Simplistic NJFET RIAA

[massimo]

My take on mirrored pcbs for the Universal Phono Shunt v1.1.....

Comments welcomed!

P.S. remote sensing can be performed just cutting two tracks.

[disco]

Massimo,

Maybe you should drop the traces for R2 and R6 connecting to the mosfet. These resistors can be soldered straight on the gate pins. The position of R7 prohibits the use of a 'fat finger' heatsink on Q1.

[disco]

Ricardo,

Regulators turn instable when input voltage drops below a certain limit.

If you haven't used them you can win half to one volt with Schottky diodes.

When I need an akward transformer I peel down a torroid and wind it up to the desired voltage. First note the total windings and the voltage under strain. Make the division and you know what to do

[RCruz]

Originally Posted by AndrewT

34.5Vdc @ what mains input voltage?
What are the minimum and maximum DC PSU voltages when mains supply is at minimum and at maximum?

I read 220v AC at the mains input.
Maybe the 25v TX is not very well specified.

Thank you Salas for the kind words. I believe I will now try the four wire shunt and report the differences.

Ricardo

[massimo]

Thank you for comments Disco.
Yes, the 4 "grid stoppers" might have shorter tracks, but, as you can see, my goal is to have two exactely mirrored circuit, one for L ch, one for R. I like all the components in the same position and thus I have to place the resistors in the middle of the TO247 and rotate the tracks toward the gates. In this way, even if a bit longer, they all are of the same lengths. I can try to further shorter them by a couple of mm anyway. The pcb is still in the debugging stage.....

R7 is not a big problem for me as I'm gonna use a flat heatsink. It can be replaced by a jumper underneath anyaway. As you probably noticed, I arranged some other pads in series for the trimpot and for some fixed resistors in // if you want to replace it once the right value has been found.

The reason why I designed the mirrored pcbs is that I would like to place the Riaa pcbs aside of each regs in order to reduce the lentgh of the V+ & Gnd cables to 4 , maximum 5 cm.
I'll show you my complete design as soon as it will be ready for etching.....

[Salas]

Is Q7 heading the wrong way on your pdf? Unless we do view the under side. Also the distance to the stopper and the stopper's to the gate is long. I am afraid you gonna hear the whistle blow. On the other hand you can always jumper it back to V1.

[RCruz]

Cool...

After several atempts and using different layouts I now believe the issue might be related with the low raw Vin I am using in the riaa. (Sometimes during the day I read 32Vin for 28Vout)

I will postpone this experiment and wait for Massimo´s report. After that I will get a bigger TX.

In the meantime I did learn a lot.... shortening the gate stopper resistor legs produces audible results in terms of overall cohesion and "musicality".

The pre Q7 shunt version is quite stable and resists all forms of layouts without oscilating but these resistors must be short wired and there must be a shortest wire between both mosfets in the +Vout line.

There is a big improvement in spaciality just by increasing the shunt current. (Care must be taken in choosing the leds otherwise we can gain in noise).

Following Salas words I just produced the 4 wire version and it is working perfectly in the bench. (50Vin for 28.2Vout, R1 (10r) 2.01Vdrop)

Tomorrow I will install it and report the benefits.

Ricardo

[RCruz]

Excuse the strange p2p but I am using this salvaged layout from a previous experiment
The fact that it works proves my previous statements.

[Salas]

Good conclusions. I use P2P construction set at 0.25A by utilizing the box's floor for sink as you know. 1mm resistor leg to gate. Q7 almost riding on the Mosfet. About 8V Vdif In-Out. How long are your cables from reg to phono, that you are going to remote node sense?

[RCruz]

12 cm for GND and 9cm for V.

I guess I must get a bigger TX for the DL160 riaa....
The initial one (Benz riaa) produces a much wider soundstage.... In that case I am using 44.6Vin for 28.1Vout produced by a 2 X 15V TX in series.

In the DL160 I am using a 25V TX (resulting in 34V after rectification and smoothing) to produce 28V ...... it is not enough due to the mains fluctuations...