Sun Microsystems Gainclone?

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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!) ;)

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).
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.

:idea: 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). ;)
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.

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.


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!


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!



Yep. And try these prices on for size:

Anchor Steam:
California: $7~8 per six pack
Utah: $13~14 per six pack, not refridgerated

Pilsner Urquel:
California: $7 per 6 pack
Utah: ~$14 per 6 pack, not refridgerated

Some decent bottle of red wine:

California: $12~16 a bottle
Utah: $24~35 a bottle

So yeah, the state of Utah not only makes it inconvenient to get these fine beverages, it makes a tidy little proft off them.

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… ;~)

Things have greatly improved since my days at the U. The only way to get real beer then (as opposed to 3.2 panther p!$$) was to do the trek to Evanston. And the Utah cops made a sport of catching people doing that, confiscating the brew, and slapping their victim with a huge fine.

Were you in CS dept?

SRMC or SE: Where is that surplus outfit? Sacramento is only an hour away from me.
Surplus Stuff

Surplus Stuff is toward the eastern end of Sacramento. If you are familiar with the area it is South of Hwy 50, and off of Folsom Blvd. between Howe Avenue and Watt Avenue. If you are heading to South Lake Tahoe some time it would be a quick side trip.

Here is a link to their web page and street address: Surplus Stuff

Unfortunately they don't put the fun stuff like rack mount cases and surplus caps on the web. Besides, they'd probably be very expensive once shipping is factored in. The rack mount cases I purchased were quite heavy and full of equipment used in semiconductor manufacturing, including various Power-One switching power supplies (too low voltage and amperage for powering a Gainclone) and circuit boards with Sprague caps. At $20, figuring that the cases usually include an IEC connector and power switch, it is hard to beat.


They use the Audax HT080G0. This driver looks to be unavailable now. Unfortunately, Audax's replacement may not be as good. It is the HP080G0. It looks good, but I haven't tried it yet.

The HT080G0 is a superb little driver… the best full ranger I've ever heard.

Enclosure: The driver is mounted on a .25" plastic panel 5.5" X 7.5", which in turn is attached to a concrete block which has been dunked several times in black laytex paint. The block must be sealed this way. The rear baffle is also .25" black acrylic. The front and rear panels sandwich the block and are connected to each other with some lengths of all thread and coupling nuts via button head cap screws on the front and rear. The hollow part of the block is quite small - just wide enough for the Audax motor to nest in.

The enclosure is lightly stuffed with 1" open cell foam cubes.

Block: "cinder block," concrete: 5.5" W X 7.5" H X 7.75" D

On the rear is a 5.25" passive radiator. It is mounted backwards because the frame will not nest inside the block. It is too big. The system is tuned to about 40 Hz by gluing a large steel washer to the radiator's dust cap. The radiator has a fairly compliant rubber surround. This yields a system F3 of about 65 Hz.

The enclosure is air tight.

Due to the response of the Audax in situ, I use a simple response shaping filter that pulls down a broad, mild peak that exists in the middle of the system's passband. It is a notch filter composed of a .5mH inductor, 6 ohm resistor, and 16mF capacitor wired in parallel with each other, with the group of them wired in series with the driver. This yields very flat response, +/- 2 dB or so from 80 Hz to about 12 KHz. +/- 4 dB bandwidth is 65 Hz to 15 KHz.

If you build this speaker, particularly if you get a decent set of matched drivers, you will not be disappointed. They are simply stunning. I listen to them at about 30" distance, slouched in my chair so that the drivers are at ear level. I usually pull them out so that they are perched at the edge of the desk for serious listening.

xsnailx, yer killin' me!!! I dearly love the original pilsner.


Very nice… I'd actually seen your page before.


No, I was a Linguistics major…


As concerns the use of the PIII sinks, I hooked up the amp to my left and right home theater speakers and drove it quite hard for almost 4 hours straight. I had the fan on, which is completely inaudible from 8 feet away, and the sinks got pretty warm, but no meltdown… not even close. So my conclusion is, at least with 31 V rails, that these socket 470 sinks with a little bit of air flow work just fine.

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