Did you connect the ground wire from your interconnect running from the tonearm to the preamp chassis?
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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?
I've had Signature 2a before, and can tell you with confidence, that the problem you are experiencing, is the EMI induced. And its generated by the power supply. EMI affects SUT in the MC section of the phono stage. If you switch to MM, or any other input, the hum disappears.
The only cure is the physical proximity from the control unit.
Keep it as far away, as the umbilical will allow.
This is "normal" for that design.
I think you have told us. I hear what I think is tube rush! There may be a bad tube in the phono circuit, which BTW can also make humming or other baseline noise. Check your tone arm wires and check the tubes. You can get very quiet tubes from Jim McShane at his website McShane Design over at audio asylum. I have no connection to him other than being a customer.
Thanks everyone, your advice is appreciated. I would normally call Kevin or Brent, but it seems like in my audiophile life, the hum-chasing episodes only happen on the Weekends.
I know you're right, Maril555. With my components in a rack, it's difficult to find much physical separation of the Sig2a from its own power supply, which is one shelf below.
Today, in addition to the hum, I heard crackle and pops, so I went all Sherlock Holmes on my amps and found the bad tube in the right channel mono block that wouldn't take a bias adjustment. Replaced it, rebiased all the tubes, and now the pop and crackle is gone, but the hum is still there, so it's not the Phi 200 mono blocks. Everything is grounded well. It could be tube rush from the phono section tubes (the line stage is quiet). I'll probably call Brent for some advice and buy some really quiet tubes from VAC if necessary.
Almarg, I've been wanting to try shorting caps, so your advice seems well-timed to help find the source of the problem. I'll report back if I encounter some big audio life lesson that I can share!
I can save your time and effort- I've had that EXACT same problem, called Kevin, and that's what he advised me to do- move PS away from the control unit. By doing so, you will get rid of 90% of the hum. And that is THE ONLY solution. I even played with some additional shielding with m- metal, no difference.
You are right saying, that switching to MM will likely alleviate the hum. But for a different reason.
It has to do with the SUT in the MC section picking up EMI from the PS, and not with the higher gain of the MC input."
I agree. But its just too simple not to try. Also, it can't be ruled out either because we don't know what the OP has, or how its set up. You're probably right, though, given this is a common problem with this model preamp.
07-27-15: Maril555Maril555, Just curious did you try covering all unused input and output connectors with Cardas or AQ caps?
No, I didn't, but I used shorting plugs, that I feel is a more effective options, than Cardas- made no difference anyhow.
I tried mu-metal sheets to shield PS and control unit- no difference.
Actually, the advice of moving PS and control units farther apart comes from Kevin Hayes himself.
I'm pretty sure he knows what he's talking about giving that advice.
Two issues with moving the power supply out of the rack: first, it looks so darn cool to have all four VAC logos lit up at night while tubes are glowing... (See rack photo on my system page). So, now that I've outed myself as one who cares about the esthetics of my system, not just the sound... Here's the real issue: I have nowhere to hide the PS, unless I stand it on its side between the rack and the couch, something I don't want to do to this beautiful component. No other place is available, and the amps are too heavy to go to higher shelves, so I think for now, if it's indeed a proximity issue, I'll just have hum along with the hum... Thanks everyone for trying to help!
You're right, it really does look cool, that's one of the things I like about my Phi 200 as well. I know it's not as aesthetically pleasing, but could you move one of the amps down off the rack and put it on a lower platform in front of the rack, then put the power supply on the bottom shelf? Otherwise, maybe get a high output cartridge? :^)
I have nowhere to hide the PS, unless I stand it on its side between the rack and the couch, something I don't want to do to this beautiful component.That's probably a non-starter for technical reasons as well, at least without an ok from Kevin. It would cause the heat generated within the PS to concentrate at unintended internal locations, very conceivably resulting in premature failure.
Hey All your suggestions are good and appreciated. I agree with the ideas and warnings about where things "should" go... I've been looking at this set-up for a long time trying to find a way to give my gear more breathing room... but it's not realistic in my living room. A new (wider) rack won't fit unless I sell the armoire, which would not earn me any WAF points. And putting the amps near the speakers, which I would love to do, would require spending about a thousand bucks on my electrician, buying two amp stands, buying a third AC Power Regenerator and acquiring two reference quality interconnects of 32ft in length!
That original hum in question is sounding like a very minor issue about now. Maybe one day I'll build a dedicated listening room with lots of room to play with and no WAF considerations. If you all have your own space, I'm envious.