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Old 9th January 2006, 01:18 AM   #11
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by janneman
OK, well I think you cannot predict the lowest impedance of a speaker easily
True, but it's not too difficult to measure...

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I think the way NAD did it was with VERY soft supplies. In other words, when the amp had to deliver high peak levels at a longer time, the supply would sag a lot, 30% or so, and that would automagically protect the amp. But that is quite a balancing act with the supply caps and transformer capacity, I don't think you would want to do it.
That is exactly how it was done. There were several approaches depending on model and power, but it's all ultimately about soft supplies. The class G models had the a tapped winding that provided both high and low rails, but the low rail winding had a lower resistance, and could deliver more current. The low rail capacitors were 2x4700uF while the high rail were 12000uF. Some also had thermal breakers mounted on the transformer bracket, since this approach essentially heats up an undersize transformer, using it's mass as a thermal capacitor. Since transients are not that common, in general it all works fine, unless the user tries to drive it to the limit all the time. I've also seen a similar idea but with a voltage doubler configured as a charge pump for the high rail, not in NAD/Proton amps, though. 'Softness' of the upper rail was 'regulated' by the capacitances of the 'pump' capacitors feeding the high rail reservoir cap, neat approach but requires very good pump caps.
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Old 9th January 2006, 07:26 AM   #12
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Quote:
Originally posted by rmihai
[snip]I listen most of the time to classical music - and I measured changes in output of up to 30db!!! That is why a 4db dynamic headroom is required. To be able to manage the HUGE peaks and transients.[snip]

Yes, not uncommon. There's one piece missing from the total puzzle, and that is the speaker efficiency. If you know the max amp power the speaker will need to sound earshattering in your room (like 120dB) then from that you can calculate the max peak power. From that you can calculate (with the headroom) the RMS power you need. Do you know this efficiency?

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Old 9th January 2006, 11:49 AM   #13
rmihai is offline rmihai  Canada
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Speakers eficieny is 83db.

My listening levels NEVER go over an average of 68db. Leaving room for 30db peaks that will make a total of 98db at peaks.

For a 12ft listening position and an amplifier with 3db headroom means I will need roughly 150W RMS.

For a 1.5db headroom amp I will need a 220W RMS amplifier.
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Old 9th January 2006, 12:10 PM   #14
lineup is offline lineup  Sweden
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I wonder
how often those 30dB peaks will happen?
A couple of times per year?
In percent of listening time?
0.0x% maybe?

My guess is those peaks will be as often
as is sound below 50 Hz.

You will do good with a more normal +12dB margin, in my opinion.
Much easier to build a good sound quality amplifier
with lower power output.

Either way you chose, you will most probably lose something.
I think you lose more than you gain going for high power and many Watts.
Because I find, you are a man that like good quality reproduction.
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Old 9th January 2006, 12:35 PM   #15
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Do you really listen at just 68dB? That's pretty quiet. How have you arrived at that figure?
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Old 9th January 2006, 12:48 PM   #16
rmihai is offline rmihai  Canada
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Measuring with the SPL meter for almost a year now.

The AVERAGE listening level is 68db.

Is true that when peaks are involved the SPL can go up.

There are couple of recordings were the SPL went all the way up to 98db instantenously.

But that is not my listening level.

For me and my neighbours 68db is a pretty healty listening level.
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Old 9th January 2006, 12:56 PM   #17
rmihai is offline rmihai  Canada
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Quote:
Originally posted by lineup
I wonder
how often those 30dB peaks will happen?
A couple of times per year?
In percent of listening time?
0.0x% maybe?

My guess is those peaks will be as often
as is sound below 50 Hz.

You will do good with a more normal +12dB margin, in my opinion.
Much easier to build a good sound quality amplifier
with lower power output.

Either way you chose, you will most probably lose something.
I think you lose more than you gain going for high power and many Watts.
Because I find, you are a man that like good quality reproduction.

Maybe you are right. Indeed those peaks are in the sub 100Hz region. How often are they coming? Well - you might be surprised, but that might happend once a week let's say.

Indeed a lower powered amp will be much easier to build to sound right.

And maybe I should stay with 75W that should give me pleanty of headroom for those peaks.
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Old 10th January 2006, 03:56 PM   #18
K-amps is offline K-amps  United States
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And in my experience that would entail a design with Lower Vce devices in my opinion which generally sound better and less harsh than high Vce devices. (Other things being equal)

Though personally I would not go with a low power amplifier, I do understand people that do.

If I were in your place, I'd make 2 amps. a 200w for the bass and a 50w for the mids and highs and Bi-amp. This set up will sound as loud as a 450w amplifier and sound much better. (The 450w was no typo... 40v+20v = 60v, 60^2/8 = 450w)

Moreover you could tweak both amps to sound the way you want, i.e. low feedback HF amp for more tubey sound and high feedback bass amp for solid punch... best of both worlds...

I can explain the above in more detail if you want... but if you read up on Rod Elliot's excellent article on Bi-amping you will get a better picture.

Power requirements are usually more demanding in the bass region, this solution while more complex and more expensive, might be the ticket if you have the time and patience.
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Old 12th January 2006, 01:25 AM   #19
rmihai is offline rmihai  Canada
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Thank you very much for your ideas and advises.
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Old 12th January 2006, 02:23 AM   #20
lineup is offline lineup  Sweden
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I was thinking how many recordings have peak +30dB?

2.0 Volt rms is max level for CD recording
2.0 /31.62 = 0.063 Vrms

This should be the average recorded level of such a recording!

I have seen articles where rockmusic
had the peaks in music sadly cut off or compressed.
In CD and DVD.
The vinyl of the same rockalbum was much better.
Now, rockmusic is not the type of music that has most dynamic span.

The normal average level of a CD, I think is about 0.5-0.7 Vrms.
I would not think you will find many below 0.2 Vrms.
And 0.2 Vrms is -20dB.

Maybe you should go for 20dB.
I think even vinyl recordings with 30dB dynamic peaks are very, very rare.
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