Carver Raven 350 Amps

@ozzy 

Are the Atma-Sphere amps entirely quite (put your ear right up next to the tweeter on the driven speaker and see if you can hear any hiss)?   The gain on the Carver 350 is 30db while the gain on the M-60 is 20db.  Do you hear the hiss if you set the carver volume knob to 2/3 (not sure if this knob is volume (output stage) or gain (input stage))?

 I am no expert but did just spend two weeks researching and troubleshooting a hiss/buzz issue in the amp the Carvers are replacing and from everything I read if you remove the inputs (in many cases the recommendation was to short the inputs) and noise goes away it is almost certainly not an issue with the amplifiers.  The trick then is to find the offending electronics.  I didn't know this up front and ended up spending hours of trying different things before finally just isolating the amplifier entirely on a single outlet circuit with all the other breakers in the house turned off and the inputs on the amp shorted only to get the same buzz.

Since you have already determined unplugging the pre-amp stops the hum, maybe start by eliminating the pre-amp and driving the carvers from your sources one at a time and see if one has a buzz while the others don't.

Erich

@ozzy 

I sent an email to Jordan asking about the volume control and he replied that it is on the input stage.  I believe this would mean it impacts both gain and volume.

Erich

erichgs,

Thanks for your reply. I would not describe the hiss as hum, but it is quite noticeable sitting even 15 feet away from the speakers with no music playing.
The Atma-Sphere are pretty much quiet compared to the Carvers.

I just tried reducing the Carver volume knob and it does reduce the hiss but it probably also reduces the overall volume too, hopefully not too much.

ozzy

10db of gain is a fairly large difference and I would think could easily account for hearing the noise coming from the input on the Carvers while not on your other amps.  LIke I mentioned before, if you pull the inputs and no longer hear the noise it is almost certainly not the amp from everything I have read.

On my Carvers I get a small amount of hum even with the input disconnected.  It goes away when I short the inputs and even when there I have to be within ~3 inches of the speaker to hear it.  This is with the amplifier volume knob at full and is the same on both amplifiers.  I also get some power supply hum from the amplifiers themselves but have to be very close to hear that as well.