by Steve Deckert
usually don't do this, i.e.... debate over-debated issues because
it starts feeling like a newsgroup discussion. This continuation
is the result of a new response that is even better than the first
one in the way it perfectly encapsulates one side of this
"great Debate", so I thought I would post it.
this email is so lengthy, I am going to respond to it a point at
a time. My responses will be in bold face.
you for your detailed and thoughtful reply. However, I must take
issue with you on a number of things you brought up.
of all, I don't listen to music (mostly classical) with my amplifiers
operating at a nominal level of 10 watts. The average listening
level is closer to 1 watt, which I have measured numerous times
with my HP A.C. voltmeter and "Mitey-Mike" based sound level meter.
Besides, if your assertion were true that 10 watts is closer to
nominal, then how could your Zen Amplifier, Pass's Zen Amplifier,
or any of the other under 10 watt Class-A Single-ended triode amplifier
possibly perform without producing excessive distortion at more
than moderate levels?
are responding to the following statement that I wrote in my previous
your 200 watt amplifier as an example and listening at a nominal
level of 10 watts, you would need 1280 watts to reproduce a 20 dB
musical peek without clipping the wave form."
don't listen to my system at an average level of 10 watts either,
but then I didn't say that was the average listening level, I said
at a nominal level of... thinking at the time what it would take
to reproduce live music at live levels on Ave. efficiency speakers
of 86 dB.
no mistake, solid state cost effectively gives more people the option
to play music loud than tubes. As far as average listening levels,
I also agree there is more content in the first magical watt than
most people realize.
Zen amp on the same ave. efficiency of 86 dB speakers cannot perform
without producing excessive distortion at those levels, nor could
(as you point out) any other 10 watt amplifier. The way this is
compensated for is by using more efficient speakers. If you wanted
to achieve those levels you could easily do so with large horn loaded
home system is tri-amplified, which I think is the only way to go
for true "high-end" performance. The output of my power amplifiers
(7 channels, including an extra sub-bass servo-feedback sub-woofer
(my design) in the rear of the room) drive my speakers directly,
with no passive crossover to attenuate (or otherwise "color") the
signal. My power amplifiers (custom-modified MOSFET -based kits)
have massive power supplies--8 amp. toroidal transformers and 80,000
mfd. of power-supply capacitors per stereo-pair. These amplifiers
drive the most excellent Morel MW-142 woofer and MDT-33 tweeter
in small satellite enclosures, which I maintain provide better imaging
and lower coloration than most (if not all) of the larger system
designs (which, often have four and five figure price tags). You
probably are not all that impressed with measurements, but, using
a pink noise source in 1/3 octave bands, my system measures within
+/- 3 dB from 40 Hz. to 18,000 Khz., on axis, or 30 degrees off
horizontal axis. This is partly due to the very small cross-sectional
dimensions of the midrange/midbass driver, the low mid/high crossover
frequency of 1,900 Hz., and the egg-shell-like small enclosure design.
I hope to perform pulse-response measurements soon, using a spectrum
analyzer program on my computer.
I am impressed by measurements (specs), they are the only tangible
non subjective thing we have to analyze performance. I just
don't care what the specs are if something sounds good and rather
like not knowing what the specs of a particular piece of audio gear
are before I listen to it. I like to audition audio gear with
an open mind, and the less I know about what I'm hearing, the more
I can hear.
the reserve instantaneous available power provided by my power amps,
at even high levels for home-listening in my 12 X 20 ft. listening
room (which, by the way has been acoustically optimized for the
system, and the satellites and sub-woofers have been optimally positioned--away
from the wall, etc.) I can achieve more than adequately high listening
levels without audible clipping.
clipping - I assume that means a form of distortion that you are
consciously able to detect. At high levels clipping could
be harder to consciously detect against the 100 dB "noise floor"
created by the music. However, I'm not saying YOUR system
focus on clipping a moment. A good solid-state amplifier will clip
a sine wave coming from a test generator with absolute symmetry--perfectly
flat on the top with no droop, and absolutely no overshoot or spikes.
