Well, the big thing in technology at the moment seems to be "The Cloud", so whatever it is, I thought I'd better allow the facility to bolt it on.
😀
Hi, Greg.
My version is enlarged to allow MT-200 output devices, has DC offset adjustment (P2-C3B-R3) and catch diodes on output. C2 is enlarged (I like bass...), bypassed by C2B and protected by D2. Some were inspired from my previous DIY build.
I´m using BD-139/140 as drivers, mounted faced up. Enjoy the next photos.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Rgds.
Last edited:
hi Sound_Buster,
Thanks for posting the information and the pictures.
When are you planning to fire it up?
I don't think you will have DC offset problems. As I mentioned earlier in the thread, for whatever reason the DC offset on my prototypes was very small, single digit mV. The one with BD139/DB140 drivers was a little higher than the others.
Is the extra pot in series with R3 or is it acting degen resistors for Q1 and Q2? (Edit: Closer look at PCB shows it is in series with R3)
regards
Thanks for posting the information and the pictures.
When are you planning to fire it up?
I don't think you will have DC offset problems. As I mentioned earlier in the thread, for whatever reason the DC offset on my prototypes was very small, single digit mV. The one with BD139/DB140 drivers was a little higher than the others.
Is the extra pot in series with R3 or is it acting degen resistors for Q1 and Q2? (Edit: Closer look at PCB shows it is in series with R3)
regards
Aha! I new there was a secret parts agenda for these amps....
Where can we buy these DB140s, Greg?
Where can we buy these DB140s, Greg?
Aha! I new there was a secret parts agenda for these amps....
Where can we buy these DB140s, Greg?
Not again..... spell checker picked it up and I ignored it. Sorry, I'll try harder next time.
BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140, BD140.... slowly sinking in.
Not very soon... many trips in the next weekends.
I'll send news when ready.
Rgds.
My version of this AKSA amp is the only bipolar amp that I want to keep (well, I haven't built the FC100 yet). I'm not a fan of bipolar, but my version matches the AKSA's review. I have built many class-A amps but none have given me the impression like this amp, except for tube amps, but tube amps are too slow for my taste!
The topology I used is more similar to the real AKSA (not this BAKSA), but I used Vbe multiplier like the BAKSA. Sometimes I wonder if it is possible to get to the ultimate sound with the topology used by BAKSA (simple feedback amp). But what has driven me to write this is:
I used matched pair 2SA978 for the LTP (and I hand select them). Oh, the BAKSA (and I think the real AKSA also) uses 2N5401. This is my favorite transistor. I have more than a thousand of these 2N transistors. But the strength of the 2SA978 is not just about matched parameters!! Who knows, may be I'm a few step ahead on the LTP? 😀
The topology I used is more similar to the real AKSA (not this BAKSA), but I used Vbe multiplier like the BAKSA. Sometimes I wonder if it is possible to get to the ultimate sound with the topology used by BAKSA (simple feedback amp). But what has driven me to write this is:
I used matched pair 2SA978 for the LTP (and I hand select them). Oh, the BAKSA (and I think the real AKSA also) uses 2N5401. This is my favorite transistor. I have more than a thousand of these 2N transistors. But the strength of the 2SA978 is not just about matched parameters!! Who knows, may be I'm a few step ahead on the LTP? 😀
Member
Joined 2009
Paid Member
I wouldn't write off bipolar amplifiers, Hugh has developed many successors to the AKSA that offer even better performance.
My AKSA clone (TGM1) is also a favourite amp of mine but I think the VAS device (BD139) needs to be upgraded to something better (like AKSA original).
My AKSA clone (TGM1) is also a favourite amp of mine but I think the VAS device (BD139) needs to be upgraded to something better (like AKSA original).
Component choice is indeed critical if you're after the pen ultimate sound 😉 You can change the schematic, but not the structure inside a transistor. That's why I like mosfet 😀
Member
Joined 2009
Paid Member
I haven't explored the use of mosfet's, static sensitive, non-linear input capacitor - and here's everyone crying about capacitors in the signal path and the worse one by a large margin is in series with every MOSFET in the chasis !
I think Mosfet does best in Class A, heavily biassed, so gate capacitors are not being charged-discharges so much. Other place is potentially the VAS, but that's another story.
I think Mosfet does best in Class A, heavily biassed, so gate capacitors are not being charged-discharges so much. Other place is potentially the VAS, but that's another story.
Actually I have been looking forward to seeing a mosfet-based AKSA. A lateral one. Something that will have the magic of this AKSA, but also have the "air" of a mosfet. The closest professional circuit around would be Rod's P101 where one stage has been reduced. Shaan also has similar version with extra stage similar to a bipolar circuit that he calls The Magic. Of course, I would imagine that it will take someone who understand what makes the AKSA sound as it does, to design this mosfet-based AKSA.
Do you think it is doable??
True. That's why lateral is preferable as they commonly offer lower capacitance and linear. The challenge is how to design the whole circuit (the driving stage) to take care of this capacitance. There is even better mosfet out there (see VladimirK' version of PF99) but too expensive.
Laterals can be used for class B (or AB). Just see the so many ideas out there to drive the capacitance. In Mooly's amplifier, the output is taken from the Drain, may be the capacitance effect is lower (Co<Ci). The drive is probably weak, but 2N5401 is used. From more than a thousand transistor I choose the highest hfe for this amp (>330).
Higher rail is also possible with extra driver like the Goldmund. And I use 2N5401 also for the driver in Mimesis3.
Stochino has more ideas using 2N5401 for driving mosfet. Vertical mosfet in class-B, which one is better than the Stochino?
Why is that? Isn't Ci as critical as Cob in a VAS? Not many mosfet has low Ci, high voltage rating and high transconductance. Bora's DOGC Mk3 is a good example of proper way to choose mosfets for an amp.
Last edited:
The best Laterals I have simmed in spice is from Profusion
ECF20N20 and ECF20P20
http://www.profusionplc.com/
Member
Joined 2009
Paid Member
in the VAS position you can use a low power FET where capacitance is less, you can run it at reasonably high voltages and decent current and you can get some good linearity - see what nelson does with small signal FETs for example. The advantage is less current being drawn off the LTP so it's possible to balance the LTP more easily without resorting to a rats nest of current mirrors etc. etc. Still, generally speaking, for several reasons I've decided that I don't like LTPs and will never design or build an amplifier using one again (unless it's buried in an OpAmp in some auxiliary circuit). I've said it, and you can quote me !
The 2N5551/2N5401 are a very good choice for VAS because the have the same Spec,s like the Toshiba 2SA1145/2SC2705 that Yamaha uses.
I was wondering I've two toroids of 2x24VAC/160VA each can I use those for the BabyAksa.What's the max. rail voltage I could use?
Hi meanman1964,
I am using 2x25VAC/160VA which gives me 37VDC rails.
I think Hugh might have done a typo in the last post, 42VDC would be the maximum.
regards
Greg,
Partly right - thanks for the correction!
The amp can be run with 62V rails with more output pairs, three in fact. Up to 42V with a single pair, 50V with two, and 62V with three pairs. Matching is essential and should be within 1mV on Vbe at 70mA, and within 5% on beta.
Cheers,
Hugh
Partly right - thanks for the correction!
The amp can be run with 62V rails with more output pairs, three in fact. Up to 42V with a single pair, 50V with two, and 62V with three pairs. Matching is essential and should be within 1mV on Vbe at 70mA, and within 5% on beta.
Cheers,
Hugh