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Chip Amps Amplifiers based on integrated circuits

Sun Microsystems Gainclone?
Sun Microsystems Gainclone?
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Old 16th May 2003, 02:46 PM   #1
mr_ro_co is offline mr_ro_co  United States
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Wink Sun Microsystems Gainclone?

Well, here's my stab at the Gainclone... LM3875T based. I used a rather nice potted Avel-Lindberg transformer I happened to already have. The only "tweaky" feature I implemented was the use of high speed diodes for the rectifiers. Everything else is of normal quality - nothing audiophile. I did use a poly cap for the input, though.

The chassis is a Sun Microsystems external scsi device box. I used Pentium III socket 470 heat sinks for the devices. They get pretty toasty when the amp is pushed hard for long duration but work surprisingly well. For extra hard extended usage, I plug in the rear mounted fan, which is connected to a 3VDC wall wart. This gets it spinning a fairly slow rpm that draws air through the chassis through vent holes in the bottom and is generally inaudible (totally inaudible over the loud playback, especially when the amp is located more than a few feet away from the listener).

The sound quality, especially on my nearfield speakers, is surprising to say the least. Detail retrieval and depth of field are astonishing. Very refined sounding, harmonically rich, but not excessively lush like a SET amp. It is also dead quiet.

It's truly amazing how inexpensively these amps can be built.

Yes, I know my volume knobs suck, and I haven't gotten my pilot light in yet (and it will NOT be blue!)

Steve
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Old 16th May 2003, 07:55 PM   #2
mr_ro_co is offline mr_ro_co  United States
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Lightbulb images

how about some photos...

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Steve
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Old 16th May 2003, 11:07 PM   #3
faustian bargin is offline faustian bargin  United States
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Default neato

so they let you drink beer in SLC huh.

j/k

anyway, fun case. is it metal? ...actually now that i look at it, it looks plastic. must have made it easier to slice up.

what is the speaker you're using?

/andrew
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Old 16th May 2003, 11:18 PM   #4
SRMC is offline SRMC
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Default It looks great

You beat me to it. I think that it looks great. I agree that the knobs mar the design, but that you can change them easily.

There is a store here in Sacramento, CA. (Surplus Stuff) that has stacks of Sparc Stations and other misc. computer surplus. Although I have been eyeing various Sun Microsystems cases I ended up buying a couple of rack mount cases for $20/ea. I thought that they would fit in with my other audio gear. However, your implementation would fit in much better in my office (and my boss wouldn't notice that I had even more audio gear on my desk).
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Old 17th May 2003, 08:21 AM   #5
Nuuk is offline Nuuk  United Kingdom
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I appreciate that you have had to fit everything into the case but it's worth stating that if the heatsinks were situated with their fins in a vertical position, the cooling would be much better.

As they are, the hot air coming off the fins is trapped. No wonder you need the fan.

I would have been tempted to cut the heatsinks down so that they did fit vertically and then cut two neat circles out of the case, above and below them creating a very nice chimney effect.

Otherwise, a very neat design and another confirmation of how good these little amps are (for those that haven't built one yet).
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Old 17th May 2003, 09:13 AM   #6
Circlotron is offline Circlotron  Australia
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Default Upcoming DIN (or whatever) standard amp?

Having seen that, I wonder who's going to be the first to build a stereo gainclone into an old CDROM drive case? Would slot into your PC just neat. In fact, if you had an old CD burner case they already have a small fan at the back. Noise would not really be an issue in a PC environment.
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Old 17th May 2003, 12:49 PM   #7
elizard is offline elizard  Canada
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hmmmmmmz .. i got an old cdrom burner
maaaaybe i'll try it
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Old 17th May 2003, 01:53 PM   #8
JOE DIRT® is offline JOE DIRT®  Canada
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Nice job on the amp....but those heat sinks need to be changed despite the fan....but that can always be done at a later time............Cheers on a Job well done!!!!!
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Old 17th May 2003, 03:35 PM   #9
mr_ro_co is offline mr_ro_co  United States
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Andrew,

Not only do they let you drink beer in SLC, they let you drink really good beer! You just have to pay the sin tax… ;~)

The chassis is abs plastic. It had metal parts internally but I removed all of them.

The speaker is one of my own design. I call it the "Neutrino." The one you see is from the prototype pair, built about 6 years ago. It's a near field design that uses a 3" Audax full ranger in a brick enclosure. The speaker has a 5" rear fire passive radiator and a simple response shaping circuit. They are incredibly coherent with outstanding midrange immediacy and are very revealing of source quality. The Gainclone sounds fabulous with them.

SRMC,

Yes, the knobs have got to go. I'm going to replace them with something that looks like it's supposed to be there. With the current knobs I can't convince anyone that it's really a very rare Sun audio product!

Nuuk,

If you haven't built one, off with you to the electronics store today! Do not delay further!

You are correct about the heat sinks, but it was a physical compromise I had to make. They would not fit otherwise and it was going to add too much complexity to build it with the sinks flipped upside down with respect to how they are now. I may revisit that, though… I think the sinks could be made to fit in the chimney config you describe, but the holes in the top would be very hard to make appear original.

Believe it or not, they work just fine the way they are. Playing my little speakers at their limits (maybe about 15 Watts/ch) causes the sinks to get very warm, but even with the lid on an without the fan, I can still leave my finger on the heat sink (once I pop the lid off to do so). These heat sinks are amazingly efficient. I would encourage anyone to use them.

The 12V fan spins very quietly with the 3V wall wart and there is a decent air current flowing through the chassis when it's on. I'm going to see what the minimum voltage is to get it to just barely tick over. I don't think it will be audible at all at that point. The air is pulled through vent holes directly underneath the sinks, then exhausted out the rear.

Joe Dirt,

I have to differ with you about the heat sinks. They work just fine!

----
Steve
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Old 17th May 2003, 04:06 PM   #10
Steve Eddy is offline Steve Eddy  United States
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Quote:
Originally posted by mr_ro_co
Not only do they let you drink beer in SLC, they let you drink really good beer! You just have to pay the sin tax… ;~)
Yeah, you just have to make sure you stock up so you don't run out don't run out on Sunday. Otherwise you're stuck with that watered down **** they sell at the grocery and convenience stores.

se
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