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iko 8th May 2009 12:19 AM

The simplistic Salas low voltage shunt regulator
I'd like to start a thread on this simple but IMHO very good design. Various changes have appeared in various places but it would be nice to have a thread dedicated solely to this subject. Here is the original schematic, and as time goes, we'll get a pcb for it and/or variations. A number of people have implemented this regulator and have praised it. Please share your experiences if you've done it, so others can benefit from it.

There is a long thread about the jfet phono stage also designed by salas, which can be found in the following link

in which the regulator was introduced first. If there are any people well versed in pcb design and would like to help, please step up.

Personally, I have implemented a few variations and can say that its performance, as far as I can tell, is very good. Besides that, it seems very stable (not prone to oscillating), easy to build, and with a low parts count.

Salas 8th May 2009 12:24 AM


We use a 2SK170 Jfet instead of R6 for a long time now. We call it the ''R6 mod'' in my Riaa thread as you know. Its measurably and audibly better that way.


Original presentation
& evaluation/explanation
Reflektor general idea

jameshillj 8th May 2009 05:30 AM

Hello, Salas and Iko,

Starting anew with a the well tested & complete circuit - this should get things off to a good start. Thanks for the confirmation about the lower noise and better sound - often other characteristics seem to be improvements but over a period, usually produce fatigue instead of good sound.

The CT rectifier system circuit is in the "Building the Ultimate NOS Dac with the 1541A" thread and @ post #2304 (4/12/08), #2347 (12/12/08), #2579 (20/2/09) & #2804, I think - jotted them down awhile ago.

I started a pcb, got complicated with the CT rectifier system and then got distracted with dac problems.
I'll go and trim it back to basics again and send it for perusal - I've never managed to work out a way to reduce the files sizes for inclusion here without badly blurring the outlines (even with jpeg), but perhaps somebody can advise about this.

I found that ---

... there are some very useful TO-220 mounting bars available that can also hold down 2 IRFP240 devices with one bolt (drill out centre thread of bar and screw down onto h/sink)

... stand the power resistors (parallelled m/oxides) up vertically or keep them well spaced above the board and away from other components - can be a problem with pcb orientation but a bit of common sense ....

... the caps DO effect the sound quite a bit and use the (NOS) Siemens Sikorel (68u/40v, 470u/16v - local supply) and some 470u/35v (from US) - best sounding caps of the lot (IMHO!) altho the SilmicsII are also pretty good too.
the Sikorels are all axial caps (lead each end), are quite big and so, end up standing vertical with no problems.

Hope this info is useful.

iko 8th May 2009 01:47 PM

salas, thanks for pointing that out. I was planning to post all of the variations, perhaps with some simulated results (ripple rejection and output impedance bode plots) so people can see the differences. I'll do that as I get time.

James, all comments of this type are helpful for anyone that is thinking of building it. Thanks! Had a look at the CT rectifier system in the DAC thread, but haven't wrapped my mind around it yet. It's definitely interesting. I'm not sure what effect it can have. Have you tried the regulator both with and without? I know we're talking about subjective experiences here, no problem.

Lumba Ogir 8th May 2009 02:15 PM

2 Attachment(s)
it`s not a big deal after all.

Melon Head 8th May 2009 02:58 PM

Thanks for starting this thread.
I hope to learn a lot hear. So simulations comparing this reg with other alternatives would be great.
I really would like to see the performance of the very simple BOZ power supply against this one.

Do LEDs make better voltage references than Zener diodes?

AndrewT 8th May 2009 03:21 PM


Originally posted by thanh1973
Do LEDs make better voltage references than Zener diodes?
if you need a Vref between 1.3V and 2.2V.

Two LEDs in series can work out better.
By the time you get to three in series there are advantages to using either.

iko 8th May 2009 03:26 PM

2 Attachment(s)
Here is the "R6 mod" regulator, and I will post before and after plots.

AndrewT 8th May 2009 03:30 PM

output.... resistor
150mA, R1 = 3r6
100mA, R1= 5r1
50mA, R1 = 9r1

iko 8th May 2009 03:33 PM

Before the R6 mod, line regulation

After the R6 mod, line regulation

Before the R6 mod, output impedance

after the R6 mod, output impedance

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