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Old 23rd June 2012, 10:26 PM   #6321
SY is offline SY  United States
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Quote:
Originally Posted by Pano View Post
If I know how much power (or current) my amp is likely to supply, then trying to figure out the size of the power supply in joules per watt or farads per ampere or whatever is lazy? It's wanting The Answer handed to me?
You've conflated several things there (like power and current). John has (and I congratulate him for being very clear and succinct in his answer) explained that a watt in load A is not that same thing as a watt in load B- the actual load range being designed for, including load angle and magnitude range versus frequency, is critical in making these estimates, not just "microfarads per watt." All amps do not have the same power supply rejection. All amps aren't required to have the same noise. All amp topologies do not have the same power supply modulation or the same voltage rails. And on and on.

Design rules are nice, but what was pointed out is that a rule for "microfarads per watt" is a meaningless one without context. The analysis to determine minimum capacitance for a given design and performance target is straightforward, so why not do it?
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Old 23rd June 2012, 10:27 PM   #6322
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by jacco vermeulen View Post
Suppose you had to pick between a car that has an engine with high torque and low revs, and one with low torque and high rpm, identical horsepower ?

Which would you choose ?
Depends on the weight

technically higher rpm means more speed , gearbox is TQ converter, now amplifier , I want big stiff supply , err , Ahh , for bedroom system too...

Last edited by a.wayne; 23rd June 2012 at 10:29 PM.
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Old 23rd June 2012, 10:32 PM   #6323
bcarso is offline bcarso  United States
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Quote:
Originally Posted by SY View Post
You've conflated several things there (like power and current). John has (and I congratulate him for being very clear and succinct in his answer) explained that a watt in load A is not that same thing as a watt in load B- the actual load range being designed for, including load angle and magnitude range versus frequency, is critical in making these estimates, not just "microfarads per watt." All amps do not have the same power supply rejection. All amps aren't required to have the same noise. All amp topologies do not have the same power supply modulation or the same voltage rails. And on and on.

Design rules are nice, but what was pointed out is that a rule for "microfarads per watt" is a meaningless one without context. The analysis to determine minimum capacitance for a given design and performance target is straightforward, so why not do it?
Yes. And we have so many tools now! Over-reliance on them is inadvisable, as it provokes laziness and won't help one determine if a simulation is sensible or not. But with a good foundation in basics going in, and decent models, what power!
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Old 23rd June 2012, 10:33 PM   #6324
a.wayne is offline a.wayne  United States
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What pano wants , as the rest of us, is....

What is Sy's formula, what is Johns formula, is there a specific formula or rule off thumb Sy uses when Building one of his 12 watt monsters ...

See , easy , nothing like asking Borne .....
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Old 23rd June 2012, 10:35 PM   #6325
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Still is going out to buy a car, and only ask how much horsepower it has.

(wavebourn supremacy ?)
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Old 23rd June 2012, 10:45 PM   #6326
wahab is offline wahab  Algeria
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Originally Posted by SY View Post
All amps do not have the same power supply rejection.
So one could count on caps inflation to balance a low PSRR amp ?..
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Old 23rd June 2012, 10:53 PM   #6327
Pano is offline Pano  United States
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Originally Posted by SY View Post
Design rules are nice, but what was pointed out is that a rule for "microfarads per watt" is a meaningless one without context.
I think you missed the "joules per watt at a given load" part. I don't think I ever said "microfarads per watt".

I'm ready to accept that there may not be a good answer, maybe amp designers don't think or power supplies in "joules per output watt" terms. I usually don't when building an amp - I just look at what others are doing and figure out what might work for me. If I wanted "One Stupid Trick for Great Power Supplies" I'd just stick as much capacitance in there as would fit. And buy a huge transformer.

But I was asking if perhaps someone had found a relation between energy stored in the power supply and sound quality. Something more than a simple "More is Better" or "Just enough to kill the ripple." Those are pretty easy to figure out by yourself. Looking at typical class AB pro amps, they tend to have fairly low capacitance and small transformers compared to their power ratings. Why? Size and cost are important for a touring amp. Weight is very important. But what about "High End" amps? (I mean that in a good way). They tend to have beefier power supplies for a rated power than their pro cousins. Low cost consumer amps are even lighter weight. Can we guess why?

Not all of us have the luxury of stuffing a huge power supply into the box. Where is the point of diminishing returns? Is there one? What might be the trade-offs of going smaller?

Amps have to be designed with some sort of load in mind. Is the only PSU design rule "Bigger is Better"?
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Old 23rd June 2012, 11:48 PM   #6328
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I have just been doing a parametric search for op amps . Not for audio exactly , an active filtering application for measuring ( GBP 10 MHz ) . I think I will buy myself a big stock of MC33079 as they are good enough for these applications and have 4 op amps in the package . They look to be going obsolete .We are then left with MC33078 NE5532 (34) and LM833 . So far so good . Then absolutely nothing . OPA134 , 2134, 604 ,2604,2227 . It is not exactly an endless list . AD823 with OPA627 seems to head the list . I think it is time to design discrete op amps . If not we become stuck in a diminishing market . I have a friend who is designing a phono stage , if low noise the list is minute . To be frank 6nV/Hz is too noisy . It needs to be < 2 nV .
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Old 23rd June 2012, 11:56 PM   #6329
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Originally Posted by Pano View Post
I think you missed the "joules per watt at a given load" part. I don't think I ever said "microfarads per watt".
Others did- but joules per watt is just as nebulous. What's the rail voltage? What's the load? At what frequency? And all the other bits I mentioned.

Someone talked about using enough capacitance to keep the amp running for 5 seconds after turnoff. I'd rather have an amp that collapses faster than that so that in the event of a power outage, my speakers don't suffer a full power BANG from the preamp.

Rail sag? Get a bigger transformer- the caps shouldn't be a band-aid.
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Old 24th June 2012, 12:24 AM   #6330
Pano is offline Pano  United States
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Quote:
Originally Posted by SY View Post
Others did- but joules per watt is just as nebulous. What's the rail voltage?
Uhhhhh..... isn't that why we use joules instead of just capacitance? Joules takes into account the voltage and capacitance. Low voltage amps need much more capacitance to store the same energy as high voltage amps.

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What's the load?
I dunno. What's the amp rated for? A minimum 8 ohm load? 1 ohm?

Quote:
At what frequency?
Audio amps are generally supposed to be consistent from 30Hz to 15KHz or better. Or do you want a specific frequency?

Quote:
And all the other bits I mentioned.
Not sure what those are.

Quote:
Rail sag? Get a bigger transformer- the caps shouldn't be a band-aid.
Indeed! But can they be an aid without being a band-aid? Is there any sonic advantage to having all that energy on tap tied directly to the output stage? If there is, how much?
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