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Old 16th January 2013, 03:29 PM   #8121
a.wayne is offline a.wayne  United States
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Originally Posted by gootee View Post
Sounds like a good idea! So we add capacitors, which should also lower the inductance a little. We could also use a thinner pcb, and/or a better hf material than fr4.

I will probably try that. I might have to order some pcb blanks if I don't have any suitable 1mm or thinner on hand. I do have "several" lots of large-ish electrolytics lying around, but will have to test them for suitability, at this point. And I do have access to high-end Agilent network analyzers. I'll probably have to solder an RF connector to the board, to be able to connect the analyzer, but I'll first do a little research to see how that should be considered.

I'm not so sure about dismissing the tweeters' requirements, although I suspect they'll be met well-enough. I am still harboring the suspicion that tiny inaccuracies in the transient response, including the tweeters, could harm the imaging. But having worked out the differential equations for what minimum capacitance is required and what maximum inductance (often connection length) is allowed, in order to provide the current necessary to reproduce an arbitrary linear or sinusoidal transient event, with a given accuracy in both time and amplitude, it seems clear that the lowest-possible inductance is desirable. So we are at least heading in the right direction. But it would probably be extremely challenging to not ruin the low impedance in the way the capacitor bank gets connected across the power output devices.
So no huge buss bars....?
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Old 16th January 2013, 04:12 PM   #8122
gootee is offline gootee  United States
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Originally Posted by a.wayne View Post
So no huge buss bars....?
Heh. Actually, maybe. If it was too difficult to have the cap array board go right across each pair of decoupling points, then maybe buss bars should be used.

Last edited by gootee; 16th January 2013 at 04:14 PM.
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Old 16th January 2013, 04:15 PM   #8123
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One of the most interesting things is to place an oscilloscope onto the power supply terminals of chips and see how effective the PSU is . As Crystal pointed out years ago the quality and placement of the decoupling capacitor is important ( shortest possible wires ) . I often add between 10 nF to 100 nF to chips . I always thought it did some good . Sometimes no amount of PSU upgrades will compensate for bad decoupling . I suspect most commercial products are less than ideal in this respect . The reason being they don't allow for hand soldering espeically with SMD ( SMD in itself is great ) . The old 100 nF to serve 10 chips is still the norm in some designs . Some use very low grade ceramic caps as someone said it would be OK in a book ( yes they are up to a point ) .COG/NPO works better ( almost as good as silver mica and very cheap ) . I do break rails and add inductors sometimes . Do use a scope if you do. Often " better " is far worse .
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Old 16th January 2013, 08:23 PM   #8124
fas42 is offline fas42  Australia
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Originally Posted by nigel pearson View Post
One of the most interesting things is to place an oscilloscope onto the power supply terminals of chips and see how effective the PSU is .
An even more illuminating experience is to drive an audio system with the "signal" in the power supply. Using a capacitor to decouple, the power supply becomes an audio input, and what a glorious cacophany of "music" can be heard! Especially with a power amp under stress, you can "hear" the power supply regulation collapsing once you put the boot in ...

Frank
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Old 16th January 2013, 08:29 PM   #8125
fas42 is offline fas42  Australia
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Originally Posted by a.wayne View Post
Well how's the art , i plan on using caps close to the outputs seperate and additional to the mains .

What ratio ...?
Rather than repeat myself, check out my responses to the chap who asked this question: Mundorf M-Cap Supreme as bypass cap?. We covered a fair bit of ground on the ins and outs of things, satisfactorily I believe ...

