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Amp Camp Amp - ACA
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Old 17th November 2018, 09:05 PM   #6581
73 and a 3rd is offline 73 and a 3rd  United States
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Quote:
Originally Posted by oc11 View Post
Look at it this way 73 and a 3rd, the journey may be as fun (or more fun) than the final product. 658 pages, great! A lot of the pages do not have much of interest in them, you do not need to read everything in detail, scan through it, read the good stuff. Remember there is a lot of information on these pages, including a lot of information on preamps.

I will give you a suggestion, try to establish a basic idea of how you want the signal to get to the amp, and follow a straight line (a theme if you wish) of thinking in your planning. For example, the ACA is a simple Class A design. I would combine it with other pieces (preamp, DAC) that follow the same rules, class A for analog, simple design. I think it would be a good idea to combine an NP designed Class A preamp with the ACA. Keep the signal pure and the path clean and do not forget volume control as part of the path. Be careful with power supplies. Understand that digital music coming through a USB can contain a lot of high-frequency junk in it which is passed right through your system. Make sure your DAC can clean the digital noise. Finally, you really do not need to spend a fortune doing this, what you need is careful planning. Keep notes as you go. You will never remember a lot of this stuff unless you keep a record.
I am totally tracking with what you are saying. Pretty much planning what you have laid out starting simple with a cd player or fm tuner as source input. Looking for stand alone preamp class A analog, possibly tube. I don't mind used or older gear if it fits right and helps with price. DIY is great too.
Seems like matching/managing/balancing voltage and gain is the trick. Also seems to be quite a wide variety of preamps to choose from.

Looking at a used Dared SL200a currently for $350. Anyone have feedback?
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Old 17th November 2018, 09:09 PM   #6582
fmalloy is offline fmalloy  United States
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Quote:
Originally Posted by MellowTone View Post
if you have access to one, a variac is an excellent piece of kit to have (although you can get by with a light bulb tester) if youre building something with a linear power supply (eg. large transformer, followed by rectification, capacitor bank, etc) which is what youd have seen used for the other (more power hungry) Nelson Pass designs built around here
For us newbies...can you explain how you'd use the variac with a linear power supply? Is it for testing purposes?
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Old 17th November 2018, 10:46 PM   #6583
astromo is online now astromo  Australia
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Quote:
Originally Posted by 73 and a 3rd View Post

I am totally tracking with what you are saying. Pretty much planning what you have laid out starting simple with a cd player or fm tuner as source input. Looking for stand alone preamp class A analog, possibly tube. I don't mind used or older gear if it fits right and helps with price. DIY is great too.
Seems like matching/managing/balancing voltage and gain is the trick. Also seems to be quite a wide variety of preamps to choose from.

Looking at a used Dared SL200a currently for $350. Anyone have feedback?

I can't find useful tech specs on an SL200A, I can find comment out there on an SL2000A, such as:
Dared Mini SL-2000A Preamplifier
but no info on the gain of the unit. I'm using the ACAs as balanced mono blocks fed by a Schiit Freya using its tube stage with a gain of 2.5


Does a great job in a 3m x 8m room with a hard wood floor.


So, it's really a question of gain that you need and if you're like me, how you intend to line up the amp(s). If you're going a single ACA in stereo, you're choice is made - you'll be lining up the ACA's RCA inputs. Whereas if you're doing monoblocks, the balance XLR inputs are an option and you'll need a preamp that can play in that world.


There's no single answer because there are so many variables. Start off cheap (e.g. a headphone amp) or borrow a unit to try out is my suggestion.
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Old 17th November 2018, 10:50 PM   #6584
astromo is online now astromo  Australia
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Quote:
Originally Posted by fmalloy View Post
For us newbies...can you explain how you'd use the variac with a linear power supply? Is it for testing purposes?

