HV Maida Regulators...

[jgrg1]

Hi,

I'm in the design phase of building a new guitar valve amp, and I'm looking at regulating the HT using a Maida regulator. My requirements are 400V DC @ 200mA as I plan to use it to supply HT to the entire amp (yes, I know the PP rejects common-mode noise, but if I have a well-regulated HT, why not use it). Having read the Morgan Jones book, I figured I'd try to design one for my higher voltage and current requirements. The amp will be an 2xEL34 PP with 5xECC83s. I already built 2 other amps (a 2xEL34 and a 4xEL34 PP).

See attached image for my PSU design (which has been ripped off of various posts here and from Jones' book).

1. Can anyone confirm my reasoning:
I have a 310Vac secondary, which I reckon will give me around 437V out (including diode drops). Given my C1 filter, the Vripple is 9Vpp at 200mA draw, which means the DC Vin will be around 432.5V +/- 4.5V.

Now, I'm having a little trouble fully understanding the operation of the maida regulator as there are some conflicting equations on the web. In particular, the exact formulae used to calculate the values of R4 and R5 in my schematic. My understanding is that (please confirm?):

Vout = (1.25V / R4) * (R4 + R5)

Following Jones' logic, he's used a high value R5 of 220k to reduce the power dissipation through it, and he then sets R4 to the appropriate value based on the equations I've shown in the diagram. So for my 400V out, R1 should be around 709 ohms.

2. The calculation of R3 (the resistor that sets the current for the D1 12V zener) I've also lifted from Jones' book. In that, the current should be above the zener current of the diode (5mA). So I make that a Vdrop of 432.5V in and 400V out, less the 12V zener voltage of 20.5V. If I want 6.5mA through the zener, V=IR gives R3=3076 ohms. So I'd use R3=3k ohm for 6.7mA. Is this correct?

3. The only other thing that has confused me is the presence and value of R2. From what I read, this seems to act as a current limiter for the IRF840 pass device. Is that correct? And if so, what value should I use for my current requirements? I couldn't find any description in Jones' book of what value to use. Also, what power rating should it be.

4. Should C2 be dropped?

5. Does D4 have any protection effects at all (I've seen it in various maida schematics)?

6. Also, is the IRF840 a suitable pass device?

Cheers all

[diagrammatiks]

might want to read this study on the effects of ripple in guitar amps before putting down all the work for hv regulation.

http://www.emsp.tu-berlin.de/fileadmin/ ... se_NTl.pdf

[jgrg1]

Is there an english translation?

[diagrammatiks]

whoops my bad I thought that was the english link.

here's the summary.

http://ampbooks.com/home/classic-circui ... AB-ripple/

lemme see if I can find where I read it.