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Maplin Mosfet Amplifier Ga28f construction thread
Maplin Mosfet Amplifier Ga28f construction thread
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Old 15th January 2018, 04:29 PM   #71
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by nigelwright7557 View Post
Speaker return goes to smoothing capacitors otherwise it will modulate the ground line.
Absolutely NOT !
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Old 15th January 2018, 04:31 PM   #72
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
Absolutely NOT !
Why not ?
It returns high current right back to source of power.
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Old 15th January 2018, 04:34 PM   #73
AndrewT is offline AndrewT  Scotland
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Originally Posted by scottjoplin View Post
That's not ideal, this will explain the best way to do it and why https://web.archive.org/web/20170712...-Autosaved.pdf
page 14 gives the correct location for the Speaker Return. Earlier pages give the impression that smoothing caps is the correct, but smoothing caps is wrong.
That way back is an old guide that has been superseded by the new guide on the still current Hifisonix website.
http://hifisonix.com/wordpress/wp-co...tober-2017.pdf
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Old 15th January 2018, 04:35 PM   #74
AndrewT is offline AndrewT  Scotland
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Originally Posted by nigelwright7557 View Post
Why not ?
It returns high current right back to source of power.
read about charging pulses on the rectifier/smoothing capacitor circuit.
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Old 15th January 2018, 04:36 PM   #75
scottjoplin is offline scottjoplin  Wales
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Thanks, I wondered what had happened
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Old 15th January 2018, 04:51 PM   #76
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
page 14 gives the correct location for the Speaker Return. Earlier pages give the impression that smoothing caps is the correct, but smoothing caps is wrong.
That way back is an old guide that has been superseded by the new guide on the still current Hifisonix website.
http://hifisonix.com/wordpress/wp-co...tober-2017.pdf
But page 14 shows return path going to smoothing caps !!!!

It makes sense to go back to power source which is smoothing caps.
If you don't you will modulate the zero volt line.

Pretty much every book and website I have read says smoothing caps are best return point.
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Old 15th January 2018, 05:04 PM   #77
AndrewT is offline AndrewT  Scotland
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Originally Posted by nigelwright7557 View Post
But page 14 shows return path going to smoothing caps !!!!
No, it does not.
It shows a tap taken from the smoothing caps to a bus that carries a variety of tappings for various parts of the amplifier and auxilialaries.
If you look at the document I linked in post73, you will see the drawing with explanation.

You will find this has been discussed on this Forum for all the time I have been a member and still the majority get it wrong.
Quote:

It makes sense to go back to power source which is smoothing caps.
If you don't you will modulate the zero volt line.
The charging pulses for the smoothing capacitors are what does the disturbing of the audio reference node.

You are right in one important respect. The current that comes out of the +ve supply rail MUST RETURN to the Zero Volts node to go back through the smoothing capacitor/s to the original SOURCE.
The current returning to the -ve supply node must be sourced by the Zero Volts node.
Those Flow and Return circuits form loops and those loops MUST have low loop area to minimise interference (EMI).
Quote:
Pretty much every book and website I have read says smoothing caps are best return point.
if you are reading those references correctly then ALL of those references are wrong. Or you are misinterpreting what they are telling you.
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Last edited by AndrewT; 15th January 2018 at 05:07 PM.
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Old 15th January 2018, 05:09 PM   #78
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
The current returning to the -ve supply node must be sourced by the Zero Volts node..
No it doesn't.
It goes from smoothing capacitor, through amp, through speaker back to centre of smoothing caps.
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Old 15th January 2018, 05:40 PM   #79
AndrewT is offline AndrewT  Scotland
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Oh dear !
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Old 15th January 2018, 05:58 PM   #80
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Well, yes, but......conventionally we imagine it flows from positive to negative, it doesn't really matter though...
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