Hi Hugh,
My transformer and bridge rectifiers are working, I have connected the same transformer and bridge rectifiers with cap mx and it’s working fine.
In the power supply-ve rail is not working as expected, giving less than 1v, +ve channel is working good.
Transformer with dual secondaries are 0-18 200va
Will try to check all the parts and share the results
A linear PSU stopping mid stream sort of indicates that either your fuse is blown or a bridge is blown or the R’s in your CRC are blown. You have the cheap Aliexpress metal thin film resistors and they go open circuit like a fuse when stressed. It may be why your amp doesn’t work. Check continuity on the large 3W R’s.
I had a rare opportunity to play with three of Hugh's amps last night and listen to them at the same time switching around. Here is the Alpha BB in the front (52w), with a new Aspen Class AB (85wpc) in the little case underneath the Omega Class A (35wpc). It's not everyday that one gets to listen to three world class amps for fun!
How is everyone's Alpha 20 or Alpha BB holding up in the new year? Are you guys still listening to your Alpha's? I played my Alpha BB last nigh on a track that had quite a crescendo (Sia's cover of California Dreaming) and it set off the home security alarm (glass breakage) and woke up the whole house in the middle of the night. Yikes.
Have to be careful with the power it is capable of putting out. Just my 8in woofer FAST speakers, no subs running. But the bass impact was immense.
One thing is clear, the sound from the Alpha BB is very refined and the bass is cataclysmic level if pushed without getting strained.
How is everyone's Alpha 20 or Alpha BB holding up in the new year? Are you guys still listening to your Alpha's? I played my Alpha BB last nigh on a track that had quite a crescendo (Sia's cover of California Dreaming) and it set off the home security alarm (glass breakage) and woke up the whole house in the middle of the night. Yikes.
Have to be careful with the power it is capable of putting out. Just my 8in woofer FAST speakers, no subs running. But the bass impact was immense.
One thing is clear, the sound from the Alpha BB is very refined and the bass is cataclysmic level if pushed without getting strained.
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Please refer to post #1432.
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Basically the CPU heatsink is bolted to the bottom side of the board using a suitable insulator washer (felt in my case). Then on top side apply thermal paste then ceramic spacer pad then more paste then the MOSFET. Then use a L section bar to clamp the MOSFET to the CPU heatsink. I used a US $0.05 nickel as a spacer with a silicone pad to give some cushioning below the clamp bar to press the MOSFET down. Gently hand tighten the screws to eveneky distribute the pressure. When running check temps - of one is too hot relative to others it may be poor thermal contact.
Here is how I did it with a MOSFET on a flying lead to a Dell CPU cooler. Also used clamp bar and ceramic pad and thermal paste. This one is on my MOAMOFO dissipating 160w with a Noctua 80mm fan (not shown as early photo before they arrived) running in silent mode with temp feedback to PWM fan drive. Very very quiet.
I need a +/-28v PSU for my Preamp in order to hit full 50wrms. Here, with +/-24.5v supply I can only do 44.4Vpp into 8ohms:
What’s a MOAMOFO ? Mother of All MOFOs running 4.65amp x 37v bias for a 50wrms MOFO.
Build This MoFo!
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Hi Juntuin,
Let me know if you want to build another BB. Now that I have run the MOAMOFO at 4.65amp, I know that a cheap cap Mx with 22mF per rail is all that is needed for an Alpha BB to have clean power. Significant savings in time, real estate and cost by not using traditional CRC based PSU.
Hi X, pm'd you back! That's pretty impressive cap mx
is there any additional info available?Edit; haven't read MoFo-topic in awhile..impressive build you have there!
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Hi Juntuin,
The MJ-Gtose-Prasi one works well:
Juma's Easy-Peasy Capacitance Multiplier
And Vunce says the JKeuterman-MrEvil Cap Mx works well too - there is a GB thread in that.
Here is another Mr Evil variant and I think Mr Evil is basis of Aloo’s cap Mx:
4 caps Mr Evil's Capacitance Multiplier Power Supply PCB
As well as this one:
Mr Evil's Capacitance Multiplier Power Supply PCB
The basic premise is that with a big BJT and a heatsink you can get 2mV ripple for a Class A amp with a small 22mF cap. A BJT and a heatsink from a case floor wall is a lot less expensive than 8 x 33mF 50v caps. And the CRC has more ripple.
The MJ-Gtose-Prasi one works well:
Juma's Easy-Peasy Capacitance Multiplier
And Vunce says the JKeuterman-MrEvil Cap Mx works well too - there is a GB thread in that.
Here is another Mr Evil variant and I think Mr Evil is basis of Aloo’s cap Mx:
4 caps Mr Evil's Capacitance Multiplier Power Supply PCB
As well as this one:
Mr Evil's Capacitance Multiplier Power Supply PCB
The basic premise is that with a big BJT and a heatsink you can get 2mV ripple for a Class A amp with a small 22mF cap. A BJT and a heatsink from a case floor wall is a lot less expensive than 8 x 33mF 50v caps. And the CRC has more ripple.
