Mono Block Ground Loop

[Guest David H]

Just a word of caution/explanation about outlet testers. They will not detect a reversal of the ground and neutral wires. All other faults yes.

Good call, and it would only take a minute to check.

Dave

[erik2A3]

JoeS.

The question you,pose to Mark or Craig is not a difficult question to answer: I have extremely high input impedance amps that have equally high input sensitivity, particularly the LEAK ST20 I completely overhauled and restored a year or so ago. The VAC amps are not the problem, nor do I think is it a ground loop the issue. It's RFI. However, that said, High input impedances on equipment can in cases make a component more sensitive to noise, but again, like Mark mentioned too, I really don't think this is a ground loop issue -- if it were, the problem would have been solved a long time ago.

An aside....if I still had my original avatar from 2002, I wonder where I'd be post number-wise. 10,000 maybe? Who cares anyway. It's a completely meaningless number.

Anyway, eth2: please re-read a portion of what I wrote. I was wondering if you simply unplugged all other components that may be associated with the same circuit used by your system. Another way of doing the same thing would be to use a mains isolation transformer plugged into the outlet you want to use, a power strip plugged into the downstream end of the isolation transformer, and then all the components plugged into that.

Edited April 18, 2014 by erik2A3

[eth2]

Hi All:

I will try and answer all of your questions:

FIRST, TO AVOID TOO MANY COMPLICATIONS, I SWITCHED BACK TO THE VAC80 IN THE LIVING ROOM WHICH IS A SINGLE AMP (E.G., NOT MONO BLOCK). THE VC 90 IS DOWNSTAIRS AND HAS THE SAME HUM. So , the hum is now occurring everywhere in the house, either with the VAC 80 or the VA 90.

90.

(However to answer the question about the VAC 90, a single power supply cannot be shared)

.

On the amp with the rca disconnected, if you connect the center conductor only and not the shield is the noise gone and music playing?

NOISE IS STILL THERE.

From the pictures of the amp I see umbilical cords from the power supply , I also see a second outlet on the PS. What is the second port for?

IT IS FOR A BALANCE (XLR) INPUT. MY PREAMPS DO NOT HAVE AN XLR OUTPUT

When you took the amps to a different room did you take the preamp as well?

YES.

I thought you had run the amps with just the preamp hooked to it and had the noise

THAT IS TRUE

I HAVE NOW HOOKED THE DI BOX BETWEEN THE PREAMP AND THE AMP. IT MAKES NO DIFFERENCE

In a previous statement, eth2 stated that if only 1 rca was plugged in the noise dropped.

IT IS NO LONGER DOING THAT WITH THE VAC 80 (DISCONNECTING ONE INPUT HAS NO EFFECT ON THE NOISE), BUT IT IS TRUE WITH THE VAC90. (DISCONNECTING ONE INPUT KILLS THE NOISE

Well I thought so....so my point is if the noise is present with just amp and preamp you stop right there...the problem is between the amps and preamp. I personally think it has something to do with the fact that the amps are primarily designed to run in a balanced configuration

I HOOKED THE DI BOX BETWEEN THE PREAMP AND THE AMP AND IT MAKES NO DIFFERENCE

THE VAC 80 DOES NOT HAVE A BALANCED INPUT AND NEITHER THE PEACH NOR THE PHASE LINEAR HAVE BALANCED OUTPUTS. THE PEACH HAS NOW GONE IN FOR A MODIFICATION SO I DO NOT HAVE IT AVAILABLE ANY LONGER.

Edited April 18, 2014 by eth2

[eth2]

Anyway, eth2: please re-read a portion of what I wrote. I was wondering if you simply unplugged all other components that may be associated with the same circuit used by your system. Another way of doing the same thing would be to use a mains isolation transformer plugged into the outlet you want to use, a power strip plugged into the downstream end of the isolation transformer, and then all the components plugged into that.

NOT SURE WHAT A MAINS ISOLATION TRANSFORMER IS, BUT I HAVE DISCONNECTED EVERYTHING ELSE ON TE CIRCUIT AS WELL AS DISABLED ALL OTHER CIRCUITS WITHOUT ANY IMPROVEMENT

[eth2]

By the way,

the B&K Reference 2200 has no hum and only a kind of soft swish sound (the tube amps also have the swish sound in addition to the hum). however when the DI Box is placed between the B&K and the preamp there is only dead silence...no hum and no swish. also, the hum comes from the horns on both the Klipshorns and the Cornscalas.. .

Edited April 18, 2014 by eth2

[eth2]

On Sunday I am going to dinner at my in-laws. They have La Scalas so I am going to bring the VAC 80 and see what happens. In he mean time, I am using the B&K. Who though a $400 amp would be my prize component?

[CECAA850]

Stupid question alert!

When working on automobiles, occasionally we'd have to shield a wire or module with aluminum foil. Would it help diagnosis to cover a cardboard box with aluminum foil and place over an amp to see if it quiets it? Obviously this would be temporary and for diagnosis only. My thinking is that this would definitively prove/disprove RFI type issues.

EDIT, I think I would place it on aluminum foil as well as cover it.

