Simplistic NJFET RIAA

[merlin el mago]

So I put a jumper instead R9 & disconnect C5?

 

[Salas]

 

[merlin el mago]

Only for your information I don't use C10, ok I will do the changes & rapport, thank you Nick.

 

[RCruz]

Hi Merlin

What is the value of the 47nF cap you are using ?

 

[merlin el mago]

Before 47.1nF, now 47.0nF both channels

 

[RCruz]

As you use (6k8r // 1M) = 6754r

6754 x .047 = 317.44 almost = 318, I would say you are spot on the 500.5Hz mid point.

It should sound very good as is.

Let us know your oppinion if you reduce the 15,2n to 15n

 

[merlin el mago]

First I will try Nick advice, if it's not enough I will try the 15nF & tell you Ricardo.

 

[merlin el mago]

After jump R9 & take off C5 I measured again the voltages:

Left channel
Leds to gnd 7.30V
Across R17 0.259V
R10/Q2 to gnd 10.30V
R1/Q3 to gnd 11.32V
R7 to gnd 10.51V
Drain Q5 to gnd 19.85V

Right channel
Leds to gnd 7.50V
Across R17 0.285V
R10/Q2 to gnd 11.24V
R1/Q3 to gnd 11.80V
R7 to gnd 11.30V
Drain Q5 to gnd 18.80V

It's necessary to adjust R10/Q2 to gnd at 10.0V with R6 trimmer & do the measurements again?

 

[Salas]

Better match channels there with R6 trimmer, yes. Also in right channel I see a bit high through R7. Its because voltage Q2 is high, but make your R7s 1.2k if you have.

 

[merlin el mago]

I have 1K21?

 

[Salas]

It goes without saying.

 

[merlin el mago]

Left channel
Leds to gnd 7.29V
Across R17 0.261V
R10/Q2 to gnd 9.02V
R1/Q3 to gnd 11.69V
R7 to gnd 10.00V
Drain Q5 to gnd 21.3V

Right channel
Leds to gnd 7.55V
Across R17 0.286V
R10/Q2 to gnd 9.86V
R1/Q3 to gnd 12.00V
R7 to gnd 10.00V
Drain Q5 to gnd 26.3V

 

[Salas]

Don't trim to match at R7, trim to match at R10/Q2 to GND. 10-11V. Current is better for your IDSS through R7 now.

 

[merlin el mago]

Don't trim to match at R7, trim to match at R10/Q2 to GND. 10-11V. Current is better for your IDSS through R7 now.

R7 11V
Drain Q5 to gnd 24.6V

 

[Salas]

The only point of interest for alike gain between channels in 2nd stage is R10/Q2 to GND. The other voltages in buffer derive from drops due to static bias differences between channels and different -Vp. They just need to be logical.

 

[Salas]

R7 11V
Drain Q5 to gnd 24.6V

Did you put the 1K21 R7 yet?

 

[merlin el mago]

Yes

 

[Salas]

OK, so now the current is under IDSS in the buffer also. Make R11 3K3 0.5W to go lower Q5 to GND and avoid some dissipation on the buffer FETS.

 

[merlin el mago]

Changed R11 to 3K3 now Q5 to GND 12.4Vhave to be 21-22V not?

 

[Salas]

Try 2K7.