Hello All
Just the other day I got to compare my AX100 with an ex DIYer equipment which was a Krell amp.
Well the Aleph was not as bright as the krell but was missing something in the bottom end, with the soundstage not as good as the Krell.
After hooking up the AX100 the DC between speaker terminals was 1.5 V.
not good for speakers, this lowered to about half this value- still to high.
So now im in the process of swapping my badly matched irfp240 with some nicely matched ones and arrange them differently on the heatsink. Since Im at it what else does one recommend for improvements, there must be something as this amp has been out for awhile.
Here is the schematic
Just the other day I got to compare my AX100 with an ex DIYer equipment which was a Krell amp.
Well the Aleph was not as bright as the krell but was missing something in the bottom end, with the soundstage not as good as the Krell.
After hooking up the AX100 the DC between speaker terminals was 1.5 V.
not good for speakers, this lowered to about half this value- still to high.So now im in the process of swapping my badly matched irfp240 with some nicely matched ones and arrange them differently on the heatsink. Since Im at it what else does one recommend for improvements, there must be something as this amp has been out for awhile.
Here is the schematic
Attachments
The double JFET diff pair was used to preserve the 20ma of total bias in the front end of the AX100 and increase the transconductance over one pair.
You'll note that the single JFET in the Aleph J is only driving a couple of output transistors. If you do the math you'll see that the AX100J-01 and Aleph J are quite consistent. I don't see anything in the Aleph J that you could adapt to improve your particular situation.
My recommendation is to stay with the AX100J schematic as a primary guideline.
Other people here on the forum have produced excellent results with matched 2SJ74's instead of the hard-to-find 2SJ109's.
If you have 1.5V of relative offset then something is very wrong with your amps. There is probably a miswire or a serious matching problem with the transistors. Do both channels have the same problem?
Cheers,
Graeme
You'll note that the single JFET in the Aleph J is only driving a couple of output transistors. If you do the math you'll see that the AX100J-01 and Aleph J are quite consistent. I don't see anything in the Aleph J that you could adapt to improve your particular situation.
My recommendation is to stay with the AX100J schematic as a primary guideline.
Other people here on the forum have produced excellent results with matched 2SJ74's instead of the hard-to-find 2SJ109's.
If you have 1.5V of relative offset then something is very wrong with your amps. There is probably a miswire or a serious matching problem with the transistors. Do both channels have the same problem?
Cheers,
Graeme
Hello Graeme
Thanks for the info.
As for the relative offset, cold start both amps are 1.5, both lower to about 200mA after a hour. My batch of 240s was not enough so matching is poor as well as my Fet layout is in need of change, newbie mistake.
So now im in the process of buying matched ones, then work out best method of laying these fets out on the heatsink. looking back i would change heatsink layout but construction is finished.
Im going to have 3 fets on top and 3 fet on the bottom of the same heat sink, so back heatsink will have no fets. Will offset fets back on the 350 heatsink.
Q: 1----------whats a good distance to seperate fets.
2---------- Should i stick with the same amount of output transistors
Cheers
here is my current setup fet wise
Thanks for the info.
As for the relative offset, cold start both amps are 1.5, both lower to about 200mA after a hour. My batch of 240s was not enough so matching is poor as well as my Fet layout is in need of change, newbie mistake.
So now im in the process of buying matched ones, then work out best method of laying these fets out on the heatsink. looking back i would change heatsink layout but construction is finished.
Im going to have 3 fets on top and 3 fet on the bottom of the same heat sink, so back heatsink will have no fets. Will offset fets back on the 350 heatsink.
Q: 1----------whats a good distance to seperate fets.
2---------- Should i stick with the same amount of output transistors
Cheers
here is my current setup fet wise
Hi Dan,
The layout of your MOSFET's looks OK but it's a really hard thing to judge from a distance and from a drawing. My preference is to run more output transistors with a lower dissipation on each. The AX100 thread states my choices and the reasons for making those choices.
Here are some posts from the AX100 thread regarding the sound of the JFET version compared to the original MOSFET front end version.
From Ian MacKenzie:
http://www.diyaudio.com/forums/showthread.php?postid=1499953#post1499953
From Nelson Pass:
http://www.diyaudio.com/forums/showthread.php?postid=1404305#post1404305
From me:
http://www.diyaudio.com/forums/showthread.php?postid=1438413#post1438413
There are additional comments in the thread or referenced in the thread.
Cheers,
Graeme
The layout of your MOSFET's looks OK but it's a really hard thing to judge from a distance and from a drawing. My preference is to run more output transistors with a lower dissipation on each. The AX100 thread states my choices and the reasons for making those choices.
Here are some posts from the AX100 thread regarding the sound of the JFET version compared to the original MOSFET front end version.
From Ian MacKenzie:
http://www.diyaudio.com/forums/showthread.php?postid=1499953#post1499953
From Nelson Pass:
http://www.diyaudio.com/forums/showthread.php?postid=1404305#post1404305
From me:
http://www.diyaudio.com/forums/showthread.php?postid=1438413#post1438413
There are additional comments in the thread or referenced in the thread.
Cheers,
Graeme
Thanks Graeme!
here is a photo showing layout. Im sure its causing the problems with offset as the back heatsink heats up more than the rest.
