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Old 18th January 2013, 06:58 AM   #8161
dvv is offline dvv  Serbia
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Quote:
Originally Posted by gootee View Post
Hi dvv,

The calculation example that you quoted was not calculating the required reservoir capacitance for a power supply. It was merely to help illustrate what types of calculations could be performed, with an equation that had been derived.

...

If we still want to just account for the whole sine wave, we should be able to simply double the C value given by equation (17), since we're considering only the positive or negative half-cycle, but not both, and the other half of the half-cycle of a sine wave is symmetrical and thus encloses the same area (its integral), i.e. the same amp-seconds value, as the first half.

[Edit: Note, too, that positive capacitor current was defined as current flowing into the positive-voltage-designated lead of the capacitor. So, typically, for this scenario, both Δi and Δv will be negative.]

For more of this exciting story, including some of the considerations involved when Δv - (ESR∙Δi) gets close to zero, go to

Power Supply Resevoir Size

Tom
Thank you for the explanation, Tom, that's what I got from a second reading, this time a careful one.

It actually shattered some of my previous beliefs in terms of how much capacitance is required for evil loads at large power outputs.

Worse, it made me almost cry when I compared those findings with what actually goes on in the industry. 2x50 WRMS/8 Ohms with just one pair of 6,800 uF caps? Wow, that should sound really powerful.

It also made me understand fully why some designers use very hig supply voltages for relatively low power levels, e.g. +/- 51V for nominally 2x50 WRMS into 8 Ohms, nominal output peak 28,3V, and the supply is just short of TWICE what you need? Oh boy, is that man is expecting some power supply sag, or what?

Lastly, it made me realize that in fact I was not half the capacitor freak I thought I was. Until yesterday, I thought I was a lone pervert for wanting 30,000 uF per supply line, 60,000 uF per channel in a stereo nominally 2x100W RMS into 8 Ohms amp. Then I learn that in fact, I am far too modest.

Oh well, as my late grandma used to say - we live and learn all our lives, yet we still die foolish.

On the plus side, it did confirm my general approach - if you want a really good 100 WRMS/8 Ohm amp, you design a good 150 WRMS/8 Ohms amp and call it a 100 WRMS/8 Ohm amp. Then you get that feeling of limitless power I covet so much, or at least, you have a good shot at it.
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Old 18th January 2013, 07:06 AM   #8162
dvv is offline dvv  Serbia
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Originally Posted by mr_push_pull View Post
dvv,

50W enough? pretty much in the ballpark. I'm a regular guy myself, but what's 6dB between friends?
a.wayne will love this discussion (if you haven't already gone through that, haven't read the last few pages)
50 WPC/8 Ohms should be enough for the vast majority of people, but only assuming:

1. That it is indeed capable of delivering all of the 50 Watts without any compression, and remember, theis translates to 50/100/200 WPC into 8/4/2 Ohms, which is a tall order, and

2. That you live in a European sized living room, listen to your music at home levels and own loudspeakers of reasonable efficiency, meaning at least 89 dB/2.83V/1m, preferably better than that.

I can understand the American point of view. Many of their living rooms are at least twice those in Europe, some of their speakers are not too efficient, and hence they really do need more power for the same effect.

As for the feeling of power, well, the little Naim integrated amp from the early 80ies, sporting 30 WRMS, proved that you do not need oodles of power to get that feeling. But, it was a fully electronically regulated amp, with more components in the regulator than in the audio circuits. If anyone is interested, I have its complete schematics.
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Old 18th January 2013, 07:10 AM   #8163
dvv is offline dvv  Serbia
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Originally Posted by a.wayne View Post
I'm using 6volt rms when playing loud , ok its nominal 1ohm (300-22k) , only man amplifiers need apply ...
Yes, but Wayne, you are THE exception, not the average. You cannot rely on yourself to be the standard.

It's like saying that if it isn't a 42" D cup, it ain't no woman.
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Old 18th January 2013, 07:19 AM   #8164
dvv is offline dvv  Serbia
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That's exactly what all systems should sound like: I found it amazing, 20 years ago, trying some monster amp that would crush my toes if it fell on them, start to collapse as you pushed the volume up. A "miserable", 20W, chip amp should give you that impression if it has a decent power supply; it's what's called "engineering" ...

Frank
There you go, Frank, living proof that there is objective, measurable power and there's the subjective feeling of power.

The two have very little to do with each other.

