Regulators

[jam]

Jonathan,

You are correct about the capacitor across the zener. I usually use 1uf in that posisition, too large a cap tends to squish dynamics somewhat. I shall try what you suggested.

The Kubota circuit seems to have a more extended high end than the shunt. About pre regulation, would you use the same type of regulator for the pre? I still have to find one that is transparent.
What are your thoughts on non-feedback type regulators?

Regards,
Jam

P.S. Please e-mail me if you want the schematic of the Primare amplifier, at

x-600@msn.com

[jcarr]

Jam: I haven't noticed any particular sonic problems when larger-value capacitors are used for noise absorption. But I do find that the type of capacitor makes a noticeable difference. Here my experience is that tantals and oscons tend to sound better than equivalent-value electrolytics, probably due to the impedance curve.

>The Kubota circuit seems to have a more extended high end than the shunt.<

If you are talking about the perceived sonics, I think that the issue with a super-shunt is that the bottom end tends to win out over the top end, leading to the _impression_ of a less-extended high end. But I don't think that the Kubota (at least as Takashi Kubota designed it) is any better on the top than a good super-shunt, and the bottom end is almost certainly less impressive.

>About pre regulation, would you use the same type of regulator for the pre?<

If the primary regulator is of a linear type, I would also suggest a linear preregulator. If the primary regulator is of a shunt type, I would suggest a constant-current preregulator (which gives you a super-shunt). Now if you take a linear primary regulator and give it some kind of bleeder mechanism at the output, I reckon that the preregulator could be of either linear or constant-current type.

>What are your thoughts on non-feedback type regulators?<

For reasons of sonics as well as measurements, I find that my general preferences are for feedback circuits. However, simply applying feedback is never a good idea. Analyzing the phase margins and carefully dialling in the proper amount provides the best results, in my experience.

>Please e-mail me if you want the schematic of the Primare amplifier.<

Thank you for the kind offer. My problem is that I have first have an exceedingly complex preamp design that I need to finish, so it is undoubtedly better that I avoid too many possibly distracting avenues right now.

I would, however, be very interested in poring over it at a later date, when I _don't_ having any deadlines looming immediately ahead.

best, jonathan carr

[carlmart]

What about using something like the OP549, or a higher voltage capable IC, and building a Sulzer/Jung/Didden supply around it?

Has anyone done that? How does it compare with a shunt or supershunt regulator?

BTW: I was looking for simplicity when I started this thread with a TL783 question. Has anyone used the 783?



Carlos

[ALW]

I'd like to say thank you for the information and thought-provoking ideas you've posted above.

I also agree it's important not to get hung up on any one performance parameter, save to say that dynamic behaviour, in a very general sense, relates to all the possibilities and is important in most applications I've encountered.

Time to play soldering irons I think...

Andy.

[jam]

Jonathan,

Thanks for your insight into the various aspects of regulation.

I actually use a 1uf tantalum across the zener.

You well may be right that the percieved high end on the Kobuta regulator is a function of it's bass qualities compared to a shunt regulator. I need more time to experiment.

You must working on version 5.0 of your pre-amp, buy the way Hi-Fi + gave you an excellent review of your current pre-amp, you could tell , even if they did not admit it, it was their favourite by a pretty big margin.

Regards,

Jam

[Christer]

Originally posted by jcarr

One worthy idea that I don't see used too frequently is to make a regulator that is fed with a constant-current source (the value should be equal to the maximum amount of current drawn by the load circuit, plus some margin). No matter what the load circuit does, the regulator will always draw a constant amount of power from the power transformer.

This is an interesting idea. It reminds me of another way of
achieving the same goal that I have been thinking about.
It is not a new idea -- it has been used to make "surveillance-
safe" computer equipment. Except for certain cases where
we get the effect as a bonus, eg. in balanced amplifiers, I
don't know if it has been used in audio, however.

The basic idea is to introduce complementary dummy
circuitry to make the supply-current demand constant.
As an example, consider an amplifier with a differential
input stage followed by a non-differential VAS and where
we want to regulate the supply to these two stages.
In this case we have access to both inverted and non-inverted
signals from the input stage. We could then introduce an extra
dummy VAS which is fed with the complementary signal.
Introducing also a dummy OPS as a load for the dummy VAS
may be going overboard, but one could probably make a
dummy load which behaves similarly to an OPS. I suppose in
the case of a BJT OPS a few resistors and diodes will come
close enough. The net result should be that the input stage
and VAS's (both real and dummy) will draw an almost constant
supply current. It should then be a farily easy job for a linear
regulator to regulate the voltage.