This was the problem with the earlier transistor designs and caused
them to sound harsh. I followed this carefully back in my college
days (late 60's) when I was selling and installing the new Marantz
8B's and Model 9's to the more wealthy people in my community when
I was working my way through college. Yes, my first amplifiers were
tube-types, Dynaco Stereo 70's and Mark III's, and they sounded
damn good, I almost cried when I finally got rid of them. This was
when the new solid-state units were just coming into existence (Carver,
also indicate that when a solid state output device clips it is
actually shutting off and then turning back on again creating DC
on the voice coils of your speakers, and causing the speaker
to stop momentarily. Severe clipping means not enough air
moves over the voice coil and it over heats, the number one cause
of blown speakers. This is why it is possible to blow up a
100 watt speaker with a 10 watt solid state amplifier.
sort of well designed transistor power amplifier is capable of amplifying
the dynamics of music without audible clipping. It has been my careful
study throughout the years that the only clipping that occurs, does
so only at the relatively fast transient peaks, and because these
peaks are fast, they simply cannot be heard. Why? Because these
harmonics occur for only a brief few milliseconds and the psychophysics
of the human hearing mechanism simply does not have the neurological
apparatus to detect them--the way the cochlea and its associated
neuro-waystations simply mask these effects is well understood.
Read a good book on psychoacoustics to find this out.
I could write a good book on psycho acoustics. It is my main
focus. What happens in the mind to make one think a system
sounds good, is the perspective from which I design audio gear and
the very reason I can come across as having little respect for specs.
And you are right about our inability to consciously hear
the relatively fast transient peaks. Again if you like numbers
the neurons in the human brain can not fire fast enough to distinguish
phase above around 2800 cycles, yet the effects of such can be heard
in the way they effect the sound stage.
simple equation dB = 10 log (P1/P2) Would then indicate that if
at my nominal 1 watt for an 85 dBm or so acoustic level, then the
loud passages of the orchestra are allowed to obtain over 110 dBm
of acoustic level before my amplifier would begin to clip to a point
that could be audible. Remember, my amplifier can produce 300 watts
or more for a several milliseconds without clipping--long enough
to sustain nearly all of these short duration peaks without clipping.
That's what is called reserve power, something that just is not
present with your preferred low power Class-A single ended tube
designs--all they can do is squash these peaks severely and in so
doing throw in the signal all kinds of harmonic content (coloration)
that simply is not supposed to be there--if you want reproduction
that is close to the original source. It's ironic that you criticize
my 200 watt RMS amplifier based upon its insufficient power and
yet advocate the use of a 6+ watt single-ended Class-A amplifier
in you Zen Amplifier article. I suspect that such an amplifier would
be very effective in driving headphones, but not much else.
don't think there is an argument here about clipping, I simply think
tubes can sound better. I am sure your system is not clipping
99% of the time at the average listening levels you operate it in.
power, called "head room" is a monumentally important thing to have
a lot of in a good solid state amplifier for reasons we have both
pointed out. If solid state amplifiers didn't clip so aggressively
(flat line DC at the peaks) the amount of head room would not be
a serious issue to the listener. In a tube, clipping is completely
different. Since a tube works by passing electrons from a
cathode through a charged screen to a plate by way of different
electrical potentials, there is no such thing as "clipping" as we've
come to know it through this discussion. The tube never shuts
off, and never puts DC on the voice coil. It never creates
an unnatural flat line at the top of musical peaks. What happens
is more like a bucket (the plate) being filled with water (electrons).
When the plate is saturated there is no longer a potential difference
- so, no more electrons are accepted on the plate until there is
room made on the plate by the dissipation of those electrons.
Instead of clipping, a form of compression occurs as the difference
between the continuous power and peak power are reduced.
too have spent many hours observing amplifiers clip on an oscilloscope.
