Anyone build a Minimal Reactance PSU?

[Bas Horneman]

Hi,

I recently added a Minimal Reactance psu by Dave Davenport has made for the Raleigh Audio Line Stage. I recently added his psu to my RALS and it has made a huge difference.
Here is an early version of http://www.raleighaudio.com/chapter_5.htm the design. the current design is more advanced with hybrid shunt reg. I.e. lm431 and 6n1p...(Something like this has been published by John Broskie as well and is therefore in the public domain...)

The MR psu is state of the art WITHOUT the cost of a choke or big expensive caps like BG of Elna Cerafine. It really is a fresh and clever way do make a psu for a low current valve amp...like a preampflier..and I am suprised I have seen very little on the web on similar concepts...apart from Allen Wright's superreg and Emile Sprenger's version of it...but that is waaay more complex and expensive.

A number of people are going to build an Aikido and have asked me to design or help with a psu for the Aikido.

Obviously I can't steel Dave's design and was hoping someone could "supply" us with his or her version of a MR psu?

Regards,
Bas

[Bas Horneman]

By the way...here seems to be an alternative for those that want an Aikido psu pcb Steve Bench's psu for his no caps phono amp

220vdc/50mA per channel..

http://www.intactaudio.com/forum/viewtopic.php?t=93

[mach1]

Bas,

I have used one on my 1LE3 pre for some time. It uses an aerovox 2uF oil cap - pimm CCS - Broskie 5687 / 431 shunt reg followed by individual Pimm CCS' to each plate. There is one additional sangamo 0.25uF oil cap just before the plate CCS' for stability. Total psu capacitance is 2.25uF.

Very nice indeed - very fast and transparent with a super solid bottom end.

I believe Gary Pimm had been using fairly small value caps / chokes before CCS-shunt reg-CCS psu's for some time before the minimal reactance article was published However, the minimal reactance psu took this concept to the limit and provided a sound theoretical base for its implementation.

A great thing about these psu's is that you don't need a choke at all and can afford to use really good quality caps.

Has anybody used one for a power amp yet ?

[wa2ise]

I don't see the point of using a vacuum tube rectifier, as seen in the schematic http://www.raleighaudio.com/ps_schematic.htm
as the mosfets would "filter" out any "tube magic" from the tube rectifier. Also the power on time delay circuit takes care of avoiding full B+ on preamp tubes not up to heat yet. So I'd use some good silicon rectifier diodes in place of the tube rectifier.

Something else to keep in mind is that the power disippated in the pass mosfets will be less if the ripple is allowed to be high before the mosfets.

[Bas Horneman]

as the mosfets would "filter" out any "tube magic" from the tube rectifier

That is what I thought as well..but listening to it ...you can even detect changes in the caps that are placed before the CCS.

But I would agree that it is subtle, and while one is doing the cost effective thing...something like BYV95D or something with RRSF and a snubber would be a cheaper solution...particularly in the long term.

[thoriated]

Of course the source impedance of this type of supply is high with its attendant limitations unless a shunt regulator or capacitor is added at its output to, for instance, limit crosstalk between different stages supplied from it. I'd probably dump the mosfet and use a tube current source, anyway

Also, I find many references to a DN2470 & DN2540, but hardly any to a DN2450 on the web.

[mach1]

wa2ise

On the contrary, I believe a minimal reactance psu constructed using Gary Pimm's latest CCS design and a decent shunt reg (preferably with a tube carrying out ac reg duties) lets all the natural magic intrinsic in a tube shine through unhindered.

If you want to give it a go try without going all the way, try using IXCP10M45S current regulators in cascode mode - in my opinion they are every bit as good (if not better than) the DN2540 in this application and are also better able to dissipate heat. Plus you can actually buy the things (the DN2540 has now been discontinued and was always extremely difficult to source).

I totally agree with Bas that the character of caps in the psu are quite audible in this topology. I have found that even the type of cathode bypass cap used in the shunt reg is critical to the overall sound.

BTW Bas, I thought one of the main attributes of the Aikido topology was its excellent psu rejection qualities - perhaps the earlier version of the minimal reactance psu using a resistor as the shunt element would suffice? If you use the 10M45S as a CCS perhaps there may be sufficient differentiation from the published circuit to allay your conscience.

[Bandersnatch]

Hey-Hey!!!,
I have tried minimum reactance PS design. Maximum reactance sounds betterevery time. Small C-L-C sounds better than just C, and L-C is even better. This all CSS-fed shunt regulated PS with VR tubes.

It is a neat exercise, but it has not been my preferred sol'n.
Regards,
Douglas

[thoriated]

The supposed primary advantage of a 'minimal reactance' circuit can be also gained with a small amount of series inductance before the first shunt capacitor at a much higher potential efficiency and without injecting nonlinear silicon parasitic capacitances.

ps:

x-post with bandersnatch

[Bas Horneman]

Hey Douglas! Long time no see. Are you banned from AudioAsylum or something?

It is a neat exercise, but it has not been my preferred sol'n.
Regards,
Douglas

Ofcourse..so many people so many tastes..

I've got to admit that I tried making my own version of Dave Davenport's CCS...and was not too happy either. Then I got his real board with the IXS parts and tube shunt reg. It was a definite step up in transparency and everythin. Anyway..I'm not trying to convince you....just my experience.