I successfully built one of these over 20yrs ago, it still works well, sounds good but there is a slight, just audible "scratchiness" (the only way I can describe it) to the high frequency sounds. Could be an oscillation problem, but the output MOSFETS barely get warm even after about 20 minutes of use. I have rebuilt the regulated power supply again successfully and it works well. However with the amps, I have had plenty of problems. I used polypropylene and some polystyrene caps. I tested all the small and medium power transistors, even checking for similar gains. The Amps just don't work, intermittently certain MOSFETS get hot, etc. I took far more trouble now than I did over 20 yrs ago. I am using the old Hitachi MOSFETS (a local supplier still had 6 pairs, claims to be unused), maybe its time to use new EXICON devices?
I have also built David White's MOSFET Amp design in ETI 1998 magazine, which incorporates an op amp (TL071 or better spec op amp) in the 1st stage. This gave trouble too, with the medium power transistor stage, with odd faults. I gave up on it eventually. It seemed very op amp dependent too and I think that the op amp offset gave problems with the functioning of the medium power stage. Different op amps of the same type (TL071's) gave different effects on voltage balances in the medium power stage that followed.
Hi "Jamesfeline", thanks. 4 or 6 should be fine. email - garywest@telkomsa.net How would you get them to me in South Africa?
I have 2 in the original Amp I built over 20 yrs ago that are still working. Then I had manually made my own PC boards using Alfac transfer (lines and doughnuts on separate sheets) and a PC pen to run over that in case of small cracks. I had used the PCB in the original 1984 ETI article, including the rectangular PCB of the regulated power supply. I modified the power supply by making a few changes and using MOSFETS instead. Surprisingly it worked. Recently I decided to make a rebuild using the HART boards. I took the photos posted, used a photographic program, squared distortion, greyed scaled the photo, increased the contrast and retouched using a graphic tool. This came out well. I scaled the PC boards using the TO3 transistor for sizing, made some adjustments for my capacitor sizes, laser printed them out onto glossy magazine paper in negative image and then ironed the image onto cleaned copper boards, soaked the paper off, then etched and drilled them. A long process but it worked pretty well.
Regards.
I have 2 in the original Amp I built over 20 yrs ago that are still working. Then I had manually made my own PC boards using Alfac transfer (lines and doughnuts on separate sheets) and a PC pen to run over that in case of small cracks. I had used the PCB in the original 1984 ETI article, including the rectangular PCB of the regulated power supply. I modified the power supply by making a few changes and using MOSFETS instead. Surprisingly it worked. Recently I decided to make a rebuild using the HART boards. I took the photos posted, used a photographic program, squared distortion, greyed scaled the photo, increased the contrast and retouched using a graphic tool. This came out well. I scaled the PC boards using the TO3 transistor for sizing, made some adjustments for my capacitor sizes, laser printed them out onto glossy magazine paper in negative image and then ironed the image onto cleaned copper boards, soaked the paper off, then etched and drilled them. A long process but it worked pretty well.
Regards.
Hello Jamesfeline. I'm just read through this topic for the third time in the past year and finally decided to go into this amplifier design, as I have a bunch of good old K135/J50 pairs. You mentioned before You will may have some "basic kits" available. Do You still offer these, or have any other idea? Since I'm new member, I still can't write private message, but let me know any form of communication You prefer.
Thank You in advance.
Thank You in advance.
That is very good news. Yes, I'm also interested in those hard to get parts also. For the output devices I have a stock of 10-12 pairs most of them selected for Ugs match (however these seems to have a very narrow range by default).
Can You make me a quote for a stereo pair?
Yes, I'm member since two years for this topic as a reason, and since didn't post anything else so maybe PM option have some activity as a mandatory.
Can You make me a quote for a stereo pair?
Yes, I'm member since two years for this topic as a reason, and since didn't post anything else so maybe PM option have some activity as a mandatory.
Ok ...
there are 2 PCB's needed one for the power supply and the other the power amp so 4 PCB's needed for a mono block pair
these are the versions that I make.
I have now produced my own power amp PCB (the power supply to follow) mine is 20z copper gold, but I don't bother with silk screening but do have the original layout pics to follow
please see below ( 2 pics of the original board)
there are 2 PCB's needed one for the power supply and the other the power amp so 4 PCB's needed for a mono block pair
these are the versions that I make.
I have now produced my own power amp PCB (the power supply to follow) mine is 20z copper gold, but I don't bother with silk screening but do have the original layout pics to follow
please see below ( 2 pics of the original board)
I have my own Gerbers for the new version (true to the same layout)
I use bare gold 2.0z copper boards with no silk screening as like the retro look if I can call it that ? I have tried tag board point to point but had to many instability issues and even though I tried my best always looked like a rats nest.
so 2 pics of the my own power amp PCB
I use bare gold 2.0z copper boards with no silk screening as like the retro look if I can call it that ? I have tried tag board point to point but had to many instability issues and even though I tried my best always looked like a rats nest.
so 2 pics of the my own power amp PCB