Simplistic NJFET RIAA

[AndrewT]

it really takes off when the second stage is starting to get pushed as a result.

do you mean as the output peaks approach rail voltage?

 

[Salas]

Not really, a few volts Pk-Pk are enough to produce 1% THD with high input capacitance JFETS and low degeneration (Rs) we use here for high gain and low noise reasons.

 

[ra7]

Salas, do you have any ideas for a balanced phono stage?

 

[Salas]

You would just need to rearrange in diff amp mode the whole thing. 3dB more noise, but you can double up on input fets for MC that noise counts.

 

[atupi]

Any opinions about this capacitor RARE!!! 0.047uF 200V PIO Capacitors K40Y-9 Lot of 10 pcs. | eBay
for interstage connection ?

 

[merlin el mago]

For interstage can be good, for RIAA NO. I use FT-3.

 

[Milos P.]

I used Russian PIO 47nF(K42-U2) for RIAA but matched them to less than 0.5% with LCR meter. If you can match them, you could use them. The sound you may or may not like, for me , those in the direct signal path are a bit too much colored, bypassing them with good PP might sound interesting.

 

[Salas]

They are a bit dark PIO but smooth. Like Jensen but without the accent. They love Teflon bypass. Add BIG subjective anecdotal IMHO non scientific caution sign of course.

 

[Milos P.]

I'm still playing with my RIAA.The last mod is that I changed R1/10R/2W to 5R.
Like it very much and

Add BIG subjective anecdotal IMHO non scientific caution sign of course.

 

[Salas]

You doubled the reg's CCS current to hot-rod you mean?

 

[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]

Matching jfet

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.