Simplistic NJFET RIAA

[massimo]

You are the big one, how do you do? a lot of time without hear nothing from you?

3 months later quite well, thanks. Now I can finish my RIAA: the pcb is on my desk, ready to be populated.
Last month I had a chance to meet some Barca supporters in Greece (during the supercup) and had dinner toghter the day after

 

[massimo]

Done, now I have to measure the voltage across LED strings?

 

[merlin el mago]

3 months later quite well, thanks. Now I can finish my RIAA: the pcb is on my desk, ready to be populated.
Last month I had a chance to meet some Barca supporters in Greece (during the supercup) and had dinner toghter the day after

I am glad to hear now you are well, please photos & schematic of your RIAA will be helpfull (you know star gnd & star power).
Barça supporters are good people, sure you enjoy the dinner

 

[merlin el mago]

4 LEDs 1.88V measure 8.33V & I need 7-7.3V

The matching Idss for 60dBs I have is for 8-9mA Idss, don't need the jfet 8-9mA Idss instead 6-7mA?

 

[Salas]

Use 3 and a diode then. The Leds Jfet has nothing to do with the rest of signal gain fets.

 

[massimo]

Salas, which is the min - max V of the led string in the RIAA 60 dB front end? Are 3 x 1.9-2 V leds enough?
I might have the same problem...

 

[Salas]

How many Ohm is the 1st stage source resistor in yours?

 

[massimo]

I'm going to follow this schem:

 

[Salas]

For this one around 7V is better bias. Use 3 leds if they are strong and one non Schottky diode. A normal one.

 

[massimo]

For this one around 7V is better bias. Use 3 leds if they are strong and one non Schottky diode. A normal one.

... such as 1N4148 or 1N400x ?

Thank you!

 

[merlin el mago]

Use 3 and a diode then. The Leds Jfet has nothing to do with the rest of signal gain fets.

Can I use 1N4007?

 

[Salas]

... such as 1N4148 or 1N400x ?

Thank you!

Both OK. Breadboard one along 3 LEDs and see what it gives. Then match another hybrid. Its as low noise as a LED but good for that 0.6-0.7V you may miss if with strong LEDs that they overshoot if 4.

*1N4007 looks OK too. Try it out.

 

[Joao@AltheaMusica]

Both OK. Breadboard one along 3 LEDs and see what it gives. Then match another hybrid. Its as low noise as a LED but good for that 0.6-0.7V you may miss if with strong LEDs that they overshoot if 4.

*1N4007 looks OK too. Try it out.

Salas,
have you tried out the ZTX450 instead of the BC550, is this an opportunity?

 

[Joao@AltheaMusica]

I understand you perfectly.
Only was curiosity I'm not enough knowledge to make a simple tonearm so for me is impossible to do a super-tonearm to fight vs the best design ever made.

Merlin,
there are many "simple" tonearms out there. For a SPU or DL103 I'd recommend the arm from Thomas Schick. A winner for it's price.

 

[merlin el mago]

Use 3 and a diode then. The Leds Jfet has nothing to do with the rest of signal gain fets.

With 15V & 0.02A measure 6.3V it's ok? wich measured voltage I need to look for 7-7.3V?

 

[merlin el mago]

Merlin,
there are many "simple" tonearms out there. For a SPU or DL103 I'd recommend the arm from Thomas Schick. A winner for it's price.

Looks nice but at this moment I prefer follows with mine Linn Ekos.

 

[AndrewT]

With 15V & 0.02A measure 6.3V it's ok? wich measured voltage I need to look for 7-7.3V?

0.02A (20mA) seems quite a bit too high.
Try 10mA and 5mA and measure the string voltage at these lower currents.
OR
use your chosen jFET+R17 as the CCS and test the string voltage using the actual jFET.
The R17 value of 180r will reduce the k170 current to much below it's Idss.

Using post4728 for circuit details & values.

 

[Salas]

It won't be wise to run that ccs fet at full idss because it sees a high potential across and it will dissipate much. He could use a dropping resistor before it if deleting the idss resistor. Say 3k3 1W between B+ and fet. Leds are at their most quiet from 2-7mA normally.

 

[AndrewT]

Salas,
I did not say that anyone should run that jFET at Idss.
I said

The R17 value of 180r will reduce the k170 current to much below it's Idss.

That is the current that should be used to check the voltage of the diode string. Not at the 20mA quoted earlier.

There is a big difference between to and too in english. Is that the problem you are having?

 

[Salas]

Salas,
have you tried out the ZTX450 instead of the BC550, is this an opportunity?

Try low Rbb Toshiba etc.