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Old 30th December 2001, 09:06 PM   #31
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Hello Grey,

Ive also come to this conclusion and Ill just put it together and have a look at it with the scope and a nice square wave........
I always think its an advantage not to be an electronics engineer when building amps cause I never know what isnt suppose to work, what can go wrong and whats impossible to have any influence on soundquality. .

happy new year to all of you,

william
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Old 30th December 2001, 10:03 PM   #32
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Quote:
Originally posted by GRollins
Actually an oscilloscope and a square wave at the input will do a very nice job of detecting any problems with ringing.

When I first started keeping bees, I read over twenty books on the subject. Every one of those books had at least one chapter on diseases and pests that can effect your bees. Dozens of nasty possibilities: American foul brood, European foul brood, tracheal mites, varroa mites, chalk brood...the list goes on and on.
Grey
Good analogy Grey that supports just what I'm saying. Grey, as a result of all that study, you have the knowledge that you can use should such a thing happen. Like all theory it gives you the background knowledge for use in the real world. The real world has taught you what will happen in your world and only your world. In other circumstances you may see other bee pests. The theory has to prepare anyone anywhere for possible situations.

And, no, an oscilloscope and a square wave generator at the input will NOT tell you if the power supply is ringing. It is not simple to detect this. There are methods, but they're not simple. Me, I avoid the whole thing by using simple capacitive filters and amplifiers that are well designed and that have good PSRR.

regards, Keith

This discussion started off as someone who wanted to know about the use of inductors in power supplies for solid state amplifiers. My advice is to forget it. He may want to try his idea out. Fine, that's his decision. There let it lie.
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Old 30th December 2001, 11:18 PM   #33
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William,
Go for it!
Some of the neatest things I've learned came about as accidents (yes, I've fried a few parts--who cares--we're not talking about living creatures that feel pain, just little pieces of metal and plastic). Theory is nice, but can paralyze you, because you're afraid to try anything, especially if you've never done it before. Theory says bumblebees can't fly, yet they do. Guess who's right, the bumblebee or the theorist. Poor l'il critter doesn't have enough brains to know that what he's doing is impossible, so he just goes and does it. Bravo, little bumble!
Should life deal you a wild card and your power supply rings...add more inductance, take some out, add a resistor, add some capacitance. <i>Play</i> with it. The operative word here is play. This is supposed to be fun. If you aren't having fun, take up bird watching or fishing or bowling...find something that does suit you.
Keith,
Next time I see Santa, I'll ask him to bring you a new oscilloscope next Christmas. Obviously, yours isn't up to the task.
In the meantime, I hear that there's a Burger King in Des Moines with a job opening.

Grey
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Old 30th December 2001, 11:48 PM   #34
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William
I agree with Grollins, go for it.
High Q for the PI filter, sure. But wat is regarded as high?
Don't waste time on the type of discussion like the glass is half full, the glass is half empty.
Build the thing, and do experiments. If you like a sneak preview (simulation) you can use a very nice little program from j.d.duncan called Power Supply Designer II (PSUD II).

http://www.duncanamps.com/psud2/

I did build my powersupplys for an ALEPH, HIRAGA, MONSTRE and JLH's always using a PI filter. They work like a charm.
After building the supplys I checked with PSUD and the results are very similar to the actual thing.

regards
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Old 31st December 2001, 02:42 AM   #35
jam is offline jam  United States
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Maybe Keith is saying that pi filtring works better on class A circuits where current draw is constant and not as well ia class B circuits.

Any comments Keith?

Cheers
Jam
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Old 31st December 2001, 09:20 AM   #36
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Quote:
Originally posted by jam
Maybe Keith is saying that pi filtring works better on class A circuits where current draw is constant and not as well ia class B circuits.

Any comments Keith?

Cheers
Jam
Well, it's nearly midnight and the entry to a new year. Off to see the fireworks shortly.

In this discussion, I've been trying to say several things. Possibly summarise as follows:
1. Power supply design is not a simple straightforward task.
2. If the current is constant, then ringing won't be excited. Jam is right and it's one of the things I've been trying to say.
3. Give it a bash. Don't assume however that a change is an improvement. It may not be.
4. If you want to modify power supplies, look at it this way. Would you modify the circuitry of an amplifier? If the answer is no, then remember that the power supply is part of that amplifier and has design criteria with which you're mucking about.
5. If you want to design something, first learn the theory. It gives you the background that you can use to make an effective job of the design. It introduces all the compromises that must be mad and tells you the basis of what you're doing.
6. By all means experiment. But do it from a background of at least some knowledge. That way you may advance the art.

And that's my last word on the subject ( I can see Grey wiping his brow and saying "phew!").

'appy New Year.
Keith
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Old 31st December 2001, 10:58 AM   #37
ergo is offline ergo  Estonia
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I've been reading the thread so far with much interest. Got to try the PI-filter some day...

I have a question though that is a bit of a jump to side but related to the discussion.

I was reading the "Rectifier Application Handbook" the other day and started thinking about LC filters. If I understood the theory correctly there is critical value of L with this configuration beyond which there will be current flowing through every diode in bridge at all times. Then this should be very desirable as the usual capacitive filter cause the diodes to only pass sharp waveforms of current and thus give unwanted impurities.....

Has anyone played with that idea and have some real life experience. I quess this is also only applicable with quite high and constant current demand as smaller currents require too large values of inductance.
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Old 2nd January 2002, 01:59 AM   #38
jam is offline jam  United States
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I have to agree with Keith this time. heh!

I have never had much luck with pi filters with class b or ab circuits due the changing current demands of these designs, at best they did not hurt the sound or helped little but most of the time they just screwed up the sound of the amp.

The pi filter works well with class a amplifier designs including preamps, tuners and dac's, the key being constant current demand.

Cheers,
Jam


P.S. Sorry Keith I will not be able to make your blood pressure rise this time, by the way how were the fireworks?
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Old 3rd January 2002, 11:06 AM   #39
Variac is offline Variac  United States
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Default remote caps

My Son o Zen will have separate pi filter power supplies.
I was thinking of having the second bank of caps in the pi filter
on board the amp instead of with the rest of the power supply
I figure that this way any very short term fluctuatuations in the average demand on the supply won't have to travel through the umbilical. Also it might filter out any noise the umbilical picks up.
Probably I'll add some film caps there later if the thing turns out OK. Any comments on this? Are both banks supposed to be similar in Mfd or can one be a lot larger?
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Old 3rd January 2002, 01:05 PM   #40
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Mark,
Having the second leg of the PI onboard is an excellent idea. If you're going to have cap banks of different sizes, make the second one (the one closest to the circuitry) the larger one.
I'm a big proponent of film caps, but have to say that the SOZ will give you less bang for your buck in that department than others. Why? Because the current draw from a differential is nearly pure DC (assuming well-matched devices and a balanced signal). I'd say to bypass the electrolytics with...oh, I dunno...say, .5uF to 1uF of film caps and let it go. More than that won't hurt, of course, but you're not going to get all that much sonic benefit from it.

Grey
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