Edited April 18, 2014 by CECAA850

[eth2]

Stupid question alert!

When working on automobiles, occasionally we'd have to shield a wire or module with aluminum foil. Would it help diagnosis to cover a cardboard box with aluminum foil and place over an amp to see if it quiets it? Obviously this would be temporary and for diagnosis only. My thinking is that this would definitively prove/disprove RFI type issues.

EDIT, I think I would place it on aluminum foil as well as cover it.

I will try this, but my guess is that if it is RF interference it is being carried in from the cables.

[JL Sargent]

It's about time to call:

[eth2]

Stupid question alert!

When working on automobiles, occasionally we'd have to shield a wire or module with aluminum foil. Would it help diagnosis to cover a cardboard box with aluminum foil and place over an amp to see if it quiets it? Obviously this would be temporary and for diagnosis only. My thinking is that this would definitively prove/disprove RFI type issues.

EDIT, I think I would place it on aluminum foil as well as cover it.

I will try this, but my guess is that if it is RF interference it is being carried in from the cables.

Well, the good news is that I got the foil back of the roll. the bad news is that it didn't make a difference.

Boy that B&K sounds nice.

Edited April 18, 2014 by eth2

[eth2]

OK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I have the PA90's on the lower level hooked to the Cornscalas AND NO HUM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The problem remains in the living room with the PA80 even with the DI Box.

HOWEVER, with the DI Box placed between the preamp and the amp and the lead lifted on the amp out side of the DI Box, the humming stops and the amps are quiet. You can lift the lead on either the input side of the DI and/or the output side. Lifting the ground on the input side does nothing. However, lift the ground on the output side and AUDIO BLISS!!!!!!!!!!!!!!!!!!!!!!!!!

I now understand why you like tube amps. The sound is just beautiful even with a ss preamp!

So what is going on??

Edited April 19, 2014 by eth2

[eth2]

Hi All,

I wanted to send all of you an individual thank you by PM. However, I just found out that you are limited to only a few PM's per day (Why?). So anyway, to all of you who spent so much time on this I truly want to say thank you. While the problem still exists in one part of the house, at least I have confirmation that it is not the amps and it would appear to be a ground loop problem. This is the first time the PA90's have not hummed like a drunken sailor downstairs (The PA80 didn't hum initially downstairs but now does. I have not moved it downstairs with the DI to see if it that makes a difference). It raises many interesting questions for me. For example, why didn't the line conditioners or the cheater plugs remedy the problem? Why is the problem still extent in the living room?

In any event, even if the problem remains upstairs I still can listen to the PA90 downstairs. Maybe that is good enough! If I can't rectify the problem upstairs I will just replace the PA80 with a decent solid state amp.

Thanks again,

Earl

Edited April 19, 2014 by eth2

[eth2]

Just tested the PA80/80 placing it next to the PA90 - it still hums with the DI Box connected. Nonetheless, the PA90 sounds great so we will see what the PA80 does at a different location tomorrow.

[joessportster]

If lifting a cable affects the noise, I would lean twords a loose / faulty connection

Either a bad solder, loose rca if they are the type that tighten down with a nut on the inside, Or a worn rca where the cable fits loosely (loose fit does not have to be sloppy it could feel firm and still have just enough wear to allow a poor connection)

Joe

PS I have ran into a worn RCA in the past which caused a lot of noise

Edited April 19, 2014 by joessportster

[eth2]

Joe,

Do you mean a bad connection in the preamp?

[joessportster]

which ever end of the cable yo are lifting that causes the noise to drop, although i would tend to think the amp

[eth2]

the VAC mono block with no input connections of any kind, and no preamp involved, would hum when connected to the speakers. Connecting two shorting plugs to the RCA inputs would stop all hum

This is correct.

What model of DI box is involved here?

Radial Engineering ProAV2

http://www.amazon.com/gp/product/B001ESK5NO/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1

[eth2]

Do the VAC 90 monoblock still hum with no preamp connected?

Yes

[eth2]

Just moved the PA90's upstairs and the DI box eliminates the hum up here as well. Again, it makes no difference in either location with the PA80/80's.

For the PA90's, if the ground on the amp side of the box is not lifted, the hum continues

Edited April 19, 2014 by eth2

[Chris Hornbeck]

It's just sunk in that you're using a real DI box. I'm sorry, I'd thought that you were just using a non-standard term, as so often seen in technical threads. (Nobody's born knowing the names of every gadget in the Universe, and sometimes folks will disagree.)

A DI box isn't really appropriate, or even wanted. For one thing, it's designed to reduce line level signals down to microphone level, and for another, it provides "galvanic isolation" which isn't needed when all the pieces are together at one location. If I understand your situation correctly, you have a preamp output with XLR/ "Cannon" connectors and power amplifiers with RCA/"phono" connectors. Is that right?

If so, my next question will be about the details of the preamp's output. These vary in sometimes surprising ways, but are all completely workable and understandable. What we really want to determine is the exact best way to connect the preamp and power amp. It will not require anything but connectors and shielded wire. I promise.

All good fortune,

Chris

Edited April 20, 2014 by Chris Hornbeck