Although this may be somewhat costlier and more complex
than using a shunt regulator to achieve a constant current
draw, I should think it possible to get a better result , since
we are actually building a shunt regulator into the amplifier
by "cloning" some of the circuitry.

[jcarr]

Christer: I completely agree with your line of thinking (would be surprising if I _didn't_ agree).

BTW, I don't know if the concepts have been incorporated into any audio product, but they certainly have appeared in an experimental audio design. Around 1990~91, Yoshikazu Tomita, a free-lance engineer who designed some amplification products for AudioCraft, created a MM phono-stage circuit with a shunt-regulation mechanism incorporated directly into the amplifier topology. Tomita died before he could turn his design into a product, but the schematic was picked up by Rajio Gijutsu, given to Shin Nakagawa, and Nakagawa published an article on this circuit.

I built this circuit, and it was definitely worth the effort. From memory, despite my using a very generic power supply, the sound was unexpectedly good in the bottom end. I also recall that this topology tended to reduce the sonic differences between various types of power supply capacitors.

I am too busy with other design work to post anything now, but in a few weeks, I may try to dig the schematic out of my files, redraw it, and post it as a gif.

BTW, the January 2003 issue of AudioXPress had an article by Mark Kelly on heater power supplies for DHT tubes. In this article, Mark discussed current regulation, series regulation, shunt regulation, and series-shunt regulation. Although there was nothing new about Mark's ideas, the interesting thing was that his schematic examples incorporated commercial ICs to create regulators that were conceptually interesting, yet had low parts-counts. I think that this article could be a good way to get acquainted with the concepts of current and shunt regulation without getting in over your head on the design, construction and debugging issues.

Unfortunately, Mark did not go so far as mentioning constant current-shunt regulation (aka "super-shunt"), but it shouldn't require much effort to make this next step.

best, jonathan carr

[Werner]

Originally posted by Christer

The basic idea is to introduce complementary dummy
circuitry to make the supply-current demand constant..

I do this in the front-end of my JFET phonostage. The circuit my even be on the breadboard right now, but as I have too many little projects going on right now, this one is dormant.

Sorry for the crappy schematic quality, but Q9 is the FET doing the trick.

[AKSA]

This idea has strong merit and I have seen it before, I believe in a US magazine.

Current source from power supply; voltage regulated shunt element, sum of shunt and load currents always a constant (conjugates). However, I have found CCS to be quite susceptible to input ripple; they don't like it, and it really should be decoupled out. The CCS is not the electronic firewall people imagine it to be.

I suspect too much is made of constant voltage output. We go to endless lengths to control voltage with huge NFB loops in active supplies; I suspect we lose out on speed because the pass element, in most cases, is in common emitter. If we placed the pass element in common collector (emitter follower), then I suspect the transient response of our supplies would be superior. I do this in all my power supplies and find it sounds much superior to the traditional active supply in common emitter.

Cheers,

Hugh

[Fred Dieckmann]

Umm...... The pass element in most regulators is an emitter follow or source follower to take advantage of the low open loop output impedance, giving lower output impedance for the same amount of feedback. I have seen common emitter mostly in low drop out regulators with the corresponding compromises in transient response and output impedance. Both the series and shunt regulators posted in this thread by Mr. Carr contain either emitter or source followers.

"However, I have found CCS to be quite susceptible to input ripple; they don't like it"

Hmmmm.... that's the whole point of using a constant current source is for its ripple rejection. An RC filter is an excellent idea on both series and shunt regulators since PSRR decreases with frequency for all regulators due to limits in gain bandwidth for all transistors. PSRR ratio is as or more important than output impedance and a RC filter of the input of a regulator is an excellent way to increase PSRR as frequency increases for a regulator. It even works on raw (non regulated) supplies for power amplifiers.

There is still lots of work to be done on regulator circuits and their design can have as much to do with sonics as the actual amplifier or preamplifier circuit. as with amplifiers, intelligent use of feed back and simple linear circuits may be the way to go despite having higher output impedance than the high feedback regulators typically used