Simplistic Mosfet HV Shunt Regs

[Salas]

Originally Posted by kacernator

Maybe there is just little less detail with unregulated, but it does sound more natural, breathes and is more 3D.

I can remember some Aikido something, maybe headphones, run by Stixx rather early in the thread that he was very much pro using the reg, but I can't remember if others have given feedback about Aikido preamps and the reg. Different strokes for different folks as they say. Unregulated it is best for you.

[Stixx]

I can remember some Aikido something, maybe headphones, run by Stixx rather early in the thread that he was very much pro using the reg, but I can't remember if others have given feedback about Aikido preamps and the reg. Different strokes for different folks as they say

Yep, that was me...
For sure it has nothing to do with the Aikido circuit but of course can depend on a lot of other factors. I am running two headphone amplifiers with the Salas reg (Nick, you should start to protect that name...), one being pure SE transformer coupled, and the other Aikido parafeed. Both made a big jump up in sonic performance with the shunt reg, and the LAST thing I would say that they are lifeless... both of them bring me very close to the music... and that's what it is all about.

[iko]

Lack of life, flat, would mean the shunt regulator doesn't have enough top voltage before the CCS or the idle current is too low. If anything is should improve dynamics! I'm also running a tube headphone amp now, with shunt regulator on B+, not exactly the Salas design (I modified it to suit my ideas), but very similar topology. Nothing short in dynamics, I can tell you that.

[merlin el mago]

Originally Posted by ikoflexer

Lack of life, flat, would mean the shunt regulator doesn't have enough top voltage before the CCS or the idle current is too low. If anything is should improve dynamics! I'm also running a tube headphone amp now, with shunt regulator on B+, not exactly the Salas design (I modified it to suit my ideas), but very similar topology. Nothing short in dynamics, I can tell you that.

+1

[SGregory]

Here is a little challenge. I am blowing the 2sk170 reference. My incoming voltage is 275Vdc filtered. My output voltage is 220Vdc. It is passing 62mA. The circuit is Simplistic Mosfet HV Shunt Regs.

It will start-up and run fine. After about 30 minutes it will stop regulating and just apply full voltage. It has happened on both channels now. It goes quietly and the circuit looks to be running fine until you measure the ouput voltage.

[merlin el mago]

Only difference Salas pass 40mA & yours 62mA, could you reduce the current or add a small heatsink for 2SK170?

[SGregory]

I will be putting a heatsink on it. What is the correct shunt current to device current ratio?

[iko]

Don't! You need to pass a lot less current through Q4. So lower the current through Q4 and increase R4.

Here's what you can do. R4 = 220k; adjust R8 in advance so that you get about 1mA through Q4. Then you get a drop of about 235V across R4 (so a 1W resistor should do), which gives you a healthy 15V across Q4.

Edit: you can set the reference current out of the circuit, that's best. You don't want to play with any adjustments while in the circuit, bad things can happen. Hook up Q4+R8 to a 9V battery and check the current with the DMM. An R8 of about 330R should give you a current close to 1mA. Then try several values for R4, starting with 220k.

The shunt current has nothing to do with the current through your reference. People usually suggest 15-20% more current than the load draws at idle, but it's really dependent on the load and what it's max current might be. You want to have enough current through the shunt so that it can supply it for every current spike the load wants.

[SGregory]

Thanks Ikoflexer
I understand that the reference current has nothing to do with the shunt current. How does the lower current effect the noise? Can I improve the situation with using a lower Idss 2sk170?

I have to orederr some 1W resistors in the range.

My circuit uses 20mA at idle so I can drop the shunt current as well and save on total dissapation.

[iko]

Oops, never mind, I made a mistake regarding the voltage drop across the jfet Q4. The voltage drop across Q4 is set by the Vbe of Q2 plus the voltage drop across R9. Perhaps the MJE350 gets hot!

In any case, the conclusion is still the same, that no heat sink on the 2sk170 will help you. You might need to have better heat sinks on the mosfets and on the MJE350.