Interesting power supply design...

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caps

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Jun 7, 2004
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Check this out:


http://www.tnt-audio.com/clinica/ssps2_e.html


Makes alot of sense for the most part, Im interested in what the knoledgable folk here think.

One thing that coonfuses me though, he states as follows:

"For this to be so, one also needs dedicated transformer secondary windings, for a stereo amp a total of four, rather than the classic two. Obviously, while good and with many advantages, this is a considerably more expensive design."

four sec.'s for stereo operation, how so? Again, sorry for the newb question, just trying to expand the knowledge, gotta start somewhere.

:grin:
 
This type of P.S. is mostly used for SS power amps where the amperage requirement is very high. Actually the main reason for the dual secondary setup is to facilitate the limitation of the rectifier, thus two is used, and for excellent stereo imaging dual power supplies are best, so what the guy is suggesting is a transformer with one primary winding and four secondaries, so that is two secondaries to each amplifier channel.
 
I've used independent windings and rectifiers etc. like this to facilitate the use of identical regulator designs following. The outputs then get combined in series after regulation. This allows the use of identical preferred devices or discrete regulators rather than the symmetrical but inherently mismatched positive and negative regulators.

One of the (small) advantages to the independent bridges: it minimizes any residual d.c. in the windings due to imbalances in the standard center-tapped bridge bipolar supply arrangement. However you incur twice the diode drop loss, so noticeably lower efficiency at lower voltages.

For tubes? Sure, nothing wrong with it except complexity. Also, for a lot of tube circuits you don't really need regulation, so the first rationale mentioned is irrelevant.

BTW, note that the author is incorrect when he sort-of alleges that the diodes in a bridge assembly like he shows are on a single piece of silicon. They are not---they are just individual axial parts in a sea of thermally conductive epoxy, and there is no matching done other than by virtue of coming from probably the same production run of individual diodes. It's true that the shared heatsink, epoxy, and proximity will help them stay at the same temperature.
 
i have used this arrangement also.. most recently the Gainclone chipamps.

It works well, probably *better* than a single bridge but certainly not a night/day difference. In fact i doubt anyone will even notice a difference unless you have a scope on it. To counter the diode drop at lower voltages and of course benefit the diode recovery noise issue, use power schottkys.
 
[quote author="Svart"]i have used this arrangement also.. most recently the Gainclone chipamps.

It works well, probably *better* than a single bridge but certainly not a night/day difference. In fact i doubt anyone will even notice a difference unless you have a scope on it. To counter the diode drop at lower voltages and of course benefit the diode recovery noise issue, use power schottkys.[/quote]

Yeah, Youd prefer to use power schottkys over a self contained bridge? Due to the increased speed of the schottkys?

And can someone please explain why tube supplies often dont use/need regulation ? Thanks guys.
 
read up a little on the reverse recovery of the standard silicon diode and compare it to the recovery of the Schottky/Hexfred diode and you'll see why they are more ideal for this application.

As for tube supplies not needing to be regulated that has more to do with the way tubes work internally, however I am not the person to ask about that, I am sure someone who knows more about valves will come along and answer that for you.. but I can tell you that most power supplies for tubes AND most sandstate(solidstate) parts don't *need* to be actively regulated as long as you can supply stable AC input to the psu and get solid DC out of it.
 
Our designer is confusing a whole load of parameters when he starts trying to justify his separate pos and neg supplies.... crosstalk is as much a function of power rail rejection as anything else, and to talk about ground planes adds to the confusion! The design engineer needs to have a good knowledge of what 'ground' lines carry what current; the golden rule is that 'ground' is never ground! True ground is that Kirchoffian point where zero current flows.... if everything makes its own way to that point, then you have an ideal situation.
There is similar confusion about capacitor inductance.... It's true that electrolytics exhibit inductance; that's why we by-pass them with smaller value caps that don't!
 
[quote author="TedF"] that's why we by-pass them with smaller value caps that don't![/quote]


Given this... it wise to always bypass a big smoothing cap with something like .10uf cap? Or would it only be done if the current draw in the circuit is expected to be constantly changing?
 
If a big cap is called for, then it's most likely that the current through it keeps changing. Adding a small cap across the electrolytic just makes it look like a 'better' capacitor; that is, one that retains the characteristics of a capacitor at high frequencies as well as low.
It's certainly a good idea to add that small cap wherever a big electrolytic is used. It's particularly important in power supplies, regulators all too often have stability problems at high frequencies, and failure to damp the circuit with say a 100nF cap across the output, can produce noise in audio circuits that's difficult to trace.... unless you know where to look! :oops:
 
As for tube supplies not needing to be regulated...that depends what you're trying to do. Most low-powered tube circuits (preamps, EQs, etc.) have poor power supply rejection, so sags in the plate supply rail will affect the sound. The reason many people leave such rails unregulated is that they're designing tubed circuits with the express intention of adding colorarion, and the sagging rails contribute their share. If you regulate the rails, you can make some very low-coloration circuits out of tubes, which I happen to like.

Power amps are a different story. Almost no one regulates the supplies of power amps, because it's such a pain in the ass -- you have to, essentially, build a whole 'nother power amp to run the supply. This applies to tubes as well as to solid state designs.

Peace,
Paul
 
we must also look at the system as a whole. In a linear PSU it is of strong importance to use a proper transformer for the application. If the trafo is marginally sufficient in size then a larger than average current draw would not be helped by just adding larger capacitors after they have discharged in their attempt to suppliment the needed current. Also, a straining trafo is going to also cause a number of problems besides the obvious overheating/burning up, one of which is noise. In this case more caps or different caps will only be putting a bandage on a serious problem.

:thumb:
 

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