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Old 13th December 2002, 02:54 PM   #1
diyAudio Member
Join Date: Feb 2001
Location: Mars
Default Amplifier Puzzle

Every forum that I post this, people struggle
with offering an opinion, this forum is my last hope
for some type of explaination - heh

Food for thought (hypothetical);
(Lets assume the ideal power supply)

Amplifier "A" - +100v/-100v power supply rails,
rating = ~1000w driving a 10 ohm woofer.

Amplifier "B" - +63v/-63v power supply rails,
rating = ~1000w driving a 4 ohm woofer.

Amplifier "C" - +10/-10v power supply rails,
rating = ~1000w driving a 0.1 ohm woofer.

All these are 1kw mono amplifiers, but deep
down inside, very different in design, each
has different rails voltages and different
load requirements.

Puzzle: Which amplifier would appear to have
better dynamic headroom and/or less
chance of the output signal clipping on
transients ?
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Old 13th December 2002, 03:33 PM   #2
argo is offline argo  Estonia
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Join Date: Feb 2001
Location: Estonia
Default Re: Amplifier Puzzle

I would like to see the Amplifier "C". Even Amplifier "B" must be a rare beast. (Burmester comes to mind. or was it 3200W Class A into 1 ohm. didnít sound that bad at all) If it exists, I would prefer it against Amplifier "A"
PA application aside, why would anybody want to have one of these?

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Old 13th December 2002, 04:27 PM   #3
djdan is offline djdan  Romania
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Location: Romania
In my opinion is : Amplifier "A" is the best option in the real life.
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Old 13th December 2002, 04:46 PM   #4
Jeff R is offline Jeff R  United States
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Join Date: Nov 2002
Location: Florida
With 10 volt rails, it wouldn't take much to get into clipping. Even if you manage to get the output within a volt of the rails, you would still be losing 10% of the available headroom and, since P = V*2/R, 19% of the available power.

As the rail voltage goes up, there is a greater percentage of voltage available for the output and, likewise, more voltage to create power.

Which amplifier is "best" depends upon the load, and I am not sure if your question can be precisely answered given the apples to oranges to pears comparision.
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Old 13th December 2002, 05:56 PM   #5
tiroth is offline tiroth  United States
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Location: Pittsburgh, PA, USA
All things being equal, 'A'. The lower the current for a given output, the less impact trace resistances (contact, cables, xover impedances) have on the sound. This system would also have greater noise immunity.

I realize this isn't the question you asked fact, I don't see how there can be an answer to your question. If all amplifiers are "perfect" they all have equal statistics into the stated loads, and no headroom whatsoever. To me, dynamic headroom is simply extra power the amp "should" have if only the supply (and SOA) didn't limit it. The perfect amplifier will have full rated power into the load continuously, and no dynamic headroom.

Either this is a trick question or it needs to be redefined.
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Old 13th December 2002, 07:59 PM   #6
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Location: Wisconsin
Given that each scenario has an idealized power supply, amp, and speaker, then scenario 'A' should have the best dynamic range. Technically this isn't 'headroom', but it could construed as such.

The reason 'A' has the best dynamic range is because of efficiency.

The amount of power wasted as heat in the speaker (IIR losses) will be greatest in 'C' and least in 'A'.

Therefore, the speaker in 'A' has a greater percentage of the amplifier's output power available for electromotive force. Hence, better dynamic range.

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Old 13th December 2002, 08:04 PM   #7
The one and only
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Actually the amplifiers you cite have continuous wattage
ratings more like 500 watts.

Assuming sufficiently big hardware, amplifier A will walk
away with the prize.
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Old 14th December 2002, 06:11 AM   #8
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Join Date: Feb 2001
Location: Mars
Thanks for the replies.

On other forums many audio enthusiasts
only factor in the power ratings of
amplifiers for comparison, ie,
a 500w amp from one company
is the same or similar in performance
as a 500w from another company.
While this has some merit, I wanted to
get opinions on how rail voltages could
contribute the sonic equation by posting
an exaggerated amplifier example,
one amplifier with 100 volt rails,
another with 10 volt rails, both
rated for the same power but both
vastly different in design.

This quest was started when I found
out some companies make power regulating amplifiers. These amplfiiers
lower the rail voltages as the load drops to maintain the same output power, ie, 500w into any load
from let say 1 ohm to 4 ohms..
This type of design is typically
a "switcher" with a "smart" power
supply that lowers the rails, either
variable or in steps.......

What would happen if you took
TWO of these amplfiers and did
some A/B tests like so........

Run one amplifier with a 1 ohm
speaker load, run the other amplifier
with a 4 ohm speaker load. Both
delivering 500w into each speaker

If you were to do A/B listening tests,
can the listeners distinguish between
the two amplifiers because the rail
voltages are much different, the
amplifier with the 1 ohm load would
have much lower rails.......

I'm under the assumption that
the amplifier running the 1 ohm
load would be sonically inferior
because it would be easier to clip
the amplifier due to less headroom
and it *may* be sonically
distinguishable, I guess if you
have a trained ear - LOL

This is an esoteric topic.....
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