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Happy New Year Juntuin!!
This is the link for the capMx I’m using with the ALPHA BB:
Simplified MrEvil / PMI Capacitance Multiplier
With a 600va, 32v secondaries trafo the BB gets 38-39vdc. The onboard rectifiers and output Mosfets need to be heatsinked. If I build another of these, I will use a pair of bridge rectifier mounted to the chassis instead of the onboard discrete rectifiers.
Cheers,
Vunce
This is the link for the capMx I’m using with the ALPHA BB:
Simplified MrEvil / PMI Capacitance Multiplier
With a 600va, 32v secondaries trafo the BB gets 38-39vdc. The onboard rectifiers and output Mosfets need to be heatsinked. If I build another of these, I will use a pair of bridge rectifier mounted to the chassis instead of the onboard discrete rectifiers.
Cheers,
Vunce
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I had overheating problems last time with Prasi's cap mx, that seemed not to be suitable with class-a bias. Or is there updated version, dunno
You too Vunce!
Thanks for pictures and info, I like this one
It’s a different one by Mark Johnson - uses a BJT with adjustable voltage drop from 1.3v and up. I run at 2v drop so for 3 amps it is 6W per rail or 12w total. Requires a small heatsink.
The MOSFET based unit had 4v drop do twice the dissipation.
Vunce said the MrEvil one is also adjustable and he runs it at 2v drop as well.
The MOSFET based unit had 4v drop do twice the dissipation.
Vunce said the MrEvil one is also adjustable and he runs it at 2v drop as well.
It’s a different one by Mark Johnson - uses a BJT with adjustable voltage drop from 1.3v and up. I run at 2v drop so for 3 amps it is 6W per rail or 12w total. Requires a small heatsink.
The MOSFET based unit had 4v drop do twice the dissipation.
Vunce said the MrEvil one is also adjustable and he runs it at 2v drop as well.
Nice! I just happen to have couple of suitable heatsinks laying around.
X,
Alpha 20 still in use as my main amp on occasion have changed to my M2 but keep going back to the Alpha 20.
Have not done any more on the BB as of yet i will have to get back into building
soon!! Still not sure wether to use cpu coolers or to use fan cooled heatsinks for the BB.
We have had some hot weather and have placed a large slab 1"and a half thick of slate under my amp which seems to have dropped the temp of the heatsinks quite a fair amount warm to the touch even on days 30 degrees plus.
Steve.
Alpha 20 still in use as my main amp on occasion have changed to my M2 but keep going back to the Alpha 20.
Have not done any more on the BB as of yet i will have to get back into building
soon!! Still not sure wether to use cpu coolers or to use fan cooled heatsinks for the BB.
We have had some hot weather and have placed a large slab 1"and a half thick of slate under my amp which seems to have dropped the temp of the heatsinks quite a fair amount warm to the touch even on days 30 degrees plus.
Steve.
My recent foray into cooling an IXYS MOSFET running 37v at close to 5amps of bias current with a surplus Dell CPU cooler and 80mm PWM Noctua fan has reaffirmed that it is possible to remove 160w and be absolutely silent. The Noctua fans are engineered with all the CFD-developed tricks in the book to minimize noise, and it works. I cannot tell the fan is even on with my ear 2in away. It is eerie how silent something that spins and moves air can be. In the low speed mode absolutely silent mode, the 160w MOSFET body is a (too hot to touch) 70C, and fin temp is 55C. If I allow it to use the temperature feedback and speed regulating feature, the MOSFET is 50C and fin temp is 37C, and sound is barely audible at 6in away, but the sound is 100x quiter than the blue 120mm Artic fans.
So, if sound emission from fans has been a concern for folks on the wall about whether or not to fan-cool, there is no need for concern. The sound is less than typical household ambient noises (HVAC, laptop PC fan, people moving about in a house, etc).
Having said that, I think that if you used a thick copper plate heat spreader to a larger aluminum fin heatsink with fans, that can work too. But it is much more costly than a $15 surplus CPU cooler with heat pipes.
Here is Vunce's MoFo with the Dell CPU coolers and Noctua fans:
Here is my MOAMOFO (Mother of All MOFO's) with same cooling setup dissipating 160w per channel:
With help of Melbourne (Aksa Lender preamp in bipolar supply mode), I was able to drive the MOAMOFO to 42.4Vpp into 8ohms (limited by +/-24.5v rai;s on Melbourne):
But to recap, the use of surplus CPU coolers (or even new ones), silent Noctua fans, and a cap Mx for a PSU can really help to make the Alpha BB a cost-effective high power SE Class A amp. The cap Mx requires only a pair of 22mF smoothing cap vs a whole bank of 8 x 33mF caps for the PSU (the single most expensive component) of the amp, next to the massive passive radiators required if not using active cooling.
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