Seduction hum (how much is normal?)

[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.

 

[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.

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

The wire is secure at the Seduction end. When I attach the alligator clip to the screw at the back of the TTPS buzzing is significantly reduced, but not entirely eliminated. Only when I take that alligator clip in hand and put my other hand on the TTPS does the buzzing disappear entirely. Alternately, if I hold the alligator clip against the back of the TTPS with my hand (so that my hand too touches the unit) the buzzing also stops entirely.

Note, buzzing is *significantly* reduced by just attaching the ground wire with the alligator clip. The addition of my body reduces buzzing down to zero.

 

[Doc B]

Yeah, this is the kind of thing I have experienced. My hunch is that your skin might be acting more as a capacitor than a resistor and somehow it is shunting off noise that's carried on the wire. As an experiment see if touching the wire at the Seduction end to the screw next to the IEC power inlet rather than the Seduction ground post gives any improvement.

 

[Grainger49]

How about a ceramic capacitor, 0.1uF, in series with the ground wire?

 

[denti alligator]

How about a ceramic capacitor, 0.1uF, in series with the ground wire?

I tried one of the Teflon caps 0.1uF and it made no difference. Neither did moving the ground closer to the ground nut on the Sed.

Any other ideas?

 

[fullheadofnothing]

Reading through this, I have a couple thoughts. Maybe not good thoughts, but thoughts...

First, is the power supply for this table the kind of thing that is "optional"? I.E. you could plug the table into a wall outlet, but instead you plug it into a box that plugs into the wall? If so, have you tried eliminating the power supply? I know it's a pain to change speeds by moving the belt, but maybe it's worth looking into. If you can clear this, it could point to the culprit  being either the power supply or its wall wart.

Also, I don't think anyone has talked about interconnects. Are you using shielded interconnects? How are the shields connected? At both ends or one end. On interconnects with arrows, the arrow points away from the side that has the shield attached. I know in my system, I get less hum if all arrows on my interconnects point away from my Seduction (the shield is attached to the Seduction going to both the Foreplay and the step up, and then all other inputs and outputs point away from the FP).

Hope this helps,
Josh

 

[denti alligator]

Power supply is not optional, due to this specific design of the P3-24.

I'm using cheap interconnects, so this could be the problem, but I doubt it. Any recommendations on fairly inexpensive but quality shielded interconnects?

 

[matthewmckay]

The shielding may be over-kill... but I love my interconnects from  'the-music-cable.com' .  They are very stiff cables, completely shielded in perforated copper, and should be bent into their correct positions before installation.

 

[fullheadofnothing]

For a cheap option, you could go to your local electronics supplier (Radio Shack or whatever), pick up a spool of shielded twisted pair and some cheap RCAs. Make a couple pairs, one pair with the shield only connected on one side and one with both sides connected. Try both and try the single sided in both orientations. From there, either you're happy with the sound or you can look at commercial designs or DIY recipes using a similar shielding strategy.

 

[Grainger49]

I think Joshua has hit on something. 

I tried several shielded and unshielded interconnects from my TT to my Seduction.  I got hum with all unshielded interconnects.  If the shield is not solidly grounded on the RCA plugs and/or the common is loose somewhere you can get horrible noise, hum, buzz etc.

Sam,

I thought that with the TT disconnected and shorting plugs in you still had hum.  Have you fixed that?

 

[denti alligator]

I'm calling what I hear when the TT is unplugged and the Sed shorted tube rush, not hum. The hum seems to be down to a minimum when I place the Sed on the floor. Right now I'm still trying to get the TTPS grounded well enough to eliminate all the buzz.

I don't think the interconnects are the problem here. Though I'm willing to try that at some point.

I'd like to be able to get the same silence I get when I hold the grounding wire with one hand and touch the PS with the other. Should I try another capacitor? A resistor, maybe? How is my body making the difference?