In fact I have a special oscilloscope (formally used for medical
signals) that has a high-persistence (P7) phosphor, which is ideal
for catching the peaks of musical content. I have also built a special
sample-hold circuit from an LED dB level meter I.C. which has been
carefully adjusted to light an LED and hold it on for a half-second
any time my amplifier clips (I also have to compensate for changing
power line voltages). Using this apparatus, I have found that my
amplifiers rarely clip. And, when they do, it is of such short duration
that it simply is not audible. Incidentally, as an experiment, I
once connected a very fine 30 watt solid-state amplifier to my Morel
Woofers and found it to be inadequate--its clipping was indeed audible!
Thank god it did not disguise this clipping by squashing it! This
was a clear indication that I needed more reserve power.
perhaps a 30 watt tube amp. And yes, thank god it did not
disguise this clipping by compressing it because that would have
been musical by comparison.
what about these clipped peaks? Observing this on the scope, these
peaks are again, relatively brief. A properly designed amplifier
of adequate power will clip these peaks (which, remember, occur
rather infrequently in the context of the rest of the mass of the
musical content) cleanly, without overshoot, etc. Thus, the harmonic
structure of this clipping is of very high frequency and low power
content. It is well above 3,000 Hz., and probably exists mostly
as harmonics above the 18 Khz. audible top end--remember, these
are harmonics of already very brief peaks--peaks of generally less
than 5 ms. which are too short in duration to be perceived.
observations have been that solid state clipping can happen anywhere
from 20 Hz to 20 kHz and usually does. In fact the kick drum
centered anywhere from 40 to 100 cycles depending on how it's tuned,
can usually by found on a scope as the number one clipping frequency.
I didn't know you could have harmonics of a fundamental clip that
high up the spectrum without either the fundamental itself or one
the first three harmonics of that fundamental clipping.
also need to mention that the load given to the amplifier by the
speaker at any given frequency and the amount of negative feedback
will largely determine where in the frequency band an amplifier
is most likely to clip. To think of an amplifier as a separate
entity would be misleading since the speaker completes the circuit,
and no two speakers are alike.
has been demonstrated that the perception of "harshness" occurs
in the critical 800 Hz. to 3 Khz. region, and it has to be sustained
long enough to be perceived by the hearing mechanism. The distortion
produced by the occasional instantaneous clipping of a sharp music
spike in an amplifier has most if not all of its power-spectral
content well above this critical frequency range.
on a linear scale it might, but hearing is non linear. Our
ears have the highest sensitivity in the 800 Hz to 3 kHz region,
so even though the majority of clipping may occur outside
this band, any clipping in this band would be perceived.
say that "even order harmonic distortion of tubes can be a non-factor
before clipping in a good circuit". That's basically true. A well
designed tube amp will probably have less than 0.1% harmonic distortion
below clipping, which is inaudible. But the problem comes when the
tube-amp runs out of steam and begins to go into clipping. I find
200 watt (RMS) tube amps. insanely expensive, and almost non-existent.
The coloration of a tube amp. is more "consistent" (your words)
if it is lower in power and thus able to squash the signal more
readily. Well designed 200+ watt RMS solid-state amps. are readily
available, easy to maintain, fairly power efficient (class A-B),
and not too expensive.
debate is not about practicality, but musicality. Tube amps
a not terribly practical. In fact a good one is not unlike
a pet, requiring special attention and upkeep. Solid state
was a less expensive more reliable means and largely more profitable
way to build amplifiers so everyone jumped on it.
differences between the even order harmonic distortion
tubes generate and odd order harmonic distortion
that solid state amplifiers generate are profound. If
you had to listen to both types at a level where they were in heavy
distortion, the solid state would make your eyes water, where
as the tubes would possibly go unnoticed. Clear an issue of
now comes the High-End (Retro Ghetto?) Politically-correct single-ended
Class-A Triode amplifier. Generally, these products can produce
about 20 watts maximum. So just imagine how these "waveform squashers"
color the signal with all but perhaps the most efficient loaded-horn
type of speaker systems (the latter of which really are "colorizers"!--believe
me, I spent dozens of hours in listening rooms during my college
days listening to these beasts, the only thing worst was the horrible
Bose 901). So, Steve, in your Zen Amplifier article, you say that
amplifiers contribute more to the quality of the sound than anything
else, including speakers. Yes, for these "Class-A Puny-Watt Triode
Wonders", you are probably right. They should definitely have the
ability to muck up the sound more effectively than anything else
in the signal chain.
