Seduction hum (how much is normal?)

[denti alligator]

In trying to locate the source of my turntable hum I got me some shorting plugs. Putting these in the input jacks, with the output going to my SEX amp I'm hearing noticeable hum when the volume pot is at 60 or higher. Normal?

It gets more noticeable when the turntable is plugged in.

 

[Grainger49]

Sam,

Very little hum is normal.  How does the SEX do with shorting plugs in the input and the volume at 60?

If that sounds very quiet then you have vindicated your table/arm/cartridge with the shorting plugs and located the hum to the Seduction (you lifted the TT ground wire, right?).  I'll post all the ground/circuit common terminals and you can check them.

Any terminal with a bunch of solder should be "wicked" then resoldered.  I'm a big fan of making a tight mechanical joint first.  That requires crimping the wire end with a pair of needle nosed pliers first. 

The fact that the hum increases with the TT on says you might not have a good ground.  Or that the TT needs the power cord flipped, rotated 180 degrees.  If you can't do that get a "cheater plug" and try flipping. 

We can beat this if you persist!

 

[Doc B]

What kind of listening level is that setting? Too loud, or just right? Also, does the noise have a buzzy component or is it a soft 60 cycle hum? If it's buzzy you may have a ground loop with other gear that can be found by unplugging the other gear and seeing of the hum changes. Is the preamp near any equipment with a power transformer? If so try moving the preamp to see if it's picking up 60Hz from another piece of gear.

 

[denti alligator]

Shorting plugs in the SEX inputs gives me ZERO hum. None at all. But that doesn't tell me anything about the turntable, which then isn't plugged in.

The hum is kind of buzzy with some hum. The volume level is just right for me, which is maybe a little loud, but not too loud. It's right where I like it.

 

[Doc B]

If it's buzzy then you usually have ground problem somewhere. I can't recommend it for liability reasons but some folks try cheater plugs to lift the ground on one piece of gear in order to break a ground loop.

 

[denti alligator]

Like a ground loop isolator? I've got one of those from Radio Shack. It doesn't appear to be making much of a difference, but let me try again.

I should say that I had a pretty nasty buzzing that was mostly eliminated by running a wire from the ground bus on the Seduction to the external power supply unit of the turntable.

Lifting that ground makes for an unbearable buzzing.

With that ground in place, I'm still getting buzzing. But I should also note that I have plugged a different turntable into the Seduction and heard almost no buzzing/humming, which seems to locate the problem elsewhere. Shorting plug experiment says otherwise...

I'm confused. And a bit frustrated.

 

[denti alligator]

More info:

The Seduction is sitting right next to the SEX on a glass shelf. Turntable above them. Turntable power supply a shelf below.

Cheap switch being used, but I'm not getting noise from the other two inputs, so I doubt this is the problem. Switch is behind the subwoofer, which is not turned on during listening. Also near wall power. Nothing else beside a floor light nearby. Phone on other side of the wall.

 

[Doc B]

Ground loop problems imply two pieces not working together. So actually the experiment with the other turntable not making noise tells you that the problem is between the current turntable and Seduction. When you shorted the inputs on the Seduction was that wire still connected between the ttable and Seduction? If so try the Sed again without the Ttable connected to it at all. If the buzz goes away it may be that a cheater plug on the ttable cord (if it is three prong) will help.

 

[Grainger49]

Sam,

To be certain that nothing is radiating hum/buzz try spreading all electronics out with a foot of two between each using shielded interconnects.  This is a situation of it can't hurt.  

Try unplugging the power supply for the table with it still connected to the Rega and the Seduction.  Does it still hum/buzz?  It should since the shorting plugs didn't remove the problem.  

When you tried the shorting plugs did you lift the grounding wire from the turntable power supply?  You want no other connections except the interconnects to the SEX.  

 

[denti alligator]

It's so hard to tell now, but I moved the Seduction just an extra 10-12" or so from the SEX and I think it's better. I'm still getting hum at 70/75+ on the volume pot (shorted SEX or from TT), but I think this is normal, no? Playing Neil Young's Zuma right now at about 70 and hum is inaudible in between tracks (well, not the cleanest record, but...) and it's plenty loud.

 

[denti alligator]

So, yes, the buzz is gone. But again, a deep hum is present. So I put that ground loop isolator in between the turntable and the Seduction input and it got rid of the deep hum. Now there's only a higher pitched buzzy-humming that is very quiet, and only really noticeable at 90+.

So I guess I'm happy...

 

[Laudanum]

The RS Ground Loop Isolator  ... like this?  ... http://www.radioshack.com/product/index.jsp?productId=2062214#

 

[Grainger49]

Sam,

You might have to stop at a hardware store or Home Depot and find a "cheater."  This is a grounded to phased plug adapter.  It removes the ground on one component, this would be your TT power supply (PS).  The first thing to try is removing the ground from the PS.  Then you should try rotating the plug 180 degrees, this swaps the hot and neutral.  Both are standard hum busting techniques.  

Then there is a whole permutation of grounding wires.  You have one from the PS to the Seduction.  Have you run a ground wire from the table/arm to the Seduction?  (I know we went through this before but I don't remember the answers.)

I would expect that the ground on the PS is carried on to the TT, but maybe not.  You just have to seek out the combination that works for you.

The grounded terminals are T3, T8, T13, T18, T23, T28, T33, T38 & T43.  These are all connected to the chassis/safety ground. 

The circuit common terminals are T7, T10, T11, T14, T16, T20 and tube pins 4. 

Somewhere they are tied together with a wire or jumper, but I'm not sure where.  It may be at the ground buss at the inputs.

You should go over all these and check.

 

[denti alligator]

Laudanum, yes, that's the one I have. I have a feeling now that the hum appears to be mostly eliminated with the ground loop isolator that the entire sound of my records has been 'thinned out,' that is, there's less bass. But maybe that's a misperception.

Can these devices affect the sound significantly? Well, I know they can, because the hum was eliminated, and also because I hid it behind some other wires that happen to have been near the switch I'm using, and this only brought the hum back. Keep the isolated itself isolated took care of that.

Grainger, thanks for the tips. I'll report back when I've found the time to investigate further.

 

[denti alligator]

Yeah, that ground loop isolator was killing the sound. Out it goes. I can live with hum if removing it means losing the heart and soul of the music.

The PS goes into the wall with a wall wart, so there's no ground. And anyway the hum is there whether it's plugged in or not.

But now I've moved the Seduction back next to the SEX and the hum does not increase, nor does the buzzing return. Weird, though it's now on the other side, so the inputs are no longer close to the other amp. Not sure if that makes a difference. Or rather, I guess that makes a difference...

 

[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.