wait, replace Q7 and Q8 with the semisouth R100 jfet, and R7 with a 500 ohm pot and adjust to taste?
easy/caveman/end meme
wonders what I can be generous with...
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For this circuit I would be inclined to leave the IRFP240
on the top, saving some money and leaving some more
Vgs for the npn transistor to work with.
😎
on the top, saving some money and leaving some more
Vgs for the npn transistor to work with.
😎
Beginning my Aleph J mono build soon. Relying heavily on Bill for help. He has taught me what little I know. Plan to replace bottom half with SS fets, but may find it unecessary if they sound as good as I hear. F4 will be next. Already have the boards. Then pearl 2 for my brother and his crazy vinyl obsession. Going to try my best to brake the valve loose that currently holds him captive. If nothing else, maybe I can make the magic smoke😀
Sometimes I'm a little slow, but I guess I don't understand what "on the top" means... The copyright 2005 schematic I have shows IRFP240 Q5 and Q6 on the top.
that means - leave mosfets in Aleph CCS , put SS down ( to neg rail position ) and adjust Aleph CCS AC gain to your liking
Maybe I really am slow, but that seems to lead me right back to post 23.
OH NO! A ZM vortex is pulling me in!
(or maybe i just go back to quietly trying to pick up the knowledge pieces)
exactly .......
or - even better - make a bastard between Babelfish J and known things from FW J2 ;
that way you'll need just one mosfet in Aleph CCS and just one SS down
ask more , if you need
The Aleph CS stays intact. The idea of the trimmer for R7 is to find the correct voltage across it to bias the SS jfets, as they apparently vary greatly in Vgs. Once the exact voltage is established, doing a little math will give you the correct resistor value you need. Dividing that voltage by half of the current going through R8 will give you the correct resistor value needed to put the front end current sharing right on the money. You can then replace the trimmer with a fixed resistor if you want.
It's not so much that the Vgs of the Jfets varies greatly,
rather that it's quite a bit lower than the vertical Mosfets,
usually 1.1 to 1.5 V for 1A current. Add to that the
drop across the Source resistor for the Jfet and you can
compute the appropriate range of resistance for a pot.
😎
rather that it's quite a bit lower than the vertical Mosfets,
usually 1.1 to 1.5 V for 1A current. Add to that the
drop across the Source resistor for the Jfet and you can
compute the appropriate range of resistance for a pot.
😎
Nelson,
As i said earlier, i will be building a (kind of) standard Aleph J to begin with. In your opinion, is it worth the investment to add the SS to the bottom half. I just thought about the fact that zhoufangs price for his SS fets may not include matched pieces. If this is true, the cost increases significantly. I'll have to check.
As i said earlier, i will be building a (kind of) standard Aleph J to begin with. In your opinion, is it worth the investment to add the SS to the bottom half. I just thought about the fact that zhoufangs price for his SS fets may not include matched pieces. If this is true, the cost increases significantly. I'll have to check.
I think it's worthwhile, and you can compensate for some
mismatch Vgs with small adjustment of Source resistors,
or simply increase the Source resistors to 1 ohm.
😎
mismatch Vgs with small adjustment of Source resistors,
or simply increase the Source resistors to 1 ohm.
😎
all Zhoufang's SS are measured and delivered matched - by price written in his thread
Do the SS jfets start passing meaningful current through their gates in this circuit? I could see where it might be a good idea to parallel the front end jfets.
Would this be considered gate leakage? I thought I heard a rumor that the front end of the J2 was paralleled.
I thought the input impedance of these Jfets were high and Ciss is quite low in relation to the amount of transconductance they offer.