[Tinkerer]

Has anyone noticed an audible chassis hum with AVA Transcendence 280 (Series 2) amp ?

Sounds like 60Hz...perhaps the power supply mechanically humming, coupled to the chassis?

Mine does it even when neither RCA input nor speaker outputs connected.

Not in the output, but the chassis itself.

Any info appreciated.

[warnerwh]

This is no doubt the transformer humming.  All transformers hum and the bigger they are the more they're likely to hum. You may want to open the chassis and tight the transformer down, don't overtighten it though, just good and snug.

[avahifi]

This was an older design of ours, built into an original Hafler chassis.  

Although the power transformers were very reliable, it appears yours has developed a loose plate and likely this is causing the hum.  If tighting the hardware does not tame it, then mounting the transformer on some kind of damping pad to decouple it from the chassis might help.

If the mechanical  buzz from the transformer is bad enough to be annoying, the only other solution is to replace the transformer.  This is a long out of production part.  The lowest cost source would be from a junk Hafler 200, 220, or 280 amplifier.  The toroids we use in new production amplifiers would work too, but that would be a more expensive solution.

Frank Van Alstine

[G Georgopoulos]

>then mounting the transformer on some kind of damping pad to >decouple it from the chassis might help

most highend manufacturers use this method

[Tinkerer]

Many thanks for the replies (especially from Mr. Van Alstine! ).

Any suggestions for a specific pad to decouple the transformer from the chassis?  

If there is no reason to hard-connect the transformer to the chassis (for electrical grounding, heat sinking, or RFI/EMI/etc. shielding/sinking reasons), then I guess I could use a generic foam pad with adhesive on both sides, as long as it can handle the heat without degrading.

Again, I appreciate the input.

[G Georgopoulos]

youre doing great, you can still connect transformer to chassis using a wire and wire bolt (EI type) etc for absorbing material heat i would think wont be too much of a problem with most materials

is mechanical hum too much of a problem? as long as it is not electrical
hum coming from the spks i wouldnt worry too much about it as a previous poster noted also tightening all removable part of the encloser
will help

good luck

[Tinkerer]

<snip>
is mechanical hum too much of a problem? <snip>

I am testing this system to see if it will work ok in my favored listening room, which has a fairly low noise floor at times.

In this place, even my LCD monitor transformer hum is audible.  (And I tried a couple of monitors, to make sure it wasn't a defective monitor I hear.  Apparently a normal LCD monitor noise.)

So a slight transformer hum may be audible in this room.

Of course, I could locate the amp on the other side of the room.

I don't think a foam pad is very feasible with this transformer - it's pretty heavy, which means it needs a positive mechanical securing method like bolts or at least tiedowns, and such connection will defeat the function of the pad.

Thanks for the input.

[avahifi]

Note that poor electrical contacts in an ac terminal strip can cause loud transformer hum from most any AV device.  If the contacts are not snug, arcing will occur on a continious basis, putting gobs of garbage on the AC line.  This most certainly can be mistaken for a transformer hum problem, when it is only the transformer protesting.

Likely there is good value in making sure your system's AC supply has wall outlets that are tight fits and good quality.  A worn out AC plug on the unit in question can cause the problem too,

Try the unit directly on a diffferrent AC outlet on a different circuit in your home.  If the problem goes away, your AC outlet is the problem.

Frank Van Alstine