Hi All. As a project looking at an ACA set up as bridged monos. Can these be wired up in one case as in four modules in one case so a mono amp on either side as have a case to use up? Also interested in the Toshiba MOSFETs jfets as an upgrade has this been done successfully? Thanks for all your suggestions
Sure. Just make sure that the heatsinks are proper.
MOSFETs and JFETs are two different things. The original ACA was likely built (but I can't confirm) with Toshiba 2SK170 JFETs. The good news is that those may already be included in the kit and/or the store or some reputable online sources. The build guide says LS or Toshiba... 170 or 370 so?
I'm not sure if I've seen anyone use Toshiba MOSFETs, but there may be someone out there that's tried a few. Which ones were you thinking of trying?
See this thread for all sorts of wonderful ideas for tweaking your ACA.
https://www.diyaudio.com/community/threads/aca-amp-with-premium-parts.328357/
Thanks for the info the heatsinks on this case are 200mm X 160mm and about 40mm thick including fins. Searched for a good way to calculate the needed size but all I could find was the ACA amp is about 32W of heat to loose and heatsink measurments that weren't of any use? Is there a good way to calculate the heat dissipation? Cheers Rob
According to the DIYaudio store, a heatsink of 200 x 40 x 165 will have a coefficient of 0.38 C/W.
The ACA Tungsten works on 24V @ 1.6A bias therefore produces about 39W of heat at idle per channel.
Now, 39W x 0.38C/W gives a temperature rise of about 15C. For an ambient temperature of 25C, heatsink temp will be at about 40C.
Above approximation is not bridged settings.
The ACA Tungsten works on 24V @ 1.6A bias therefore produces about 39W of heat at idle per channel.
Now, 39W x 0.38C/W gives a temperature rise of about 15C. For an ambient temperature of 25C, heatsink temp will be at about 40C.
Above approximation is not bridged settings.
Thanks for that was trying to find some details for the dissipation. So having two boards on one heat sink would rise by 30° so 55° at 25°. Might look at a small fan possibly just to keep it cooler. Thanks for the help. Will order boards and components then look at a power supply as well this being first build taking my time to make sure it's right.
^ I would not put 80W over 4 devices on that sink. Those numbers posted above don't account for de-rating. They're calculated based on the thermal saturation of the heatsink => HOT!!!!
For 64W to 80W per side... I'd go with something a little closer to what would be used for a First Watt amplifier.
The 4U/300 is commonly called the "Jack of All Chassis"... I'd start with heatsinks around that size and work from there.
YMMV
For 64W to 80W per side... I'd go with something a little closer to what would be used for a First Watt amplifier.
The 4U/300 is commonly called the "Jack of All Chassis"... I'd start with heatsinks around that size and work from there.
YMMV
Thanks might look at possibly just using this case for one ACA and then build another one later for monos. This might be a safer build for heat. At least would give me an idea on ACA capacity. Have either of you had experience with the linestage build off diyaudio
40W dissipation would work great for that 0.38C/W heatsink but not 80W. I’m not even sure if a 4U/300mm would be ok to dissipate 80W, these heatsinks are rated at 0.31 C/W…it depends on people, I prefer my heatsinks below 50C at idle.
@Robstr556 - Any time... BTW, hang onto that data that @e_fortier posted. It's super useful. You'll find a comfortable % that you like to "de-rate" them based on the temps you want to run.
I like my sinks (to start with the lowest dissipation I'll run) to target ~20C rise over ambient. Then I can go to town if I want to spice things up. I've found that de-rating the numbers above by ~1/2 gets me nicely in the ballpark. As the temps rise, it's not quite linear, but if they start off cool enough... then I'm good. I also want to acknowledge that not everyone has the space or wants to spend the money to have extra 'heat headroom', but if I de-rate by 1/3 (ish) then I'm typically running pretty warm. I matched my data with the study Gianluca published, and it's actually not too far off. 
Which one? Yes, several. 🙂 I'm working on one now...
I like my sinks (to start with the lowest dissipation I'll run) to target ~20C rise over ambient. Then I can go to town if I want to spice things up. I've found that de-rating the numbers above by ~1/2 gets me nicely in the ballpark. As the temps rise, it's not quite linear, but if they start off cool enough... then I'm good. I also want to acknowledge that not everyone has the space or wants to spend the money to have extra 'heat headroom', but if I de-rate by 1/3 (ish) then I'm typically running pretty warm. I matched my data with the study Gianluca published, and it's actually not too far off. Yea I think the original design for the amp case I'm using his amps being class AB just not enough room as all the boards have failed after playing. Thanks guys been a real help
A fabulous project. It's never easy to determine someone's level of experience ... so forgive me if I lean toward conservative recommendations / comments.
There is no full build guide per se...
You will need to solder some SMD components.
I may have made the incorrect assumption that you were potentially going to configure your ACAs in sort of a permanent balanced/bridged configuration. If you want a balanced pre-amp / line stage...
There are a number of people that have made Wayne's linestage in a balanced configuration, I believe, but you'd likely need to dig around in the thread or ask for a bit of help. For some reason, I have it in my mind that it wasn't as direct a solution as I'd originally thought.
Other than that... it's reasonably straight forward.
Mainly, have fun!
There is no full build guide per se...
You will need to solder some SMD components.
I may have made the incorrect assumption that you were potentially going to configure your ACAs in sort of a permanent balanced/bridged configuration. If you want a balanced pre-amp / line stage...
There are a number of people that have made Wayne's linestage in a balanced configuration, I believe, but you'd likely need to dig around in the thread or ask for a bit of help. For some reason, I have it in my mind that it wasn't as direct a solution as I'd originally thought.
Other than that... it's reasonably straight forward.
Mainly, have fun!
Thanks @ItsAllInMyHead will see how I get on in some more research for linestage. Looking forward to having another project. Thanks again for the help as the amp I have had no support or information as was a kind of a DIY build from previous person.