Hmmmmmm....
model J2sj109 PJF(Beta=39.21m Rs=0 Rd=0 Betatce=-.5 Lambda=4.338m Vto=-.5762
I have the pcb's and most parts but open question to all, because a 2SJ109 is basically 2X2SJ74's thermally bonded, has anyone tried them on the input to the Alpha-J?
wouldn't be hard to adapt. I bought a pair of these from Denmark years ago, BL grade. not that they are hard to pull from equipment, lots of amps and preamps use them, like my Acurus RL-ll in the output with their compliment or lots of Classe CA series on the inputs. But I did pay a premium for NOS, BL grade from an estate (I think)
I also have another question, has anyone tried QFets as subs??? I've seen that Mr. Pass has greenlighted FQA25N20 (probably got a letter or number wrong) but how about something a bit more high powered
I have a pile of tru-blu, supply chain verified, FQA46N15's, enough to match them. can I just substitute or maybe complete instability. the rds on values and other features are quite attractive for a design like the Alpha-J
any input is appreciated, I'd like to assemble the pcb's fairly soon and crudely mount to a heatsink, just to experiment. if successful maybe an interesting amp project in progress
these are just questions I have because I'm in a mode where I'm trying to adapt my stock to some cool experiments.
I'm sure many will be able to relate on this forum
shawnra
model J2sj109 PJF(Beta=39.21m Rs=0 Rd=0 Betatce=-.5 Lambda=4.338m Vto=-.5762
- Vtotc=-2.5m Cgd=67.64p M=.2562 Pb=.3905 Fc=.5 Cgs=61.12p
- Isr=158.7p Nr=2 Is=15.87p N=1 Xti=3 Alpha=10u Vk=100
- Kf=109.9E-18 Af=1)
I have the pcb's and most parts but open question to all, because a 2SJ109 is basically 2X2SJ74's thermally bonded, has anyone tried them on the input to the Alpha-J?
wouldn't be hard to adapt. I bought a pair of these from Denmark years ago, BL grade. not that they are hard to pull from equipment, lots of amps and preamps use them, like my Acurus RL-ll in the output with their compliment or lots of Classe CA series on the inputs. But I did pay a premium for NOS, BL grade from an estate (I think)
I also have another question, has anyone tried QFets as subs??? I've seen that Mr. Pass has greenlighted FQA25N20 (probably got a letter or number wrong) but how about something a bit more high powered
I have a pile of tru-blu, supply chain verified, FQA46N15's, enough to match them. can I just substitute or maybe complete instability. the rds on values and other features are quite attractive for a design like the Alpha-J
any input is appreciated, I'd like to assemble the pcb's fairly soon and crudely mount to a heatsink, just to experiment. if successful maybe an interesting amp project in progress
these are just questions I have because I'm in a mode where I'm trying to adapt my stock to some cool experiments.
I'm sure many will be able to relate on this forum
shawnra
1) The original schematics for the AJ shows 2sj109: https://www.diyaudio.com/community/threads/aleph-j-schematic.111197/#post-1341101
2) Hopefully others more knowledgeable will chime in but I think you can probably get away with just one each in the upper and lower halves.
2) Hopefully others more knowledgeable will chime in but I think you can probably get away with just one each in the upper and lower halves.
Aleph is much different thing to Alpha
1. 2SJ109 is pair of 2SJ74 on same substrate; so, practically it is irrelevant what you're going to use - 2SJ109 or pair of 2SJ74
2. one pair is good for Aleph J range of power and dissipation; see this - soon to be in Store, everything solved; though - if you prefer to devise your own, even better
The FQA46N15 looks like it could be a suitable device for the Aleph J. I believe it would be best used as singles rather than matched pairs, as there could be an improvement in clarity.
I used a set of singles in my Aleph J SS build - IRFP048 above and FQH44N10 below, and was quite pleased with the results. A similar approach could be used with different device pairings. The FQA46N15 has higher input capacitance than other parts, and will probably require some experimentation with gate stopper resistors to achieve a voice that suits the listener.
I used a set of singles in my Aleph J SS build - IRFP048 above and FQH44N10 below, and was quite pleased with the results. A similar approach could be used with different device pairings. The FQA46N15 has higher input capacitance than other parts, and will probably require some experimentation with gate stopper resistors to achieve a voice that suits the listener.
I see their input capacitance on the FQA devices are about twice the IRFP series. I will try this but first match some devices. I have a tester but of late I'm not sure it is reliable. It has a fet test but these are not your average fet's and would they test properly. I'll look up the schematic jig for matching these devices.
seems to me, after reading up on the IRFP series, they seem to be made to play well with each other. whereas the FQA devices and more about performance. big distinction and must be considered.
seems to me, after reading up on the IRFP series, they seem to be made to play well with each other. whereas the FQA devices and more about performance. big distinction and must be considered.
compare your part with IRFP150, which is practically pair of IRFP240 in one case
I didn't point you to future Store Aleph J just for fun - you can analyze some choices there, which can help in making yours
in short - for regular Aleph J (power, dissipation) you don't need several output pairs, with proper type, one pair is enough
if you're worrying about interelectrode capacitances, introduce emiter follower in between JFet drain and mosfet gate ...... piece of cake to do it properly
though, Pa and Wayne taught me years ago - think in context; even if capacitances are there, signal swing on gate is small ....
I didn't point you to future Store Aleph J just for fun - you can analyze some choices there, which can help in making yours
in short - for regular Aleph J (power, dissipation) you don't need several output pairs, with proper type, one pair is enough
if you're worrying about interelectrode capacitances, introduce emiter follower in between JFet drain and mosfet gate ...... piece of cake to do it properly
though, Pa and Wayne taught me years ago - think in context; even if capacitances are there, signal swing on gate is small ....
after reading up on both the IRFP150 and the FQA46N15 devices I have they are quite similar. gate capacitances, RDS on value and other similarities, power rating. seems like it will work