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Old 6th August 2005, 01:11 PM   #1
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Question converting a computer smps to a class d amp

Hello!

I had a brainfart last night about convertiong a computer smps with the push pull topology to a class d amp by inputting the audio signal on the feedback pin that is to keep the voltage constant and stable during diff loads, as well as removing the transformer and redo the power transistors config to a half bridge config and then feed it off a dual rail power supply and the controller from its own voltage source from 12v to 30v.

Would this work for a subwoofer amplifier or would it be too nonlinear, and is the switching freq too low ?

I was thinking it would be fun to test when i get my hands on a old working 200w AT smps.
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Old 6th August 2005, 02:13 PM   #2
mzzj is offline mzzj  Finland
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Default Re: converting a computer smps to a class d amp

Quote:
Originally posted by Tekko
Hello!

I had a brainfart last night about convertiong a computer smps with the push pull topology to a class d amp by inputting the audio signal on the feedback pin that is to keep the voltage constant and stable during diff loads, as well as removing the transformer and redo the power transistors config to a half bridge config and then feed it off a dual rail power supply and the controller from its own voltage source from 12v to 30v.

Would this work for a subwoofer amplifier or would it be too nonlinear, and is the switching freq too low ?

I was thinking it would be fun to test when i get my hands on a old working 200w AT smps.
you can salvage some ferrite cores and that controller from AT supply, rest of it is useless for D-classs. Well, there is also couple of high-current shottkies if you happen to need. I was told about someone who built sub-amp with some smps controller, but I doubt about its performance.
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Old 6th August 2005, 03:12 PM   #3
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Ok.
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Old 6th August 2005, 04:38 PM   #4
Pierre is offline Pierre  France
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A small correction: an AT Power supply has half-bridge topology, at least the vast majority of them.
They usually work at less than 100KHz, too low for full-range audio.
The switching elements are usually transistors instead of mosfets, not very useful for audio.

Best regards
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Old 6th August 2005, 06:19 PM   #5
mzzj is offline mzzj  Finland
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Quote:
Originally posted by Pierre
A small correction: an AT Power supply has half-bridge topology, at least the vast majority of them.
They usually work at less than 100KHz, too low for full-range audio.
The switching elements are usually transistors instead of mosfets, not very useful for audio.

Best regards
Yes, something like 30khz, bipolar switches, but IMHO they are usually 2-transistor forward converters, not half-bridges. More powerfull ones nowadays might be half-bridges.
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Old 6th August 2005, 07:57 PM   #6
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by Pierre
A small correction: an AT Power supply has half-bridge topology, at least the vast majority of them.
They usually work at less than 100KHz, too low for full-range audio.
The switching elements are usually transistors instead of mosfets, not very useful for audio.

Best regards
I recall even in the Aplle II days the SMPS was 1MHz, and the PC ones run at only 100K?
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Old 6th August 2005, 09:14 PM   #7
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I did write in the first post that a rewire of the power transistors were needed, and that i intended it as a subwoofer amp only. But nevermind this thread, i dont have any puter power supplies to play with and i dusted off the ICEPower module instead.
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Old 7th August 2005, 11:40 AM   #8
mzzj is offline mzzj  Finland
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Quote:
Originally posted by soongsc


I recall even in the Aplle II days the SMPS was 1MHz, and the PC ones run at only 100K?
CPU maybe 1MHZ, but no way power supply in Apple II
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Old 7th August 2005, 12:29 PM   #9
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Remove this thread please. Pinkmouse, the remove button is yours
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Old 8th August 2005, 02:36 AM   #10
Kenshin is offline Kenshin  China
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The PC SMPS could only push current but can't pull current, so you need a pull down...that makes a class-A thing
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