Simplistic NJFET RIAA

[Milos P.]

Yes. Also I bypassed 10kuF caps with 1uF PIOs. It sounds even better, IMHO, with 10uF PIO bypass, but I could not fit them in the box, due to their XXL size. My VSPS sounds like a toy compared to this great pre, and VSPS is not a bad preamp, at all.

[atupi]

I have built also VSPS and is like his name, very simple app of a opamp. For a first RIAA preamp is ok but nothing more.
Maybe if you power VSPS from as Salas shunt this could be better.

[RCruz]

What is a VSPS ?

[Milos P.]

RJM Audio - The Very Simple Phono Stage

[RCruz]

Thank you Milos

It is a very different approach so results are also very different

[rclourenco]

Dear all,
Been trying to match a bunch of 2Sk170BL, tried to use the same circuit showed on the PDF doc by Salas, but something must be wrong, when I set the DVM for mA I get on a determined unit for instance 3mA, and when measuring in uA the same device shows 6uA???

But never 8, or 9mA as it should for BL version.

What's wrong?

Thanks for your help!

[Salas]

Could be high burden voltage from the shunt resistor inside the DMM when in series, could be showing max uA if 6000 count meter, could be fake Toshiba. If you will see 38 Ohm D to S on a genuine BL its about 8.5mA.

[rclourenco]

Many thanks Salas.

Hope they are not fake, bought them from a DIY audio member.

Will try to see what happens.

[Salas]

Cross check with drop resistor voltage method too. Stick 100 Ohm off a 9V bat. (+) series to drain, short G&S to bat (-). Use Mr. Ohm's law I=V/R by measuring drop across the resistor.

[AndrewT]

DON'T use the ammeter function of your DMM !!!!!

Insert a resistor between drain and power supply.
Select a resistor value that gives an acceptable voltage reading on an appropriate Voltage scale of your DMM.
eg. for 2sk170bl I would choose a 100r resistor. @ 8mA of Idss this resistor will drop 8.00V as read by the 19.99Vdc scale of the DMM.
The Idss should be measured at 10Vds. Allowing for the resistor Vdrop the PSU must be set for 18.00Vdc. BUT this does not give an accurate Idss. the Tc & Tj will be wrong. It does give a good enough selection of Idss for batching and for this RIAA circuit.

If you want to use a 9V battery, then a much lower value resistor MUST be selected.
eg. 1r0 will drop 8.0mV as read by the 199.9mVdc voltage range of the DMM. Vds will now be 8.992Vds. Good enough for batching.