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-   -   Class D Power Supply??? (http://www.diyaudio.com/forums/class-d/28589-class-d-power-supply.html)

Co_Driver 20th February 2004 07:06 AM

Class D Power Supply???
 
Hi,

Still completely new to any DIY Audio stuff, so I'm sorry if I don't put things into words correctly.

I was wondering if it would be possible to use any of the currently available, class A or A/B, diy amplifier modules made by anyone and instead of just using a conventional power supply, use a class D amplifier in between to continuously varry the rail voltage just above the input audio signal. Obviously to keep the output devises as cool as possable and by reduceing the voltage across the output transisters you can use their full current capability or up to the full rated amperes of your output devices. Now before you reply, I think this is sort of how Bob Carver's "Tracking Downconverter" works, but my description is way over simplified and I'm not sure.

But back to my question, could this be done? As simple as it sounds to me and with my lack of knowlage in this field, I can't find anything where any person has tried this or even talked about it (in the DIY world).

Hopefully I can get some good (but please keep it simple) posts to this, that will help me to understand and feed me with some new ideas?!?!?!?!

Thanks for your replies,
Jay Meredith

P.S.
I have purchased 2 books by Randy Slone #1- High-Power Audio Amplifier Construction Manual / The Audiophile's Project Sourcebook. If any body has any other suggestions or recommendations to any other books or web sites that could help me learn more I would greatly appreciate it.

Thanks Again,
Jay M. :)

Ouroboros 20th February 2004 08:08 AM

You could run the supply rails of a normal amplifier from a switch-mode converter. If the switching frequency of the converter is high enough it is possible to get the supply rails to track the voltage requirement of the amp. The problem is that even the fastest responding converter will still be far too slow to provide the increased voltage when it is needed.
You would need the incoming audio to be peak-detected, and feed this peak value signal to control the converter. You would then need a delay in the audio before it went to the amp so that the PSU had already 'anticipated' the increased power demand so that the power rails were at the right value for the audio that was about to appear at the input of the amp.

It's a lot easier to incorporate the converter and the amp in one, which is effectively what a class-D amp does.

By the way, the latest switching amp modules from D-2-audio have an impressive published spec. We'll be trying them here at work soon, so I'll let people know if they sound as good as the spec!

phase_accurate 20th February 2004 08:43 AM

Apart from Carver there are the BASH amplifier, the new Audio Physic Mono and some amps by LAB-Gruppen that use such downconverter technologies.

I think that pure class-d is mature enough nowadays to be used without additional linear output stages.

Regards

Charles

djk 20th February 2004 09:27 AM

Bob Carver's tracking downconverter is pretty straightforward in concept, a single switching supply tracking the audio envelope. A bridge amplifier is used so as to only need a single supply rail. A simple all-pass filter provides the delay.

In the multichannel home theater amplifer the supply tracks the channel with the highest audio level.

Do we even need this switching supply?

Not really.

The Carver M1.5T put out 1200W/8R in bridge mode, no heatsink, no fan, and from a 3.5" chassis. 16lbs, a couple of those from the 3/16" thick front panel.

You could build a 6 X 200W piece for home theater using the same ideas.

You could even use a heatsink for cosmetic purposes if you wanted, or make the chassis larger.

Switching amplifiers have been around for about 50 years now, about every ten years or so a bunch of noise gets made about them.

Maybe this time around there will be some that: sound good, don't blow up in your face, and don't cost an arm and a leg.

You are welcome to hold your breath.

PS:

Battery powered equipment doesn't count in my book, I don't own any, YMMV.

millwood 20th February 2004 11:19 AM

if the switching power supply tracks input signal, wouldn't it be simpler to just use the switching power supply as a power amp directly?

Ouroboros 20th February 2004 11:27 AM

Quote:

Originally posted by millwood
if the switching power supply tracks input signal, wouldn't it be simpler to just use the switching power supply as a power amp directly?
The ideal would be an isolated mains-input SMPSU whose output can drive the speaker directly. (with the audio signal being summed in with the PSU voltage feedback signal).
Perhaps feasible for bass drive, but the SMPSU would need a very high switching frequency to give good performance over the full audio range.

Perhaps someone has tried out the concept?

phase_accurate 20th February 2004 11:27 AM

Quote:

if the switching power supply tracks input signal, wouldn't it be simpler to just use the switching power supply as a power amp directly?
http://www.peavey.com/products/shop_.../tcode/2/d.cfm

http://l2.espacenet.com/espacenet/vi...h&LG=de&DB=EPD

Regards

Charles

millwood 20th February 2004 11:32 AM

Quote:

Originally posted by Ouroboros
Perhaps feasible for bass drive, but the SMPSU would need a very high switching frequency to give good performance over the full audio range.

Perhaps someone has tried out the concept?


if the smpsu had trouble tracking high frequency signals, how could it be used as PS to a conventional amp at those frequencies?

subwo1 20th February 2004 11:36 AM

It can work, but for the DIYer, better quality sound is easier by means of either a straight class D or linear. I simulated one without the delay, and for most music, the supply can keep up with audio demands. That was using a regular response switching supply. The switching supply design could be modified to respond faster, but would work with normal response for powering a sub amp.

Hi phase_accurate, how is you switching amp project coming along?:)

Ouroboros 20th February 2004 11:42 AM

Quote:

Originally posted by millwood



if the smpsu had trouble tracking high frequency signals, how could it be used as PS to a conventional amp at those frequencies?



But as a PSU it wouldn't need to track the individual waveform of the signal. It simply provides power to track the envelope of the signal. The output caps on the suppply remove the need for it to track the voltage rail needs on a cycle-to-cycle basis. The delay on the audio signal allows for the PSU to charge up the caps to provide enough headroom for the signal burst that's about to appear at the input to the amp.


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