Seduction hum (how much is normal?)

[denti alligator]

Alright, back to the start. The Seduction is definitely humming. It's a low, deep hum, not buzzy.

I'll go ahead and check those ground terminals and see if anything is loose. What else can I try? And again, how normal is this? Grainger, you're first response to this question could be read in two different ways:

1. It is normal to have a little bit of hum

Or

2. Normal is to have very little, i.e. almost no, hum.

[Grainger49]

I go with normal is to have very little hum, almost no hum.  Part of it has to do with the S/N ratio with your cartridge being the signal.  IIRC it is around 4mV, right?

[Paul Joppa]

Yes, that ground isolator is a pair of tiny transformers. They are probably designed to work best at 1K or 2K ohms, not 47K like the Seduction input.

The good thing is, now you know it is a ground current problem - there is hum current in the ground side of the interconnects between the turntable and the Seduction. The puzzle is where does it come from. You say that removing the power supply from the wall socket has no effect, so it has to be capacitive coupling from something else, or a ground loop within the turntable/power supply/interconnect/ground wire system. Sometimes the "cold" side of the cartridge wires is grounded at the turntable, which allows some (or all if you don't have the separate ground) of the current to go through the interconnect grounds. Does the ground wire (turntable to Seduction)run close to the interconnects? If not, that would allow for magnetic hum pickup in the loop area.

Since this is a puzzle - the obvious ones have not helped - consider the possibility of old-style flourescent lights, light dimmers, etc.

[Laudanum]

The arm on his table is a Rega.  Internally, there is a ground wire for the arm tube and the arm base, both are carried on the shield of the left channels cable.  There is no seperate, external ground wire.
For the record, liberating the grounds from the left channel RCA and using a seperate ground wire with my Rega arm didnt make much difference if any at all.  Re-wiring the arm did but that was because the internal wiring was a mess with atleast two cold solder joints.

Denti --- I was going to tell you that I tried that RS ground loop islolator in a car audio system installation many years ago.  It kills the bass as you already found out.

It's been mentioned to flip two prong plug for TT if possible.   If you havent tried it yet, try flipping two prong plugs for everything.   The culprit of the last bit of low level hum and buzz in my headphone system ended up being the CDP.  Strange because the CDP and the digital player were quiet but selecting the TT as source, I still had a little bit of hum and buzz.  Once I unplugged the CDP it was gone.  There may be a little bit still there with FPIII and Crack wide open but I would never come close to listening that loud and I doubt that my HP's would survive it.  For all intents and purposes, it's quiet.  I havent heard anything between tracks even at my highest listening levels.   Also, I noticed that there was more hum from an Ortofon OM10 compared to the other carts I tried ... Shure, Pickering, Music Hall.  But I havent tried the Ortofon again since the fix.   This is on my headphone system - Rotel TT (RB250 arm) - Seduction - FPIII - Crack.  Keep at it, it can be very quiet if not silent. 

[denti alligator]

Thanks, guys, but the turntable can't have anything to do with it, since the hum is there when it isn't even plugged in to the Seduction. That's how I've been using the shorting plugs, at least: they go in the inputs, the outputs are still going to the SEX.

[Doc B.]

The normal noise floor of the Seduction has a very slight bit of 60Hz (soft low hum, not buzzy) in the right channel (due to the right channel circuit components proximity to the power transformer) This is usually only heard when the system is really cranked up to excessive loudness. As Grainger points out, whether it intrudes or not will depend upon the output level of your cartridge. If it is down around 2mV it might. If it is up around 4-5mV as we recommend it shouldn't be a problem.

[denti alligator]

Output voltage of the cart I'm using is 5. But again, I'm getting the hum even when the table is not connected to the Seduction.

Should I check out the grounding at the terminals Grainger suggests or is there another troubleshooting tip you might suggest?

[Doc B.]

If it's just low (60Hz) hum, not buzzy, it's not grounding issues. That would be magnetic coupling, similar to the kind of problem one can run into when using a step up transformer. I'd suggest trying to move the Seduction away from the SEX and other gear with power transformers as far as possible, and also try rotating the Sed relative to the other gear. Sometimes you can null out the magnetic fields that are coupling with the circuit that way.

