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
maineiac
649 posts
 
If the VAC phono fits your needs and you love it, then the repair costs will likely be a fraction of what it would take to get a closely performing outboard unit . I bet you the cost of repair would not even be what you would want to spend on a good power cord for an outboard phono stage. Call Kevin or Brent and they will tell you if there is something obvious to check or do and the range of how much you are looking at in terms of repair.

The advantage of an outboard phono is that most have a great deal of flexibility in terms of gain and other settings that allow you to use many different cartridges. VAC might box you in a little with the phono but I am guessing it is extremely good for the carts that can be used with it.
pubul57
3,712 posts
 
Have you asked Kevin what he thinks the problem might be?
alonski OP
158 posts
 
SOLVED! Well, almost.

Maineiac, Thanks, I really wonder how much I would need to spend on an outboard tube Phono Preamp to be significantly better than the VAC's.... sounds like it might be a lot. I would love to audition the Fosgate Signature, it's received good reviews and it looks so cool.

Pubul57, I spoke with Brent at VAC and he never heard of this problem and said to send it in for a check up. I guess the very notion of being without music for a few weeks was bad enough to kick my brain into gear and identify the problem's source.

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.

Every time the hot tub motor turns on, the hum shows up in my phono stage. If I then turn off the tub, the hum disappears.

Considering the system and the tub are on completely separate dedicated circuits AND my gear is completely (supposedly) isolated from the wall power... how could this be?

I'm calling the electrician back in and I'm going to call PurePower and have a little talk with them. I don't think this has anything to do with my VAC.
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?
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