: 1,788
edited August 2009 in Electronics
I found a AVR someone is selling on CL but they say it recently started a "Hum" when connected to the speakers. They said it does not show up on the pre-out, Zone 2...so they are guessing it is something in the amplifier circuit.
I do not know if it is also in the Preout Z1 (primary, 7.1 output)

Does anyone know what would cause this?

I have not heard back from them yet to get more details, but it sounds like it is a great deal, IF it is a fairly inexpensive fix. It is a B&K 307, and they are asking $150. These sell on the Gon for around $500 and is 150wpc@8ohm, High Current, 7.1 in & out with 2 additional preouts, and has alot more features than my AVR 101.(yeah)

Any input would be appreciated. Ideas? Cost to repair?
Thanks
Post edited by kcoc321 on
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Comments

  • thuffman03
    thuffman03 Posts: 1,325
    edited August 2009
    My Carver TFM 55 has a slight hum when no audio is coming from the preamp. You have to be close to the speakers to hear it. I was told that on my amp this is a normal event. Don't know if that is the same with the B&K.

    Also they might not have clean power to it. I also read a while ago that someone had a hum and when they put a power conditioner between the amp and the wall the hum went away.
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  • kawizx9r
    kawizx9r Posts: 5,150
    edited August 2009
    thuffman03 wrote: »
    Also they might not have clean power to it. I also read a while ago that someone had a hum and when they put a power conditioner between the amp and the wall the hum went away.

    You know, you'd be surprised of the many possibilities you can receive a "hum." For instance I was SO certain that one of my plate amps in my RT1000P's was going bad. I went through the entire process of troubleshooting, connecting/disconnecting through different outlets, eliminating components/etc to see if it was RF interference, you name it. Well I plugged a power conditioner in the outlet I'd normally use and still received a hum, but my panamax said there was a line fault/lack of ground. Plugged it in to another outlet with a good ground, plugged in my rt1000p to the panamax and the hum went away! I had even tried the rt1000 itself straight into the good outlet and still received a hum.

    Yes, keep in mind it was in only ONE of the speakers that created a hum on all counts, so I was for certain it was the amp itself. Who woulda thought? Sometimes a single component is susceptible to such things, and I can't explain why.
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  • billbillw
    billbillw Posts: 7,491
    edited August 2009
    Ground loops are the #1 cause. After that, it is most likely a cold solder joint on a filter caps (or a bad cap) in the amp or preamp section of the AVR. Hums are usually not that hard to fix.

    FYI: B&K does work on all of their equipment and they are quite reasonable. Since they know the product so well, they usually only take 1 hour of labor to fix them. They always have the parts in stock, so turn around time is excellent. I sent an amp+preamp to them and they fixed both in 2 days and they upgraded several things on the amp at no charge. The only drawback is the cost of shipping it to B&K in Buffalo.
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  • TNRabbit
    TNRabbit Posts: 2,168
    edited August 2009
    Cable connections are NOTORIOUS for ground loops; I use digital TOSLINK connections to my cable for that very reason.
    TNRabbit
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  • kcoc321
    kcoc321 Posts: 1,788
    edited August 2009
    Thanks Guys, you give me hope....

    Now IF the guy will call me back & IF it only a ground loop issue, I'm golden...

    hhmmmmm ing...hehe

    Say a prayer to the audio gods for me....:D
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