Simplistic NJFET RIAA

[Salas]

You should have no voltage across the phono input RCA. Do you find DC there? If yes DONT connect the cartridge.

 

[atupi]

I have no DC across RCA-in but my my preamp is so quite, dead.

 

[Salas]

Start checks. All your Jfets must show voltages from drain to ground. Your BC550 must show voltage from collector to ground. Note them down on your schematic and post it so we check.

 

[atupi]

I will do this tomorrow. Thanks !

 

[atupi]

I am about to buy some matched transistors. Is that enough to buy 4 matched transistors with 9mA Idss ?

 

[vgeorge]

You are going to need 6 2sk170.

 

[massimo]

I am about to buy some matched transistors. Is that enough to buy 4 matched transistors with 9mA Idss ?

eseller from Israel? Highly reccomended!
P.S. ask him for 6 pcs

 

[atupi]

It's alweit also from Israel

 

[massimo]

Yes, Alex, feel free to ask him what you need.

 

[atupi]

Start checks. All your Jfets must show voltages from drain to ground. Your BC550 must show voltage from collector to ground. Note them down on your schematic and post it so we check.

I noticed that i have the same voltage on G and S of the last transistor. Most probably is shorted.

 

[Salas]

Last one's a follower so it should have just a tiny difference G-S ~0.2V, what reads on its drain?

 

[atupi]

That's right. So, where to look ? What else to check ?

 

[Salas]

If the output one shows near 20V D-gnd, then the DC conditions are OK. If not you change it, or you change one output Fet anyway and you check listen. Takes to feed 1kHz 5mV signal and trace with scope where it does not continue is the proper procedure. I hope that you haven't killed your cartridge in any case.

 

[atupi]

The D-gnd of the last one is 20v. I changed one just in case but nothing is changed. Unfortunately i dont have a scope.
My cartridge is ok, i'm listening right now using my old opamp riaa preamp.

Its strange that both channels died in the same time, or in the same way. I'm i missing something?
Looks like a human error

 

[Salas]

Human error. Never happened before in the thread. See changing the input Fets.

 

[Milos P.]

Hi
would IRFP9140N do the job? Or better to go IRFP9240 route?
Thank you

 

[Salas]

It has 100pF more Crss, better the 9240 in shunt output position.

 

[Milos P.]

OK, thank you.

 

[dimkasta]

Salas would the Toshiba 2SK170BLF available from Mouser be suitable for the phono?

 

[Salas]

That link carries the normal 2SK170 datasheet, so as far as it shows, yes.