The Maida Regulator

I already built a Maida-style regulator for my tube phono preamplifier, but I didn’t develope a PCB for it. Now, searching in my hard drive, I found a design I did some time ago, that never saw the light. So I post it here in the hope that someone finds it useful!

This regulator is well suited to tube preamplifiers and similar low current loads. To adapt it to heavier loads, perhaps you should remove (or reduce) R3, remove C1 (with low currents those are useful to obtain higher noise rejection) and increase heatsinking for the power mosfet. In this case however, I figured that a standard heatsink such as this pictured here will be enough.

It all started with this:

You can modify the output voltage by tweaking R6: with the LM317, there’s a fixed 1.25V between the output pin and the adjust pin. I used 1kOhm resistor here between those pins, to obtain at least over 1mA in the divider chain: output voltage is

Vout = (1.25/R5) * (R5 + R6)

In reality in R6 flows also a little standby current for the LM317, about 50-100uA, so the output voltage will be a 5-10% higher. Use a 1W resistor for R6, it will get barely warm.

Note: make sure the regulator’s output gets proper loading, at least 5-10mA, or it could lose regulation.

Please note that both the metal tabs of the mosfet and the LM317 are at HV voltage. Do not touch them or let metal objects touch them: you should use mica or silicon insulator between the mosfet and the heatsink, or you can use a plastic package isolated mosfet.


Parts:     Values:                              Parts:     Values:                                                    Parts:     Values:   

C1       100nF 400V                        
Q1       IRF840 or similar HV power mosfet            R3       47ohm 1/2W                  
C2       1uF 400V                            IC1      LM317                                                     R4       330ohm 1/4W   
C3       470nF 400V                        IN          screw connectors                                     R5       1k 1/2W   
D1       1N4007                              OUT      screw connectors                                     R6       180k 1W (see text)    
D2       1N4007                              R1       100k 1/4W                                                R7       4.7ohm 1/4W   
D3       1N4742  12V Zener             R2       100ohm 1/4W