David,

The Loesch/Tempo amp has a switch on the rear panel for this, you can see it in the picture in the middle just above the Amphenol connector.

This will simply disconnect the earth/shield of the single-ended source(s) (or Pin 1 on an XLR) from the ground plane of the amp circuit which is typically referenced to mains earth. This means the potential of signal ground is not fixed relative to mains ground and is therefore said to 'float'. If your amp doesn't have one a skilled EE could probably (depends a little bit on the circuit design and board layout) add one quite easily, although it would involve minor surgery on your amp which would void any warranty etc.

Ground loop problems can be notoriously difficult to isolate but there are easier places to start. One very simple measure that solves many problems is to plug all mains-driven components in the system into the same mains socket pair or even the same actual socket via a multiboard.

Good luck!

Quote:
In his Listening column, Art Dudley mentioned that he removed a troubling hum by "floating the signal." I have searched for this term but haven't found it anywhere. I tend to suffer from the sort of hum he describes because of the sensitivity of my speakers (an Altec Lansing 210 Voice of the Theater, split into a stereo pair of highly customized cabinets for home use and WAF, and one Altec mid-/high-frequency lenses with compression driver for each channel) -- about 108db/1m/2v based on conventional wisdom. Can anyone tell me how to "float a signal" so I can try it with some of my more troublesome (hum-wise) components? Thanks in advance for any help.

Several links here that go into some detail about balanced/floating connection and circuits.

1st four questions;
http://www.nagraaudio.com/highend/pages/faq.php

Can be useful read.
http://www.rane.com/note110.html

Section 4 onwards for URL below explains in greater detail for both Line Output and Line Inputs (ignore the circuit diagrams if none techy but the explanations are good).
Section 5 is related to line inputs.
http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm#4

Hope the info is useful, but will still need Art to explain what he did if looking to replicate a solution.

Cheers
Orb

I believe that what he is talking about is with your mains ac cord having the ground plug (the neutral and gound lugs are joined), that often a ground loop finds it way into your amp. Often times by buying one of those grey adaptor plugs you can lift the ground away from your ac mains and often solve a hum problem.

I have even seen some newer aftermarket AC cords that have a screw-out ground pin. A nice idea.

Quote:
I believe that what he is talking about is with your mains ac cord having the ground plug (the neutral and gound lugs are joined), that often a ground loop finds it way into your amp. Often times by buying one of those grey adaptor plugs you can lift the ground away from your ac mains and often solve a hum problem.

I have even seen some newer aftermarket AC cords that have a screw-out ground pin. A nice idea.

I don't think this is what Art was talking about Jim, I am pretty sure he was referring to the ground lift switch on the back of the unit. Hopefully he will hop in and confirm.

Lifting the safety ground is a quick and very dirty solution to the problem of ground loops. A signal ground lift switch is a much safer solution, the safetly ground remains in place but the signal ground is floated free of it. I would really advise strongly against removing the chassis ground of any equipment designed to be grounded. Removing the safetly ground could result in the chassis becoming live, which is just plain dangerous. Y'all be careful out there!

From reading the article Art's problem was caused by a ground loop between his turntable and the amp. The problem didn't manifest itself when he was using the step-up transformer (which by providing galvanic isolation was preventing the loop) but appeared when he connected the phono lead directly to the amp. Lifting the signal ground achieved the same end, i.e. broke the ground loop without removing either component's safety ground.

Hi, Struts -

Thanks for the information. I appreciate your comments about ground loop problems related to the mains power. However, I think I have that problem covered--I have a dedicated circuit for my system, with a manufacturer-approved chain of power conditioners providing a single source of power for the audio components. I also experimented with using both sockets on that circuit, but it didn't change anything, for better or worse.

As for your description of what you believe Art was doing, I was thinking it was along those lines. However, I had overlooked the switch on the hardware as the way he achieved this. What I have been wondering is whether I could achieve the same result by modifying my interconnects rather than my amplifiers (I bi-amp with monoblocks, so it would take a lot of work, and voided warranties, to add a switch to all four amplifiers). Most of my interconnects are home built unbalanced cables, so I could easily disconnect the lead to the ground shield at one or both ends. Do you know if this give me the same result as the Loesch/Tempo switch--or is this a dangerous thing to try? Or would it be better to connect the ground wire of the interconnect cable to the chassis of the component at one or both ends (when there is an appropriate grounding point, such as on my phono pre-amp)?

One of the articles cited by another writer in this thread indicated that you could build test cables that would let you quickly connect and disconnect the ground line of cables, but while the diagrams showed various types of cable terminations with such a "flying" lead, the graphic for single-ended, unbalanced cables had no such option. I am confused!

Thanks again for your interest.

The links I provided go into some detail explaining the ground lift switch and also cable designs/next best way to connect and all relate to your experiences.
They just need time to read.

Cheers
Orb

David,

If your problem is in fact a ground loop and you are using single-ended interconnects then the problem is not with your cables it is with the equipment at either end.

You say you bi-amp with monoblocks and it occurs to me that this just might be your problem. If the chassis are metal and are somehow electrically connected (touching directly or indirectly via some conductor) this might be creating the path for a loop. Even if they don't appear to be connected you could try disconnecting three of the amplifiers (the problem might be between a stereo pair or a bi-amped pair or both) from the mains and seeing if the hum goes away. If it does add them back in one by one and see at what point it comes back. With a bit of luck this might help you put your finger on the problem.

However don't rule out other possible causes. Your problem might be caused, for instance, by EMI, a poorly shielded power cable lying too near a signal cable etc. Not all hum problems are caused by ground loops.

David,
you may want to check out the Supra AGS-10k, basically it is a transformer isolation solution but you would really need to test it before purchasing as it may affect the sound.
It is not cheap though (about $185), but you may be able to get a deal.
Some more info:
http://www.supracables.co.uk/groundseparators/gs-ags10k.html
And a seller in USA (they have dealerships can look at their websites - www.sjofnhifi.com)
http://www.audiogon.com/cgi-bin/cls.pl?accstwek&1276462883&/Supra-AGS-10k---KNOCK-OUT-hum/

Let us know how it goes if you decide to contact them.
Cheers
Orb

On the plus side I just read this from their audiogon;

Quote:

And like all the products we sell, you

Quote:
you may want to check out the Supra AGS-10k, basically it is a transformer isolation solution but you would really need to test it before purchasing as it may affect the sound.
It is not cheap though (about $185), but you may be able to get a deal.
Some more info:
http://www.supracables.co.uk/groundseparators/gs-ags10k.html

Good catch Orb, never noticed this before (despite the fact that Supra is a Swedish company). I wonder if it noticably impacts SQ? David, please let us know how you get on if you try it!

Thanks Struts,
yeah if it does what it says without changing SQ then this should be one in the top 5 products in the other thread.
Hope David he gets to test it, or maybe even Art.

Cheers
Orb

Very interested in your experiences with the Devialet, Orb. Left you some questions in the other thread, please give us a bit more detail!

Quote:
Very interested in your experiences with the Devialet, Orb. Left you some questions in the other thread, please give us a bit more detail!

Struts you got your wish
Check it out in Entry section of Forum.
Any questions or thoughts even if critical fire away I will not mind
Cheers
Orb

Quote:
Struts you got your wish

Much obliged. Thank you!