Mcintosh transformer hum

Discussion in 'Audio Hardware' started by twoegg, Mar 5, 2006.

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  1. twoegg

    twoegg New Member Thread Starter

    Location:
    Palo Alto
    I recently acquired a Mcintosh MC 7104. It is in mint condition, and works perfect except for one annoying issue. There is a physical/mechanical hum eminating directly from the transformer. It is not loud, but is audible from a few feet away when the room is completely quiet. It is sometimes noticeable on quiet passages from my chair. I haven't had this problem with any other audio equipment, but feel it might be the age of the wiring in my house (built in 1932) or a power issue. Could this amp be more sensitve to power conditions or could it be defective? It does sound great except for this. Any suggestions?

    B&K 4090 pre
    Sony S9000ES DVD/CD/SACD
    Mc 7104 (bridged to 2 ch) replaced B&K 120x2
    Yamaha MX830 (for sub)
    B&W 705
    Peerless subwoofer 12DVC (DIY)
    Dahlquist active crossover
    audioquest and vampire interconnects
     
  2. Steve Hoffman

    Steve Hoffman Your host Your Host

    Sounds like it's going bad. Can you return the thing?
     
  3. Yeah, the laminations in a transformer start to break down due to age and, to a certain extent, bad luck. I think the only way to fix it would be to get a replacement piece of iron--which would probably have to be scavenged off an old Mac unit.
     
  4. twoegg

    twoegg New Member Thread Starter

    Location:
    Palo Alto
    ok, I know I'm going through the denial stage, but any chance it could be something more benign? Is it possible to re-epoxy the laminations? I also read someting about transformer vibrations being caused by DC voltage in the power line (from the outlet).
    Also, when I switch on the other amps in the system with the amp playing, the hum stops for a few seconds, with no affect on the sound coming from the amp.
     
  5. I have heard about DC in the power line causing mechanical hum. PS Audio makes a product called the Humbuster Ultimate Outlet which is supposed to fix these sorts of things. There may be another, simpler fix, though. Why don't you send Paul McGowan at PS Audio an email about your problem? He is a super nice guy and really helpful.

    http://www.psaudio.com/products/upchb.asp
    http://www.psaudio.com/products/humbusterac.asp
     
  6. twoegg

    twoegg New Member Thread Starter

    Location:
    Palo Alto
    I am leaning towards the DC theory due to the relative new age of the amp, build quality reputation, and known history of little use. The former owner had the amp in a AV closet and wouldn't have noticed the hum. I have emailed PS Audio and will see what they have to say. I love the amps sound, but the hum would be an issue that would make it unacceptable. I hope a simple device like this could help. BTW- I measured the DC voltage at the 20 range and got a .37 - .64 reading, is this considered excessive?
     
  7. twoegg

    twoegg New Member Thread Starter

    Location:
    Palo Alto
    I will be trying the DC filter from OH! If it's not a DC issue, I don't think it will be a problem to replace the transformer. I peeked inside and the transformer seems to be a simple affair to replace; six screws and six colored wires.
     
  8. twoegg

    twoegg New Member Thread Starter

    Location:
    Palo Alto
    It must be DC in my home outlet, the hum went away at a friends house and returned when I got it back home. I'll be gettig a DC filter.
     
  9. loomis

    loomis Forum Resident

    Location:
    akron ohio
    Head over to the audiokarma.org tube and vintage web forums and search for "buzz" or "hum" and "transformer." Then go through the search results to avoid the threads where people are asking about hum through the speakers and not actually tranny buzz like you have. Then read and see what you can find out. Some of those guys re-shellac the windings and so forth. Email some people over there before you just go replacing the transformer!
     
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