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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
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
4,093 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.
mybuddy
13 posts
 
i have an arc ls25 mk2 with bryston 7bst. these components i believe have very similar impedance specifications as ur arc and pass. both components are dead quiet and even with my ear to the speaker, no noise.

i don't think its an impedance mismatch. i recall reading something from the pass website that the x600 amps can be driven by anything and impedance mis-matches is rarely a problem.
audioengr
3,282 posts
 
Sounds like an internal ground-loop. I fix lots of these in my mods. They are common even in high-end gear.
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