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Thread: speaker hum

  1. #1
    Senior Member pyonc's Avatar
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    speaker hum

    Currently McIntosh MC30 mono block hooked on to JBL Olympus, with McIntosh C22 (just serviced).
    Now, I hear audible hum from one of the speakers. 60Hz, I think.
    As this is the tube preamp, I swapped the tubes with the other ones on the other MC30.
    Still the hum is there. Any comment or advice?

  2. #2
    Senior Member HCSGuy's Avatar
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    I don't have any experience with vintage tube stuff, so I can't give you any advice on repairing your equipment, but hopefully can help with troubleshooting.

    If you disconnect the inputs to the amps, so it's just the amps connected to the speakers, is there still hum? If yes, you have an issue with one of your amps.

    If not, connect the preamp, with no sources - does the hum appear? If yes, and it is only out of one speaker, then swap the preamp outputs Left to right - if the hum moves to the other speaker, the problem is with the preamp. If it stays, the amp is suspect. I'm assuming your vintage stuff does not have a 3-wire grounded plug, so the chassis are the neutral/ground, which would mean the RCA cables ground them together, so playing with a ground wire wouldn't do anything.

    If you still don't have hum, plug in your sources, one by one, and test them. The most problematic sources are those that that get an input from somewhere else - cable boxes used to always cause hum, satellite receivers sometimes, or anything with an ethernet cable or external/mounted antenna may be causing a ground loop, but let us know how far you get with the first steps.

    Hope this helps.
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  3. #3
    Senior Member pyonc's Avatar
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    Quote Originally Posted by HCSGuy View Post
    I don't have any experience with vintage tube stuff, so I can't give you any advice on repairing your equipment, but hopefully can help with troubleshooting.

    If you disconnect the inputs to the amps, so it's just the amps connected to the speakers, is there still hum? If yes, you have an issue with one of your amps.

    If not, connect the preamp, with no sources - does the hum appear? If yes, and it is only out of one speaker, then swap the preamp outputs Left to right - if the hum moves to the other speaker, the problem is with the preamp. If it stays, the amp is suspect. I'm assuming your vintage stuff does not have a 3-wire grounded plug, so the chassis are the neutral/ground, which would mean the RCA cables ground them together, so playing with a ground wire wouldn't do anything.

    If you still don't have hum, plug in your sources, one by one, and test them. The most problematic sources are those that that get an input from somewhere else - cable boxes used to always cause hum, satellite receivers sometimes, or anything with an ethernet cable or external/mounted antenna may be causing a ground loop, but let us know how far you get with the first steps.

    Hope this helps.
    Thanks for your kind reply.
    With no input, just MC 30 & speakers:
    With GAIN button all the way down, I hear a little, but still audible hum.
    Clearly it's loud60 hz hum.
    Looks like I take it to the tech shop... filter cap issue, maybe.

  4. #4
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    hi,

    You could try the amp on a separate circuit (different floor or something) just to be sure it isn't that wall socket and wiring..or a different house. any speaker would play the hum if it s coming from the amp
    Think center channel for 250TIs; (2) 108s, a 104 and a 44ti, now what?

  5. #5
    Senior Member pyonc's Avatar
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    Quote Originally Posted by opimax View Post
    hi,

    You could try the amp on a separate circuit (different floor or something) just to be sure it isn't that wall socket and wiring..or a different house. any speaker would play the hum if it s coming from the amp
    Hi, glad to hear from you.
    Actually I don't hear any hum or noise from the amp itself.

  6. #6
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    The correct test for hum is with the amplifier input shorted, not open.

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    Remember an audio system should always be connected to 1 single phase of the power coming into your house. If you use 1 phase for 1 component and another phase for another component then the voltage difference between them is 240v. The insulation is designed for 120v and it could cause a problem or even a fatal accident. Your heart could stop and you can't get it going yourself.

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