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Old 19th July 2002, 07:36 PM   #1
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Default Dynamic Headroom: Where is the limit?

We all know that sustained output power is directly proportional to an amps size but is it possible to build amps with smaller output power (ie:10W instead of 100W) and make up the difference with peak headroom? How much peak headroom is possible and what is the best way to get it? To give some commercial examples of what I am talking about, take the typical NAD amps. They describe +6dB (2 to the second power above the rated power) of "headroom" in their literature. How do they achieve this? What would need to be done to an 8W Zen-X to make +21dB (2 to the 7th power above rated power) of dynamic headroom on it? Bigger, higher power rated amps sound better because they have the power in reserve when large dynamic range is required but can we achieve the same with a smaller output stage? After all, who wants to go through the trouble of matching large mosfet sets if we can get the result with the power supply alone?

Mr. Pass, is there a practical limit to "dynamic headroom" on a small output stage and if so, what is it?
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Old 20th July 2002, 02:20 AM   #2
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Default Truth In Advertising.

Hello Nania,
The NAD spec of having a 6 dB headroom is the marketing and sales department's way of saying that the amp has a lousy power transformer that sags badly, and low power rated output transistors.
Big and solid amplifiers quote 0 dB headroom.
Having a droopy PSU causes more problems than it solves and is bad engineering.
Class A amps are by definition not suitable.

Regards, Eric.
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Old 20th July 2002, 02:43 AM   #3
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Talking They so to say hides the truth

It's not unusual.
So any additional information
from fellow DIYers is always welcome.
Well done! mrfeedback
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Old 20th July 2002, 03:15 AM   #4
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Default nania

When I use the thinking "dynamic headroom"
I usually think in recordings.
A recording can be compressed or dynamic.
A dynamic recording doesn't cut the tops, peaks
of recording.
That means that a dynamic recording have to have
lower average dB output.
The standard for CD output is set to +-2.8 volt peak.
(for other sources it can be different)
Can as a consekvens require some more voltage gain,
not to be to quiet when you listen.

Also I associate to the working-space of the voltage-gain-stage
in my amplifiers.
good working space=supply voltage,
provides smaller procentual changes to handle
for the transistor.
If I use that term you refer to correctly,
that is a matter of language.

But to be sure that we are "on talking terms"
I explain what I mean.
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Old 20th July 2002, 05:51 AM   #5
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quote:
--------------------------------------------------------------------------------
The NAD spec of having a 6 dB headroom is the marketing and sales department's way of saying that the amp has a lousy power transformer that sags badly, and low power rated output transistors.
--------------------------------------------------------------------------------


Eric is basically right, although he has a "glass half empty" way of putting it. The NAD transformers and transistors are fine for delivering the continuous rated power. You have the added bonus of being able to operate in the "red zone" for a short time which give you the headroom to keep away from that rude transistor clipping for a few extra db. It has probably saved a tweeter or two somewhere.


quote:
--------------------------------------------------------------------------------
Big and solid amplifiers quote 0 dB headroom.
--------------------------------------------------------------------------------


Right again, but you pay for the "big and solid". The whole idea behind "dynamic headroom" is economy. "Get the power of a big amp at the price of a medium size amp". It's not very fair to compare the performance of a multi-thousand buck amp with that of a sub-thousand buck amp. Although the NAD's (at least the 80's versions) will hold their own against more then a couple of the high dollar amps around even today.


quote:
--------------------------------------------------------------------------------
Having a droopy PSU causes more problems than it solves and is bad engineering.
--------------------------------------------------------------------------------


Now here I have to kindly disagree. The NAD amps were "engineered" as a low to medium priced amp that could attract some hi-end support. They have done just that. The NAD's are an excellent example of good solid engineering.

We all love to have the super hi-end, pull out all stops amp that double as a welder, and you can buff up with moving it around to just the right spot. But there aren't many that can afford it. My wife was happy with her NAD for years. At least until she heard my Pro Bryston 4B. Now its her Bryston. Oh well, I went an got a 4BST.

Rodd Yamashita
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Old 20th July 2002, 06:20 AM   #6
fcel is offline fcel  United States
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Default OT: Women in Hi Fi

Rodd,
It's not too often to read someone of the opposite sex to be "into" hi-fi! Or your wife is more into music than the hareware itself?
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Old 20th July 2002, 06:22 AM   #7
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Default Power supply and price correlates

More perhaps than other things in an amplifier.
so I understand you perfectly, roddyama.

also Eric, I understand, if you sacrifice
some of transformer power-margin, ie small trafo,
you make most profit

which they do, not NAD, what I know,
but others
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Old 20th July 2002, 07:02 AM   #8
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fcel,

My wife is into the music. Although, she is almost the perfect equipment tester. She hears with her ears, not with her brain. I had 3 amps that I had an opinion on, and wanted to qualify what I thought them. They were an AR D52, the Pro Bryston 4B, and an NAD 2600. She listened to each off and on for a few days, and she would tell me what she thought of each amp. So when we were done I put the NAD in her system, and the Bryston and AR went in my system. In the mean time, I pick up a Bryston 4BST to drive the mid bass in my tri-amp system. Thats when the brow-beating started. To make a long story, she got the Pro Bryston, and I got the NAD for my subs. It takes the SAF to a new level.

Rodd Yamashita
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Old 20th July 2002, 07:20 AM   #9
fcel is offline fcel  United States
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Rodd,
Sometime I wonder what would happen - good or bad - to my hobby if my wife is also into this kind of stuff ....
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Old 20th July 2002, 07:29 AM   #10
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No fcel,

You will never have the Claw in the livingroom! You'd better make room in the basement.

Rodd Yamashita
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