Seduction hum (how much is normal?)

[2wo]

How about a Mr. Potato Head , or a very large value resistor, like 10 meg or so...John

[Paul Joppa]

Try a resistor - several values, whatever you have available. I suppose your body is less than 200K and more than 1K ohms.

[mchurch]

I am joining this thread a bit late but I have a question based on an similar experience I had. The question is do you have any fluorescent lights on or wireless phones (not cell)? Another thing to try is using an extension cord and relocating the power for the TT to see if the noise goes away.

Cheers;

Mike

[denti alligator]

I'm bumping this thread. I found a little hum in the Quickie (see that thread), which I've mostly dealt with, and am realizing that it's the Seduction that hums to levels I find unacceptable.  Moving it 1.5 meters away from my SEX makes little difference, though bringing it within 2 feet definitely makes it worse.

When I pick up the Seduction with both hands and with one finger on the ground lug the hum decreases significantly. Big time. I wish I could get it that way all the time. It's similar to the effect I described earlier in this thread, putting my hand on the TT power unit.

What can I do to get rid of this hum. To clarify, it's a low level hum with some higher buzzing. The buzzing almost completely disappears and the hum drops down in volume when I hold the amp and touch the ground lug.

I've got it grounded to the TT power unit, without which the buzzing is much louder.

But it's definitely the amp. Other sources don't have the same problem, and when I use shorting plugs on it I still get the sound.

Since I'm not using shielded cables, this may still be the best solution. I wish I had some to test out. Maybe I'll get some Blue Jeans cables to hold me over till I can afford the Bottlehead ones...

[Paul Joppa]

OK, so let's simplify to help isolate the source.

I think you hear the hum with the Seduction (shorted inputs) > Quickie > SEX amp > speakers.

First, some checks for ground current issues (also called ground loop):

1) I guess perhaps the CD player is also connected to Quickie? If so, remove its cables from Quickie. Does that help?

2) Are the Seduction and the SEX powered from the same outlet? If not, try that. If they are, try to run the power cables close together as much as possible (minimize loop area).

3) Are the power outlets all grounded (3-wire)? If not, run everything from a 3-wire power strip, so that the Seduction and SEX share a ground connection even if the wall socket does not have one.

4) Are the signal grounds inside the Seduction and SEX well connected to the chassis plate and to the safety ground? Do those connections go all the way to the power plug ground pin (the round one)?

[Doc B.]

When I pick up the Seduction with both hands and with one finger on the ground lug the hum decreases significantly. Big time. I wish I could get it that way all the time. It's similar to the effect I described earlier in this thread, putting my hand on the TT power unit.

My hunch is you might (and I certainly could be wrong too) have something going on with the safety ground in your home wiring. Not trying to pass the buck, just observing that phono preamps deal with tiny signal levels and it sounds like a situation where one of the possible issues is a lack of safety ground continuity that is working against you and injecting more hum than usual into the signal path. I deal with that in my own 71 yo house quite often. My Tode sounds great at our 5yo office, but hums a bit at my 71yo house. In my case it's probably time for new ground rods at the house.

If touching with your finger helps, only sometimes using a wire to make the same connection can help. This hum pickup stuff can be fickle...

[denti alligator]

Thanks guys.
Paul, yes, the CD player was adding to the buzzing A LOT. Turning it off (instead of leaving it in standby) made a big difference. But not enough.
The amps are going to a power strip/conditioner and into the same outlet.
The outlets are grounded. It's an older house, but I had the same problem just a few months ago in my previous residence, which was a new (<10 years) house. Anyway, why the Seduction and not the other amps?

I will check the ground on the amp tonight.

[Grainger49]

  .  .  .   When I pick up the Seduction with both hands and with one finger on the ground lug the hum decreases significantly. Big time.  .  .  .

I think this is a big clue.  It points to the ground loop hum PJ is guiding you through above.  

You say when you use shorting plugs you use shorting plugs on it I still get the sound.  Do you remove the ground lug from the TT Power Supply too and still get the sound?

Check that your outlet that you are using is properly grounded.  Home Depot has a plug in tester with three LEDs on it.  See a picture in my Pictures Of Tools thread, in my corner.

As a follow up to Dan's thought...  a quick check is to pull the interconnects out at the Seduction and check the resistance from the ground lug of the power cord to the top plate.  It should be under an ohm.

[denti alligator]

Can the wall really not be properly grounded if the SEX alone works fine, without noise?

I'll test the grounding and see if I can find anything.

[denti alligator]

4) Are the signal grounds inside the Seduction and SEX well connected to the chassis plate and to the safety ground? Do those connections go all the way to the power plug ground pin (the round one)?

OK, without checking the manual (which I'm not even sure I could find so quickly, having moved since I built this), there's the signal ground coming of the solder tabs on the outputs and from the plate on the inputs. This ground runs through all the terminal strip. There's also a ground coming from the ground lug and going to the transformer and the power input. These two ground are not connected, as far as I can tell. But they apear to be solid. Should they be connected somehow?

[denti alligator]

I should note that when I spoke of turning off the CD player to reduce the buzzing, I wasn't even referring to a CD player that was plugged in to the Quickie. It was just on. I noticed the amount of noise it was causing when I accidentally brushed up against the RCAs plugged in to it. That caused a hell of a lot more noise. Again, the CD player is there (you can see where by looking at the pic in the Quickie thread I started), but it's not plugged in to anything, except the wall.

[Grainger49]

Sam,

Yes, the wall might not have the ground connected properly and the SEX still work properly.  It could also have hot and neutral reversed.

I'm looking at my schematic and I don't show a jumper from the power (safety) ground and the signal common, aka signal or circuit ground.  I see the power ground to the transformer and to the top plate.  I don't see a jumper to the signal common.  Edit: A jumper from T10 to T11 does it.  At least it looks like those two terminals on the schematic.

Did you measure the resistance from the power plug ground to the chassis plate?

[denti alligator]

Resistance measures 0.3 ohms.

So that leaves the wall ground? What else can I check? Would adding a jumper between the two grounds help?

[Grainger49]

Ok the chassis is grounded as it should be. 

You could see if the hot blade of the wall outlet measures 120V AC, plus or minus a little, to the ground lug.  The outlet has three holes.  The odd one is ground.  The smaller of the other two is hot.  Be careful, this voltage will kill you if you touch the hot and a true ground.

[denti alligator]

I've got a power strip that tells me if I'm grounded, and it says I am.

I think it's the Quickie amplifying the hum that has returned me to this issue, since it's not that noticeable without the preamp.

Right now it's fine, IF I'm holding the amp. The second I set it on a surface (ground, shelf, etc.) the hum doubles in volume. And when I let go of the ground lug a buzzing is introduced into the hum. So it appears I'm dealing with two different types of noise.

I'm about to give up here.

(Maybe I'm being overly sensitive. The noise isn't that audible, if at all, at normal volumes through speakers. Only with quiet music turned up to a high volume on 'phones can it be heard. I'm testing without music and with volume turned way up with 'phones on, so the hum can sound pretty dramatic.)