Simplistic NJFET RIAA

diyAudio Chief Moderator
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Hi, Salas,
I have built your phono stage for MM cartridge. I use the phono stage with transformers Sowter 9580 with Denon DL103; the sound is very good.
But I have some questions for you:.............................................................
................
Many thanks.
Mario.

Hi

:up: for working on first hit. 1. With weaker leds just find R1 value that satisfies the current that you were looking for. ICCS=VR1/R1. 2. 7.5mA is near enough in gain to 8-8.5mA, but weaker dB overall. Post various DC voltages like drains to earth, collector to earth, so we see the bias is still logical if the dB are enough total with your Sowter. If no danger, and dB enough, no worries. 3. Yes, GDS you put correctly. We will be happy to see it in box and learn how you like it in the long term. What you had before?
 
azur mm pre to mm-mc

hi Salas, guys,
here are pics of my mod on azur 540 mm pre
not tried out yet though with my mc cartridge and I decided to use alkaline batteries after several attempts failed using existing regulator. Azur's positive rail always going down when MC is on...not good

200R trim-pot for R1 and R5 under the board. Salas I keep the 1000uF caps, is this ok or do I still have to use BC550?. Please let me know if you have better ideas.

thanks (sorry for poor pics)
TeguhPS
 

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7.5mA is near enough in gain to 8-8.5mA, but weaker dB overall. Post various DC voltages like drains to earth, collector to earth, so we see the bias is still logical if the dB are enough total with your Sowter. If no danger, and dB enough, no worries.

Attached your schematic with various DC Voltages. Inform me if is O.K.

With weaker leds just find R1 value that satisfies the current that you were looking for. ICCS=VR1/R1.

Please, can you explain?

The voltage of the shunt regulator is 28V; i set the voltage with the trimmer, adding a 470 ohm resistor (R = V / I, 28V / 0,06 A).

Regards, Mario.
 

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diyAudio Chief Moderator
Joined 2002
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Its OK, just runs lower currents, its safe. If your gain is enough with step up, don't bother changing the Jfets.

I explain, to find the current that the reg runs in CCS, you divide what voltage you have on R1 (green fat one), by R1 in Ohm. So if it is below target, one way is not to use stronger LEDS (make more V across R1) but to use smaller R1.

Not 470 Ohm, but 4K7 because 6mA = 0.006A. But it is going to be +0.6V, there is transistor's Vbe under it also.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
hi Salas, guys,
here are pics of my mod on azur 540 mm pre
not tried out yet though with my mc cartridge and I decided to use alkaline batteries after several attempts failed using existing regulator. Azur's positive rail always going down when MC is on...not good

200R trim-pot for R1 and R5 under the board. Salas I keep the 1000uF caps, is this ok or do I still have to use BC550?. Please let me know if you have better ideas.

thanks (sorry for poor pics)
TeguhPS

R5=220K terminal resistor, not 200R trimmer. You have to use 550, it sets the voltage lower also. Plus, its not going to play long on batteries. 14mA bias.
 
Its OK, just runs lower currents, its safe. If your gain is enough with step up, don't bother changing the Jfets.

I explain, to find the current that the reg runs in CCS, you divide what voltage you have on R1 (green fat one), by R1 in Ohm. So if it is below target, one way is not to use stronger LEDS (make more V across R1) but to use smaller R1.

Not 470 Ohm, but 4K7 because 6mA = 0.006A. But it is going to be +0.6V, there is transistor's Vbe under it also.

There is an error in your PDF
(Use R=V/I and P=V*I, to compute the value of your load resistor for testing your shunt.
Where V is the output voltage of the shunt and I is the consumed current. (If you are going to use one
shunt for both channels then I = 0.06 A).
 
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How you finalized decisions? New longer listening sessions?

Yes new longer listening session & your very good tweak/advice getting off the resistor & capacitor is a very huge upgrade, remember me near the same subjective than getting off the cap in the 1st stage but the cap in the 1st stage was still worse. Output caps Mundorf Silver Gold in oil are very very transparents so I can hear very easy the differences to god or bad.

it should... taking in consideration all your fine tunning, work and care :):):)

;)