May be an off topic, I am building the ACA amp, and used a heatsink of size 190mm *95mm *33mm, but its getting very hot after some 15-20 min of playing (using 19v power supply) as in below post:
http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-492.html#post5495596
Now thinking of 2 options, using a larger heatsinks or to use CPU cooler as used in amps in this thread.
I purchased a CPU cooler Antec Product but its heatsink plate is not big enough to hold 4 IRFP240 MOSFETs (stereo).
Please suggest a way to use this CPU cooler for holding these 4 MOSFETs or its better to go for a bigger heat sink (passive cooling) for ACA amp?
http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-492.html#post5495596
Now thinking of 2 options, using a larger heatsinks or to use CPU cooler as used in amps in this thread.
I purchased a CPU cooler Antec Product but its heatsink plate is not big enough to hold 4 IRFP240 MOSFETs (stereo).
Please suggest a way to use this CPU cooler for holding these 4 MOSFETs or its better to go for a bigger heat sink (passive cooling) for ACA amp?
Bolt your 4 ACA MOSFETS onto a thick (circa 5mm to 12mm thick alum plate) heat spreader on one side, and mount the CPU cooler on the other side. 50mm x100mm plate should do it. Run flying leads from MOSFETs to your ACA boards. Or redesign ACA as stereo board with all 4 MOSFETs hanging off one edge.
Or just add a fan to blow on your existing heatsinks (easiest way). This is what I do and it works fine. Simple 12v fan with 100ohm resistor to drop speed to inaudible,
http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-260.html#post4653828
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Hi X,
I think so, but the quiescent current would need to be 5A. I would drop the rails to 18V, because with a 2R load you could then get around 24Vpp output, which would correspond to 36Wrms output. Each output would then dissipate around 90W, not inconsiderable, so you'd need forced air cooling. You could do this with the FQA40N25 and FQA36P15 Fairchild mosfets, which are each rated to 280W. You'd have 360W dissipation in both amps in stereo - continuously. You could not do this in a car!!
I do not think you'd have to change anything else.
HD
I think so, but the quiescent current would need to be 5A. I would drop the rails to 18V, because with a 2R load you could then get around 24Vpp output, which would correspond to 36Wrms output. Each output would then dissipate around 90W, not inconsiderable, so you'd need forced air cooling. You could do this with the FQA40N25 and FQA36P15 Fairchild mosfets, which are each rated to 280W. You'd have 360W dissipation in both amps in stereo - continuously. You could not do this in a car!!
I do not think you'd have to change anything else.
HD
Recently I have had a few people contact me that they were preparing to start a new build on a 4ohm Alpha 20. Here is a schematic with the changes needed for a 4ohm speaker Alpha 20. Thanks to Pinocchio for adapting the schematic with new values for 4R operation.
Which reminds me, did you ever finish your build of the Alpha, Pinocchio?
Hi Xrk
Could you please let me know the transformer ratings
Thank you, Hugh. 5 amps! Yikes.
But then again, 18v rails is not that much and to get 36wrms is not a bad thing. CPU coolers and PWM fans can handle the 90w easily though. It would be like a mini BB.
2 Ohms!?!? New subwoofer design in the works or something, X?
Minimum would be 400VA for a single transformer. 200VA if going dual, but as this is Class A, doesn’t hurt to go extra. 500VA For single and 300VA ea for dual.
Voltage sag is a problem so to get true +/-25v, you will need 20V secondaries. Orbif using a cap Mx, get 22V secondaries.
Darn! I got excited for a second. I'd like to see someone try the 2 Ohm version though. This amp is SO versatile!
Nice work JP! That PS board is a monster!
Hugh D., & others,
I’ve got a 5U/400 chassis here with UMS heatsinks which should make this 4R version happier since it’s 112W dissipation per channel. Each of the 4 sinks is rated at 0.28 degrees C/watt. 56 watts x 0.28 = 15.7 degrees C + 25 degrees ambient = ~ 41 degrees C = ~ 106 degrees F per heatsink. I’ll use Keratherms on each MOSFET to maximize heat transfer.
The current transformer I have is about 420VA. I am thinking this is just about adequate given that one shouldn’t exceed 50% of the max VA, which is about 210 watts. It will be installed vertically with an L-bracket to maximize cooling through natural convection. I might order a larger Toroidy in the future if my current toroid ends up being too warm.
The power supply is a CLC for each rail but shared for both channels.
That being said where can I tweak Do’s schematic for just a little less current than 2.4A, say 2A? (~30 watts/4 ohms):
Thanks in advance,
Anand.
I’ve got a 5U/400 chassis here with UMS heatsinks which should make this 4R version happier since it’s 112W dissipation per channel. Each of the 4 sinks is rated at 0.28 degrees C/watt. 56 watts x 0.28 = 15.7 degrees C + 25 degrees ambient = ~ 41 degrees C = ~ 106 degrees F per heatsink. I’ll use Keratherms on each MOSFET to maximize heat transfer.
The current transformer I have is about 420VA. I am thinking this is just about adequate given that one shouldn’t exceed 50% of the max VA, which is about 210 watts. It will be installed vertically with an L-bracket to maximize cooling through natural convection. I might order a larger Toroidy in the future if my current toroid ends up being too warm.
The power supply is a CLC for each rail but shared for both channels.
That being said where can I tweak Do’s schematic for just a little less current than 2.4A, say 2A? (~30 watts/4 ohms):
Thanks in advance,
Anand.