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Do all compressors hum ? Dynamics Processors (HW)
Old 31st January 2007
Gear Nut

Do all compressors hum ?

I will be recording voiceovers in my project studio. For a few reasons (one being that I will be recording myself) I need to have my compressor (along with the pre) in the same room as I will be doing the recording itself (using a condensor mic). The room will be acoustically treated, with the computer being outside thus very quiet.

Just got a second hand Aphex 651. It appears to be in a very good condition, however, it does make a tiny humming sound that in a very quiet room is somewhat audible even from a a few feet away - at least to my ears. Is that normal? i.e. do all compressors make such a little buzzing/humming sound or there are certain brands and/or models that are dead silent? I have a couple of days to return the item, so it would be nice to have your input...

thanks, greg

(note: got Expressor 651 because I heard its very clean when used for light compression during tracking of voiceovers and around $200. Didn't want to get RNC because its unbalanced)
Old 31st January 2007
Gear Guru
AllAboutTone's Avatar

yes return it, you can buy a symetrix 501 compressor on ebay and get a great warm sound, at least a lot better then aphex. 501s are good on about anything .
Old 31st January 2007
Tim Farrant's Avatar

He probably can't return it, it's second hand!

It will be the power transformer, more than likely a laminated steel transformer, that is mechanically vibrating with the AC power. It's possible you could get inside (unplug it first!) and if the transformer has bolts holding it together, you might be able to tighten these and the noise should reduce. Failing that, a tech could swap it out with a toroidal type, which will not vibrate.

Hope this is of some help.

Last edited by Tim Farrant; 31st January 2007 at 07:53 AM.. Reason: typos tpyos sytpo
Old 31st January 2007
Lives for gear

Acoustic hum/buzz from transformers is a pet peeve of mine.

Funny - I understood toroidal transformers were worse for this??

If it's really bad, it's usually a sign that your AC power quality is very bad. Specificially - instead of being a pure sinewave, it has harmonics - tending towards a square wave. There are many reasons for this - mostly outside of your control.

I'm investigating sinewave UPS to solve this problem. Certainly some gear is better than others - but even my best gear makes this hum.

The important thing is that the unit is totally free of electronic hum and hiss in the audio signal.

Otherwise, the solution is to put all your gear outside your room, or at least get some distance from your ears/mics. This is why I hate active monitors - cheap amps with buzzing trannies right in your face. Brilliant.

Sine waves ...
Old 31st January 2007
I have 4 651's, all modified and draw more current than the stock one's do. All are very quiet. It's the transformer, of course. It's got some wraps or a laminate loose so it needs to be replaced. A torroid is difficult to mount in these due to minimal spacing in the bottom panel to fit the mounting screw. A replacement from Aphex is the way to go as I've not ever seen another with this problem and have reworked well over 100 of these.

Jim Williams
Audio Upgrades
Old 1st February 2007
Gear Addict
RobMacki's Avatar

Originally Posted by grexter View Post
it does make a tiny humming sound that in a very quiet room is somewhat audible even from a a few feet away - at least to my ears. Is that normal?
This one hummed.
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Old 1st February 2007
Gear Nut

i appreciated your input, thankx
Old 1st February 2007
Gear Addict
Ravian's Avatar

Originally Posted by RobMacki View Post
This one hummed.
mmmmmmmmmmhhhhh if it was mine it who'd be humming all day.
envy the world is'nt FAIR CHILD
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