Geez mate, you're in luck thanks to one of those helpful Ozzies:
Transformers - The Variac


Give that a read and see where you get to.
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Old 17th November 2018, 11:45 PM   #6585
oc11 is online now oc11  United States
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I have had good luck buying inexpensive but fine equipment pre-used. However, I have stayed away from tubes because I am weary of tube replacements. I know tubes produce a great sound, but I stick to solid state. The variety available and buildable (DIY) available is what makes this a really interesting challenge.

And yes, I fully agree with Astromo.
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Old 18th November 2018, 02:48 PM   #6586
ellisr63 is offline ellisr63  Mexico
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Does anyone know if this would work for some ACA moons?
2412B Full Aluminum Enclosure / mini AMP case/power amplifier box/ chassis | eBay
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9 DIY B&O Bridged amps for biamped horns, 3 Pass ACA, Yamaha cxa5100 preamp, Oppo 203, Samsung 65" 4k fp, KLH sub. DIY projects... 7 horns with 3 being DIY Synergy horns for living room.theater
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Old 18th November 2018, 03:41 PM   #6587
Alan4411 is offline Alan4411  Wales
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Quote:
Originally Posted by ellisr63 View Post
Does anyone know if this would work for some ACA moons?
2412B Full Aluminum Enclosure / mini AMP case/power amplifier box/ chassis | eBay
Should be more than big enough!
As long as you do not mind drilling and tapping the heatsink holes for the Mosfets and board mounting.

I have mine built into a slightly smaller version as I wanted to have my power supply integrated and have a narrower front panel than the 'standard' ACA chassis. (Example only Express Delivery Full Aluminum Power amplifier Enclosure chassis case heatsink | eBay) and it runs nice and cool at 43 - 45 degrees Celsius.
Attached Images
File Type: jpg IMG_8591.jpg (984.6 KB, 297 views)
File Type: jpg IMG_8692.jpg (1,007.7 KB, 272 views)
File Type: jpg IMG_8695.jpg (823.6 KB, 275 views)
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Old 18th November 2018, 06:31 PM   #6588
oc11 is online now oc11  United States
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As long as the heatsinks are larger in size and the fin size is similar they should dissipate more heat than the ones in the ACA kit. The fin size of your heatsinks appears, by visual inspection, to be similar to ACA's.

Last edited by oc11; 18th November 2018 at 06:34 PM.
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Old 18th November 2018, 08:47 PM   #6589
olen is offline olen  United States
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I built a stereo ACA using a variant of that chassis (no knob) and the previous gen ACA boards with an internal 24V power supply and mine runs hot: 60C at 25C ambient. If you run an external supply you might be ok. An external 20V should run it even cooler. The latest ACA boards have the FETs placed further apart, and that should help with the spreading the heat across more of the heat sink. This chassis has fins that are only 1 tall/deep as compared to 2, but the heat sink has more area than stock. To reduce the case temperature Im planning to mill vents in the solid bottom cover, to improve internal convection cooling (the top is vented). One other caveat is that there isnt much meat on the heat sink so it was difficult to tap blind holes and have enough thread engagement for the standoffs. If youre ok seeing the standoffs through the heatsink then its a lot easier to tap a through-hole.

Heres my ACA:
Pictures of your diy Pass amplifier
Attached Images
File Type: png ACA_thermal_1.png (534.4 KB, 233 views)
File Type: png ACA_thermal_2.png (576.7 KB, 222 views)
File Type: png ACA_thermal_ambient.png (597.9 KB, 79 views)
File Type: png ACA_thermal_internal_PS.png (567.1 KB, 85 views)

Last edited by olen; 18th November 2018 at 09:01 PM. Reason: Added thermal images
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Old 18th November 2018, 10:09 PM   #6590
oc11 is online now oc11  United States
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Olen, to improve convection of your unit you should consider adding legs that leave about an inch clearance from the surface where it lies to the bottom of the unit. This will increase the ease for air intake into the enclosure. You may want to consider milling or drilling the top cover as well as the bottom to increase convection.
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