Back in the late 1970’s and early 1980’s when I was purchasing quality
stereo amplification equipment for various projects, I became quite familiar
with the techniques used by manufacturers to overstate the power output of
their amplifiers – specifically statements presenting total instantaneous
power, peak power, or other such number-inflating techniques. I had thought
that the practice of requiring power output in RMS to be specified at a
specified distortion level had put an end to that type of power inflation
technique and provided serious buyers with an appropriate yardstick for
comparison.

In those days, amplifiers that were capable of 50 Watts RMS per side or
higher were relatively beefy with massive heat-sunk power transistors, heavy
power transformers, filter chokes and substantial electrolytic capacitor
banks to meet the RMS power requirements. I still enjoy a number of
amplifiers from those days and appreciate their “clean” power delivery,
particularly in the bass range.

While I recognize that advances in power supply design, such as switching
mode, and newer amplifier designs, such as classes G, H and D, have afforded
the ability to eliminate significant weight and size from amplifiers, I’m
concerned that somehow the RMS rating criteria is somehow being bypassed in
current stereo and home theatre products.

For example, I recently trialed a name-brand stereo amplifier that was
specified at 100 Watts per side into 8 Ohms. I really didn’t need a new
amplifier, but couldn’t believe the price for what was claimed to be
equivalent to my 15-year old Akai, which isClass G and rated at 130 Watts
per side into 8 Ohms and 100 Watts per side into 4 Ohms. The name-brand unit
was about ¼ the size and weight of my Akai, which cost five times as much 15
years ago.

When I connected the name-brand unit to my Altech "Studio Monitor" 8 Ohm
speakers and played a favourite CD, I immediately recognized that this unit
was dramatically underpowered, particularly in the bass range – probably
doing no better than 10 Watts in terms of what I associated with RMS power
performance.

When I returned the unit (at the speed of sound) to the big box store audio
expert, he emphatically stated that I needed a “high-current” amplifier,
pointing to a much more expensive / expansive name-brand unit that was in
the same, size, weight and price range as my Akai and Pioneer units.

Still adhering to the belief that Ohm’s Law is applicable to the
specification of power, and assuming a fixed speaker impedance, I could not
understand the relevance of “high current” to getting better sound out of an
amplifier with the same 8 Ohm RMS power rating, but no “high-current”
designation. For a given power output, if the current is lower, the voltage
must be higher, per Ohm’s Law.

I note seemingly incredible claims being made for home theatre
systems –seven channels at 100 Watts RMS output – “simultaneously”, as
promised by a “sales engineer” in a professional audio shop that I recently
visited. I can’t believe that amplifiers of this size, weight and price on
offer at this shop could possibly deliver that type of relatively
undistorted RMS power simultaneously from five channels, let alone seven.

How are the manufacturers and sales agencies getting around the old RMS
power specification “equalizer”? I note reasonable specifications for IMD
and THD associated with these current power claims, so what am I missing???

Comments would be very much appreciated.

Bill Evans

In article , "Bill Evans" wrote:
Back in the late 1970’s and early 1980’s when I was purchasing quality

How are the manufacturers and sales agencies getting around the old RMS
power specification “equalizer”? I note reasonable specifications for IMD
and THD associated with these current power claims, so what am I missing???

Comments would be very much appreciated.

Bill Evans



I don't know what requirments there are. You can pretty much judge the approximate worth
by picking it up, unless its a switching type. Some of these current amplifiers
have thermal breakers in the transformers.

greg

February 27, 2006

E-mail Insert

Appreciatethe comments and on this thread and its UK counterpart, but most
comments seem to focus on the definition of RMS, not the basic issue of
misrepresenting power output capabilities of modern amplifiers. What I
recall from the late seventies is that the International Institute of High
Fidelity (IIHF) had established detailed technical specifications that
defined the measurement techniques that would necessarily be used to
establish the specified amplifier power output on an RMS, continuous power
basis. This specification process was, as I recall, very rigorously
described.

What happened to IIHF? Is there no accepted industry standard, either in
Europe or North America or elsewhere on rating audio amplifier output power
levels?

"

Bill Evans wrote:

Appreciatethe comments and on this thread and its UK counterpart, but most
comments seem to focus on the definition of RMS, not the basic issue of
misrepresenting power output capabilities of modern amplifiers. What I
recall from the late seventies is that the International Institute of High
Fidelity (IIHF) had established detailed technical specifications that
defined the measurement techniques that would necessarily be used to
establish the specified amplifier power output on an RMS, continuous power
basis. This specification process was, as I recall, very rigorously
described.