Ask yourself - how do the people with 2x10 WRMS in tube get away with it? The techie view is that they should start choking about 30 seconds after they switch it on, yet they are happy and listening to this day.

I said it before and I'll say it again - most buy 100+ WRMS amps only to get the first 30 WRMS right, which tells you that it's the engineering that's lacking, in most cases due to economic reasons and "market positioning".

Beat that rap by making a decent 50 WRMS amp, then throw in two 300 VA toroids and install 2 x 22,000 uF caps per channel - see what you get. Watch those commercial 100 WRMS amps struggle where your little guy sails smoothly through.
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Old 18th January 2013, 08:00 AM   #8165
fas42 is offline fas42  Australia
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Originally Posted by dvv View Post
50 WPC/8 Ohms should be enough for the vast majority of people, but only assuming:

1. That it is indeed capable of delivering all of the 50 Watts without any compression, and remember, theis translates to 50/100/200 WPC into 8/4/2 Ohms, which is a tall order, and

2. That you live in a European sized living room, listen to your music at home levels and own loudspeakers of reasonable efficiency, meaning at least 89 dB/2.83V/1m, preferably better than that.
Spot on, dvv -- my tweaked HT, of very lowly born parentage, has speakers of about that efficiency, 20W chip amps per channel. If I put on some modern compressed rock, say Foo Fighters, at 3/4 volume my ears will start ringing after a couple of tracks at normal listening distance. You only have to work out the very simple maths involved to appreciate that a "minimal" system will do the job, IF working properly ...

Frank
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Old 18th January 2013, 09:24 AM   #8166
dvv is offline dvv  Serbia
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Spot on, dvv -- my tweaked HT, of very lowly born parentage, has speakers of about that efficiency, 20W chip amps per channel. If I put on some modern compressed rock, say Foo Fighters, at 3/4 volume my ears will start ringing after a couple of tracks at normal listening distance. You only have to work out the very simple maths involved to appreciate that a "minimal" system will do the job, IF working properly ...

Frank
Exactly, Frank.

I assume your comment on your amps, the ears splitting, refers to sheer volume. One of the sure-fire signs of inadequacy in an amp is when its tonal balance changes with increases of volume.

On quality fare, louder simply means more of the same. With such systems, it's easy to err on the side of too loud, the key reason being that other than SPL, NOTHING else changes.

How will you then know you're being too loud? Easy! You'll get an express message via a utensil from the kitchen.
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Old 18th January 2013, 09:31 AM   #8167
dvv is offline dvv  Serbia
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I forgot ...

Frank, NEVER forget that the point of audio is not to have low THD and IM, high slew rates, and so forth, but to make YOU happy.

Thorsten had a good saying, paraphrasing here: you can design for specs, but you should design for the sound.

While I completely agree with this, I realize some of us do this for a living, so naturally they have to cater for market whims, and the world market is - most ufortunately - completely ruled by specs.

You and I are not. We are the fortunate ones, with perhaps some intelligence thrown in.
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Old 18th January 2013, 09:44 AM   #8168
fas42 is offline fas42  Australia
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I sort of laugh and sigh about this at the same time, that seemingly very few people get it -- that one can get quite excellent sound from relatively ordinary equipment if one goes about it the right way. It's within most people's grasp really, but ego, market pressures as you say, and inertia keep it just beyond their reach, mostly, I'm afraid to say ...

Cheers,
Frank

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Old 18th January 2013, 11:41 AM   #8169
DF96 is offline DF96  England
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Originally Posted by dvv
On the plus side, it did confirm my general approach - if you want a really good 100 WRMS/8 Ohm amp, you design a good 150 WRMS/8 Ohms amp and call it a 100 WRMS/8 Ohm amp.
Yes, that just about sums up the capacitor size thread. As it is somewhat counter-intuitive (to those who want ever bigger caps) I assume that many people will continue to use lots of big caps with barely sufficient transformer voltages. Journalists will continue to judge caps and transformers by size alone, when a 50V 500VA transformer might work much better on real music than a 40V 800VA transformer.
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Old 18th January 2013, 12:15 PM   #8170
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to me this topic is very interesting.
it's my feeling that the "amp with cojones" subject is surrounded by an aura of myth.
I often hear claims that even a speaker with benign impedance and moderate sensitivity needs a huge amp so it can sing. I've been trying to investigate if such claims can be somehow supported by an ignored phenomena that is measurable and quantifiable, with no success.
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