Simplistic NJFET RIAA

[merlin el mago]

I still prefer my beloved Shinkoh

 

[RCruz]

I did find metal bulk to be even better than shinkoh

 

[merlin el mago]

Of course naked Vishay sounds more neutral, but I prefer the euphonic sound of Shinkoh.

 

[RCruz]

Depending on placement, Shinkoh are really good.

 

[merlin el mago]

What are the placements Ricardo?

 

[rtd]

help , while measuring my probe slides and ... "catastrophe"
Dc in is ok, but rail + fails at 5v, tp1,tp2 at 5v too, D1..D4 don't light anymore (normal at 5v). all other led (in the regul) are ok (means are shining).

Any advice or other measure to detect the faulty component (before changing everything )

edit : it works and sound well before what should have been the last measure

I check the regul as i can, Q1x/Q2x seems ok, 52 Dc in, 46.5 v at R2x...
after 5v . As the riaa cannot be separated from the regul (without desoldering), can i use the next chanel Dc regulated (35v) to power the faulty channel at the same point (rail+).

this will allow me to see which area is faulty (regul or riaa)
if riaa faulty, i will of course quickly disconnect it

N.B : Q6x is cold

one Rail + can it support two chanel ?

 

[Salas]

No, don't supply two channels from one reg. From your description very possibly the slip probe accident did something that affected the reg area only. Check Q3X and Q5X (when power is off) with the DMM in resistance mode. There should be 50-150 Ohm drain to source for each and not a short or near short. With the power on, Q4X should be reading about 0.6V Vbe also if those JFETS are OK. Then Q6X must be reading 3.5-5V Vgs.

 

[rtd]

Thanks for your supporting at such hour ,
Q5x is 86r, Q3x 32r, Q4x is 0v and Q6x 0v
which one could be ko, the Bc550 ?

(i will recheck measure later, should be less exhausted)

 

[Salas]

Change the 550 first to see if its the only one gone, else its gone along with the MOSFET

 

[rtd]

Rds of the IRF9530 is high but not shorted.
it seems the mosfet is ok.
Will try to change the BC550, hope it will be enough

 

[Salas]

Keep an eye on Q3X also because 32 Ohm RDS for it is not a short but a K117GR is usually higher

 

[rtd]

Bc550 changed, all leds are on, but rail+ goes up quickly to DC in...
I stop power in before BC550 fails again.

I have sk117 spare, so i will change it too.
If not enough it will be time to shop, i don't have IFR9530 spare

 

[Salas]

Do that with Q3X because it maybe gives too much current to the Vref making it climb too high by being partially blown, its gate could be not controlling its field

 

[rtd]

Q3x changed, Rail goes to 25-26v, Dc in 52v, about 46v at R2x,
R of Q5x, Q3x is about 80R, Vbe is 0.7v, and Q6x Vgs is 3.5v

V2rx is 1k9, i cannot turn it clockwise anymore.

 

[Salas]

Works alright now, you only chanced on low new Q3X IDSS. Just try higher value R3X until in useful voltage adjust range.

 

[rtd]

just be back from M. Gardot concert... bought one LP, wait for our pre to listen to it

back to diy, i'd rather change Q3x, finding mills resistor at proper higher value won't be easier.

So i cut the one i just solder which gives 3.3mA Idss.
i have 4.51ma and 5.70ma spare, I guess 4.51mA is ok ?

 

[Salas]

Probably yes. It may reach 35V. Depends on what R3x value you got installed and how much Idss those K117s lose after installed in that low Vds position. Are they certified genuine?

 

[rtd]

6k2, jfet comes from gb here.

 

[Salas]

Should reach 33V or bit over it with the 4.51 one. The 5.7 may not allow low enough adjust range.

 

[RCruz]

What are the placements Ricardo?

Shinkoh is good as drain resistor and also as interstage but for cart loading I do prefer bulk metal