I am repairing an sphinx amplifier and have to swab 3 pieces 2sk135 and 3 pieces 2sj50 , what is the best and simple way to match these fet's .
thanks in advance René.
thanks in advance René.
Use same batch numbers if possible and match for equal Vgs.
(or Jan de Groot, aka transparantsound.com)
PJ-12 bakkies ?
(or Jan de Groot, aka transparantsound.com)
PJ-12 bakkies ?
Hello Jakko,
Yes indeed PJ12, I have replaced the fets and have an offset off about 10 volts !! that is not good. i am now thinking that the ne5534an ic's (2 on top off each other ?) are also bad. I removed and checked all the other semiconductors but they are all in good shape, so I am a bit in a dead end over here.
Do you have any suggestion for me ?
Yes indeed PJ12, I have replaced the fets and have an offset off about 10 volts !! that is not good. i am now thinking that the ne5534an ic's (2 on top off each other ?) are also bad. I removed and checked all the other semiconductors but they are all in good shape, so I am a bit in a dead end over here.
Do you have any suggestion for me ?
is there ~0V DC offset on the other channel? if so, make comparison measurements between the same components on the different channels, starting with the input stage and working toward the OPS. when a reading on one channel differs significantly from the same reading on the other channel, you are homing in on the problem.
Hi gain,
Thanks for the advice, finally they are working it was a 470pf styroflex capacitor with a short 😕 This was the first time in many years I had a styroflex with a short never had this before. So I was al the time looking in the wrong way.
Regards René.
Thanks for the advice, finally they are working it was a 470pf styroflex capacitor with a short 😕 This was the first time in many years I had a styroflex with a short never had this before. So I was al the time looking in the wrong way.
Regards René.
Good that you solved the problem. 
René mentioned to me that 2 NE5534 was connected "hard" in parallel, on top of each other, has anyone done this or seen this before? Paralleling opamps in this manner is something I would do unless I had full controll over the situation.
René mentioned to me that 2 NE5534 was connected "hard" in parallel, on top of each other, has anyone done this or seen this before? Paralleling opamps in this manner is something I would do unless I had full controll over the situation.
peranders said:
One of the British brands, but something you'd do with ceramic case opamps only, not plastic.
(quiescent current level of the 5534 is rather low)
Wouldn't opamps get hot if the offset voltage was too much? It seems like a real budget solution to me.
Hi guy's, just to be sure I just phoned a friend of mine who also has the PJ12 and got him so far to open up the case and inside also the two NE5534 on top of each other.
Any way it is not some sort of modification he is the first owner.
I do find it rather strange the only thing i can think of is that the opamps can deliver more to the rest of the cicuit
Greetz René.
Any way it is not some sort of modification he is the first owner.
I do find it rather strange the only thing i can think of is that the opamps can deliver more to the rest of the cicuit
Greetz René.
Eeh, selected ones ?
They exchanged them for Mr Wurcer's baby when that hit the market, which has a supply current level double as high.
(it's a cascoded supply rail drive thingy, similar to SAC and T&A designs, to name a few)
They exchanged them for Mr Wurcer's baby when that hit the market, which has a supply current level double as high.
(it's a cascoded supply rail drive thingy, similar to SAC and T&A designs, to name a few)
Hi Per,
They are indeed a bit hot not to much but you can feel it very well with your finger, about 45 degrees or so. They run on +- 15 volt rails.
Would love to have the schematic and maybe it is an idea to replace the Ne's with a better opamp AD, OPA etc. ????
What is inside is 2SK389, BD902, BD901, 2SB649, 2SD669, two NE5534 and three 2SK135 and three 2SJ50. And of course powersupply with two bridge rectifiers and a lot of small capacitors, not much special but somehow they managed to get it sounding very very good. Normally I listen to an Audio Research D100B or an Hawk Audio A60 hybrid but i was very supprised with the PJ12 .
Ther must be something special about it?
René.
They are indeed a bit hot not to much but you can feel it very well with your finger, about 45 degrees or so. They run on +- 15 volt rails.
Would love to have the schematic and maybe it is an idea to replace the Ne's with a better opamp AD, OPA etc. ????
What is inside is 2SK389, BD902, BD901, 2SB649, 2SD669, two NE5534 and three 2SK135 and three 2SJ50. And of course powersupply with two bridge rectifiers and a lot of small capacitors, not much special but somehow they managed to get it sounding very very good. Normally I listen to an Audio Research D100B or an Hawk Audio A60 hybrid but i was very supprised with the PJ12 .
Ther must be something special about it?
René.
Hi Jacco,
What do you mean with this :
"They exchanged them for Mr Wurcer's baby when that hit the market"
Gr, René.
What do you mean with this :
"They exchanged them for Mr Wurcer's baby when that hit the market"
Gr, René.
Read my previous post, Mr Wurcer is the designer of the AD797.
(most of the similar design stuff use the same opamp)
(most of the similar design stuff use the same opamp)
AD797,
Good idea, I wonder why they didn't use such an opamp in the first place ?
Should it be done for budget reasons ?
Good idea, I wonder why they didn't use such an opamp in the first place ?
Should it be done for budget reasons ?
Mmmm, because it wasn't there yet ?
The Project Twelve comes in MK-I, MK-II and MK-III.(MK-III is the cosmetic pimped version)
The Project Twelve comes in MK-I, MK-II and MK-III.(MK-III is the cosmetic pimped version)
jacco vermeulen said:
Jacco,
Do you know if there was a big difference in the MK1 MK2 versions exept for the extra xlr input. I heard something about different lateral fets because the 2sk 2sj were out of production.
Gr, René
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