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Old 20th December 2008, 07:01 PM   #1
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Default Compact Single-Ended Class A Build

Hi guys! My name is Aaron, and I'm new to this board, but frequent other audio-related sites as well.

Until recently I had been running a pair of Channel Islands Audio D-200 Class D monoblocks. They are superb amps, but I recently bought a CEC AMP53 single-ended class A amp. It sounds truly amazing, and has inspired me to set about building a pair of amps for myself.

I am a Mechanical Engineer, and have some ideas roughed up for the enclosure/chassis, but am looking for some tips on which circuit to use. The plan is to build a pair of monoblocks - single-ended Class A, that put out somewhere between 30 and 50 watts per channel into 8 ohms. Problem is, this forum is daunting, with 50+ pages in some of the threads. What would be a good circuit/build to go with to accomplish this? Simplicity and purity are key...

I also want these to be fairly compact amps, so a small circuit would be preferable. Cooling won't be an issue, I have that taken care of. Also, planning to go with external matching enclosures to hold the power supply and associated circuitry. Elegantly industrial is what I'm going for. Or industrial elegance?

So, with those goals in mind, what can you recommend? Glad to be a part of this community now
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Old 20th December 2008, 07:27 PM   #2
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Check out the Aleph30 or mini-A threads. The A30 is 30 watts into 8 ohms and pretty easy to built.

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Old 20th December 2008, 10:46 PM   #3
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How small is small?

Most of room inside your chasis will be taken up by the power supply. Depending on the dimensions you are aiming for, you might want to find something at the lower end of your stated power range.

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Old 20th December 2008, 11:27 PM   #4
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The intent is to have a seperate power supply box, to aide in keeping the amplifier part compact.
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Old 21st December 2008, 11:48 AM   #5
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In that case, your only limit would be the size of the heat sinks. Even a relatively complex circuit like the A-75 can be put on a very small board. ( I think the stereo board from AudioXpress is around 4X4). So you could build pretty much any of the Pass labs projects: A75, Mini A, Aleph X, F5, F4.

I really like the A75 and the F5. (never built an aleph X though.)

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Old 21st December 2008, 06:41 PM   #6
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Get a fan or water cooler and you can be any size you want.

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Old 21st December 2008, 07:03 PM   #7
lineup is offline lineup  Sweden
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Most Pass amps are not designed to be very compact.
Some can be made small, if you wish.

But if your requirement number one is COMPACT, you will have better choices:
- Class D
- Gainclones like LM3875, LM3886
Class D amplifiers ( Class D Forum ) can be extremely small.
Because they can do with very small heatsinking.
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Old 21st December 2008, 07:34 PM   #8
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The words "compact" and "class A" aren't normally found together. I'm assuming that when you say you want the amp to be compact, you're speaking of the active circuitry, since you indicate that you're going to have a separate power supply.
A few more-or-less random points:
--Class A circuits need to dissipate a lot of heat from the output devices. This requires heat sinks of some sort and if you want air to carry off the heat, you're going to be depending on fans to keep the size down. The smaller you want it to be, the more air you will have to move and the louder the fans will be. This will be a balancing act.
--Water cooling allows you to move a preposterous amount of heat and do it quietly if it's done properly. I did a thread on this once upon a time wherein I described a system built around a pair of Aleph 2s. The downside to water cooling is that it isn't portable. Other than that, you're pretty much good to go. For what it's worth, I can easily get the active circuitry of an Aleph 2 into a 1U chassis with water cooling. The power supply is another matter. Transformers don't compress easily. Nor do big electrolytics.
--I'd suggest an Aleph 3/Aleph 30 or Aleph 4 (wasn't that the 60W one?)/Aleph 60 depending on how much power you want. They're relatively straightforward and you'll have oodles of people who can guide you over any bumpy spots, as there are scads of those amps in the field. The A-75 is a wonderful piece, but requires more parts and some adjustment. That may or may not suit you. The Aleph-X might be a contender, but also requires some fiddling and seems to conceptually confound some folks.
--Some of Nelson's First Watt spin-offs might be of interest, depending on power available and scalability.
--Amps with separate power supplies are pretty nifty, but can be difficult to carry around. Consider a detachable umbilical. Neutrik makes some suitable plugs. See also Amphenol, Hubble, et. al.

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Old 21st December 2008, 08:27 PM   #9
steenoe is offline steenoe  Denmark
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There is always the Zalman approach

And another one like it:
Aleph 5 PC-fan

Keep them fans clean and running, though.

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Old 21st December 2008, 11:38 PM   #10
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Water cooling crossed my mind, but that get more complicated than I want, and with the amount of power I'm talking about, probably unnecessary . I'll be using a fan, as Nelson mentioned. You can dissipate substantially more heat than with just natural convection, and make things smaller

The next couple days I'm going to sit down with my buddy and discuss how the circuit will be laid out so I can start getting into more of the packaging details.
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