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Old 7th February 2006, 07:25 PM   #1
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Thumbs up YAY - another LM3875 lives!!!

I have finished my 2nd LM3875 amp thanks to loads of info and help on and from this forum

The chip is P2P which was interesting - quite fiddly really Thankfully one of my soldering irons has a really small tip...

I used chipamp.com PS boards with Philips 20ns diodes and 4 x 10K uf caps fed by a 225VA 25V shielded transformer to give me a supply voltage of +/- 35.9V. These feed 12 x 2200 uf caps with 22nf bypass caps.

I have used slightly different values for the resistors - see attached diagram - these are 1% metal and 5% carbon as indicated. I used Panasonic 1200 Uf FC caps.

Comparing this to my other LM3875 which is a kit from madabout sound.com with the carlosfm snubberised PSU and zobel; the sound is more open and forward - really delightfully transparent but imaging is not quite as good and it isn't quite as refined. The amp is still running in so maybe that will change.

This is my first go at making a case - there is still a bit to do but it hasn't fallen to bits yet which is nice Other bits of tidying up will include adding copper sheet to the insides of the wooden bits and on the power supply wires.

The sides are MDF painted with car paint - I can't photograph them with a flash because they are so shiny and flat, the autofocus keeps focusing on the reflection

Next one will be all aluminium - probably... I have set of experimental speakers to do first though
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Old 7th February 2006, 07:27 PM   #2
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The amps new home

I managed to get rid of the dust on the CD player with photoshop - if only it worked like that IRL
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Old 7th February 2006, 07:28 PM   #3
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The inside.
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Old 7th February 2006, 07:30 PM   #4
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The inside... from the other side...
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Old 7th February 2006, 07:32 PM   #5
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Quote:
Originally posted by quickshift
The inside.
That looks just beautiful!
I give it out of five.
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Old 7th February 2006, 07:35 PM   #6
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Quote:
Originally posted by lineup


That looks just beautiful!
I give it out of five.

Thank you very much indeed

And thanks again for your help
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Old 7th February 2006, 07:51 PM   #7
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Nice! And also neat! Must be fun to build.

Are there any heat problems? I'm asking because a friend of mine wants an amp for his 19"-rack-PC-tower-whatever-with-wheels and I'm considering building a Gainclone. Can't wait...
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Old 7th February 2006, 08:04 PM   #8
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Quote:
Originally posted by Rodeodave
Nice! And also neat! Must be fun to build.

Are there any heat problems? I'm asking because a friend of mine wants an amp for his 19"-rack-PC-tower-whatever-with-wheels and I'm considering building a Gainclone. Can't wait...
Thank you.

Yeah, I really enjoyed building it. I need to invest in something that can power sand at 90 degree angles though I ended up using a ruler with sandpaper wrapped round it...

My other one is built into a 2U 19" case for the PSU and a 1U 19" case for the amp. The heatsinks don't get hot at all - I have used P3 heatsinks and they only get to about 12 degrees C above ambient when played loud.

As long as there is a sensible path for air in / out it'll be fine.
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Old 7th February 2006, 08:05 PM   #9
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Insides...
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Old 7th February 2006, 08:10 PM   #10
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Beautifull machine !!
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