Dear schultzsch,
if i had found that MOSFETs yield better results than BJTs i would have used them as VAS.
I tested those tiny gm small laterals (j77 and k216) as well as nice pi-MOSFETa (j313 and k2013) but BJTs took the cake.
The behavior of MOSFETs and BJTs is too different so you can't just use them as drop-in replacement in this design.
So, if you don't know what are you doing, you either revert to original, proven design (post #1) or you start from the scratch...
Good luck, have fun
if i had found that MOSFETs yield better results than BJTs i would have used them as VAS.
I tested those tiny gm small laterals (j77 and k216) as well as nice pi-MOSFETa (j313 and k2013) but BJTs took the cake.
The behavior of MOSFETs and BJTs is too different so you can't just use them as drop-in replacement in this design.
So, if you don't know what are you doing, you either revert to original, proven design (post #1) or you start from the scratch...
Good luck, have fun

At this point I can try them all and see what I like the most.if i had found that MOSFETs yield better results than BJTs i would have used them as VAS.
You are right, some compensation caps on the vas did the job.The behavior of MOSFETs and BJTs is too different so you can't just use them as drop-in replacement in this design.
Thanks juma!
Today (finally) I finished The Cubie 3 amplifier!
I installed both channel into the final enclosure. It is a keeper amplifier that is sure.
Thank you Juma for your knowledge and for sharing with us!
I have 37 to 38 VDC rail voltage, I set up the bias 520 mA. Heatsinks get comfortably warm like 45-50 C degree.
I can keep my hand even more than 10-15 sec.
No smoke, this time no problem at the set up.
Thank you Prasi for the PC boards and designed!
I installed between the main Gr and signal Gr a 3.1R resistors.
Some pictures.
The enclosure will need some cleaning, maybe painting.
Yesterday I ordered a brass color know from Ali-express to match the front of the amplifier.
I encourage all those who has the PCBs or populated but never finished it to finish it. It is a good sounding amplifier! It worth to be finished.
Greetings to all
I installed both channel into the final enclosure. It is a keeper amplifier that is sure.
Thank you Juma for your knowledge and for sharing with us!
I have 37 to 38 VDC rail voltage, I set up the bias 520 mA. Heatsinks get comfortably warm like 45-50 C degree.
I can keep my hand even more than 10-15 sec.
No smoke, this time no problem at the set up.
Thank you Prasi for the PC boards and designed!
I installed between the main Gr and signal Gr a 3.1R resistors.
Some pictures.
The enclosure will need some cleaning, maybe painting.
Yesterday I ordered a brass color know from Ali-express to match the front of the amplifier.
I encourage all those who has the PCBs or populated but never finished it to finish it. It is a good sounding amplifier! It worth to be finished.
Greetings to all
Attachments
It is OK.... This preamp is ...
This one even better :
I dont like lights in my amplifier 🙂
In 12v psu version am i have to use them. If yes can i replace LED witn 1N4007 diodes or any suggestions?
In 12v psu version am i have to use them. If yes can i replace LED witn 1N4007 diodes or any suggestions?
Jfets available here-
https://www.ebay.com/itm/2560703159...UXBIsOrjmGP4g2IWvkYEFpYQgk|tkp:Bk9SR9rtkOiBZQ
https://www.ebay.com/itm/2560703159...UXBIsOrjmGP4g2IWvkYEFpYQgk|tkp:Bk9SR9rtkOiBZQ
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