Amp Camp Amp - ACA

Let me just add that a dual mono configuration is also a possibility. This uses the Peter Daniels PS boards and an Antek AN-2215 toroid that produces 20.5 Vdc. That's a little high but sounds really good. One could put everything in one chassis or do separates with short power leads. This build uses PC CPU coolers but one or two of the standard heatsinks could be used. HeatsinksUSA has many profiles.

Sorry for the mess - too many projects going at the same time.:eek:
 

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Toobhed: I mounted my PCBs to the sink by drilling a hole all of the way through the sink and used an M3 screw with nuts for a custom standoff. Two nuts provided enough clearance for the PCBs so the wouldn't touch the sink. I would definitely recommend "dimpling" the sink with a hammer and punch to keep your drill bit from wandering before it bites into the sink. There is little recovery from a mounting hole that is off by 2mm.

Billy: that is one great looking integrated amp! I like the spacious chassis design. I was contemplating another ACA build with a DCB1 like you did.

Bert: thanks for the compliment! My daughter is thrilled with her amp and speakers! I just used one PS for both channels. If you wanted to make the two channels completely independent, you could use the power bricks. I don't see a huge benefit from separating things due to the relatively low power draw. Similarly, I don't find the need for any shielding with this design. The completed amp is VERY quiet as is. It has made me go back to my Aleph-X amps and rethink the power supply to reduce some speaker hum that I have. In all builds, you should isolate the RCA input barrels from the metal chassis with the plastic spacers that they come with. This will help reduce the potential for hum caused by ground loops, especially with more complex builds.

Bob: I've been admiring those CPU-sink mono block amps of your for some time now. If I am remembering correctly, toy reported some nice sound improvements with a more robust power supply.

Jason: it's good to hear that you are on the mend! Are there any plans to restock those great little 2U and 3U 200mm sinks in the store?
 
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Bob: I've been admiring those CPU-sink mono block amps of your for some time now. If I am remembering correctly, toy reported some nice sound improvements with a more robust power supply.........

Thanks, My impression is an increase in the general body/fullness and a slightly more engulfing image... both depth and width of stage. Not a lot but a definite improvement over the bricks.
 
Thanks for the added details, Bob! Curious, your impressions of a more robust power supply for the ACA mirror the impressions of those who have built a larger power supply for their DCB1 preamp. I feel a "Tim the Toolman Taylor" moment coming on: More Power!

One of these days I'll have to read my posts more carefully before I submit them. Darn iPad auto correct...
 

bkby

New member
2012-07-06 9:42 am
Bankok
My ACA
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Power By......
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Teak Wood
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A general question to bkby and others here about the ACA.

bkby how hot do the heatsinks get on yours?

I am about to build the kit I received from the diyaudio.com store and was wondering about the heatsinks for the ACA; can I go horizontal versus vertical?

I have read and re-read the many threads about orientation of the fins and most are for the larger F5 (and variants) and the other Pass Labs Fx amplifiers. But for the ACA, it is smaller in terms of output and heat, so how much difference would it make? Is it negligible enough to go either way?

I was planning a single chassis unit with both sides being built on a single kind of tall and wide piece of heat sink running across the back of the unit as Plan A and a transformer in the front half of the unit supplying both boards and outputs coming from the front or recessed at an angle from the top of the chassis.
 
Love those wooden chasses! Interesting design with heat snk configuration. It looks like you can run bias a little higher than normal with sinks that large.
Those sinks aren't particularly big for an ACA, and the horizontal fins will affect it a bit too. All and all a bit less passive cooling I think than the original or the coming chassis from the store, but close. My experience is that the most important thing is if it's in a slightly enclosed area, like with a shelf above it, the temp goes up fast! Ambient temp matters too. In a tropical climate I'd double the size!

I believe there's been some discussion that MOSFET's will tend to fail over the long term more often if they are run hot.
 
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Finally got around to using something other than computer/Walkman for volume control. The first pic is a shielded box containing an Alps Blue Pot. It sounds delicious but only offers attenuation. Completely sufficient for most systems IMO.

Being a big band jazz fan/player, I like a little more SPL than that, so I hooked up a J-Fet preamp. It has more gain than I need but also sounds clean and clear. If I'm reading the power transistor spec sheet properly, which I could easily be mistaken, the high temp theoretically can go to 150 C. (TJ = Operating Junction and Storage 55 - 150 C). Can someone with more experience report what a reasonable, practical temp ceiling is. Probally will never go there but it would be nice to know.
 

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Hi Bob,

I wouldn't worry much about those IRFP240 devices, they are virtually indestructible. The data sheet shows the de-rating curve for them:

[IMGDEAD]https://www.facstaff.bucknell.edu/esantane/movies/irfp240.jpg[/IMGDEAD]

My Aleph-X amp runs them at less than 2A bias each with a case temp that is less than 60c. This is well within the safe operating area. I don't think you can run an ACA high enough that they would break a sweat:D

I see you have some nice home spun cat5 speaker wires, too! Cool stuff!

Eric
 
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Some followup...

There really isn't a hard-and-fast maximum power dissipation figure for the 240 devices as this is dependent upon the size of heat sink. Dissipating more power means needing a bigger sink and to some extent, larger sinks "compensate" for greater power dissipation by keeping things cooler- though there are limits.

I ran some numbers through WuffWaff's spreadsheet that he developed for the Aleph-X amp. With 20v rails and 2A bias per device (40w dissipation per device) with each device mounted on a 1.0c/w sink, you would have junction temp of about 100c and a sink temperature of about 65c - this is about as high as you would want to take it. You would have a maximum power dissipation figure per device of about 53w, so you're coming pretty close by running them at 40w each.

If you then double the size of your heat sink (0.5c/w per device), this brings the junction temp down to about 85c and sink temp down to closer to 45c - this is much more sane. With cooler temps, the "danger zone" of power dissipation becomes more like 77w per device, (instead of the previous 53w) so at 40w per device, they can breathe a little more easily on a larger sink.

Eric
 
That tells me, though adequate with attenuation, my little PC CPU coolers are close to max capacity. If I continue to use the ACAs with a gain device I'll bump up to something more substantial. When my devices read ~ 52 C the heatsinks are ~38. They are hot to the touch but don't burn the fingers. I suspect the very thin fins are helping in the current configuration, but I understand the advantage of using more metal mass.

Don't know how far I'll push these as they weren't designed for high sound levels, but thanks for your replies and useful information.

P.S. Been listening to the Alps/ACA combo with a Paul Desmond/Chet Baker duo + percussion...sweet, and again - thumbs up Mr. Pass.