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Old 22nd August 2012, 11:33 PM   #771
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Quote:
Originally Posted by DF96 View Post
A roll-off of 15Hz might be more sensible than 1.5Hz, unless you have a very big room, very big speakers and definitely never use a turntable. I was disagreeing with your suggestion that we all agree about wide bandwidth. I prefer appropriate bandwidth.

DF96

Probably agree with you (not an appreciable effect) but in the interest of turning all stones, a simple RC rolloff at 15Hz would leave roughly 20deg phase shift at 40Hz.
I originally just commented that one doesnt need to use these low F's for estimating ripple.

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Old 22nd August 2012, 11:42 PM   #772
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Thanks Antonio from another Left Coaster down the coast.
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Old 23rd August 2012, 12:22 AM   #773
fas42 is offline fas42  Australia
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Just to add a tangent to where the conversation is at the moment, because my belief is that the perceived quality of an amp is due to how well it handles the high frequency stuff, and also that I wanted to show a simple technique for comparing different approaches, here's a variation on Tom's latest test jig:

DualOutputs01.gif

Note that the original circuit still stands, but I've duplicated the circuit loading the power supply, hooked that one up to perfect voltage sources, and am now driving both versions with the same signal. This makes it easy to compare one scenario with another, without having to worry about comparing the output to the input. And here are the results, driven by a full bore 20KHz signal:

DualOutputs02.gif

The top waveform, which shows the difference between the signals across the two versions' loads indicates where the problem is using class AB with real rather than theoretical supplies: nasty glitches, at very high frequencies, at the time when the current draws through the active devices switch off, ie. crossover artifacts. This of course will be supposedly corrected by feedback, but if it can't quite do the job properly because the supply is glitching at the time, then things might start looking, and sounding, worse ...

Frank

Last edited by fas42; 23rd August 2012 at 12:27 AM.
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Old 23rd August 2012, 07:02 AM   #774
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Default How much more capacitance than basic?

Quote:
Originally Posted by DF96 View Post
LF rolloff is not really relevant to this thread, but there may be good reasons to limit the bandwidth. There is little point in forcing a transducer to attempt to reproduce a frequency which it cannot handle. There will already be significant LF phase shift from the loudspeaker, and this would be a second or third-order rolloff. A first-order rolloff from the amplifier could be harmless in comparison.
Power supply board has so many similarities to an output cap and the roll off is not harmless. Unfortunately, I fear that speaker support requirement of the power board has inflated and therefore hindered the capacitance per ampere calculation efforts. Problem: Up to a certain point (it is speaker support) the power supply capacitance is the same for 1 watt amplifier as for 1000 watt amplifier.

There's 2 tasks for the power supply reservoir. Can we calculate them individually?
To me, it is nicer to contemplate a fixed basic power supply that accomplishes the speaker support and then afterwards the super interesting part becomes how much more capacitance must we add per higher power amplifier? That question is a bit different.

My apologies if the prospect was unsuitable.
Other way to go is to try calculating for 10,000 watt amplifier since that power supply could so easily swamp the speaker support minimum requirements.
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Last edited by danielwritesbac; 23rd August 2012 at 07:04 AM.
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Old 23rd August 2012, 02:05 PM   #775
Krisfr is offline Krisfr  United States
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I think that a 10,000 watt amp is not practical. How about designing for the max size amp that can be built using a standard 110 volt 15 amp source of power. That amp should more than satisfy the normal requirements for home listening even if it is a mono amp for a sub woofer. That to me is just what is practical. The previous chart is also very helpful.

All in all this has been a very enlightening thread, I certainly learned a lot.
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Old 23rd August 2012, 03:53 PM   #776
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Krisfr,
That statement is the most poignant statement I have seen in this thread so far. What use is designing a power supply that you don't have the current to supply. The upper limit may be a 20 amp circuit though if you use a dedicated electrical outlet if we are talking 110v. You could also look at a 220v limit if you used a single phase system with both legs of the power. But what do we need even a thousand watt amp in our homes for? You could go and get a PA amplifier with a SMPS and get more than you could ever use but the sound of most of those amps are not exactly hi-fi in nature. I would be interested to see what are the upper limits with the limitation of supply current and voltage.
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Old 23rd August 2012, 04:03 PM   #777
tsiros is offline tsiros  Greece
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an 8KW amplifier is not impossible in a household setting.

You will need to draw power from a separate fuse on the fusebox and dedicated cables.

the other question though is... WHY? WHY would you NEED that sort of power? And where would you find the speakers to handle it? I want one person, (deaf or otherwise, it doesn't matter, at those SPLs, the small veins in your lungs will resonate, along with your cerebral cavity) to claim that they actually listened to 1KW going into one speaker and they were in the same room.
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Old 23rd August 2012, 04:28 PM   #778
AndrewT is offline AndrewT  Scotland
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What's the problem?
If the maximum output power of the installed multichannel system is say 10kW, then the average output power will be around 100W total, for all the channels.
If the amplifiers, taking account of the quiescent currents and the transformers losses, make up for another 100W, then on a 240Vac supply the average current draw from the wall socket is ~ 800mAac.
As I said, what is the problem?
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Old 23rd August 2012, 07:04 PM   #779
DF96 is offline DF96  England
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Quote:
Originally Posted by danielwritesbac
Power supply board has so many similarities to an output cap and the roll off is not harmless. Unfortunately, I fear that speaker support requirement of the power board has inflated and therefore hindered the capacitance per ampere calculation efforts. Problem: Up to a certain point (it is speaker support) the power supply capacitance is the same for 1 watt amplifier as for 1000 watt amplifier.
I don't know what you mean by 'speaker support'. Perhaps LF rolloff at the output?

The PSU caps don't behave like an output cap, because the PSU caps get (approximately) clamped to a fixed voltage 100/120 times a second - this makes them behave like a low value resistor rather than a cap, for LF signal voltages.
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Old 23rd August 2012, 08:11 PM   #780
AP2 is offline AP2  Italy
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I answer: what is the power for listening at home, I mean a lover of good music as audiophile.
well, in my living room 8x4mt with good absorption (carpets, curtains and sofas), I wanted to measure the current absorption, while listening to a song composed by bass, trumpet, drums, female voice. speaker a pair of B & W 802 D2.
apparently the volume looks very clean about 80w, bass enveloping everything very well defined. you want to know how much power was out? repetitive peak 10Amp per channel, with impedance around 3.3R on the load. this was part of some tests to see how much power without thd, must be able to provide an excellent high end amplifier. is very insignificant power to declare the 8R or 4R on an amplifier. the amplifier under test can deliver 750w (2R) with 0.05% thd.
then, if I produce an amplifier for audiophili, it is obvious that I have to declare the power and performance, the lowest impedance obtained.
apparent, this amplifier have only 200w at 8R. so it looks like a small amp.
but in reality, everything is designed for high current output clean.
So, what should be dimensioned power supply?

Last edited by AP2; 23rd August 2012 at 08:39 PM.
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