2. amps-preamps
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VAC Preamp: Is my Phono stage failing?

My VAC Standard LE preamp is exhibiting a loud, strange hum, heard in both speakers equally when MC Phono is selected. However, the hum doesn't show up until about 10 minutes of normal sounding LP playback. It gets louder with volume.

I think it may have to do with the unit getting to a certain temperature, since it starts the process over again if I turn everything off for 30 minutes – quiet for 10 minutes or so, then Wham! a loud hum that has me diving for the mute button!

If I switch the selector to any other setting, such as CD... dead silence. Could it be a phono tube going bad, and if so, how is it in both channels?

Any ideas (aside from calling Kevin, which I will do)?
alonski
pubul57
3,712 posts
 
The plot thickens:)
alonski OP
158 posts
 
The techs at PurePower were awesome, and they're in Canada, so they worked on thanksgiving! We narrowed it down to a safety ground loop. The unit is fine, as is my VAC. Seems this safety ground cannot legally be disabled, so I'm counting on my electrician to at least separate the safety grounds for each circuit so they don't bleed over. What remains a mystery is how this hum got into the signal path... Any ideas?
almarg's avatar
almarg
8,673 posts
 
My system is on two 20amp dedicated lines and all components are fed power from a AC regenerator that completely isolates the system from the wall power. I also have a hot tub in the back yard on its own separate 20a circuit.
I don't quite understand this. Do you have one AC regenerator or two? If it is only one, and all components are powered through it, how is the second dedicated line being used, if at all?

Regards,
-- Al
alonski OP
158 posts
 
Sorry Al, I should have clarified. My two channel analogue music system is my first priority. The PurePower regenerator is on this system plugged into the first dedicated line.

The other dedicated line is feeding the home theatre system which I keep completely separate. Although they are the same room, when I'm listening to vinyl, all power to the digital HT system is off. I use two Panamax power conditioners on this system.

When I'm in critical listening mode, i even turn off the refridgerator, which is quite loud in our open-plan home. Now, if I could only remember to turn the fridge back on, I would get fewer of those looks from my wife!
maineiac
649 posts
 
Alonski, FWIW, I have a dedicated line and a power conditioner and have found that the sound is improved (opened up) on my VAC integrated amp if I go straight into the wall with the amp. I have seen a number of threads that back up the assertion that amplification performance is better going straight to the wall. I know it is a bit of a risk but I take precaution to unplug during storms or if I am away for extended periods. Also, as a last resort, I guess my homeowners insurance will cover me if there is a sudden and accidental surge that wipes out my VAC.
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