The simplistic Salas low voltage shunt regulator

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iko

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Joined 2008
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.

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

http://www.diyaudio.com/forums/showthread.php?postid=1665552#post1665552

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.
 
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

Ex-Moderator
Joined 2008
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.
 
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?
 

iko

Ex-Moderator
Joined 2008
Re: Re: The simplistic salas low voltage shunt regulator

gallon said:


Are we really sure that Salas is simplistic?

The choice of wording is his, so I comply :D

Andrew, I think the community would definitely benefit from a battery of real life tests; I don't know Jan well enough to impose such a task on him, and also don't know if he's interested in this but would definitely appreciate any help from an experienced man like him. I know salas ran some tests with his super duper sound card. You may find those results in his simplistic RIAA thread. Alas, my equipment is not sensitive enough for such tests.
 

iko

Ex-Moderator
Joined 2008
The circuit in post #8 has been built by quite a few people. That's the version that I would recommend to anyone who is interested in this.

However, tweakanitis is a heavy burden for one to bear, and personally am heavily infected. The variation shown below offers a slightly better output impedance in the higher frequency, including audible range. In the bode plots below V(outa) is the circuit of post #8, and V(outb) is the circuit below. Note that higher idle current results in lower output impedance across the (almost) entire frequency spectrum.

Note, this is highly experimental and AFAIK this circuit has not been implemented yet. So, with a 1R resistor, the shunt mosfet passes 676mA, and is supposed to dissipate about 15W. We can perhaps agree that one that is willing to do this may not be all there in the sanity department, but hey, I am planning to try it out soon.


reg-salasiko-comp1a-zout.jpg


Edit: typo fixed.
 

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Back again Ikoflexor,

Yes I did try it both ways ! The CT circuit, that is!
A brief genesis. The first supply was a simple C-R-C with good bits, added the Cmx, then the ZenMod "Shunty" series reg and then the poor Toole shunt - in the middle of this, tried the Minnesotta unit (not bad at all!) and some other variations.
Then the lashed up Salas, removed the Series Reg (you were quite right about that), and set about assembling the DOA unit and the +/- rail shunt (Salas - post 309) and played about with the different caps for sound.
Being quite mindful of Jan's advice about low ESR caps on output, I was quite pleasantly surprised to find the Sikorels, Silmics or FCs didn't cause any problems in the spaghetti patch - may not behave the same with a good pcb..
The sound was extremely good in my opinion, with a NOS dac source and Pass X2.5 preamp (the DOA still needs a buffer for the lightspeed)

Then I added that weird collection of bits called the Charge Transfer circuit between the 2 supply caps and the whole system became dead silent and much more detailed with no "grain" at all. That's when I heard all about the problems in the source - got a loan of a couple of good players to make sure (quite like that Linn CDP!)

So YES, the CT circuit is worth the trouble - I'm surprised we haven't heard from Murcurio before now - he's done quite a bit of work on it and uses it on his power amp, too.

Now, the pcb.
Using the Circuit above on your post #8 as the starting point, (and let's see if we can stick with the same component numbers all the time) there are a few questions to include some variations already tried.
1. One pcb for + and - rails?
2. Using inverted 2skk170s rather than j74? or other devices, pinouts?
3. pads for a k170 option for R10?
4. extra Resistor as per your new Cct in series with C1 or is that a SIM thing?
5. Is there a Resistor between j1 source and 0v?
6. Is there to be a Resistor between the Shunt M2 and 0v?

I would like a small adjustment to the voltage - about 0.5 volts to compensate for zeners, correct for amp offset, etc, etc. Would a small pot (50R?) between zener and rail stuff up the performance?
Could you check this out with your magic circuit cruncher thing!!

Suggestions are MOST WELCOME - I'll start out with the extra tracking that we learned about with the Toole shunt layout and see what happens.

I'll get started into the pcb tomorrow (or today actually!)

For now ... Jh
 
AndrewT said:
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.

I'm curious . . . is there any reason not to use any of the dedicated Vref's that are available from Linear Tech, et al., as opposed to diodes or LED's? I realize that there's a small cost issue, but those chips aren't exactly expensive. Are there other issues, (fidelity?), that I'm not aware of?

Thanks.
Artie
 
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Paid Member
Artie said:


I'm curious . . . is there any reason not to use any of the dedicated Vref's that are available from Linear Tech, et al., as opposed to diodes or LED's? I realize that there's a small cost issue, but those chips aren't exactly expensive. Are there other issues, (fidelity?), that I'm not aware of?

Thanks.
Artie

I preferred the simple and widely available Zener solution. Somewhere I have read that it is even better, but I have not tested.

Its a finished project as much as I am concerned. Many people are very happy with it. But of course its up to you guys if you want to test it with more elegant additions or performance boosting twists.
 
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Re: Re: The simplistic salas low voltage shunt regulator

gallon said:


Are we really sure that Salas is simplistic?

Its a simplistic circuit concept. I made it so to pair the simplistic Riaa.
Its good trade off against parts count, cost, time, lends itself to P2P etc. It happens to give statistically good subjective results also.
Its accessible to the simple DIYer. Nothing like a super circuit or a new idea. No claims here.
 
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