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MIR Power xformer/choke hum

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Posted on December 22, 2019 at 06:23:41
Cpwill
Audiophile

Posts: 1096
Location: DC
Joined: December 22, 2003
Contributor
  Since: October 24, 2008
 My MIR has developed a hum that is telegraphing through the speakers. I am not sure when it started, but I recently changes speaker from 96-ish dB sensitivity to 99-ish dB sensitivity. When I take the top off, I can hear that the hum is coming from either the power transformer and or the choke, but neither seem to be vibrating when I touch them.

Any suggestions as to how to fix. It's annoying, but not un-listenable. Thanks in advance.
"Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra.

Cpwill

 

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RE: MIR Power xformer/choke hum, posted on December 22, 2019 at 17:16:56
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Craig,

With the power amps off, you hear a mechanical hum from within the MIR chassis? If that's so, it's more likely to be the power transformer than the choke.

You can test the idea of the mechanical transmission of the hum to the tubes and there onto the speakers by loosening the power transformer mounting screws and shoving enough paper towels in between the power transformer and the chassis to make a loose pad so that they are not in intimate contact and the loosened screw heads are not in intimate contact with the bottom of the chassis. Think of it as a crude isolation mount... Share the results and we can decide what to do from there
Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: MIR Power xformer/choke hum, posted on December 23, 2019 at 04:49:46
Cpwill
Audiophile

Posts: 1096
Location: DC
Joined: December 22, 2003
Contributor
  Since: October 24, 2008
 Thanks, Kevin. I will try that, hopefully, this afternoon.


"Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra.

Cpwill

 

RE: MIR Power xformer/choke hum, posted on January 6, 2020 at 05:08:38
Cpwill
Audiophile

Posts: 1096
Location: DC
Joined: December 22, 2003
Contributor
  Since: October 24, 2008
 Finally got around to finishing this. I did check for the hum with the cover off and the amps turned off. Loosening ht screws and just lifting the transformer up by the PCB's on each side deadened the hum. So when I had enough time and in the right mood, I unhooked everything,removed the transformer, and then remounted it with Museum Putty under it. It worked; knocked down the hum by at least 20dB or more. It's now quieter than my currently installed power amps. Thanks.


"Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra.

Cpwill

 

RE: MIR Power xformer/choke hum, posted on January 6, 2020 at 12:08:22
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 You nailed it! Good job!

Kevin Carter
K&K Audio
www.kandkaudio.com

 

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