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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

Showing 6 responses by jazzgene

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.
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.
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?
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
 
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?
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