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Chip Amps Amplifiers based on integrated circuits

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Old 9th June 2003, 09:03 AM   #1
Thomas is offline Thomas  Denmark
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Yes, I too had to see what all the fuss is about.

It had to be minimum cost, so I looked arround my tiny dorm room, to see what I got.

Inspired by the Sun GC, I lay my eyes on two old AGFA external SCSI discs. These things are large 4Gb discs from an old graphics system I believe. I pulled the SMPS, fan and the disc, a 5,25" by 8 cm tall monster.

Next thing: Transformers. Not much to choose from, but I got a few 2x37V @ 1000VA toroids. Hmmm... too much voltage, then I'll just take and series two of them at the primarys and then parallel the secondarys. Tadaaa - a 2x18V @ 2000VA.

The GC is inverting and the most simple design I could find. Just the LM3886, two ELNA RJH 1000uF caps (had to buy these) and two resistors (1% metal film). Ofcouse, I need another resistor to bypass the mute function, so that's three resistors.
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Old 9th June 2003, 09:06 AM   #2
Thomas is offline Thomas  Denmark
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The connections and switches:
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Old 9th June 2003, 09:08 AM   #3
Thomas is offline Thomas  Denmark
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Close up at the toroids: You can see a lot of wireing here. I use stripped cat5 wire for all signal levels and 0,8mm transformer wire for supply and out. The heatsink to be fastened with L shaped aluminum and the wires will be shortened to look nice...
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Old 9th June 2003, 09:12 AM   #4
Thomas is offline Thomas  Denmark
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Picture of two channels finished. I have planed for 6 channels, guess the transformer can take the load. The visible resistor is the mute resistor. The feedback resistor is hidden by the caps.
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Old 9th June 2003, 09:22 AM   #5
Thomas is offline Thomas  Denmark
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Huh...

Almost forgot the most important thing; it sounds great! Except, it's very sensitive to noise from light switching on/off.
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Old 9th June 2003, 09:33 AM   #6
carlosfm is offline carlosfm  Portugal
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Talking Man, I whant those toroids

Thomas,

Congratulations, it's very nice.
Oh, and those toroids...
You talk about sinsitivity from light switching.
And what about mobile phones?
Yes, that's why I'm going to connect my case to earth (with a resistor and a cap), it seams to be the solution.
Now, enjoy the music.
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Old 9th June 2003, 09:42 AM   #7
Thomas is offline Thomas  Denmark
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Default Re: Man, I whant those toroids

Quote:
Originally posted by carlosfm
Thomas,

Congratulations, it's very nice.
Oh, and those toroids...
You talk about sinsitivity from light switching.
And what about mobile phones?
Yes, that's why I'm going to connect my case to earth (with a resistor and a cap), it seams to be the solution.
Now, enjoy the music.

Do you think the toroids' too much?

I have a small mains filter lying around, I'll try to see if it helps. Don't own a cell phone at this moment and don't wear a watch either. I kinda likes to be 'free' from all these things when I'm out.
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Old 9th June 2003, 10:05 AM   #8
carlosfm is offline carlosfm  Portugal
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Default Re: Re: Man, I whant those toroids

Quote:
Originally posted by Thomas

Do you think the toroids' too much?

No!
Let them be, you can add more channels if you need.
Those toroids will handle a 6 channel GC.
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Old 9th June 2003, 11:06 AM   #9
Mad_K is offline Mad_K  Norway
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Very nice! Ironic to have 2000VA toroids in a low budget amp that can get away with 200VA. Cool
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Old 9th June 2003, 08:19 PM   #10
Olle Bard is offline Olle Bard  Sweden
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you are using the lm3886, right?
what value do you use for the resistor on the mute-pin?
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