Seduction hum (how much is normal?)

[howardnair]

http://www.onlinemetals.com/merchant.cfm?id=753&step=2&top_cat=6
i buy from these guys they are excellent-if you search the site you can create anything you want-with thin sheet you could put it inside the wood chassis-and get a perforated bottom
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or   vt4c.com--takes awhile to populate
also
http://www.ebay.com/itm/Full-Aluminum-Chassis-for-audio-DIY-Power-amplifier-2109-/230858336808?pt=US_Amplifier_Parts_Components&hash=item35c03aaa28
hope this helps ---howie

[denti alligator]

Looks good, Howie, thanks. But what thickness should I get? And how to attach (glue, staples?)

[denti alligator]

Alright, one last time (I SWEAR):

Going back to phono after a week of only listening to digital, I am surprised again by the background hum.

Normal volume with speakers it's not really noticeable.

But normal volume on 'phones it is. Those using the Seduction with SEX/Crack and 'phones: before the needle hits the record, do you hear a background hum? In between tracks? Again, I just want to be sure this is normal, and that I don't have a more serious problem.

[Grainger49]

Sam,

At 8 pages it is going to take a long time to sort it out.  Can you post what you have tried?  Also, can you measure the hum on each channel, Seduction input shorted.  Hum is AC.  A quick reading would help. 

And maybe you have done that.

[denti alligator]

I forget if I've measured, though I think I have and got no reading, or near 0.

Let me do it again. I can say it's definitely the Seduction (i.e. when shorted I still get hum) and that moving it several feet from the other amps doesn't appear to help much. I may just send it to you, Grainger, to check out, if that's OK.

[Grainger49]

I'm willing.  I agree, we had nailed it to the Seduction.  Or at least the Seduction TT/PS combo.  But I do think it was finally isolated to the Seduction.

[Grainger49]

Sam,

I looked up the Sennheiser HD-600 headphones.  The spec is 1k Hz at 1V 112dB.  If that were a speaker you could power it from the Quickie alone (I exaggerate)!  If I am reading Sennheiser's site right they are very sensitive.  So this is part of the problem. 

[denti alligator]

But isn't this all relative to the volume at which I listen? I hear the hum at normal listening volume.

[Grainger49]

Normal listening volume is different for your speakers and headphones, right?

You have said that the noise is not a problem with your speakers but is a problem on phones.  Compounding the problem of sensitivity is that you are so close to the transducers with phones, there is only a little air between them and your ears.  There is a lot more between the speakers and your ears.

[denti alligator]

Another potential clue (for those who are still reading this thread):

With shorting plugs in the input and not powered on, the Seduction buzzes pretty bad. When I switch the power on it is DEAD QUIET until (no buzzing, no humming) for a few seconds until it's fully powered up, at which point the buzzing disappears and is taken over by humming.

I really want to get to the bottom of this. Is this just because my speakers and headphones are so sensitive?

[Doc B.]

We can't answer your question with any accuracy unless you can measure the hum level or better yet get a picture of it on a scope. There will be a very small amount of 60Hz in the right channel of some Seductions, based primarily upon the sensitivity of the rear tube to magnetic coupling with the power transformer. But in general the question "is this hum normal" is very difficult to answer without access to the device.

[Paul Joppa]

...With shorting plugs in the input and not powered on, the Seduction buzzes pretty bad. ...

That's a big clue!
I've lost track of the details in this thread, but you can only know that with other things downstream of the Seduction. Most likely, here's what's happening:

Something downstream has a power transformer. That transformer's primary has some capacitance to the secondary which goes to the power supply and signal ground. That capacitive coupling induces a current from the ground of the device power supply, through the grounds of the interconnects, to the chassis ground of the Seduction which is connected to safety ground. The voltage drop across the resistanceof the interconnects, RCK\A jack/plugs, circuitry, etc. creates a voltage which is amplified by the downstream device(s) and is what you hear.

There are other possibilities. It's possible that the neutral and hot are reversed at the power socket, so that the neutral is switched and the hot stays connected when it's switched off, causing some ground current from the Seduction.

It's also possible that it's radio frequency pickup, with various bit of metal acting as an antenna. You can check this by unpluggin the Sediction from the wall. If it still buzzes, you are picking up an environmental sgnal which is detected by some device downstream - probably the first one.

[denti alligator]

I'm not sure I entirely understand you, Paul. But would the buzzing-when-not-turned-on be related to the hum-when-turned-on?

I'm pretty sure I heard the buzzing when the power cord when not plugged in.

Recall that my SEX/Quickie is mostly very quiet with the CD or digital input. No hum or buzz.

I need to get a cheater plug to flip the hot-neutral on the Seduction. This is one test I haven't tried yet. Could it really be what clears this up?

[Doc B.]

Cheater plugs can clear up buzzy 120Hz from ground loops. But they won't do much for soft 60Hz hum, because that is from coupling between the power transformer and another component. You seem to be describing the latter as what you hear after the amp comes to life and the buzzy component goes away. Am I following you correctly?

[denti alligator]

Yes, except distance to the other amps doesn't seem to make all that much difference.

My shielded interconnects aren't that long, though. I'm assuming interference with the SEX would be the main culprit, right? So if I can get it 6 feet from the SEX and 3 feet from the Quickie and still get hum, then can I rule this out as a source?