SemiSouth power Jfets .......... FW J2

[Zen Mod]

for protection of output Jfets look at this schematic - there are two zener diodes ( small - 10 to 13V / 300mW ones ) added between G and S ;

solder them underneath pcb , in any convenient position

for upper Jfet - say between adequate pins of R22 and R27

for lower Jfet - say between adequate pins of R31 and R32

edit : schm deleted by ZM

[generg]

Hi Zen Mod, For the input capacitance, can I calculate with 100kOhm like original J2, or is it symmetrically only 20kOhm?

[Zen Mod]

same as J2 - unbalanced 100K , balanced 200Kbecause input Jfets are cascoded , we don't have Miller capacitance , so you can count on pure input capacitance of Jfets

[generg]

THX Zen Mod, did you get your shuro mox 1 ohm/ 3w?Otherwise I could send you 6 , I have here enough!

[Zen Mod]

they're almost there , tnx save those , you'll need them for future Babelfish-es( soon we'll proceed to M2 )

[generg]

With such a fine amp the question what kind of pre one should use arises once again....... I played with pumpkin, aleph p 1.7 and avc and stepped attenuators shunt type...........at the moment I prefer the last possibility.babel J2 seems to be a very good candidate for passive solutions and I can take a lower gatestopper again and compensate the loss of highs and dynamics a bit.......Dear Zen Mod, what do you use.... ?Can you hear already two channels?

[Zen Mod]

....Dear Zen Mod, what do you use.... ?Can you hear already two channels?

still not stereo ........ it's pretty low on my list , now when I'm finished with construction for decent buffer between attenuator and J2 ,try this one ; and you really need buffer , to avoid loss of highs and dynamicsif you like it , I'll point you to decent shunt reg ; frankly - with red leds , but I know that you will not mind .... :Viannen_loungelizard:PSU voltage can be anything between +/-18 and +/-25V

[generg]

you are again incredible ..... My cd-player output is balanced and the attenuator also. I tried unbalanced, but there is a loss of micro information and space ....

[Zen Mod]

........My cd-player output is balanced and the attenuator also. I tried unbalanced, but there is a loss of micro information and space ....

then you must make two of these per channel :buehehe:double fun

[generg]

o.k. quadro fun for me ......... thanks! :Viannen_loungelizard: :Viannen_loungelizard:

[generg]

I have a ZM collection! PSu must be this one ..... red LEDs.....

[Zen Mod]

better this one , with few changes ( dissipation and input/output voltage accommodation )http://www.diyaudio.rs/topic/2644-mali-shunt/page__view__findpost__p__51822that one with 317/337 have some compromises ( needed for exact intended project)

[Tea-Bag]

Hi Guys,

Hooked up the bad channel to the fet's - hasn't gone to well. It's getting embarrasing. This board has had a hard life with me as a father.

I am getting a bunch of odd voltages, thought it was the optocoupler, but replaced that to no effect.

I've taken the voltages, and added them to the attachement.

I've tested the R100's solo and they test fine, and kept Vgs values as before, but in circuit - no love. Q13 in this case seems like it's getting nothing to work with.

Most interesting is the 3v6 reading - to be taken from pin 5 on CNY17 to Drain on Q 14, shows 0v here.

My intuition tells me to replace Q4 and Q6. The voltage across R35 should be at least double....The voltages are certainly not right there. My understanding of the working's of the circuit are not deep enough to understand where this is going wrong.

Any help would be appreciated.

edit : schm deleted by ZM

[generg]

Very sorry to hear this tea-bag ...... .....After so man different problems one does not know where to start again.........The only thing a I can tell you at the moment..... Don't forget to make a break, until desperation has gone out of the body....... Best for you!Hi Zen Mod, Zhoufang is active again and he offers SJ74 matched, even for the wanted Idss, what would you recommend? He also offers j109, but suppose it will be difficult to put them in the pcb.

[Zen Mod]

better to buy myriad 74's , than 2 109's :rofl:Tea - I have sort of flue these days , so I'm even more un-useful than usual ;also - I have some guests for weekend , but I'll try to think about your issue

[Zen Mod]

Tea - have you both inputs grounded while powering up ?please - try to follow procedure I wrote in one of pprevious posts - with variac etc.also - don't forget to solder two zeners as gate protection for outputs

[Zen Mod]

generg - playin' with buffers ?

[Tea-Bag]

No worries about time at all. Hope you get well and have fun with friends.Zeners are on order - grounding of input's yes. Figured I would ask some questions before replacing more stuff.Generg, lots of other projects to work on.....House stuff, garden stuff, and building some MJK baffles to listen to various 3-4" full rangers I have around.

[generg]

generg - playin' with buffers ?

My foot damaged by loudspeaker cabinet still forces me to stay inside, I need to buy some parts........Next week is time enough ...... Because I just feel tired building things.... Incredible but true.... I must talk a little bit ..... why shouldn't I build four times papas B1 buffer? Or better asked, dear Zen Mod, do you see an advantage in the build with SJ74/Sk170? I see the higher voltage giving more headroom, on the other side it might be better to match four SK170 for a balanced channel than to match a complementary pair. But the feedback in your suggestion could compensate the differences.........Have a nice weekend with your friends........ :Viannen_loungelizard:And tea-bag I am very eager to hear what the matter with your second channel, it got like a crime thriller and we all want to know who is the murderer:........

[Tea-Bag]

And tea-bag I am very eager to hear what the matter with your second channel, it got like a crime thriller and we all want to know who is the murderer:........

Of course I am the murderer. It's been awhile sense I've been in a good mess. For now I will leave the crime scene alone.

[Zen Mod]

........why shouldn't I build four times papas B1 buffer? .......

simple said - complementary and cascoded is simply better ;in fifi vocabulary - less sonic signature tech speaking - lower output impedance , works in constant voltage regime off course - choice is all yours

[Zen Mod]

Tea- let me know ( probably again , so sorry ) - what's Ugs/2A of outputs used in that broken channel ?