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Old 6th September 2004, 08:22 PM   #1
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Question A new kind of Class D amp ?

Hi all,

I have read a lot of threads here and I have a simple question regarding class D amps you can with out a doubt answer me

One of the more expensive parts in an amplifier is the transformer it adds a lot of weight and is expensive.

Has anyone done a class D amp with one 320V rail ?
Just the 230V and a rectifier, no trans.

I know it could simply kill anyone who is trying to connect the speakers while the amp is on, but this is DIY, I'm willing to bet a few bucks that you don't let people mess around with your equipment

The output stage would be a mosfet, and a small transformer, somewhat like the valve amplifiers use. (Why not do PWM at 1MHZ?)

The "front" side of the transformer would be from the +320V to ground through some high frq mosfet.

The "back" side of the trans would some feedback circuit and a lpf to the speaker.

Would this be at all doable or are the some major flaws in doing an amp like this ?

Best regards,
Gunnar I. T.
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Old 6th September 2004, 08:31 PM   #2
Netlist is offline Netlist  Belgium
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Hi Gunnar
You probably didn't notice but since yesterday we have a brand new Class D forum.
I'm sure you don't mind I moved your interesting thread over here.

/Hugo
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Old 6th September 2004, 08:55 PM   #3
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Hi Gunnar

I have done something like that, and it worked just fine!

I used IRF730N for MOSFET's for 200 Watts output power.

For transformer i used something from a tube amplifier.

All The Best from Denmark

Lars
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Old 6th September 2004, 09:02 PM   #4
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Hi Lars,

Do you have schematics for the amplifier you would be willing to share with the rest of us ?

Why do you think most class d amps use +- 70/50/30/24 rails ?

Is it easier to build? less hazardus (sp?) ? cheaper components ?

Is it hard to get the output trans ?

All the best from Iceland,
Gunnar.
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Old 6th September 2004, 09:10 PM   #5
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Gunnar: When you go above 200V (rail to rail) the MOSFET's tend
to get a much higher on-resistance, resulting in poorer efficiency of the
amplifier. Component price is more or less the same.

For audio i would probably rather have a slow and unlinear componnet as the transformer in the power supply, than in series with the output. That might be the reason you are looking for ..
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Old 6th September 2004, 09:15 PM   #6
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Lars, that is a very good reason

But would it be at all possible to build a class D amp without a transformer ?

Or would that just be silly, one would have to have a LP circuit in series with the speaker ?

Best regards,
Gunnar.
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Old 6th September 2004, 09:24 PM   #7
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Some would say you have a safety issue ..

But it as been done before in some commercially availble
subwoofers. I'm not sure they exist anymore
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Old 6th September 2004, 09:33 PM   #8
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LOL

Lars, thank you for good answers.

And if anyone comes across any links or schematics of transformerless Class D amps then please post it on this thread

Best regards,
Gunnar I. T.
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Old 7th September 2004, 03:35 AM   #9
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by GunnarIT
LOL

Lars, thank you for good answers.

And if anyone comes across any links or schematics of transformerless Class D amps then please post it on this thread

Best regards,
Gunnar I. T.

Here you are:

http://www.flyingmole.co.jp/en/index.shtml

Everythin integrated on one circuit board and no transformer.

This stuff seems to be quite popular in Japan

Best regards

Gertjan
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Old 7th September 2004, 05:27 AM   #10
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I think the main problem is to insulate the amp from the rest of your stereo equipment. A transformerless amp would never be approved in Europe and and in 230 V country. You have to make a switched mode power supply which can be quite light, not small though.
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