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Amplifier hum - normal?

Is it normal for amps to emit a slight humming noise from the transformer when turned on?

I never noticed it in my old integrated that I lived with for over 10 years, but that was lower power. Now I've gone from 50wpc to 120wpc... don't know if that makes a difference here though.

I mean, it's not nearly enough to bother me or even really be audible past 3 feet away... but I am curious if this is typical for amplifiers to do this.
djembeplay
gbart
290 posts
 
Djembeplay, hum can come from things like loose transformer laminations, loose mounting bolts, other internal issue, or DC. Trying to do an accurate diagnosis on the Internet is difficult and the best that can be done is to offer suggestions.

You need to go through a process of elimination, IMO the first and least intrusive step being to rule out DC. Try disconnecting devices/shutting off breakers to see if a connected device is the cause. You could also try the amp at a friend's house to see if the hum persists or goes away.

If you are still getting the hum, the next step would be to remove the amp's top cover and check for loose mounting. In the end it could just be that the transformer is noisy. If DC is the cause, there are solutions that include eithar a manufactured or DIY DC blocker.
tvad
9,467 posts
 
Channel Islands Audio makes a CD blocker called the XDC-2. You could give it a try. It's available with a 30 day trial period (10% restocking fee applies for returns).

In my system, the XDC-2 knocked down the transformer hum, but it did not eliminate it completely.

YMMV.
gbart
290 posts
 
There's also the Humbuster III from PS Audio. The DIY solution costs much less though.

http://diyparadise.com/dablok.html
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djembeplay OP
169 posts
 
Hmm... DIY you say... how would one go about such a project?
gbart
290 posts
 
Install the DC blocking circuit in a metal enclosure with a 120V 15A single or duplex receptacle. Insert the blocker between the incoming HOT line and HOT terminal of the receptacle.

Its probably easiest to install everything in a 4" x 2 1/8" or deeper steel electrical junction box and use a cover plate with holes for a single or duplex receptacle. Alternatives are a metal power strip enclosure or aluminum project box.

You can use a 3-wire grounded 14 gauge or 12 gauge power cord for the input and be sure to bond the incoming ground wire to both the metal box and ground terminal of the receptacle. Also use an appropriate strain relief at the point where the cord goes into the box.

The caps and diodes can be obtained from Radio Shack, Parts Express, Mouser, etc. Radio Shack does not seem to have 3,300uf caps but they have 4,700uf 35V which will also work.

See this circuit:
http://img.villagephotos.com/p/2003-5/191557/DC%20Blocking%20Circuit.jpg

Enclosure and two types of 1/2" cable connector/strain relief:
http://img.villagephotos.com/p/2003-5/191557/J_BOX.jpg

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