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How to wire up an Amplifier
How to wire up an Amplifier
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Old 21st April 2019, 02:01 PM   #11
keantoken is offline keantoken  United States
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Quote:
Originally Posted by Bonsai View Post
They are confined to the amp module board because the loop is smaller through the local on board decoupling.
The loop area doesn't matter at 10KHz when the ESR of the capacitors is dominant and 100x larger than the resistance of the umbilical.
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Old 21st April 2019, 02:19 PM   #12
Bonsai is offline Bonsai  Europe
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That's why the decoupling on the PCB has to be wideband - you should do this with either method (this applies to small signal stuff as well). And I don't think disregarding loop area above some frequency is good advice - if you have AC current flowing through a loop, its always best to minimize the loop area.

If you have HF currents flowing in the 0V umbilical rather than the local loop, the on-board bulk decoupling is inadequate.

For an extreme example, look at a class D amp. Would you want HF switching hash and HF signal related garbage on the 0V umbilical?

Last edited by Bonsai; 21st April 2019 at 02:21 PM.
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Old 21st April 2019, 03:12 PM   #13
keantoken is offline keantoken  United States
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Does my example of a 1uF film cap not qualify as wideband? What do you use then? 100uF motor run capacitor? The 1uF film cap only hits 10mohm at 15KHz. That means 15 harmonics of 1KHz are entirely unhindered by it.

EDIT: My mistake, 1uF has a capacitive reactance of 10mohm at 15.6MHz, not 15KHz. So that's 156000 harmonics of 1KHz.
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Old 21st April 2019, 03:20 PM   #14
Bonsai is offline Bonsai  Europe
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I am a little confused as to what you are proposing here (your post 4 response).

If the on board decoupling removes HF from the 0V umbilical (which I think it does), what is the problem with returning the speaker -ve to the PCB?
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Old 21st April 2019, 03:27 PM   #15
keantoken is offline keantoken  United States
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I hope you aren't thinking about the diagram I posted in Cordell's thread, because I'm not. I was just answering your question. That diagram was something totally different from what I'm discussing here. I am assuming you mean a typical amp, where you just move the speaker return off the PCB. I didn't expect you to carry context over into a new thread without explicitly saying so, that would just confuse everyone.
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Old 21st April 2019, 03:50 PM   #16
Bonsai is offline Bonsai  Europe
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Some crossed wires - lets put it aside.

So the question them is, if the decoupling on the amp module board is wideband and it therefore keeps HF currents off the 0V umbilical, what is the objection to taking the speaker return back to the module 0V?
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Old 21st April 2019, 04:17 PM   #17
keantoken is offline keantoken  United States
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If there is no significant noise voltage across the umbilical 0V then I don't see a problem with it. I'm not onboard with that hypothetical though.
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Old 21st April 2019, 04:56 PM   #18
Bonsai is offline Bonsai  Europe
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Well we are probably then in some kind of agreement.

I've used both techniques BTW with good results, so I don't think one is right and the other wrong, but I really try to focus on minimizing loop areas in my layouts now.
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Old 21st April 2019, 07:49 PM   #19
Bonsai is offline Bonsai  Europe
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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.
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Last edited by Bonsai; 21st April 2019 at 08:04 PM.
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Old 21st April 2019, 09:07 PM   #20
brian92fs is online now brian92fs  United States
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How to wire up an Amplifier
Bonsai (and Poldaaudio) - What are your thoughts on Douglas Self's recommendation is chapter 25 of his "Audio Power Amplifier Design" book? He suggests tying the signal input ground to the audio-chassis ground at the input connector. Self says this causes ground loop currents to flow to the chassis ground and then mains ground and not through the loop in Poldaaudio's diagram presented above (Assuming I'm reading it correctly).
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