GainClone ground loop help

[DeanP]

Hi,
I know I have a ground loop problem, but would like advice on how to delete it.
The two lowpass amp boards are the "parallel" type amps and the high pass amp board is a "stereo" type amp.
All three are from Peter Daniel (LM4780s).
All three are powered from a single source and the PG - & + are daisy chained on the amp boards as well as the V - & +.
The "chassis grounds" are also daisy chained to a common ground via a 10r resisitor.
In the attached JPEG is the wiring diagram that I used.
I believe I should connect all grounds after the x-overs from the pot to a single wire and run this to the amp boards as shown in green.
Do you think this is a good idea?

 

[okapi]

is the pot attached to the grounded chassis?

 

[okapi]

i am also having trouble distinguishing what is power vs signal in your diagram.

 

[okapi]

oops. i guess it is all signal. a seperate diagram of the power hookup might be helpful. a photograph would be useful as well.

 

[DeanP]

is the pot attached to the grounded chassis?

Yes, but when I measured the resistance I get 10r and I also physically removed it(unattached it & held it in my hand) and I still got the noise.

i am also having trouble distinguishing what is power vs signal in your diagram.

I'm only showing the signal + & - wires, no actual power supply wires...

 

[DeanP]

a seperate diagram of the power hookup might be helpful.

All three are powered from a single source and the PG - & + are daisy chained on the amp boards as well as the V - & +.

 

[Peter Daniel]

If the potentiometer is for low pass only you do not need to run high pass grounds through it.

 

[Peter Daniel]

Run all signal grounds separately to each amp board and don't tie them together.

Connect all power grounds (preferably at OG points) with a single high gauge wire. From PS run PG+ and PG- to the central point on that wire. That becomes your star ground. From here, have a single connection to chassis through 10R resistor.

It is similar to what I described here: http://www.diyaudio.com/forums/showthread.php?postid=787773#post787773

 

[DeanP]

If the potentiometer is for low pass only you do not need to run high pass grounds through it.

The x-over has these out connections: low, high & ground.
So would this mean I would continue the ground at the pot to the appropriate low pass amp board? As of now, I only have a ground wire from the x-over to the pot and it ends there.

Run all signal grounds separately to each amp board and don't tie them together.

So if I am interpeting this correctly:
(Applicable for each channel.)
-x-over ground >pot >low pass amp
-x-over ground >high pass amp(stereo board)
and do the same for the other channel?

Connect all power grounds (preferably at OG points) with a single high gauge wire.

Yes, I thought of this for the ps but I don't have any problems for my other two stereo boards that share their own ps system. [I built a 6 channel + two(parallel, low pass amp)So I actually have five boards total]

 

[Peter Daniel]

Maybe you should try this first:

I believe I should connect all grounds after the x-overs from the pot to a single wire and run this to the amp boards as shown in green.

Then the other suggestions.
Also, disconnect the chassis grounds, you don't really need them and maybe this is causing the loop?

 

[DeanP]

Well I just finished soldering all separate wires, so I'll try that first.
Testing to be done after Supper.

Also, disconnect the chassis grounds

I have the other pair of amp boards connected to each other then to their own chassis via a 10r resistor. No ground loop there.

I think that the pot is causing my problems, we'll see if the extra soldering of wires cures this.

 

[DeanP]

Well turned it on and now it is quieter but not as quiet as the other four channels. Just for curiousity, I cut off each signal wire ground while listening closely and it got noiser and then touched them back together and, of course, it got quieter again. I think I might try to by-pass the x-overs just to see what happens. At least it will eliminate both the x-over and pot...
If anyone else has some other ideas, please let me know...

 

[DeanP]

Well I conquered the ground loop problem with running single separate wires.
Thanks Peter!
Now I have magnetic strays inducing my signal output wires. I'll try to get some sheilding implemented.

 

[rambojj]

I have got a problem: I build two monblocks. Each ampboard has a tube (like the original Gaincard). I mad a paasive Preamp. There is a 10 kOhm Log Attenuator and an input slector switch. For the output there are two connectors wich are simply soldered paralell. If I use one Amp the sound is ok. If I use both Amps in Bi-Amping (vertikal or horizontal doesn't make a difference) there is Distortion and hum. If I do a wiring from one amp to the other (speaker ground) the sound is better, but there is still disortion and hum. If there are three cables from the pre to the amps, ther is no hum or distortion. Earlier I had bi-amping in one chassis and there was no hum or distortion. Can it be a problem with impedance? or should I use a resisor between the parraleld soldering in the pre amp?

 

[AndrewT]

A monoblock has one amplifier inside the chassis.
Your description makes me think you have two amplifiers inside the chassis.

 

[rambojj]

There are two squaretubes. One Amp per tube. The tubes have got a plate at the frontside and at the rear side. This is one stereo amp. Two of them I want to use for Bi-amping. It looks like the 47 lab Phonocube.

 

[AndrewT]

building one channel in a chassis is different from building two channels into two electrically connected chassis.

 

[marce]

Two excellent articles regarding ground loops etc and audio, they may test you beliefs, but are worth reading.
A Practical Interference Free Audio System (Part 2)

Designing for Interference-free Audio System Components

 

[rambojj]

I think that the bi-amping-theme is layed on ice for me until I change my equipment from passive to active crossover. When I know wich crossover I want to use (digital or anlaog) then bi or tri amping is the theme again. Thanks for the hints.