Simplistic NJFET RIAA

[merlin el mago]

Mine DVM read 0V.

 

[Salas]

Bad situation.

 

[nicoch58]

you need a better ones 🙂

 

[merlin el mago]

Worse, now the leds of the right channel of the RIAA do not lit😡

 

[merlin el mago]

you need a better ones 🙂

Sure, could you tell a better one not very expensive?

 

[RCruz]

R3 = 43,06 and 42,95 takman carbon
R4 = 6,829k and 6,835k shinkoh
c2 = 47,05n and 47,01n Obligato // silver mica
c3 = 16,009 and 16,013 Russian silver mica // silver mica
(C2 and C3 can be adjusted to lower values)

Also thinking to try for C4 a Hovland instead of the usual FT-3(I have both, what do you think?

Taking in consideration your resistor values, I would be happier with C2 = 46.6n.

Can you remove the silver micas ? If so it will sing very well !

If you need finer tune, I would suggest a 2M // 6k835 (R4 Right channel only)

The FT-3 are quite neutral, transparent and extended, but that size 🙁

It is an interstage cap so it will leave it´s signature but not affect the riaa curve.... Use the Hovland and report latter please 🙂

 

[merlin el mago]

Leds don't lit right channel

I measured right channel (Leds don't lit):

Leds 0.001V BAD
R17 340mV OK
R10/Q2 10.06V OK
R1/Q3 49V BAD
R7/GND 10V OK
DRAIN Q5/GND 21.1V OK

It's possible the problem are the Leds, so only changing the Leds for news solve the problem?

 

[Salas]

Change q6 maybe. You took it out because you allowed 49V. Go down to 45V first.

 

[vgeorge]

Taking in consideration your resistor values, I would be happier with C2 = 46.6n.

Can you remove the silver micas ? If so it will sing very well !

If you need finer tune, I would suggest a 2M // 6k835 (R4 Right channel only)

The FT-3 are quite neutral, transparent and extended, but that size 🙁

It is an interstage cap so it will leave it´s signature but not affect the riaa curve.... Use the Hovland and report latter please 🙂

Thanks Cruz!

Nothing is soldered yet. Trying to match components.
If I remove the micas I have 46.6n and 46.4n so I wil add 200p to one chanell only.
I have spare FT-3 also. This is what I am using now, but I found these on my stach and wanted to hear opinions. So I will try them and see. FYI these are about the same lenght as FT-3, only slimer!

 

[merlin el mago]

Change q6 maybe. You took it out because you allowed 49V. Go down to 45V first.

Ok now I have 45V, I changed Q6 SK170BL with 9,26 Idss that' maximum mA that I have on hand, Leds lit but R1/Q3-GND have 40,03V😕

 

[Salas]

Leds alight, good progress. Now, you got the BC550 killed I hope and not the two JFETS under it. But it can be the other way or both. Change the 550 first.

 

[merlin el mago]

I changed Q3 BC550, now the measurements are:

Leds-GND
Right 7.66 need to reduce to 7.3V?
Left 7.32 OK

V across R17
Right 328mV need to increase till 350mV?
Left 350mV

R10/Q2-GND
Right 8.4V need to increase till 10V?
Left 9.4V need to increase till 10V?

R1/Q3-GND
Right 7.4V need to increase till 11.5V?
Left 11V need to increase till 11,5V?

R7-GND
Right 8.6V need to increase till 10.3V
Left 10.3V

Drain Q5-GND
Right 21V adjusted with trimmer R6
Left 21V

 

[Salas]

Do you have 45V B+ on both channels?

 

[merlin el mago]

Measurements done loaded with RIAA:

Right B+ 42.1V
Left B+ 45.2V

Have I to increase or decrease till 45V B+ with RIAA loaded?

 

[Salas]

When the system is loaded as it really plays, see that you got 45V B+ on both channels and then compare/trim DC points between channels.

 

[merlin el mago]

OK adjust two channels for 45V B+

 

[Salas]

OK. Trim the right referenced to the left.

 

[merlin el mago]

45V B+ both channels:

Leds-GND
Right 7.3V
Left 7.32

V across R17
Right 331mV
Left 351mV

R10/Q2-GND
Right 11.53V
Left 9.94V

R1/Q3-GND
Right 11V
Left 10.63V

R7-GND
Right 11.57V
Left 9.99V

Drain Q5-GND
Right 17.5V
Left 21.1V

 

[Salas]

Trim your right R6 trimmer to get 9.94V on R10/Q2.

 

[merlin el mago]

Done both 9.94V