What happened to IIHF? Is there no accepted industry standard, either in
Europe or North America or elsewhere on rating audio amplifier output power
levels?

The IHF "specification" was one of the most useless, misleading
and uninformative means of specifying aplifier around. It lead,
quite intentionally to completely fictitious numbers.

What you are thinking of is a regulation written by the US FTC
(Federal Trade Commission) on how amplifier power specs
had to be determined. It basically required that the amplifier by
thermally conditioned by running at 1/3 of its rated continuous
power output for a period of 1 hour before measurements
commenced. The manufacturer had to state the continuous
power (they called it RMS, a misnomer) the amplifier was
capable of, both channels driven simultaneously, at its rated
distortion over the specified bandwidth of the unit.

It was a rigorous spec, perhaps too rigorous, because the
1/3 rated power heat soak was unrealistic for home use.

And the term "RMS power" is incorrect. The rating for continuous
power is derived by taking the RMS voltage of the amplifier's
output into the rated load and deriving the power as:

P = Erms^2/Z

Now the square of the root-mean-square is the mean, avaerage
or continuous power. Simple as that.

But the IHF as a standards setting body? Forget it: it's an industry
promotion group.

If you want to refer to a body of international standards, check out
IEC (International ElectroTechnical Commission), specifically,
60268 and its various subparts such as IEC 60268-3 "Amplifiers",
and the like.

Hi ,

That was the way I understood things. Since that time, did the FTC drop or
modify the requirements for amplifier power specifications? I think that is
the crux of the original question.

Mark


What you are thinking of is a regulation written by the US FTC
(Federal Trade Commission) on how amplifier power specs
had to be determined. It basically required that the amplifier by
thermally conditioned by running at 1/3 of its rated continuous
power output for a period of 1 hour before measurements
commenced. The manufacturer had to state the continuous
power (they called it RMS, a misnomer) the amplifier was
capable of, both channels driven simultaneously, at its rated
distortion over the specified bandwidth of the unit.

It was a rigorous spec, perhaps too rigorous, because the
1/3 rated power heat soak was unrealistic for home use.

And the term "RMS power" is incorrect. The rating for continuous
power is derived by taking the RMS voltage of the amplifier's
output into the rated load and deriving the power as:

P = Erms^2/Z

Now the square of the root-mean-square is the mean, avaerage
or continuous power. Simple as that.

But the IHF as a standards setting body? Forget it: it's an industry
promotion group.

If you want to refer to a body of international standards, check out
IEC (International ElectroTechnical Commission), specifically,
60268 and its various subparts such as IEC 60268-3 "Amplifiers",
and the like.

"Bill Evans" wrote in message

February 27, 2006


What happened to IIHF?

I believe it was absorbed by the EIA.

http://www.eia.org/index.phtml

In article , "Arny Krueger" wrote:
"Bill Evans" wrote in message

February 27, 2006


What happened to IIHF?

I believe it was absorbed by the EIA.

http://www.eia.org/index.phtml

Seems like all the amps were getting 1/3 power when I was last reading
Audio. I wonder how many home theater receivers could
stand this. Most system would require separate component amps for
each channel

greg

"GregS" wrote in message

In article , "Arny
Krueger" wrote:
"Bill Evans" wrote in message

February 27, 2006


What happened to IIHF?

I believe it was absorbed by the EIA.

http://www.eia.org/index.phtml

Seems like all the amps were getting 1/3 power when I was
last reading
Audio. I wonder how many home theater receivers could
stand this.

IME all of them, but not indefinitely.

Broadly speaking, good solid state audio power amplifiers using
conventional technology should weigh at least one pound for every five
watts of continuous power, in a stereo amp. The power transformer
should be very heavy and the heat sinks should be large and heavy also.
If it is much lighter than say the old Hafler amplifiers something is
very definitely wrong. They were a little light to begin with. You can
calculate the heat rise of the transformer core approximately by
measuring the change in DC resistance. In a really good solid state
design the heat sinks and the outside of the power transformer should
be cool enough you can touch them without burning yourself.

Most commercially built solid state amplifiers are somewhat overrated
for power because they are purchased by numbers and cost. The old
Dyna/Hafler designs are when modified actually still pretty good. Many
more sophisticated designs are really not very good at least for home
use.

"Bret Ludwig" wrote in message
ps.com...
Broadly speaking, good solid state audio power amplifiers using
conventional technology should weigh at least one pound for every five
watts of continuous power, in a stereo amp.

snip

Using conventional class A/B technology, as you say. The home theater amps
seem to be going increasingly to switchmode (class D?), which is much
lighter, and probably the only practical way they can get 5x100W channels
into a pizza box. Five channels is three more than I need, but marketing
marches on. I think the jury is still out on "audiophile" sound quality for
these things.

