In a quiet room late at night, standing several feet from the RR2150 which is not enclosed in any cabinet, I hear a slight buzz (which I assume is coming from the transformer), not coming from any speaker, and separate from any volume setting or any other setting on the receiver. Is this normal and how many db over ambient level should such sound not exceed?

I have a db meter. If it would help, I can give you the db reading above ambient room noise with the amp on and off.

If the noise is loud enough to register on the db meter I would call Outlaw. The noise isn't normal.

Well, my hearing may be a touch better than I give it credit for. Using my Radio Shack analog sound level meter set for "fast" response on the 60 db scale (the most sensitive) with either A or B weighting, this is what I get:

With the meter set up on top of the unit, the meter varies from no change between on and off, to an occasional slight pulsing of the needle between -10 (no sound registering) and -8 db on the scale. The -10 is 10 db below the zero (which represents 60 db), so some of the pulsing may be in the 50 to 52db range, if I'm reading the meter correctly.

Except, of course, for a quick jump from -10 to -4 db when the relay clicks on and off.

In reading the instructions for the meter, it indicates that the lowest (60db) "range of measurement" is 50 to 60 db. I would probably require a more sensitive meter to give an accurate reading of what I faintly hear.

In any event, I wonder if the sound I'm hearing could be due to a variable dirty power thing going on occasionally.

All my previous amps were in some sort of cabinet, so I didn't notice any mechanical noise from them at all, even if they made some.

The torroidal transformers in the Outlaw equipment seem to be pretty sensitive to any DC component on your home power lines.

I "solved" my problem by getting a power conditioner to give me a nice, clean power. However all I really did was move the hum from the amp to the power conditioner. This works for me because I am able to hide my power conditioner and can't hear the humming.

There was a noticeable improvement though because when the amp was humming some of the noise was coupling into the speakers and I could hear it during quiet moments in the soundtrack. No audible humming now.

Which power conditioner did you get? Is there such a thing as a quiet filter?

I have a Tripplite, I forget the model number.

Outlaw sells the SurgeX. I've never owned one of those so perhaps someone else can comment.

Two things:

1) Either my hearing at transformer-buzz frequencies suddenly went bad, or the transformer on my amp doesn't buzz anymore. And if it doesn't buzz anymore it is due to either "burn in" or having moved a wall wart or two around on my power strips.

2)Tripp Lite claims its products are intended to be buzz free, and if it does make an objectionable buzz to let them know and they will exchange under their lifetime warranty (I haven't quite determined if that sort of warranty is the life of the product or life of the person.)

UPDATE 1 day later - cause discovered.

First the buzz returned this evening. Hmm. The only difference is my desk lamp is off during the day (no buzz) and on at night (buzz).

The cause of my transformer buzz is a high intensity desk lamp plugged into a switching box plugged into one of my surge protectors under my desk. Light on= buzz; Light off=no buzz.

So now to figure out how to eliminate the buzz without eliminating the lamp.

1) Try different outlets for the lamp.
2) Get a filter of some sort for the lamp.

This should be cheaper than getting a $50 to $100 power cleaner for the amp.

Has your other noise changed?

I got rid of 90% of my USB (other) noise. It does not change with the lamp on or off.

What kind of lamp? VFs are really noisy. Maybe changing technology of the bulb will work.

You could try plugging into a different circuit. I don't think a filter for the light is a solution.