in this country and market, I clearly expected you would also be
an anti-horn person, so let me just say that the horns you listened
to sucked, and you probably heard them on solid state gear which
is a no no. Good horn speakers have the most intimate coupling
to amplifiers of any speaker. For that reason, you do not
want to try to separate the two with feedback, and that eliminates
almost all solid state circuits. There are no good horn
speakers in this country.
so, is 2nd order or even-order harmonic content distortion really
what we want? Does it exist on the original master-tape? These Class-A
designs are really tone-controls in disguise, as I mentioned in
my last letter. I see people insist on buying preamplifiers (even
passive preamps) that are devoid of bass and treble controls (even
a tone-defeat is not good enough for these "purists") and yet connect
these preamps up to Class-A amplifiers that are rich in adding the
sort of "warm" coloration that is raved about--nice tone control,
eh?--except you can't turn it off!
we really want is zero distortion, but this is audio where no one
can have it all. And IF we ran amplifiers to a level where
they begin to distort, even order would be far less of an offense
that odd order would it not? You imply again that tubes are
always producing even order distortion, yet you yourself agreed
that a good tube circuit operated within its parameters can have
less than .1% I have been told and have done double blind
listening tests to see, that humans can't detect harmonic distortion
until it reaches 3%. I found that to be basically true, so
when I see people basing buying decisions on the difference between
.01 and .0001 % harmonic distortion I just have to shake my head.
of the fewer parts needed to construct a tube circuit, I find
a good tube amp not only has LESS coloration than solid state, but
it can also sound faster.
I want to achieve is a music system that does nothing to the signal
coming from the source--be it compact disk or master tape. I want
all the creativity, artistry, and hall effects to end where the
rarefactions of air hit the microphone capsule. At least as much
as possible--I know I am still victim of the whims of the recording
engineer. But the recording companies are getting better and better
all the time. A fine example of this is the improved CD quality
of Deutsche Grammophon over the years.
classic statement made by all engineers and audiophiles absorbed
with specifications.. I want the same thing stated in a different
way... to achieve a music system that breaths with openness and
is not veiled by negative feedback and excessive parts to insure
great specs. You see even more important than great specs
are the things that specs can not yet measure, like clarity, depth,
width, focus, delineation. These are the things that
determine how REAL a recording sounds. If you take your average
solid state amplifier with perfect specs and compare it with my
Zen amp, you will discover that the Zen amp lets you hear several
additional levels of detail, the result being far more realistic
and involving at moderate listening levels.
phonograph records and vacuum tube amplifiers don't do this, they
add color--something which was not present in the original. After
listening to such a system for months or years it would be natural
for one to say that a CD/Solid-state system sounds thin or lacking
in warmth, etc. But on this basis so would perhaps be the sound
of a live performance. This reminds me of the psychology experiment
where young chicks are given two containers of "water". In one container
is pure water, but the other container contains mercury. the chicks
immediately go for the container of mercury--it is more shiny and
reflective than the water--a sort of super-stimulus--more warmth,
more air around the instruments. In college I got the same effect
smoking a joint!
can't agree with that, but I will suggest that getting stoned before
listening would be similar to hearing my Zen amp. You would
be so lost in the music you wouldn't care about clipping.
wonder what would happen if individuals of the Pro-Tube camp were
asked to listen to two sources hidden behind a curtain. One curtain
would be a live performance--say a string quartet playing Schubert,
while being miked. And, they would then be asked to listen to the
amplified reproduction of that string quartet through the best Single
Ended Triode Class-A amplifier system money can buy. I suppose they
would favor the latter, as they would hear the warmer sound and
the increased "air around the instruments" produced from the increased
coloration introduced by the amplifiers.
would favor the later because the later would have the ability to
deliver a far more accurate presentation. In fact it should
be almost impossible to tell the two apart. I can assure you
that the triode camp could pin point a solid state amp in the signal
path in less than 5 seconds every time.
your comment about negative-feedback. You, and many others like
to imply that negative feedback is a bad thing. Sorry, but this
only indicates your ignorance of electrical engineering concepts.
