ARC VS60 hum in speaker

[GeneJazz]

I have a brand new ARC VS60. When I connect my Focal 1027 Be speakers to them, I have a very soft 60hz hum coming from them. I tried disconnecting the input of the amp and hum still remains. I also tried lifting ground and the hum is still there.

The hum is not loud at all but I am concerned if this is a defective amp. Should this amp be dead silent at the speaker or is a small amount of hum normal? For what it's worth, I upgraded from a solid state Arcam amp and that amp was dead silent.

[analog_sa]

Have you tried it with the inputs shorted? The Focals are not high sensitivity, so yes, it should be completely silent.

[Zen Mod]

considering what's written on their web page ARCDB - VS60 , I think that's time for you to call your dealer

don't do anything , because of warranty .

with this :

Hum & noise Less than 0.2mV RMS - 100dB beow rated output (IHF weighted, input shorted).
Power supply energy storage Approximately 166 joules.

there must not be any hum

[GeneJazz]

Originally Posted by analog_sa

Have you tried it with the inputs shorted? The Focals are not high sensitivity, so yes, it should be completely silent.

No. Just unplugged. I've been told the Focal 1027 Bes are high sensitivity at 91db. Is this low? or high?

[GeneJazz]

Originally Posted by Zen Mod

considering what's written on their web page ARCDB - VS60 , I think that's time for you to call your dealer

don't do anything , because of warranty .

with this :



there must not be any hum

I have called them and waiting for Calvin to call back.

[GeneJazz]

After a quick search on "hifi strereo tube amp hum", this problem is not uncommon at all. Vast amounts of tube amp seems to emit a soft hum in the speaker from what I read. The hum is quiet and only noticeable when I put my ear to the speaker. However, I'd like to correct this if possible. I'll test it with the inputs shorted and see what's up.

[analog_sa]

Originally Posted by GeneJazz

No. Just unplugged. I've been told the Focal 1027 Bes are high sensitivity at 91db. Is this low? or high?

Speakers which are above 100db sensitive are known to make hum problems a lot worse. 91db is just above average.

Unless you actually measure the hum with the inputs shorted it will be hard to say anything for certain. And to what end? Is it worth shipping the amp back for a minute amount of hum? Not sure if ARC would be able to do much about it anyway.

[GeneJazz]

I did just that. I took the amp to my bench and measured the hum with the inputs shorted. The published spec states 0.2mV IHF weighted.

I measured on the right channel, 0.25mV and on the left channel, 0.7mV. Nearly 3 x more hum. I did notice the left channel hum to be louder so I wanted to confirm. It is not the tubes as I swapped the R and L channel tubes and still got the same measurements.

I think there is something wrong with this amp and will call ARC for an exchange or repair. A brand new amp shouldn't have 3 x more hum in 1 channel, I would think.

[analog_sa]

Originally Posted by GeneJazz

I measured on the right channel, 0.25mV and on the left channel, 0.7mV. Nearly 3 x more hum.

A friendly advice: unless you intend to listen exclusively on headphones, ignore the hum. I don't believe it can actually interfere with yours or anyone else's enjoyment of music.

As an academic exercise it is certainly interesting to analyse the source of it. Without knowing anything about the circuit i would venture that it is most probably a design oversight, rather than a defective component. As HT and heater supplies are common you can remove the PS as a culprit. Which mostly leaves poor ground layout or inductive coupling as possible sources of hum. Not likely ARC will fix either of those but a good technician, after investing some time and effort might.

[GeneJazz]

Originally Posted by analog_sa

A friendly advice: unless you intend to listen exclusively on headphones, ignore the hum. I don't believe it can actually interfere with yours or anyone else's enjoyment of music.

As an academic exercise it is certainly interesting to analyse the source of it. Without knowing anything about the circuit i would venture that it is most probably a design oversight, rather than a defective component. As HT and heater supplies are common you can remove the PS as a culprit. Which mostly leaves poor ground layout or inductive coupling as possible sources of hum. Not likely ARC will fix either of those but a good technician, after investing some time and effort might.

VS60 is a power amp so for headphone listening, I would leave it off. You are right with your insight. From a practical point of view, the hum is not too objectionable.

On the other hand, my tech interests wants to get to the bottom of this. Who knows, it might be as simple as using a chopstick and shifting some wires a bit.

I'll speak with ARC again. Perhaps they can send me another one and if that one is good, I'll do an exchange. These amps aren't cheap and I don't think one channel should be so out of spec.