Agfa Gc

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Thomas

Thomas

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Joined 2001
#1
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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#3
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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#4
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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#6
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.😎
 
#7
Re: Man, I whant those toroids

carlosfm said:
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.😎
Click to expand...


Do you think the toroids' too much? :scratch:

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.
 
#13
Magnetmaz said:
When you use a higher value Torroid ( like in my case, a 500VA), can you still get away with using MUR860 diodes in the bridges? Or do you have to have higher rated ones?


-Maz
Click to expand...

You still draw the same amount of current, right? 🙂

The transformer won't ruin your diodes regardless of it's potential, unless you draw a serious ammount of (startup) current from it. You can also draw verry large currents, short term, from smaller transformers.

Unless you have large capacitor banks, the diode rating should only follow the load current (and some safety margin). If you use large caps, like in class-A designs, you may have to compensate for a large inrush current.

I use a single 50A bridge for all 6 channels (when done). But GC's don't have much inrush current, so this is almost as ridiculous as 2KVA toroids.
 
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