You should refer to articles already written by Tom Nousaine, David
Rich, Tomlinson Holman and others who have already gone into depth
about such misunderstandings. Negative feedback is part of the reason
solid state amplifiers can achieve extremely low distortion figures
of say less than 0.05%. But, according the Pro-Tube Camp, low
distortion must be a bad thing--something to be avoided, or at least
not discussed. It's no wonder then why manufacturers of tube amplifiers
seldom publish any meaningful distortion figures. Besides, according
to many who make all those subjective testimonials, careful laboratory
measurements are meaningless. If what they claim is true, the laws
of physics somehow magically do not apply to audio equipment!
laws of physics do not apply to the laws of psychoacoustics, nor
do specs (as I previously pointed out) define all the variables
of realistic playback. Also I do not feel terribly ignorant
of electrical engineering concepts. I obviously have done
more with negative feedback study than yourself because I was willing
to look beyond specs. Oh believe me, negative feedback is
the best thing since sliced bread for engineers. It lowers
distortion and raises dampening by a considerable amount.
The problem is that by taking the output of an amplifier and running
it back into the input stage, you create a time delayed input super
imposed over the original signal that veils and homogenizes the
output. Quite frankly it is a speaker dependent argument,
but in general I find negative feedback has the exact same sonic
effect as throwing a blanket over your speakers.
you mention that solid-state amplifiers have more capacitors in
the signal path. Well, nothing could be further than the truth.
Besides, a properly spec'ed coupling capacitor has absolutely NO
effect on the sound. All it is doing is blocking DC. All of this
talk about one brand of capacitor having superior sonic characteristics
to another is absurd superstition and could never be proven with
objective A-B listening tests. Besides, most modern solid state
power amplifiers have only one coupling capacitor. It is at the
input--to block any small DC offsets. The rest of the design is
direct-coupled, all the way to the loudspeaker. My home system has
no passive crossover network at the loudspeaker either. I'm using
24dB/Octave (Linkwitz-Riley) active equalization using 1% matched
components for nearly identical response characteristics from both
stereo channels for maximum "holographic" effect. The instruments
of my reproduced orchestra have excellent spatial placement. In
fact, better than anything I have yet heard at my local High-End
Saloon listening to five figure-systems, but, of course, this is
just my subjective (and therefore biased) opinion. Here, Double-blind
ABX testing would be a bit difficult.
position on coupling capacitors is depressing and absurd.
Capacitors are the single most worse thing
you could ever pass a musical signal through, necessary evils.
What kills me is that the time constants associated with capacitor
design can be easily measured, and you should like that. BTW,
I've never heard a system in a High End Saloon (grin) that sounded
better than my own either. They typically don't.
at the sketch of your Zen Amplifier at the top of your article,
I believe I see three coupling capacitors per channel, if this is
true, aren't you being a bit hypocritical here? The vacuum tubes
and output transformer are much bigger contributors to coloring
(distorting) the signal than a coupling capacitor. A coupling capacitor
simply exhibits a very low reactance (resistance) throughout the
entire audio range--that's all. And, all the absurd theories by
proposed certain tweako capacitor manufacturers are just plain fancy.
One 2 Mfd. mylar capacitor will have the same effect as any other
2 Mfd. mylar capacitor--it has no "sound" of its own.
schematic you're referring to was an integrated amplifier from which
the Zen amp project was born. The Zen amp is only the last
stages of that circuit, and does use only one coupling cap.
And none is used on the input, the input is direct coupled.
