You could say the same about an original Sony XES-M1 or M3... I think
you need to establish an apples to apples comparison, can't compare
premium product with run of the mill stuff and expect them to "age" the
same.

JD

John Andreen wrote:

Mr Zarella

You are correct, there is always a trade-off between a "clean" amplifier and
a "dirty" amplifier. But the "dirty" amplifier will always loose in terms
of reliability, distortion, sound quality etc. All at the expense of good
Engineering practices and a handful of parts.

On a side note, what would you rather be driving, a Yugo or a Mercedes? Ok,
not the same, but how about a Yugo or a Ford Focus? But if your life
depended on its proper operation all the time, which would you choose?

Here is another case in point. Old school PPI amplifiers. Some of these
amplifiers are over 15 years old and they are still operating and making
great sound. In fact, these units are still highly sought after. Can you
say the same for an equally aged Pioneer or Sony? I think you are perhaps
using a shifting baseline as to what is "clean" today.

Could you also be confusing distortion with noise? They are not the same.
You should do some investigation on these subjects. What you say is a
measurement of distortion is actually called "THD +N" a.k.a. Total Harmonic
Distortion + Noise. Then to make matters worse, some audio companies use
filters (read A-weighted) to make there units appear to have low THD+N. To
add even more confusion into the mix, this "THD+N" is almost always
computationally measured using FFT methods. There are more than a dozen
FFT windows ( read measuring envelope ) that can be used to make the
measurement. Each will give a return a different value for "THD+N". There
is one more thing about measuring "THD+N". One must also specify the power
of the signal being measured. One can measure at 1W, 5W, Full rated power,
etc. "THD+N" is not constant at all power levels. It is usually higher at
very low power levels and very high power levels. At very low power
levels, the major component comes from "noise". At very high power levels,
the major component comes from "THD". Really "clean" amplifiers have "TH
+N" values nearly equal at all power levels under clipping.

I can take even the "dirtiest" amplifier and measure extremely low values of
distortion. On the order of 1/1000 of a %. That is, if I can choose my
own method and power level of distortion measurement.

There is also harmonic distortion caused by the sum and difference of two
signals. Let's say a 40 kHz square wave from a power supply and a 1 kHz
sine wave. There will be strong harmonic distortion at 39 kHz and 41 kHz.
There are also artifacts called sub-harmonics of these two signals that
will be present. These are the artifacts that can appear down in the audio
spectrum. I would also like to point out that music isn't just 1 kHz, but
a plethora of frequencies.

I have told this group many times not to be concerned with "THD+N" as a
figure of merit when buying an amplifier. The human ear doesn't mind even
1-3% THD. It is a "Marketing Tool" designed to sway the masses. Go listen
to a high quality pure tube amplifier and a high quality transistorized
amplifier of the same output power specifications. Do this test blindly.
I am absolutely certain that you will always pick the tube amplifier over
the transistorized one as having the better sound. But, that tube
amplifier will have distortion figures SEVERAL HUNDRED TIMES WORSE than the
transistorized amplifier. Instead, try to buy an amplifier that has Low
"TIM" and low S/N. TIM stands for Transient Intermodulation Distortion.
Good audio distortion analyzers can find this kind of distortion using the
"IMD" settings.

Now, onto the subject of noise. Noise is ever present in the audio world.
It comes from the amplifiers SMPS. It comes from the Automobiles charging
system. It comes from solar wind. It comes from the power transmission
lines. In short, it comes from just about everywhere. In my last post, I
stated several things that make for a "clean" amplifier. Those things are
the items or methodologies used to eliminate or diminish the ingress of
noise into an amplifier. I forgot one them. Decoupling capacitors. Once
again, do not do any or all of those items, and more effective noise will
make it into the audio path. Do all of them right and you will diminish
the ingress of noise into the audio path and have a "clean" amplifier.

I have measured and tested amplifiers from many of the "top" car audio
companies. Some had signal to noise ratios of -50dB, some had signal to
noise ratios greater than -100dB. In other words, the best amplifiers S/N
was 64 times better than the worst. The reason, one amplifier was more
"clean" than anothers. Once again, you can fudge these numbers too. S/N
is different depending upon the position of the gain pot. At max gain, S/N
to noise will be different than min gain. The difference, a handful of
parts and good Engineering practices. QED

John Andreen


Mark Zarella wrote:



There is such a thing as "clean" and "dirty" power. A perfect case in


point


would be to run your amplifier with a cheap battery charger as its B+
supply. You will hear a tremendous amount of "hum". In other words, it


is


"dirty" power. At the other extreme, hook up a whole bunch ( maybe 10 )


of


automotive batteries in series. Tap the "GND" from the connection
between
battery 5 and battery 6. Tap the amplifiers output rails (+/-) from the
the top and bottom posts. to do this, you must eliminate the SMPS
section
and some other items. The Rectifying diodes and the bulk rail capacitors
to be exact. You now have "clean" Power for your 400W/ch RMS amplifier.

Many things can affect just how "clean" an amplfier is. Power supply
topology, filter capacitors, Inductors, ferrite beads, transformer type,
board layout, star grounding, trace capacitance, trace inductance, PCB
layers ( e.g. 1, 2, 4 ). Do all these things right, and you have a


"clean"


power amplifier. Do any one or all these things wrong and you now have a
"dirty" power amplifier. There is even an extreme case where when the
output rails do not have enough bulk capacitance, the output feedback
circuit goes "open loop" for just a microsecond or so. In this time, the
output transistors modulate or "burst" at their peaks causing audible
distortion. Lots of cheap amplifiers will do this just before clipping
at full power.

Not all things are created equal. Power is one of them.

If you want a mechanical analog, how about a V-8 piston engine and a jet
turbine


That's all well and good, but the important thing to examine here is
whether
the results are significant during normal operation. Hint: by
significant,
I mean audible. While there are several ways to lower distortion
(sometimes at the expense of noise, or at the expense of reliability, or
at the expense of other forms of distortion, and so forth), there is of
course a threshold at which further reduction is not warranted, nor is it
necessarily recommended since there's almost always a tradeoff in some
manner or another.

So your engine analog holds true, but if your application is to just drive
down a road, then either one will perform as well as the other.