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How to wire up an Amplifier
How to wire up an Amplifier
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Old 21st April 2019, 09:21 PM   #21
Bonsai is offline Bonsai  Europe
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I have not tried Self’s way or really thought about it in detail, but since he’s been doing this stuff commercially for a long time I have no reason to doubt it works. There’s a presentation somewhere on the web by a Japanese guy showing it wrt a tube amp.

You would still have to control the loop areas in the amp and think about cross channel ground loops.

Last edited by Bonsai; 21st April 2019 at 09:23 PM.
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Old 22nd April 2019, 04:36 AM   #22
Walkalone is offline Walkalone  Viet Nam
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Originally Posted by Bonsai View Post
Here is a look at Poldaaudio's set-up and how I'd approach it.

I have an amp with a similar set-up to that shown in the diagram. But, I located the input connectors next to each other and bonded the connector grounds together and then ran the screened cable directly to each amplifier module input - so the shortest route from connectors to modules. If I ran the screened cables together to the fist module and then continued the second screened cable around the front of the amp all the way around to the second module, it was much quieter (talking -110 dBV vs -90 dBV). In the second approach, the loop area between the two amp modules in minimized, so the cross channel loop current is minimized. I use 15 Ohm HBR's but also got good results with a 3.3 Ohm.

If you bond the input connector grounds together, and locate them next to each other, you trap cross channel ground loops inside the amplifier. In the attached diagram, having them separated and not bonded means you have a large loop area for noise pick-up.
Hi Bonsai,
Thanks for your describe. I tried using this way. The amp is dead silence. Using HBR is also usual way in DIY amps.
However in commercial amps i've seen, can't see any of HBR and speaker return to 0V power supply. Clearly it still available a large loop between 2 input.
How they reduce ground loop?
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Old 22nd April 2019, 10:26 AM   #23
Bonsai is offline Bonsai  Europe
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Walkalone,

Through very careful layout optimization. I have a Marantz PM7000 that is very quiet. I know that they built about 100k units, so the incentive to get it right at minimum cost is certainly very high. The Marantz uses a GOSS band to reduce radiated noise (EI core).

HBR’s are used quite often in commercial gear - I’ve seen circuits showing them but of course some designs don’t have them - it’s just a case of a different approach like the Self scheme mentioned in an earlier post above.

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Old 22nd April 2019, 11:43 AM   #24
avtech23 is offline avtech23  Australia
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How to wire up an Amplifier
Thanks for sharing the knowledge here Bonsai.

Quote:
Remember that the Hum Breaking Resistor inside the amplifier will act to reduce the loop currents and divide any internally arising noise voltage down – so always make sure this is fitted.
I always got the impression that using hum breakers was a last resort and I felt like I had failed in some way whenever I'd used them to rectify a noisy project that I just couldn't tame.

So it's nice to read that they are not always used as a last resort but can be integral to a design.
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Old 22nd April 2019, 12:34 PM   #25
Bonsai is offline Bonsai  Europe
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It’s knowledge I hovered up from all sorts or sources - so I wont claim it’s mine

I short my HBR’s out and get the noise as low as possible then un-short them. I usually start off with a pair of headphones connected directly to the output. You can dress your wiring etc then for lowest noise - if you do a good job, you have to progress to a sound card as the noise level drops below audibility.

Last edited by Bonsai; 22nd April 2019 at 12:37 PM.
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Old 22nd April 2019, 01:31 PM   #26
Bonsai is offline Bonsai  Europe
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I took a look at Selfs method and it makes perfect sense.

Usually you run the signal ground back to the amp module and to the [perhaps via an HBR as I do] system ground through the PCB, making sure of course to obey all the star ground and associated PCB layout rules. You take your main ground to the chassis after T’ing off the reservoir cap grounds. You then take the incoming mains ground and connect it to the same point on the chassis so there is only one ground connection to the chassis.

How he is doing it is he is placing this ground connection at the input - so he now has the power earth connection to the chassis, the T off from the reservoir ground (ie the main amplifier ground) and the incoming signal ground all located at the signal ground where it comes into the amplifier.

This then causes externally generated ground loop currents arising in the area bounded by the power earth wiring between equipment and the signal interconnect ground to flow away from the small signal circuits - sort of like a revolving door - ‘straight in and straight out buddy’.

But, any ground loop current flowing in the interconnect screen will still cause noise, so it does not prevent this type of problem arising due to external magnetic fields cutting the loop.

I think you will still have to deal with internal cross-channel ground loops, and an HBR will help. But careful layout and cable dressing should be carried out before doing that (link the HBR first out as I mentioned before).

Last edited by Bonsai; 22nd April 2019 at 01:36 PM.
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Old 22nd April 2019, 01:58 PM   #27
scottjoplin is offline scottjoplin  Wales
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I can't see how you can incorporate HBR into that since the screen of the input cable has to be able to carry fault current?
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Old 22nd April 2019, 02:07 PM   #28
keantoken is offline keantoken  United States
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Does anyone have a diagram?
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Old 22nd April 2019, 02:11 PM   #29
scottjoplin is offline scottjoplin  Wales
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I presume they are referring to this?
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Old 22nd April 2019, 02:16 PM   #30
keantoken is offline keantoken  United States
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Well I definitely would not connect the input signal hot to earth, but I assume that is a mistake.

It looks pretty good to me except that I don't see where you can put the hum breaking resistor, which is important for sources with ground noise.
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