Seduction hum (how much is normal?)

[Grainger49]

The first question is, do you listen to quiet music with the volume all the way up?  This is a sickness brought to us by magazine writers who report that the XXXXXXX was dead quiet in my system even with the volume all the way up.  It is not a real world test for most of us.  I listen to my Eros at 9:00, used to listen to my Seduction a quarter turn louder.  Eros has more gain.

The hum and buzz can be measured at the output jacks of the Seduction with the inputs shorted.  That will help put it in perspective.  Unplug the table, including ground, from the Seduction and the Seduction from the Quickie then set your meter to AC and measure.  There are low level noises that will always be there.  

When you asked "Would adding a jumper between the two grounds help?"  Which two grounds were you speaking of?

The components of the noise can be seen on an oscilloscope.  I have one.  It doesn't really measure the RMS value of AC signals but will reveal the peak to peak voltage there.

 

[denti alligator]

I'm measuring 0.00.  ???

This is driving me bat crazy.

 

[Grainger49]

Sam,

I edited the post above and were you measuring AC volts?  

If you are bat crazy you must retire to the Bat Cave for a cold one.

 

[denti alligator]

Yes, measuring AC.

And yes, I sometimes listen to quiet music with the volume higher than usual. I find that with headphones I the pot ends up around 2/3 up. With quieter music it may go higher. And no, it's not totally blasting my ear off.

What's the next thing to try?  By connecting the two grounds I meant the one at the inputs/outputs/terminal strips and the one at the power/transformer/ground lug, which, as I said earlier, do not appear to be connected.

 

[Laudanum]

I know there are other things at play but just out of curiosity, what cartridge are you using?  On my Rotel table with Rega arm,  the Ortofon cart (Super OM10)  exhibited the most hum but it was still low level such that it was not heard at the highest I would listen.  On the Technics table I havent tried all my budget carts.  I use either an M97 or a Pickering XV-15 and again, whatever low level noise (hum) there is with the Crack volume cranked up,  I dont hear it with music playing or between tracks at my highest listening levels.    System = Table - Seduction - FPIII -  Crack.  Still need to make room to be able to add one of my small amps and some speakers.

 

[denti alligator]

The TT is out of the equation. I've tried to isolate the source as much as possible, and it's really the Seduction that is bringing in the most hum/buzz. That is: I'm now using shorting plugs for the input.

 

[Grainger49]

Sam,

The schematic doesn't indicate a connection.  Edit, it is between T10 and T20, according to the Bottlehead schematic. 

Using a wire touch to the top plate and the ground buss.

 

[denti alligator]

Will try it tonight. What do you mean by "touch to the top plate and ground buss"? I was just going to solder a piece of ground buss from one of the grounds to the other.

 

[Grainger49]

Soldering is good.  Touching them together is faster.  There should be no voltage difference between them.  Touching will answer the question.  If it works, solder.

 

[fullheadofnothing]

Looking at this thread, I am very confused about what is being discussed.

All Bottlehead gear uses a few techniques to minimize noise that I don't necessarily understand, but they seem to work for most people. First, all the pieces (except the Quickie) use a ground tab that connects the chassis to earth ground (3rd prong); this makes the basis for the star-ground. The signal ground is connected to the ground at one point. [EDIT: not 100% sure about this being a "single point"] In the Seduction, it's at the inputs

 

[Grainger49]

Joshua,

Just looked at the manual, one wire from the RCA inputs' common lands on the ground plane.  Is there a connection between the chassis and the ground plane?  Are the inputs connected to the chassis and then through the ground plane?

The FP 2 had no connection between the signal common and the chassis/safety ground.  If noise persisted it was a common fix to jumper terminal 13 to terminal 14 which made that connection.

Even with Shielded Twisted Pair (STP) the signal common is usually, but not always, connected to the chassis of the sending and receiving pieces.  But the additional shield grounded to a chassis, a grounded chassis, gives additional noise abatement.  It sounds like this is redundant.  Won't hurt if it is redundant and might help if it isn't.

I think Sam and I are on the same page as I suggested connecting the incoming ground/safety ground to the known signal common.  

 

[denti alligator]

Next, Grainger asked if Sam actually listened at a loud enough volume to hear the noise while listening to music. This is the crucial question-all systems make some noise, particularly when they are amplifying very small signals. If you are hearing the noise at full volume but never listening at that level, it does not matter.

Yes, this is key. But I'm persisting because the hum is loud enough that is CAN be heard in quiet passages or when listening to music with few instruments (jazz trios, quartets, folk, classical...). Even if it's not nearly as prominent, it's there. And I don't like it.

Granted, when listening through my speakers I can't tell the difference, unless I'm really cranking it--and then only in between tracks (but hey, that's still annoying). Mostly this is a headphones issue.

