"I should use my ear to judge... Bingo!
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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.
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.
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.
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.
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?