Well with these comments of the changes of the X100 to XJ100 im surprised more people have not done the conversion!
now to get some 2sj74 or 27j109
Cheers
here is a photo showing layout. Im sure its causing the problems with offset as the back heatsink heats up more than the rest.
Well with these comments of the changes of the X100 to XJ100 im surprised more people have not done the conversion!
now to get some 2sj74 or 27j109
Cheers
Thanks Graeme!
here is a photo showing layout. Im sure its causing the problems with offset as the back heatsink heats up more than the rest.
Well with these comments of the changes of the X100 to XJ100 im surprised more people have not done the conversion!
now to get some 2sj74 or 27j109
Cheers
here is a photo showing layout. Im sure its causing the problems with offset as the back heatsink heats up more than the rest.
Well with these comments of the changes of the X100 to XJ100 im surprised more people have not done the conversion!
now to get some 2sj74 or 27j109
Cheers
Attachments
Hi Dan,
Your schematic appears to be based on one from KK's website. I have never seen any evidence that KK actually built and/or tested any of the circuitry that he puts up on his site.
The Aleph-X is a minimalist circuit. Changing almost any component in the signal path will have some effect on the sound. I would really really strongly recommend that you start with a proven implementation, get that running as published, THEN start to modify things to your own taste or requirements.
The GRollins/Hifizen version is the default standard. The AX100/AX100J has been successfully built by macka and daly41k as well as by me. If I was the only one who had built it I wouldn't have the courage to recommend it. There are also several other experienced, long-time members who have built versions of the original and published their results.
As a practical matter, by the way, it is very difficult to comment on a schematic that has no part designators (such as R1, R2, etc).
Cheers,
Graeme
Your schematic appears to be based on one from KK's website. I have never seen any evidence that KK actually built and/or tested any of the circuitry that he puts up on his site.
The Aleph-X is a minimalist circuit. Changing almost any component in the signal path will have some effect on the sound. I would really really strongly recommend that you start with a proven implementation, get that running as published, THEN start to modify things to your own taste or requirements.
The GRollins/Hifizen version is the default standard. The AX100/AX100J has been successfully built by macka and daly41k as well as by me. If I was the only one who had built it I wouldn't have the courage to recommend it. There are also several other experienced, long-time members who have built versions of the original and published their results.
As a practical matter, by the way, it is very difficult to comment on a schematic that has no part designators (such as R1, R2, etc).
Cheers,
Graeme
Hello Graeme
I modified kks to be a copy of the one Macka posted or was it yourself. The only real difference is the output stage, having 3 output parallel Fets instead of the 5 which was shown on the schmatic. As far as KKs design all I can say he has expensive boards.
Thanks for your comments
Cheers
I modified kks to be a copy of the one Macka posted or was it yourself. The only real difference is the output stage, having 3 output parallel Fets instead of the 5 which was shown on the schmatic. As far as KKs design all I can say he has expensive boards.
Thanks for your comments
Cheers
Hi.
Just to say, I have a pair of KK’s AX boards (the only higher power AX types I could find) and will probably try to modify these to ‘J’ type (are these among the mods required to take an AX to .5 status ?) . I have built an Aleph 5 using his boards which has worked out well, and if people look at the PassLabs Diy site under gallery, misc amps, and others you will see many examples (not mine yet!) of his boards being used. People seem happy with the results. I would say that, though not the cheapest boards, they are readily available, well documented and his assistance with questions has been very good. They have allowed a novice to upgrade from Denon POA 4400 and learn a lot while doing it. Without his boards I would not have had a ‘Doorway to Pass Heaven’.
Next on the list is a Pass F5 using CViller’s boards. (see below)
Regards.
(When I learn how to post images!!)
Just to say, I have a pair of KK’s AX boards (the only higher power AX types I could find) and will probably try to modify these to ‘J’ type (are these among the mods required to take an AX to .5 status ?) . I have built an Aleph 5 using his boards which has worked out well, and if people look at the PassLabs Diy site under gallery, misc amps, and others you will see many examples (not mine yet!) of his boards being used. People seem happy with the results. I would say that, though not the cheapest boards, they are readily available, well documented and his assistance with questions has been very good. They have allowed a novice to upgrade from Denon POA 4400 and learn a lot while doing it. Without his boards I would not have had a ‘Doorway to Pass Heaven’.
Next on the list is a Pass F5 using CViller’s boards. (see below)
Regards.
(When I learn how to post images!!)
Hi Dan.
Sorry to say I haven’t, next on my list is an F5, then Aleph P1.7. I have AX high power boards (KK’s) but wanted to see what was required to mod them (hopefully to .5 status).
I find most of my parts on EBay. Had good luck so far, some very good U.S. (shipping never a problem) and U.K. suppliers. What are you short of ?
All the best.
Jotom750
Sorry to say I haven’t, next on my list is an F5, then Aleph P1.7. I have AX high power boards (KK’s) but wanted to see what was required to mod them (hopefully to .5 status).
I find most of my parts on EBay. Had good luck so far, some very good U.S. (shipping never a problem) and U.K. suppliers. What are you short of ?
All the best.
Jotom750
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