USSA-5 Build with Review

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spaceistheplace

spaceistheplace

Member
Joined 2012
xrk971 said:
It depends on the bias current and rail voltage. A +/-24v Class A running at 1.25amps is 60w dissipation. I have a 4U and that’s about 45C so 3U would be possibly 55C to 60C, right at the limit of what is acceptably touchable with bare hands. But if running high bias of 1.5amps or 1.75amps, 3U is too small (unless a small fan is also employed).

I personally like Class A amps with small heatsinks and quiet fans now as size, weight, cost are much more manageable with CPU coolers and PWM fans as done on the Alpha series. Here with a Alpha BB dissipating 200w per channel, two compact and silent $25 CPU coolers keeps the MOSFET body at only 15C above ambient.

672472d1522616478-aksa-lender-mos-hybrid-aleph-alpha-amplifier-alpha-bb-test-mono-fast-closeup-jpg
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Can you explain perhaps with more photos and detail your implementation of CPU coolers? Water cooled? Quantity of fans and speed?

I’ve used Noctua fans before in other applications with good results. I assume your fans are on a separate supply?
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
You can read all about it in the Alpha thread:
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier

Basically it’s an air cooled CPU cooler with heat pipes and PWM fans. We use separate 12v wall wart DC PSU to power the PWM controller board (set to minimum speed). It needs a CLC filter between the PWM controller and he wall power to prevent PWM switch noise from getting back into mains.

The key thing to look for is a CPU cooler with sufficiently large active area that can fit the mosfet. Also, use ceramic insulators for 2x more heat transfer than best silicone pad. These setups are very cost effective means to run a high power Class A amp without needing a huge and expensive radiator fin panel. Up to 150w per mosfet is no problem.

Used Dell CPU coolers are very good - some have a very large copper surface.
 
T

tonza75

Member
Joined 2010
Grandmother used to say a battery (voltage&current) device.
Monocrome thinking of FAB USSAF5-TBC. Fab builded before Greg.B SKA amps.
Fab F5 exotic redesign of not so great F5 Nelson pass buys pcb from jim's audio store F5.
Decides more of the older tech. is a good idea .
((Likes or loves to share for profit (rather small)) design many years decade for to make 2016 one of Fab 0.4.5 in a practical, real-world laboratory setting.anual dump in the front with CFP,CFB (not the CFOB).
CFP,CFB with bjt Comlinear Corporation style (Active Learning and Project Based Learning in Electronics & Practical uses).
Get's members to build and finish build, praise the (sound quality subjective). Well done FAB , & by those who finished and published this Amp.

Stability over next 30 years. ( CCTA,CFOA,CDBA,CCII,CCCCTA,DVCCTA,CG-CCTA,CDTA,CFTA,CG-CFTA,ZC-CFTA,CCCFTA,ZC-CG-CDBA,MCDTA for F6 FAB TBD )

+ pros
-Predict-Observe-Discuss-Synthesize teaching methodology is presented
-GB build
-Easy manual to understand // not EE manual
-Support group
-Fun in the end :)

- cons


-fab does not maintain work on database, componets used or bought (diy)
-if not bought a modushop case 3U you should buy one suggested,
-contraversial
-history knows :)
 
ggetzoff

ggetzoff

Member
Joined 2004
sthcoaster said:
Doesn't help when Modushop folks are enjoying a summer break!! :)
And my chosen reservoir caps are on back order - expected mid-Sept :(

Stymied in all directions
Click to expand...

Yeah, a lot of Europe takes the whole month of August off. We don't have that mentality in the U.S. It's just work, work, work.....

As far as I'm concerned, they do it right :D


35USG33000MEFCSN35X50 Rubycon | Capacitors | DigiKey

339LBB035M2EH Illinois Capacitor / CDE | Mouser

I used the Rubys, but that Illinois Cap is cheaper and conforms to Fab's manual cap specs. It looks like an excellent product, regardless of $
 
ggetzoff

ggetzoff

Member
Joined 2004
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