"Bret Ludwig" wrote in message
ps.com

Broadly speaking, good solid state audio power amplifiers
using conventional technology should weigh at least one
pound for every five watts of continuous power, in a
stereo amp.

That would place a 100 wpc amp or receiver at 20 pounds - the controlling
phrase being "conventional technology".

For reference this stereo receiver is probably one of the very cheapest
around, and comes surprisingly close:

http://www.jr.com/JRProductPage.proc...eed.SHE+RX4103

weight - 18 pounds.

The power transformer should be very heavy
and the heat sinks should be large and heavy also. If it
is much lighter than say the old Hafler amplifiers
something is very definitely wrong.

DH 220 - 120 wpc or so, weight about 32 pounds. Less than 3.8 watts per
pound. This is a significantly different standard than the one at the top of
Bret's post.

They were a little light to begin with.

Self-contradiction, anybody?

You can calculate the heat rise of
the transformer core approximately by measuring the
change in DC resistance. In a really good solid state
design the heat sinks and the outside of the power
transformer should be cool enough you can touch them
without burning yourself.

Agreed.

Most commercially built solid state amplifiers are
somewhat overrated for power because they are purchased
by numbers and cost.

Actually, the FTC rules for power amps result in a power amp that is always
overbuilt.

The old Dyna/Hafler designs are when
modified actually still pretty good. Many more
sophisticated designs are really not very good at least
for home use.

Whatever that means!

In article , "Arny Krueger" wrote:
"Bret Ludwig" wrote in message
ups.com

Broadly speaking, good solid state audio power amplifiers
using conventional technology should weigh at least one
pound for every five watts of continuous power, in a
stereo amp.

That would place a 100 wpc amp or receiver at 20 pounds - the controlling
phrase being "conventional technology".

For reference this stereo receiver is probably one of the very cheapest
around, and comes surprisingly close:

http://www.jr.com/JRProductPage.proc...= google.data
feed.SHE+RX4103

weight - 18 pounds.

The power transformer should be very heavy
and the heat sinks should be large and heavy also. If it
is much lighter than say the old Hafler amplifiers
something is very definitely wrong.

DH 220 - 120 wpc or so, weight about 32 pounds. Less than 3.8 watts per
pound. This is a significantly different standard than the one at the top of
Bret's post.

I have gone to the discount storeslooking at stuff, and frequently lift the receivers.
Some of them are very light. Tends to go with price. I'm also
trying to think what a Marantz 2290 used to weigh. Mabe close
to 30 lbs?

I'm trying to think what my old Tigersaurus's weighed. I'm thinking about 25 lbs
for 200 watts each mono. Quite a trick to carry both. My heaviest amp
is about 65 lbs at 1000 watts per channel, but is fan cooled.

greg

"GregS" wrote in message

In article , "Arny
Krueger" wrote:
"Bret Ludwig" wrote in message
ps.com

Broadly speaking, good solid state audio power
amplifiers using conventional technology should weigh
at least one pound for every five watts of continuous
power, in a stereo amp.

That would place a 100 wpc amp or receiver at 20 pounds
- the controlling phrase being "conventional technology".

For reference this stereo receiver is probably one of
the very cheapest around, and comes surprisingly close:

http://www.jr.com/JRProductPage.proc...= google.data
feed.SHE+RX4103

weight - 18 pounds.

The power transformer should be very heavy
and the heat sinks should be large and heavy also. If it
is much lighter than say the old Hafler amplifiers
something is very definitely wrong.

DH 220 - 120 wpc or so, weight about 32 pounds. Less
than 3.8 watts per pound. This is a significantly
different standard than the one at the top of Bret's
post.

I have gone to the discount storeslooking at stuff, and
frequently lift the receivers. Some of them are very
light. Tends to go with price.

In the end weight costs money.

I'm also trying to think what a Marantz 2290 used to weigh. Mabe
close to 30 lbs?

I dunno, but I do know that a QSC USA400 (120 wpc) weighs about 25 pounds
as compared to a Pioneer SX 255R (100 wpc) which weighs 14 pounds.

I'm trying to think what my old Tigersaurus's weighed.
I'm thinking about 25 lbs
for 200 watts each mono. Quite a trick to carry both.

Dyna Stereo 400 rated at 200 wpc, weight 54 pounds net.


My heaviest amp
is about 65 lbs at 1000 watts per channel, but is fan
cooled.

The USA 850 (about 240 wpc) is fan cooled and about the same size but
weights 10 pounds more than the convection-cooled USA 400 (120 wpc). Its
almost all in the power transformer.