Well I finally finished my A40. I had initially Used 2SA1320-Y/C3423-Y for the VAS and I just couldn't get it working. I got in some more MJE340/350 so I changed those out and now the amp plays perfectly as one would expect. Listening to it all morning. Another winner!
Blessings, Terry
Blessings, Terry
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I'm glad to hear it's working , sound it's perfect even without ton correction 😎 I hope you understand why I added at offset ,one more capacitor .....🙂
Have you change 470 ohm resistor to 470K in offset adjust circuit?
Regards,Alex
Hi Alex,
Yes I did see Mile's post about the 470K change. The board is set up per the silk except I used those 2SA1360/C3423 for the thermal transistors. I will probably change those too because the bias takes a long time to settle and I think thy maybe to blame. I also used MJL4281/4302 for the outputs. I running it on +-60V rails and it isn't breaking a sweat.
I figured the back opposite facing polar caps on the NFB were to take the place of a non-polar. Cheaper option.
Lol, I suppose I could but I have about 7 amps stacked up next to my work bench that I switch between.
The high Cob of the slow transistors may be adding compensation that ends up just about right.
Hello guys here is AX-14 that I did and just change the size of some 1/4W resistor macros so the can fit better also I will share Sprint file so you guys can used as reference for other projects please used only for diy 😎 I do this because I do love this hobby 
have fun with it 🙂
Regards
Juan
have fun with it 🙂
Regards
Juan
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Hi Terry and all,
did you try using ksa1381/ksc3503 for the drivers?
I find in sims that they usually give an amp slightly better performance.
Since you posted your impressions of AX-14 and OS slewmaster, I did some sims comparing against original AX-14 and other designs to see what is going on.
It would be cool to compare sims vs real life testing just to refine the design process.
Do you actual own a distortion test setup?
I wanted to figure out in sim, why people praise one topology vs another. Just for the fun of it of course.
I wonder if Mile, does any design sim at all or all pen/paper,testing?
where the inspiration comes from, just dreams these circuits up or looks at other designs as references, to get ideas?
btw, in my sims I have also looked at SF3.1 pre-amp, what is impressive is how it clips!! all nicely rounded edges, no flat lines what so ever. i will try the bjt version, sb3.1 to compare.
A ? for Mile, for sf3.1 the output jfets are in a common source or drain configuration? I do realize that many mfg say that s/d are inter-changable. Comparing against sb3.1 I assume a common drain config like the common collect in sb3.1.
thx Rick
did you try using ksa1381/ksc3503 for the drivers?
I find in sims that they usually give an amp slightly better performance.
Since you posted your impressions of AX-14 and OS slewmaster, I did some sims comparing against original AX-14 and other designs to see what is going on.
It would be cool to compare sims vs real life testing just to refine the design process.
Do you actual own a distortion test setup?
I wanted to figure out in sim, why people praise one topology vs another. Just for the fun of it of course.
I wonder if Mile, does any design sim at all or all pen/paper,testing?
where the inspiration comes from, just dreams these circuits up or looks at other designs as references, to get ideas?
btw, in my sims I have also looked at SF3.1 pre-amp, what is impressive is how it clips!! all nicely rounded edges, no flat lines what so ever. i will try the bjt version, sb3.1 to compare.
A ? for Mile, for sf3.1 the output jfets are in a common source or drain configuration? I do realize that many mfg say that s/d are inter-changable. Comparing against sb3.1 I assume a common drain config like the common collect in sb3.1.
thx Rick
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Do not be a problem with bias if the driver (Q13,Q11) are not on the same heatsink with Q14,Q12?
AX-14
AX-14
Hi Rick,
I did not try the KSA1381/KSC3503. I suppose I could try them now that I have it working. I can't be sure that the 2SA/2SC were the problem. I changed them out on one of the boards because the board wasn't working and the MJE's were what was called out on the screen print. After I changed them and there was still issues so I went over the board again with a diode tester and discovered I had one diode reversed on both boards. When I flipped the diode the board with the MJE340/350 worked and the other one didn't. At that point I changed out the pre-drivers to MJE and at the same time I reflowed all of the solder joints on the whole board. After that the board worked but I don't know for sure if it was the transistor change or the reflow. I won't have time today but tomorrow I will change them back or even install the KSA/C devices and see how that goes. I would hate for someone to go to a lot of trouble finding a certain device if it is not necessary.
I don't have distortion testing equipment. The guy to go to is Thimios. He is a much better tester and builder than I am.
I did not try the KSA1381/KSC3503. I suppose I could try them now that I have it working. I can't be sure that the 2SA/2SC were the problem. I changed them out on one of the boards because the board wasn't working and the MJE's were what was called out on the screen print. After I changed them and there was still issues so I went over the board again with a diode tester and discovered I had one diode reversed on both boards. When I flipped the diode the board with the MJE340/350 worked and the other one didn't. At that point I changed out the pre-drivers to MJE and at the same time I reflowed all of the solder joints on the whole board. After that the board worked but I don't know for sure if it was the transistor change or the reflow. I won't have time today but tomorrow I will change them back or even install the KSA/C devices and see how that goes. I would hate for someone to go to a lot of trouble finding a certain device if it is not necessary.
I don't have distortion testing equipment. The guy to go to is Thimios. He is a much better tester and builder than I am.
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Just finished ...after few my mistakes is running.... Offset is OK, but bias still no OK. When I set bias 50mA, after On/Off procedure is 100 mA and slowly decreasing back to 50mA...maybe some temperature compensation, or something totally different 🙂 I have to check it tomorrow..
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Andrew said it right,slower transistor acts as faster with added compensation. as i have read (not much to be sincerely) that is most common thing happening when output transistors from vintage amplifiers were replaced with newer that have lower parasit capacitance - an amplifier starts to oscilate - and problem is most commonly solved by adding some compensation to those newer transistors,to make them slower.
faster transistor on wrong place can make troubles...
