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Old 15th July 2003, 01:55 AM   #1
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Location: Republic of Berkeley
Smile my GC is beautiful!

Actually, it looks rather like Final's battery powered wiring monstrosity. But who cares about looks? It sounds wonderful!

It's a "minimal" inverted circuit I found here:
http://www.decdun.fsnet.co.uk/gainclonecircuits.html
Differences to the above schematic are: I use an attenuator on the input (not the 56k resistor), I don't have an input capacitor, I used single 220k feedback resistors, and I left out the ground filter.

Just now I bypassed the Panasonic FC 1000uF PSU caps with 1uF Auricaps, and the sound was transformed. Before it was merely "good solid state" - now it's simply "excellent". The PSU cap bypass got rid of the grain I was hearing in vocal sibilants, added warmth, and improved soundstaging.

Before this last tweak it was a tossup whether my tweaked Belles 150a or the GC sounded better. Now I'm pretty sure the GC has come out on top.

I built the amp as a dual mono circuit sharing one heatsink, completely point-to-point. I used way more heatsink than required; it's stone cold. In fact, I used a lot more of everything than required. The whole shebang weighs around 30 pounds.

PSU
surplus 10A line filters
Plitron 300VA 18V secondaries
10A bridge rectifiers
1000uF Panasonic FC caps (electrolytic)
1 uF Auricaps (metallized polypropylene)

chip
LM3875 insulated version
Riken metal film resistors
generic 16 ga primary wire, CAT5
DACT 50k attenuator

My speakers are DIY - the infamous Parts Express 69 cent surplus TV drivers, in a open baffle line array of 9 per side, roughly 95 dB sensitivity. Drivers are tweaked with coating and foam strip damping.

Source is a Dan Wright modified MSB Link, fed by an M-Audio AP2496 sound card via a Monarchy DIP.

I could get some pictures up of the amp for you to admire, but trust me, it's a horrendous looking rat's nest, a short circuit waiting to happen.

Sincere thanks go to National Semiconductor for engineering such a great chip, Peter Daniel for inspiration, Thorsten for prosetylizing, Decibel Dungeon for schematics and instructions, 47 Labs for starting the craze, RJM, CFraser, the Thor-amp page, and everybody else in the Top 20 of Google "Gainclone" links!

Cheers,
Andrew
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Old 15th July 2003, 03:05 AM   #2
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You might try the amp without line filters. I found that mine work better when filter is not present.
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Old 15th July 2003, 12:54 PM   #3
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Nuuk,
People keep visiting your site.

Andrew,
Don't be ashamed to show a picture, that would be nice.
Not all Gainclones have to be as the ones Peter Daniel "San" makes.
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Old 15th July 2003, 01:05 PM   #4
fedde is offline fedde  Netherlands
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Congratulations with your new gainclone! Will you invite us for his first birthday next year ?

Fedde
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http://www.fedde.nu, gainclone and non-oversampling DAC audio projects and kits...
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Old 15th July 2003, 03:26 PM   #5
ronc is offline ronc  United States
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Yes , go ahead and post pics. We are DIY ers and use to seeing a buncha components and wires spread out,its a natural scene for us.
ron
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