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ARC VS60 bias

I just rec'd my new ARC VS60 amp and I think it sounds quite good out of the box. The document says the burn in period is like 600hours!

My question is the bias. The amp out of the box shows 65ma. The manual says 60ma. This is my 1st tube stereo amp so I am looking for veterans advice on where to set it. I suppose the tubes will last a bit longer at 60ma and I should use my ear to judge...
jazzgene
14 responses Add your response
jazzgene OP
145 posts
 
Yes. I swapped the tubes from R to L. Measurements remain the same.

I want to add that the ARC spec of 0.2mVAC with input shorted is IHF weighted. I don't know if it is A-weighted but most likely it is. If that is the case, then my measurements of noise is well within spec of 0.2mVAC RMS.

hmmmm... Any tech guru's out here? What do you think?
bjesien
1,283 posts
 
Have you swapped tubes from one side to the other?
jazzgene OP
145 posts
 
Spoke with ARC. They say the slight hum in the speaker is normal for this amp. However, the published spec states 0.2mVAC with inputs shorted.

I checked it out and the left channel shows 0.7mVAC and the right channel shows 0.25mVAC. I'll have to get to the bottom of this. A new amp shouldn't have nearly 3x more hum in one channel than the other.
jazzgene OP
145 posts
 
I have called ARC. Waiting for Calvin to call me back.

The efficiency of the speaker is 91db. It's Focal 1027 Be pair.

The amp is brand spanking new from a dealer here in the NYC area.

Cmalak - are you saying that this amp should be dead quiet in the speaker with no hum?
bjesien
1,283 posts
 
What is the efficiency of your speakers? I've used similar ARC amps with 87-94 db speakers and never had humming and buzzing except when it was in the music or connections were bad.
cmalak
681 posts
 
Jazzgene...that should not happen at all. Did you call ARC? If you bought this through an authorized dealer, you should be able to get the unit replaced or fixed so that there is no hum.
jazzgene OP
145 posts
 
The buzzing is from the power transformer. As for the hum in the speaker, I think it is because the transformers are so close to the power tubes. The hum is there with nothing connected on the input. I've also tried lifting ground but the hum remains.

I'm considering PS Audio's Humbuster III. They told me this would stop the buzzing.
bjesien
1,283 posts
 
I think you should carefully check all of your cable connections. You should not hear any buzzing sounds with this amp. Are all interconnects clean and firmly secured?
jazzgene OP
145 posts
 
The transformer on the VS60 buzzes a bit. And the amp puts out a small amount of hum to the speaker. How can I get rid of these noise?
jazzgene OP
145 posts
 
I went with 60 ma. The music sounds better to me at 60ma as well.

I called ARC. The guy I talked to did not know that VS60 was lowered to 60ma and had to consult a manual. I guess all the older 6550 amps were set to 65ma. So I guess ARC is still sending out the new VS60 set to 65ma.

Anycase, the amp sounds very good.
rrog
1,958 posts
 
Your AC voltage is higher than the voltage at the Audio Research facility. Lower the bias to 60ma as recommended.

This is not something you do by ear.
hifihvn
943 posts
 
Voltage variations may have caused it too.Its better to have
it to low,instead of to high.That way it will run cooler,that
is the amp,and tubes.
cmalak
681 posts
 
I should use my ear to judge...

Not when it comes to tube biasing. I would call ARC and reconfirm that it should be biased at 60 vs. the 65 it was shipped at. Normally, tube bias will drift with inital use but since they came set at 65 when ARC sent them before use you may want to confirm which is the right setting. Just my 2c worth.
stereo5's avatar
stereo5
6,385 posts
 
"I should use my ear to judge... Bingo!
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