The output transformers do more for creating
a harmonious impedance balance between the amplifier and speakers
than they do damage by coloration, and are the very reason why horn
speakers can sound so good on a tube amp.
stuck with my Dynaco Mark III's up until the early-eighties, for
my more serious listening of opera and orchestral music. But, as
a hobbiest, I began to build better and better solid-state amplifiers.
And, when the better MOSFET designs came out, it was clear to me
that it was time to make the switch. No more annual replacement
of those expensive 6550 matched pairs, or monthly checking of the
grid-bias. Better, cleaner, purer sound resulted from my transition
to solid state amplifiers.
Apt/Holman company nearly 20 years ago designed a transistor amplifier
that would simulate the squashing effects of a tube-amplifier going
into clipping. Using special circuitry they made the edges of the
clipping rounded, just like the effect you get with vacuum tubes.
They then did some serious blind-testing with a group of listeners,
comparing this experimental design with their standard design which
clips very squarely, with no overshoot or droop. And, to their amazement,
their listeners reported that they preferred the sound of the un-modified
square-clipping amplifier to the sound of the vacuum-tube-like clipping
effect. I wish I had my hands on the paper they published on this--I
would send it to you.
I should think they would have found the unmodified amp more open
sounding , and the other modified amp to be slightly more veiled
by the additional complexity of the circuit.
find the preference much of the High-End community has (as exemplified
by Stereophile Magazine) towards the preference to vinyl recordings
to the superior CD, and Vacuum Tubes to transistors (especially
the Single-ended Class A Triode four and five figure nicknacks
probably only purchased by the very rich who, not caring a diddily
about the sound quality, only want the stuff to impress their colleagues
at cocktail parties) took two equally giant steps backward in the
progress of making sound reproduction more real. When these such
digressions became rampant, many very brilliant electrical engineers,
being designers of fine sound equipment, left the industry to seek
other occupations in computer technology, video, etc. I personally
know at two of them. They simply could not stand the insanity.
lot of truth in that statement.
Steve, you are a musician and therefore I
applaud you. We need more musicians, especially musicians of a classical
music bent. Interest in classical music is waning in the U.S.,
as witnessed by a progressively declining attendance to live concerts
(and NOT the allegedly inferior 44.1 Khz. sampling rate of the CD--how
absurd!), perhaps just another indication of the gradual "dumming
of America". Perhaps, it would be more beneficial to humanity that
you concentrated your efforts to the making of music, or the reporting
of fine musical recordings, than the retrograde and ultimately fruitless
interests of yet another vacuum-tube amplifier design. It is probably
a waste of your creative potential as an artist. Instead of trying
to design amplifiers, have you thought seriously about composing
offense Larry, but I am focused in the correct direction.
My work will make it possible for many people to enjoy listening
to music again who otherwise may not have.
I find interesting parallels between the High-End audio industry
and the fashion industry. Insanely expensive stuff--wives thumb
through fashion magazines that advertise four-figure designs while
their husbands thumb through Stereophile Magazine imagining themselves
owning that five-figure amplifier or speaker system advertised.
Oh, yes, tubes are definitely more photogenic than transistors.
correct about the similarities from a market perspective,
I have no real argument with that.
Larry, you certainly haven't left anything out.. except possibly
an open mind. Let me conclude this, my last response, with
years ago I had a friend who I used to involve in my speaker
design work because he had good ears. He went to school to
become an engineer. As the first year passed I watched the
magic of audio leave his spirit as his schooling defined boundaries
from which to think inside. Once he knew the laws, there was
no point in trying to work outside those laws "because it won't
work". One day at the repair bench we were finishing up a
job, and having a beer when I bet him I could turn the beer can
into a speaker. I explained that by cutting it in half and
installing a magnet inside, reassembling it and wrapping a coil
around the outside that I would have a working speaker. He
though about it for a minute and bet me that no sound would come
out because there would be no linear travel possible by the voice
coil. I still have that beer can and it still measures +/-3dB
from 300 to 10K.