Another possibility is to try different tubes if you have any handy. Some might be a wee bit less susceptible to picking up hum, though I don't know if the tubes are really the main culprit in picking up the magnetic field so I don't know that you would hear a night and day kind of difference.

[denti alligator]

Switched out tubes. Same.

Moved the Seduction. There's a very, very low hum that goes away when it's placed right, but the main noise is still there. What is this noise? Well, it's a kind of sshhhhh white-noise-ish sound. Not really buzzing, and not just a low hum. Somewhere between the two. Again, it's only audible at 70+ on the volume pot. But that's where I listen, a lot of the time.

[Doc B.]

The shhhh part of the noise is tube rush, pink noise coming from the tube itself. The only cure for that is to look for tubes that do it less (or use a cartridge with a higher nominal output level). Unfortunately the tube price often tends to be inversely proportional to the noise level. Tubes like 7308s were designed for lower noise output and may help.

[denti alligator]

OK, I've played around with this a bit. I think what I'm hearing is a combination of three noise sources: 60hz hum, tube rush, buzzing from poor grounding.

The hum is reduced when I move the Seduction to the floor, but only to the floor. I don't really want to leave it there, so I'll have to figure out a way of positioning it to assure reduced hum.

The tube rush is minimal, especially once I plugged in the turntable again (I was testing with the shorting plugs in).

That leaves the buzzing. Yes, there's still some buzzing. But I know where it's coming from. It's the turntable power supply. I've already soldered alligator clips to the ends of a piece of wire (leftover Teflon coated from the Sed kit) and attached one end to the ground bus of the Sed and the other to a screw at the back of the TTPS. This reduces buzzing significantly. However, not fully. If I hold the other end of this wire in my hand and touch the power supply it goes away entirely. So my attempt at grounding is not good enough. How might I make a more solid grounding?

[Doc B.]

If I hold the other end of this wire in my hand and touch the power supply it goes away entirely.

Oh man, that is one effect that makes me nuts, when somehow touching a ground wire works better than actually grounding it. I can't quite wrap my head around what is happening that isn't working when the wire is directly connected, but I have sure experienced it many times. I'm guessing that somehow the path through the Seduction chassis and safety ground wire is actually allowing the injection of noise into the preamp as it passes thru it. Maybe try touching the wire from the screw on the TTPS right to the safety ground in the wall socket? (REALLY CAREFULLY)

I'll say it's 50/50 whether it makes it better or a lot worse... Grounding issues are a challenge indeed.

[Grainger49]

Sam,

Let me see if I get this right.  With your body as a high value resistor in series with the ground wire from the TT to the TTPS you get no buzzing at all?  Do you see where I'm going here, try a 100k resistor in series with the ground wire.

I'm thinking that you should take a meter and see if the chassis of the TTPS is grounded to the TT when plugged into it.  It seems to me that the power supply connection should include an integrated ground.  

That also makes me wonder how close to the TT the TTPS is.  The whole reason for outboard power supplies is to remove the noise producing components (mostly hum) from the audio generating components (cartridge/arm).

After that let's try wrapping the TTPS in aluminum foil and swinging incense above it.  Maybe a Voodoo doll?  (I'm not really serious with those two.)

[denti alligator]

No, ground wire is from the Seduction to the TTPS. And that's where my body adds something to reduce buzz to zero.

The TTPS is over two feet below the turntable.

Should I add a resistor to the ground wire going from the Seduction to the TTPS?

[Grainger49]

No, ground wire is from the Seduction to the TTPS. And that's where my body adds something to reduce buzz to zero.

I'm not sure I follow, is the wire secure on both ends but your touching it makes the buzz go away?

The TTPS is over two feet below the turntable.

That should be more than enough distance to keep one from inducing hum into the other.  It is something else.

Should I add a resistor to the ground wire going from the Seduction to the TTPS?

I don't think so.  It depends on your answer to the first question in this post.