Frank
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Old 16th January 2013, 08:35 PM   #8126
jcx is offline jcx  United States
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or you could design with PSRR, PS variations with load in mind...
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Old 16th January 2013, 10:30 PM   #8127
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just watched an 1979 video interview with conductor and composer Sergiu Celibidache (which btw was born in the city I live in). he basically bashed sound reproduction as unable to convey the intention of the composer (in more colorful vernacular). I translated a small portion to English:

The so-called technical advancement is a complete mutilation of the true connections between sound and movement. Sound is in movement. But you are projecting it in a completely different reference system. And it ends up not maintaining either of the human measures which gave it life. You and your new equipment... amplifiers and stereophonics, you create sonic values, sonic impressions but never the ones carrying the composer's idea, the way he heard it. Thus, by the nature of things, you are departing from the essence of music.

wonder what he would've said, had he heard a good stereo, and I'm not being sarcastic.
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Old 16th January 2013, 11:03 PM   #8128
a.wayne is offline a.wayne  United States
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Originally Posted by jcx View Post
or you could design with PSRR, PS variations with load in mind...
Zmin - 1 ohm ...

Quote:
Originally Posted by fas42 View Post
Rather than repeat myself, check out my responses to the chap who asked this question: Mundorf M-Cap Supreme as bypass cap?. We covered a fair bit of ground on the ins and outs of things, satisfactorily I believe ...

Frank
Thanks will give it a look over ....
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Old 17th January 2013, 04:53 AM   #8129
gootee is offline gootee  United States
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Originally Posted by nigel pearson View Post
One of the most interesting things is to place an oscilloscope onto the power supply terminals of chips and see how effective the PSU is . As Crystal pointed out years ago the quality and placement of the decoupling capacitor is important ( shortest possible wires ) . I often add between 10 nF to 100 nF to chips . I always thought it did some good . Sometimes no amount of PSU upgrades will compensate for bad decoupling . I suspect most commercial products are less than ideal in this respect . The reason being they don't allow for hand soldering espeically with SMD ( SMD in itself is great ) . The old 100 nF to serve 10 chips is still the norm in some designs . Some use very low grade ceramic caps as someone said it would be OK in a book ( yes they are up to a point ) .COG/NPO works better ( almost as good as silver mica and very cheap ) . I do break rails and add inductors sometimes . Do use a scope if you do. Often " better " is far worse .
Nigel,

I am just a beginner. But you might find this interesting:

Power Supply Resevoir Size

And this:

http://www.diyaudio.com/forums/attac...om3a_33kuf.jpg

Highest regards,

Tom Gootee
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Old 17th January 2013, 06:39 AM   #8130
dvv is offline dvv  Serbia
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Quote:
Originally Posted by gootee View Post
Nigel,

I am just a beginner. But you might find this interesting:

Power Supply Resevoir Size

And this:

http://www.diyaudio.com/forums/attac...om3a_33kuf.jpg

Highest regards,

Tom Gootee
As I understood it from an admittedly brief lookover (no time now, will dive in later on), you got 53,050 uF per channel for a nominally 100W/8 Ohms amp?

Tom, as I see it, no amp ever made satisfied this criteria, or perhaps a few wildcard products did, but I never heard about them.

By such values, even in monetary terms, it's time to think about fully electronically regulated PSUs. These days, power devices are cheap, so the real penalty one has to pay is the added space requirements for the regulator heat sinks.

It would also be very interesting to compare two identical amps (in terms of the audio circuit), the only difference being that one is fed off capacitor filtered lines only, and the other used split supplies, with the input stage and VAS being fed off separate, slightly higher but fully electronically reguated lines.

This is a concept I have been using for well over two decades now. I adopted it after maing two very simple, low power (app. 30 W/8 Ohms) amps. The one with separate power supply lines was very clearly the better one, more focus, more definition.

Having said that, I must point out one very frequent caveat - even when people do use full regulation, i.e. electronically regulated power supply lines, but only one set of + and - for each channel, for resons I fail to understand they seem to think they can start skimping on the electrolytics preceeding the regulator. In my experience, this is wrong. You can safely SLIGHTLY reduce the cap size, from say 27,000 to say 22,000 uF, but not more as this will become audible,subtly at first and progressively more and more.

A friend, one Dan Banquer of Boston, who used to own a company named R. E. Designs, was (for family reasons, he is no longer in manufacturing) one of the few people who understood this. He used fully regulated power supply lines, developed his own regulator and so forth, but still used 33,000 uF caps for a nominally 80W/8 Ohms amplifier.

Any experience with that, Tom? I'd love to hear about it, please.
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