I think that you could improve the combination greatly if you got two pieces of aluminum (or better, copper) strap and bolt one on either side of the center flat on the sinks with thermal goop. Clamping above and below. Easy, cheap, and better radiation. Thanks for showing us the way tall mini.
Are you saying it's just pressed in friction fit to connect them?
Thermal paste seems like a good idea to further improve.
I'm gonna give this a try and turn up the bias a little. Good stuff.
@birdbox: It's not even a friction fit. The pins on the bottom of the top heat sinks slip into the grooves in the heat sinks underneath, and good old gravity holds the top level down. The heat sinks are well made, and they touch each other enough for some good heat transfer.
You are right, of course, that something like thermal paste might help.
You are right, of course, that something like thermal paste might help.
Re Skyscraper Mini: A question.
Does the Mini work (sound) better when it transfers more heat away from the MOSFETs? It seems like it to me, now that I'm doing some critical listening with the Skyscraper Mini. But maybe I'm just imagining it.
Does the Mini work (sound) better when it transfers more heat away from the MOSFETs? It seems like it to me, now that I'm doing some critical listening with the Skyscraper Mini. But maybe I'm just imagining it.
It will certainly change the junction temps and surrounding components, so yes, in theory the distortion products will be different. I think the measured difference would be minuscule but subjectively it could be heard.
After months of powering mine with 6s lipos ( previously posted all the details) I think the amp on battery power is simply amazing. Its dynamic are noticeably present (you get those amazing and eerie images jumping out of the loudspeaker) with much improved smoothness in upper octave energy. It’s just all day enjoyment and handily competes with all of my full size Nelson designs. It’s very good on the brick and with MJs filter becomes excellent, but to me, the ACAmini is just a revelation on battery power. Is this necessary? Not really, but it does get the very best out of this amazing design.
After months of powering mine with 6s lipos ( previously posted all the details) I think the amp on battery power is simply amazing. Its dynamic are noticeably present (you get those amazing and eerie images jumping out of the loudspeaker) with much improved smoothness in upper octave energy. It’s just all day enjoyment and handily competes with all of my full size Nelson designs. It’s very good on the brick and with MJs filter becomes excellent, but to me, the ACAmini is just a revelation on battery power. Is this necessary? Not really, but it does get the very best out of this amazing design.
Q3 sets the current in the ACA. Q1's temperature will affect DC operating point set by the pot, and it does affect THD as I showed in post 576 of the original ACA thread: https://www.diyaudio.com/community/threads/amp-camp-amp-aca.215392/
Other way around, a higher temperature (more bias) makes somewhat less THD.
However, you’ll run out of heatsink long before making much difference, so just adjust to the recommended setting.
However, you’ll run out of heatsink long before making much difference, so just adjust to the recommended setting.
Most people say you can never have a heatsink that’s too big.
More bias will normally lower THD but does the temperature of the output devices have anything to do with THD ?
I’m asking because I’ve got some heatsinks from Class A amps running at 43C and others at 53C…do you believe the THD will be different if everything is identical between both amps except the heatsinks sizes..?
I’m not a person who only pays attention to THD..I enjoy tube amps a lot.
I’m just curious now about the THD vs output devices temp.
Thanks
Eric
More bias will normally lower THD but does the temperature of the output devices have anything to do with THD ?
I’m asking because I’ve got some heatsinks from Class A amps running at 43C and others at 53C…do you believe the THD will be different if everything is identical between both amps except the heatsinks sizes..?
I’m not a person who only pays attention to THD..I enjoy tube amps a lot.
I’m just curious now about the THD vs output devices temp.
Thanks
Eric
@6L6: Thanks for joining the discussion.
Given that my ACA Mini is already set to a higher bias, namely 370mV, what I was wondering was whether drawing off more heat with double heat sinks would affect THD. Maybe not.
The single heat sinks got pretty hot, to the point where I could only touch them for maybe two seconds when the room was 72 degrees Fahrenheit. Nelson told me this was OK, and I used the amp for five months this way without a problem.
I added a second set of heat sinks just so that I didn't have to worry about excess heat when the room temperature got higher than usual, say 75 or 80 degrees Fahrenheit instead of the usual 69 to 72 degrees.
The double heat sinks are already a win, in that the temperature of the lower sinks is low enough now that, when the room is 72 degrees, I can touch the bottom sinks for a long time, vs. the former two seconds. I was just wondering whether I was also getting better sound. Again, maybe not.
Given that my ACA Mini is already set to a higher bias, namely 370mV, what I was wondering was whether drawing off more heat with double heat sinks would affect THD. Maybe not.
The single heat sinks got pretty hot, to the point where I could only touch them for maybe two seconds when the room was 72 degrees Fahrenheit. Nelson told me this was OK, and I used the amp for five months this way without a problem.
I added a second set of heat sinks just so that I didn't have to worry about excess heat when the room temperature got higher than usual, say 75 or 80 degrees Fahrenheit instead of the usual 69 to 72 degrees.
The double heat sinks are already a win, in that the temperature of the lower sinks is low enough now that, when the room is 72 degrees, I can touch the bottom sinks for a long time, vs. the former two seconds. I was just wondering whether I was also getting better sound. Again, maybe not.
Temperature is certainly part of the operating condition of an amp's output devices, along with bias current and Vds. Whether your amp sounds better at a lower temp vs the higher one will depend on your system and your ears.
Sorry, my comments were for the original ACA, not the ACA mini. I was confused having just read about the ACA Redux.
yes, my first and only ACA-mini with stacked heatsinks and a heavy top plate (alu), which is in wintertime hand warm, in summertime about some 40+ C°, running now with ~0.360 - 0.370mV sounds in my taste more exciting than with lower bias.
@Skip Pack , Like your idea but having a hard time visualizing the setup. Have you a rough hand drawn diagram showing the copper interface with the heatsinks.
Cheers
Cheers
https://www.diyaudio.com/community/threads/diy-aca-mini.379037/post-7406181
I‘m using 6x9“ (some say 6x10“) Goodmans 15 Ohms