Multichannel amplifier internal ground loop

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AndrewT

R.I.P.
Joined 2004
It is all about LOOP AREA.

A loop with a changing current around it emits interference. It is a transmitter.
A loop in the influence of a changing field gathers/collects interference. It is a receiving aerial.

For both aerials and transmitters it follows that BIG LOOPS make for good interference coupling.

For both aerials and transmitters small loop areas make for poor interference coupling.

Every CIRCUIT has a FLOW and RETURN for the SOURCE.
That Flow and Return can be assembled with a small LOOP AREA or can be assembled with a BIG LOOP AREA.

In your first diagrams, I could see MANY LARGE LOOPS.
You did not understand that the LOOPS were the CAUSE of the HUM pick up.

In JN's diagram, he has physically MOVED some of the wires to make SMALLER LOOPS.

It is for a gathering of understanding that I keep repeating the suggestion that you go back to building a single channel amplifier and LEARN what is important and HOW to get to the better solutions.
 
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jneutron

jneutron

Member
Joined 2004
Luke123 said:
JN

Hard to follow, but...
What caused the shape modification of "lines" from DRW1 to DRW2?
Because when you look at both DRW the connectivity did not change.
Actually, are these lines... wiring?

Luke
Click to expand...
Andrew is correct.

The lines are wiring, the connectivity is exactly the same. But I reduced the physical loops that trap time varying magnetic field.

Look up Faraday's law of induction, the hyperphysics site has some good stuff.

jn
 
Attila I

Attila I

Member
Joined 2009
hi luke 123,
i just can confirm what jneutron and imulse suggest:
build a firm cable tree with your shielded inputs and audioground so that your signal wiresare guided from entering point to amp pcbs and no space
is opening inbetween.
i had a hum in my f5 and after a month taking everything apart and build new
that was the solution:
no change in connections, just routing!
good luck!
 
A

AndrewT

R.I.P.
Joined 2004
The input RCAs are part of the signal circuit.
The Barrel of the RCA is the Return Signal that goes to the Source FROM the Amplifier.
The Return Must stay close coupled with the Flow that goes from Source to Amplifier.

These two wires including the relevant parts of the connectors, MUST stay together as the Flow and Return.

There are NO EXCEPTIONS.

The options come in when the amplifier OUTPUT needs to be referenced to the Signal INPUT.

Here a one wire reference connection is ADDED to the two wire OUTPUT to the Speakers and the two wire INPUT from the Source.

This voltage reference connection theoretically carries no signal current. It is allowed that this reference connection can have some added resistance.

This added resistance reduces interference current passing along the reference wire.
 
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Sangram

Sangram

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Joined 2002
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That does work, but my personal preference is to use two central conductor wire for RCA and float the shield at one end. Of course for PC based multichannel using 3.5mm jacks, this is not possible and floating the shield will sometimes create its own issues.
 
A

AndrewT

R.I.P.
Joined 2004
AndriyOL said:
Perhaps not creating interconnects from common source ground would solve hum problem? I mean to use only one return screen and 5 left screens from source are floating, if available.
Click to expand...

sangram said:
That does work, but my personal preference is to use two central conductor wire for RCA and float the shield at one end. Of course for PC based multichannel using 3.5mm jacks, this is not possible and floating the shield will sometimes create its own issues.
Click to expand...

AndriyOL said:
If you have separate input return and shield
Click to expand...
All the (commercial) Source equipment I have, all use a commoned Signal Return.
The few bits I have DIYed, use the same commoned Signal Return.

That creates a loop that picks up interference when connected to two channel amplifiers.

using screened two core does not solve that problem.
using separated return and shield does not solve that problem.
using a single return and multiple separated "hot/Flow" cores does not solve that problem.
 
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AndriyOL

Member
Joined 2008
I have the same amount of noise if stereo input connected or not connected to stereo amplifier with one transormer. Noise become worse if use another stereo amplifier for two more channels and if inputs connected. However, I could be wrong, without inputs connected 4ch amplifier is almost deadly silent
 
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