Simplistic NJFET RIAA

[Salas]

Keep in mind that due to the charging angle, in practice I have seen RC in that point (R to main filter cap) overshooting and needed to be lower than calculated. I would get 150R 5W, 120R 5W and 100R 5W, and see which one gets me where I want (7-8V Vdif in-out).

[RCruz]

Salas

So if I use a 150w before the smoothers should I expect a reduction from 50v to 33 ?

I am considering this solution so I can use the small TX I got (2x18v 50 va)... 50v - 8v = 42v... does that mean that my working riaa sounds so good due to the excess of power ?

[Salas]

It will depend basically on Ohm's law for voltage drop, but be equipped with 120R and 100R as well, as I said because of different charging angles given the main cap's value and chosen Iccs, I have experienced deviations of dropping more than expected for resistor input RC filter & V dropper. That is if you draw 100mA total as assumed by Jaap. But you don't draw what the 2 phono channels need. You draw what the shunt(s) runs. So you calculate accordingly. Your 8V dif helps the shunt to work as intended. Your Riaa sounds so good because you put much care in to tuning it.

[RCruz]

Hi Salas

I found another TX : 2 x 25v 80VA..... Maybe this is better and I will not need to reduce the voltage. What is your oppinion ?

I am also searching for shinkoh resistors... I will use one 1k for the DL160 load and another 47k for R3.... All other resistors will be takman carbon 0,5w . Is this a wise choice ?

Ricardo

PS: I was considering cutting costs but can not resist the high quality approach.

[Salas]

Wise choice both on trafo and resistors. I have them resistors chosen such in a 56dB build. Don't forget the trimmer thing I posted about fine tuning, since you are our official tweaker. 100R trimmer parallel to 100R resistor for Rsource. After tuning I get 0.0025% THD and 0.005% IMD with 0.5mV RMS input. Nice for a non loop feedback simplistic circuit. Check out FFT.

[RCruz]

I will not forget the trimmer..... Just need a little more info regarding it´s position on the schematic...

[Salas]

Instead of R2 and R6.

[RCruz]

Thank you Salas

I will be posting the evolutions.

[AndrewT]

Originally posted by RCruz
I do not want to use any cap after the smoothing cap... is that possible ?

It's technically possible.
But why?
You are throwing out the potential to improve the sound quality of all subsequent stages by adopting this "ostrich" philosophy.

[RCruz]

Because I am using some left over 15000uF Nichicon KG for smoothers and would need something even bigger and better after the resistor to create the RC circuit.

As I have the luck to be living in a place with quite clean mains, I believe I am better off with a 2 X 25v.... this way I can feed both shunts with a dedicated winding.

Ricardo