Need help from Pass X-600 + ARC Ref 2 MK1 user

Does it humm out the speakers or is it a mechanical hum from the transformer of the amps?

Are you using balanced cables?

Well, here's another dumb observation....If you are listening to noise with your ear near the tweeter/midrange and if your amp has a highish imput sensitivity you might just be listening to the noise floor of your amp, or its tubes. When I crank up my SP10II I get both a light hum and tube rush using two different amps, one with a .5 and the other a 1.v input sensitivity. With a third amp and a 1.5v sensitivity I get very little noise or hum. A different tube pre-amp is dead quiet into the same amps. Both with my ear at the speaker.

Cytocycle: It humms out of the speakers and a little bit from preamp's transformers as well (no mechanical hum at all on X-600's). I have tried PS-Audio's HumBuster, but it doesn't help on the mechanical hum from Ref2. I am using balanced cables. X-600's take only XLR.

Newbee: Humm... I can't find input sensitivity from my X-600's spec. Do you imply that there is some kind of mismatch between X-600 and Ref2? The humm is somehow auditable from the listending position.

Nope. Not implying anything. I'm sure your X600 is probably just fine and the match up may be fine as well, just that the noise could be normal. I thought you might just be new to tube pre-amps. Continuing on that assumption....

Tube pre-amps in general just are not as quiet as SS pre-amps. Do you hear the hum when the volume control is at its minimum level or do you only hear it after you rotate the contol well past 12 o'clock? Do you hear the noise with any source input selected or only with phono and with a phono pre connected?

Hearing the hum at the listening position is not good if your volume control is any where near a normal listening level or at its minimum. If you are hearing this hum with only certain sources, like phono and only then with the volume control rotated well past a normal listening volume you may have a poor source or, in the case of phono inadequate gain for your cartridge. With some some sensitive amp and efficient speaker combos amps I have inserted in-line attenuators to bring the "noise" floor down to inaudible levels. Am I helping you yet?

If it humms out the speakers it's a ground issue, I tried a hummbuster also and it didn't work for me so it's not a huge DC problem. The Pass's already have a DC filter built in.

Have you tried the preamp at someone else's house to see if the transformer humm problem or an interaction/power/ground problem. ARC has great support.

Try floating the ground on the CDP, and then preamp , and then break the ground on one of the amplifier monoblocks (not both).