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A DC Blocker to help stop transformer HUM


Master Contributor
Technical Expert
Mar 15, 2016
Monument, CO
I'd expect a line DC problem, or ground loop, to start immediately. Hum coming later sounds more like failing capacitors to me. You could try a DC blocker to see if it helps.


Senior Member
Sep 2, 2019
Yes. From what you describe, that’s sound like DC induced hum.

Seems to be correct, I dug out an old Emotiva CMX-2 I bought over 10 years ago and left in storage and it appears all the noise is gone now. Interesting, I actually bought the thing because I thought it looked nifty but got annoyed due to the lack of outlets, somehow it turned out its actually pretty useful.


Active Member
Sep 17, 2021
Hmm, I'm having a bit of a humming issue with a Yammy AS-1200. The amp dead silent when playing music and idling at first start, but if it idles for more than about 10-15 mins, it starts humming audibly from a few feet away. The sound doesn't go away unless I power cycle the receiver, or goes away on its own after playing music for a few minutes. I wonder if this is something that would benefit from a DC blocker?
Almost certainly not. A DC blocker helps with DC, and DC doesn't magically appear or disappear when playing music or after having your system on for a certain amount of time. It may come and go on the line but would do so independently of what you do with your music (do you play with crappy dimmers and high powered lighting, is the wife drying her hair with the hairdryer on the low setting, do you have a dodgy fridge compressor, etc, etc).

Other things can cause hum such as uneven loading of the transformer windings. Most likely a failing capacitor or a failing diode in the bridge rectifier.
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