VAC Signature 2a Preamp Question


Before you say, "Dude, there's already a thread posted about this question!" Well, forgive me, I could not find it. This is an inquiry for Signature 2a owners who have the built-in MC/MM phono stage: When the selector is on #6, which is the turntable, I get a background hum and some of what is probably tube rush, and it's especially audible with no music playing with the volume up. When I switch to the DAC setting, with the same volume setting, everything is dead quiet. Do I have a problem or is this normal?

Your feedback is welcome and appreciated,
Alón
Ag insider logo xs@2xalonski
If you're not 100% sure, try the MM setting regardless. You can't damage your system in any way. You're essentially lowering the volume, so don't be afraid to try it.
Is there any other equipment above or below (in close proximity)to the phono board? If so move it/them away and hear what happens (after doing Zd542's excellent suggestion, of course).
Adding to Dweller's comment, is the control section of the preamp sitting on top of or close to the power supply?
The phono stage uses additional tubes plus the line stage tubes. So you could have more tube noise. That said, did you buy new, or a used unit? How many hours on the 6 12AX7 phono tubes?

I would contact VAC, Kevin and Brent have always been very helpful and responsive to my queries.
Alón, a couple of experiments that may shed some light on what is causing the issue:

1)Disconnect the turntable from the preamp and insert shorting plugs into the preamp's phono inputs, and assess the hum and noise levels under that condition. (Have everything turned off, of course, while you make the change). Googling "RCA shorting plug" should turn up a number of such plugs you can buy, or else you could simply buy a couple of RCA plugs at Radio Shack or wherever and solder a wire between the center pin connection point and the ground sleeve connection point.

2)Temporarily, as an experiment, put a cheater plug (a 3-prong to 2-prong adapter) on the preamp's AC power plug, without connecting its safety ground (what would normally be connected to the wall plate screw) to anything. That will break any ground loops between the preamp and the other components it is connected to. Ground loops, of course, can sometimes contribute to hum and noise.

Those two experiments should help to determine if the problem is due to something internal to the preamp, or to some external influence.

Also, as I recall you purchased the Signature 2a a couple of years ago. Has this issue been present all along, or did it just arise recently?

Best regards,
-- Al