 

[fullheadofnothing]

I am working under the assumption that this discussion is based around the S.E.X. Am I right? Please be explicit here, I can only help if I know what we are talking about. My biggest source of confusion is in statements like this "I think Sam and I are on the same page as I suggested connecting the incoming ground/safety ground to the known signal common. " Very specific, yet completely vague.

Looking over the S.E.X., the chassis plate forms the main ground, it is connected to earth ground via the solder tab near the power inlet. The right input is connected to ground: black from the input goes to the pot, which goes to 12L, which is jumpered to 13L, which is a center terminal on the strip, therefore chassis, therefore ground. The left channel does not repeat this connection, most likely for noise issues of some kind (ask someone smarter than me for full details). Both channels are definitely connected to ground with the jumper from the headphone jack to 23L (again, center terminal). The specifics of this connection will vary depending on the jack used (varied yet again if the Impedance Switch Boards are used), but the connection is made regardless. I will edit my previous post since I'm not so sure about the statement about signal ground being connected only at one point.

As for the STP interconnects, they worked for me. I was having terrible hum with a coax based interconnect, I made something as described, my hum went away. Like I said, YMMV, but a few bucks at Radio Shack and a few minutes at the solder station can go a long way.

 

[Grainger49]

Touch to the top plate and the ground buss.

Is this vague?  This will hard wire the safety ground to the signal common.

As the title implies, it is a Seduction hum problem.

You didn't answer the question about the RCA input jacks and the ground plane.  Do you have a Seduction near to check?

My comment on STP was to point out that it doesn't remove the ground from signal common.  It just adds an additional shield.

 

[fullheadofnothing]

Grainger, it's vague because when you are clearing up a systemic issue, it needs to be said which piece of gear you want to make the connection in. This issue is quite possibly caused by a difference in ground potential between two different pieces of equipment, so there are at least two ground busses and top plates in play.

You said "wire" which made me think you weren't talking about the Seduction, since the inputs aren't connected with wires, but directly to the ground plane (shell) and via resistor leads (pin). I've got my Seduction right in front of me. The ground post is not insulated from the chassis or the ground plane. The RCA inputs are not isolated from the ground plane. Grounded.

 

[denti alligator]

Yes, I have the SEX amp. That is indeed what I'm using with the Seduction. On its own the SEX is dead quiet. Dead. Quiet. Hence also my surprise at the levels of hum coming from the Seduction.

Not home yet, but any suggestions for what to try out when I get home would be welcome.

 

[Grainger49]

Joshua,

We are 5 pages and 74 posts into this thread.  Sam and I have been talking back and fourth about only the Seduction, starting today in my reply #52.  I don't see my mentioning the SEX amp, since Jan. 9.

In addition I have emailed and PMd him today.  I am sure that Sam and I are on the same page.  I am sorry if we have confused you.  You were not privy to the emails and PMs.

Sam,  I think that Joshua is suggesting to also try a wire from the Seduction to the SEX.  I believe this is redundant with the interconnects, but it never hurts to try.  It is also cheap, quick and might help.

 

[denti alligator]

Ground from Seduction touching chasis plate of SEX makes no difference.

I soldered a ground buss on the Seduction to connect the two grounds. No difference.

And I just put on Coltrane's Live at the Village Vanguard Again. The Jimmy Garrison solo at the end of side A is a perfect test. On the speakers I can turn it up and not really hear the hum. With phones I can, though just barely.

EDIT: By contrast, I'm now listening to a great obscure gem, the self-titled album by Lewis Furey. This record doesn't need the volume very high to get it to my preferred volume, so hum isn't an issue at all. So I guess it will depend on what I'm listening to if I choose the 'phones.

What I want to know is: is what I'm hearing normal, but most of you folks just don't turn the volume WAY up? What do you hear (those of you who have my set-up or something close) when you turn the volume to 10 on pre and main amp but don't play a record. Is there hum? a little buzzing? Does holding the Seduction and putting a finger on the ground lug cut out the buzzing and reduce the hum? If yes, then I'm not alone.

 

[Grainger49]

If, as you describe, the only problem is at the highest end of the volume control and with very quiet music, I would say that is normal.  

The Seduction amplifies the lowest voltage level signal in a stereo.  It is more likely to introduce hum in the system than any other component.  

To me, the problem centers around the low level of the signal (cartridge output), the low signal level (small jazz etc.), low recorded levels (quiet passages or the dead band between cuts) and the amount of gain that is required to make the cartridge's signal usable by the rest of the system.

My comment about equipment reviewers meant to indicate that most of the equipment on the market, except a very few, will have hum when the system is WAO.  Wide Assed Open.

 

[denti alligator]

I can accept that. My only question would be: why can I reduce this hum by half just by holding the amp and touching the ground? Shouldn't I be able to do this via some other means?