In the thread “Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier”，xtk said:
" Edit April 4, 2018 - here is the updated as-built schematic for Alpha 20 with 1.35amp bias and no turn-on thump feature. Note that if all pots are removed the amp is a simple adjustment-free Class A amp with DC coupled output that has DC offset within 10mV (typical) and self-tracking, bias current is auto-regulated and very stable. "I wonder if the Alpha Nirvana amplifier also has this feature?
Is it possible to modify the Alpha Nirvana to 10w output like my JLH1969, because I don't like such a hot machine, or I don't have a suitable case with cooling. Or since the Alpha Nirvana is so efficient, it can be modified to output 15w or more and generate about the same amount of heat as my JLH1969.
Hi Members,
Is there any minimum amount of large filter caps (C7,C8, C13, C14) on the SLB psu that one should build with wrt to the AN. From the thread I see that most everyone is using 30,000 uF per rail. My large cap inventory available is 4 x 15,000uF and 4 X 10,000uF. I would be using 25,000uF per rail, building 2 x SLB psu's. Is this sufficient for +/- 42VDC.
Is there any minimum amount of large filter caps (C7,C8, C13, C14) on the SLB psu that one should build with wrt to the AN. From the thread I see that most everyone is using 30,000 uF per rail. My large cap inventory available is 4 x 15,000uF and 4 X 10,000uF. I would be using 25,000uF per rail, building 2 x SLB psu's. Is this sufficient for +/- 42VDC.
Yes, dc offset is self adjusting since input stage is the same. Just reduce voltage of the supply.
Hi dear friends,
I'm struggling a little bit with selection of components. For me BOM for snubber isn't so clear, or at least, I don't understand it.
I have carefully read the entire tread and still I feel lost because some components on the main board should be ommitted if placed on the snubber boards.
On the schematics, these components are just in the footnote, at the bottom of the schematics, in red:
1. which resistor values are for R101 and R102
2. which is proper direction of V101
3. which are Mouser part numbers for the snubber components.
I am sory for asking dumb questions but I feel lost and wouldn't like to smell the smoke at the start-up.
Any help will be appreciated
I'm struggling a little bit with selection of components. For me BOM for snubber isn't so clear, or at least, I don't understand it.
I have carefully read the entire tread and still I feel lost because some components on the main board should be ommitted if placed on the snubber boards.
On the schematics, these components are just in the footnote, at the bottom of the schematics, in red:
On the snubber boards there are:
I have three questions:
1. which resistor values are for R101 and R102
2. which is proper direction of V101
3. which are Mouser part numbers for the snubber components.
I am sory for asking dumb questions but I feel lost and wouldn't like to smell the smoke at the start-up.
Any help will be appreciated
Just an observation, I found changing the bootstrap caps C131,132 from Elna Silmic II to Nichicon UFG made a significant difference to the sound quality. I feel the Silmics airbrush the presentation more: smooth and laid back in comparison. I prefer the UFG's in my set up, but it could be the reverse for you. A useful tweak point!
If you feel like experimenting, try moving the upper bootstrap so you have it connected to the other side of the source resistor (connected to the source of the upper fet), this will lower output impedance and also change the sound of the amp. I wrote about it somewhere earlier in this thread. I liked it better like this, but tastes may vary.
Interesting but opens up a whole world for “cap rollers”. Try bypassing it a 2.2uF MKP film cap perhaps?
X, Hugh,
I will be repackaging the Alpha Nirvana in it’s own enclosure with a BTSB at the front end as such I was wondering what is the maximum supply voltage I can try? The speakers are mostly 4 to 8 ohm loads, so let’s just say 6 ohm. I have heard it at +/-30V DC and it sounds great. Any higher or is that a comfortable maximum? The heatsinks are on a 4U/400, so dissipation maximums per heatsink (200mm deep, 160 mm tall, with 40 mm deep fins) is 0.28 degC/watt. There are two heatsinks per side since each one is only 200mm deep. Obviously there will be only one MOSFET per heatsink. I will probably consider creating a heatspreader to bridge the two heatsinks together. Maybe 50 watts for each heatsink which will give a rise of 14 degrees C per heatsink. Or near 100 watts/ch perhaps? If +/- 30VDC then 1.6A quiescent?
As always, the heatsink dissipation figures and overall MOSFET temperature at pin 2 will probably be the impasse.
Best,
Anand.
I will be repackaging the Alpha Nirvana in it’s own enclosure with a BTSB at the front end as such I was wondering what is the maximum supply voltage I can try? The speakers are mostly 4 to 8 ohm loads, so let’s just say 6 ohm. I have heard it at +/-30V DC and it sounds great. Any higher or is that a comfortable maximum? The heatsinks are on a 4U/400, so dissipation maximums per heatsink (200mm deep, 160 mm tall, with 40 mm deep fins) is 0.28 degC/watt. There are two heatsinks per side since each one is only 200mm deep. Obviously there will be only one MOSFET per heatsink. I will probably consider creating a heatspreader to bridge the two heatsinks together. Maybe 50 watts for each heatsink which will give a rise of 14 degrees C per heatsink. Or near 100 watts/ch perhaps? If +/- 30VDC then 1.6A quiescent?
As always, the heatsink dissipation figures and overall MOSFET temperature at pin 2 will probably be the impasse.
Best,
Anand.
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Yup. In that first round of single ended Class A solid state designs, the Alpha Nirvana was the topper. And overall its a very enjoyable amplifier. If more power can be eeked out of it, all the better. But I can only accommodate 400mm deep enclosures for now!
I can kick up the voltage (and that helps 8 ohm loads), and/or kick up current (which helps 4 ohm loads) but at some point you start thinking about more efficient methods of cooling the chassis than just passive convection.
Best,
Anand.
Thanks Anand. Given your experience with a variety of amps that amounts to a significant accolade.
That’s very kind of you to think that I have “experience”!!
I’m just another diy’er!!
Best,
Anand.
Well Anand your “experience” 😉 is relevant to me because we seem to like the same kind of amps. I love the neutrality and transparency of my Neurochrome amps, but I also love some class A amps - I suspect its the ones that have the type of harmonic distortion profile that Hugh (and others) talk about.
Hi Anand,
Xmas day in Oz!
Yes, I would think 30V would be fine technically. Can't answer for the sonics, but if X thinks it's OK I believe it could do 47W, and probably 60Wrms into 6R load provided you increase the bias to 4.5A, at which point each device will dissipate about 135W. This is hockey puck territory, Anand, and I would use high dissipation mosfets with more than 300W dissipation, more than twice the use. Let me know which mosfets you use; some do not work well in linear use as they are designed for switching only.
This is a highly stressed amp thermally; but you know that and with care you will get around this I'm sure.
Merry Xmas and Happy New Year to you, to other DIYers, and to our families. I have my daughter and her husband from NYC, it's a special time!
Hugh
Xmas day in Oz!
Yes, I would think 30V would be fine technically. Can't answer for the sonics, but if X thinks it's OK I believe it could do 47W, and probably 60Wrms into 6R load provided you increase the bias to 4.5A, at which point each device will dissipate about 135W. This is hockey puck territory, Anand, and I would use high dissipation mosfets with more than 300W dissipation, more than twice the use. Let me know which mosfets you use; some do not work well in linear use as they are designed for switching only.
This is a highly stressed amp thermally; but you know that and with care you will get around this I'm sure.
Merry Xmas and Happy New Year to you, to other DIYers, and to our families. I have my daughter and her husband from NYC, it's a special time!
Hugh
