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

I am matching Pass X-600 with ARC Ref 2 (MK1) and encountering a strange hum issue. I have tried couple combinations and it seems like the hum is coming from only X-600 + Ref 2. X-600 and Ref 2 do not seem to have any problem individually. Following are the combinations that I have tried and they show no hum at all.

1. X-600 + Pass Aleph P
2. X-600 + Wadia 861 (using build-in preamp)
3. Mark Levison 331 + Ref 2

I have also tried couple power conditioners and even power regenerator, but the hum still. I was told the hum might be from power & preamp impedance mismatched. However, it shows pretty healthy from the specifications. Any comments on this will be appreciated. Thanks in advance!
jshaw1004
cytocycle
1,043 posts
 
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).
guidocorona
4,298 posts
 
I had an identical Humm problem on ARC LS2B into a pair of Rowland 7M monoblocks. Humm was from speakers and was insensitive to volume control. Humm went away when I applied a ground cheater on LS2B.
jshaw1004 OP
53 posts
 
I have tried Mark Levison 331 + Ref 2 at friend's house and no hum at all. The humm doesn't increase as I increase volume control. The humm occurs without connecting any sources from preamp, simply power amp + preamp. I have tried star connection and leave only one ground for fixing ground loop, but the humm still.

Newbee: What's in-line attenuators? Where can I get one? Will it affect/downgrade the sounding?

Thanks for all your comments.
newbee
4,767 posts
 
The in-line attenuator that I was referring to is made by Rothwell. It is, in essesence, a resisor that is placed within an adaptor that you plug into your amp and then plug your I/C into it. You can buy these on line. They reduce the pre-amp output by 10db and in my system its enuf to lower the pre-amp's line stage noise floor below audibility. Cost about $60 on line for a pair.

About your problem - I've not a clue. But since it wasn't a problem at your friends house, it must be something in your power supply. Do you have a dedicated line, etc?
jshaw1004 OP
53 posts
 
No, I don't have a dedicated line. I thought about the power issue at my home before, but why even the power re-generator (PS Audio Power Plant) still doesn't help?

Another symptom is that I still can hear the music playing while turning the preamp volume control down to the minimum. Therefore to reduce my preamp (gain) output can probably benefit to both... I will do the research on in-line attenuator. Thanks for your info.
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