Lenard's Series Pass MOSFET Tube Regulator Qs

[ITPhoenix]

Hi folks. Does anyone have experience with this zener contolled MOSFET regulator?

I was wondering if this regulator works. I see all kinds of elaborate regulators like the Maida and Aikido, claiming low noise.

Also, my application is just 4 preamp tubes, so I wonder if that 2.2k resistor should be increased. Here is my preamp:
The unregulated power supply:

I had planned on a massive overkill 10A MOSFET, to eliminate heatsink, and also the lack of heat would keep thermal noise low.

Any comments welcome. Thanks.

 

[Elvee]

I was wondering if this regulator works.

Yeah, it works reasonably well and is rather reliable. Of course, with such a simple scheme, you mustn't expect miracles: regulation and ripple rejection will not be of the highest standard, but are probably sufficient for the application you have in mind.
With unbypassed zeners, the noise performance will be moderate; you could improve this aspect by adding a parallel capacitor, but then the circuit will not forgive any short at the output, even very short.
If you split the 47K and add a capacitor at the junction, you will greatly increase the ripple rejection without adding a safety penalty

Also, my application is just 4 preamp tubes, so I wonder if that 2.2k resistor

You have to figure out the total current drawn by your preamp and see if the regulator still has enough regulation room.
The best method is to build it and decide later, by measuring the actual dropout voltage

I had planned on a massive overkill 10A MOSFET, to eliminate heatsink, and also the lack of heat would keep thermal noise low.

A small or big MOS doesn't change the amount of heat generated. The temperature will depend on the Rthj-a, that's all

 

[ITPhoenix]

Thank you so much.

If you split the 47K and add a capacitor at the junction,

Like this?


I got you on the series drop resistor, but not completely on the thermal situation. I am concerned with thermal noise, but not sure if its a factor since all the resistors are metal oxide. They are over-rated and the reservior capacity is liberal.

 

[Elvee]

Thank you so much.

Like this?

Yes

I got you on the series drop resistor, but not completely on the thermal situation. I am concerned with thermal noise, but not sure if its a factor since all the resistors are metal oxide. They are over-rated and the reservior capacity is liberal.

On thermal noise, I don't think it will make any difference compared to background noise, but this is an informal opinion not based on any quantitative aspect, even back of an envelope calculations so I may be wrong.

Metal oxide resistors are not particularly good for noise. I know they are favored by many audiophiles, but from a purely objective perspective, they are now rather low-end.

Anyway, relying on purely passive means for ultimate filtering is probably the best option whenever possible.
Good capacitors generate no noise, non-linearities or other funny artifacts, unlike active circuits even the best ones.

 

[ITPhoenix]

Cool. There are 10uF F&Ts on the early stages. The design is well worn with plenty of support and mods. None of the resistors are specifically low noise, but there is a choice of decoupler caps around the tubes; Sprague orange drops vs. the Mallory yellow cans. It is also recommended that the overdrive gain pot be conductive type to reduce hiss.

It appears the avoidance of thermal noise is acheived by overrating the resistors---everywhere, the use of the higher quality decoupler caps, and the conductive pot makes the machine quiet enough. Well, we'll see.

Thanks, back to Smoke Rise.. Um...I mean the bench....