Zen Triode Amp
- Power Mystery Unveiled.
by Steve Deckert
this current world, consumers seem to gain all of their knowledge
about stereo gear from magazines and sales people. Manufacture's
literature certainly being at the heart of it. Yes, I would say
that pretty well represents the masses. Then there are those who
turn to books for answers. I wish more people read books instead
of magazines, but even books being largely written by "math
guys", can be just as misleading in the wrong hands.
would think the gear pictured above would be the end all, superior
to books for gaining the real facts and in a way it is. Ironically
though, it too suffers from the same miss-understood interpretations.
It's either a failure of engineers to communicate or a failure of
engineers to understand. (Both? ... sometimes yes.)
pains me to see that every day someone makes a purchasing decision
based on specifications. Besides RMS power, I'd have to say that
THD is by far the worst overblown subject in audio. Many people
who call me haven't had the opportunity to realize that there are
two basic forms of distortion encompassed by the spec: THD, and
that one can actually be good. They don't realize that tubes are
very different than solid state devices and that distortion and
power output are tightly linked.
of late, the Zen way of doing things has been challenged by the
math guys again, and the actual power output of the SE84B has been
questioned. In this rambling, I hope to shed some light on the matter.
TRIODE POWER RATINGS
Zen Triode for those who don't know, is not an ordinary amplifier.
It's sole purpose in life is to see how pure we can reproduce sound.
That is the reason for it's size and power output. It's a classic
example of the phrase "Less is more!"
on the observation that the less parts used in an audio circuit
the less coloration the circuit has... (Coloration's like grain,
defocused sound, and biased frequency balance)
based on the observations that more powerful amplifiers require
and use bigger parts and generally more complex circuits - it's
easy to conclude that larger amplifiers while having higher performance
will also have higher coloration's.
you made an imaginary line chart with Fidelity on one end and Power
on the other, you could design an amp to fit anywhere in that line,
but regardless of where you chose to put it, you would be balancing
between the two. That's a classic example of the phrase "Good
sound is a balance of compromises" Too far on the fidelity
end and you don't have enough power to drive anything, hence it's
useless. To far on the power end and you no longer have a class
A high fidelity amplifier.
found during the development of the Zen Triode Amp that there is
a magic spot on the line of power vs. fidelity where the balance
of compromise is minimal. Guess where on the line the Zen sits?
TRIODE RMS POWER OUTPUT
our web site, we mention that the Zen Triode is around 5 watts per
channel. Since then competitors have jumped at the opportunity to
interpret this as RMS (Root Mean Square) power output. After all
that has become the standard way to determine the power of most
amplifiers albeit far less meaningful in the tube world. In fact
around here (in the tube world) and in the spirit of good Zen thinking
we found that RMS really stands for "Real Meaningless Spec".
It would certainly go against the theme of our little amplifier
to post allot of real meaningless specs when we can
instead post allot of real meaningful reviews.
is not my intention to apologize for miss leading the public with
a 5 watt rating, because it was never stated to be RMS power. RMS
power is what you read using a 1000 cycle pure tone into a non inductive
"dummy load" consisting of large silicon resistors. This
makes a wonderful reference to the designer when comparing one amp
to another, or modifications within a single amp. However it makes
a rather pathetic reference of how music will sound through it.
Obviously music is not a pure 1000 cycle tone, and speakers are
not large non inductive dummy resistors. Our rating of 5 watts is
a peak power rating that takes into account things like: Peaks in
the music and the amplifier's ability to generate power peaks in
excess of it's RMS abilities not to mention distortion signatures
and clipping characteristics. It also takes into account the fact
that speakers are ever changing complex loads that behave very differently
than "dummy loads". We felt based on the less than
clear common interpretation of RMS watts that a more realistic
"music power" rating was in order.
the picture above you can see we have the gear to get anal about
specifications, but have always chosen not to complicate our sales
approach or your mind with excessive specification information which
we feel is commonly misinterpreted. The picture above is a blow
up of the picture at the top of this page. It shows the RMS output
of a single channel of our Zen Triode Amp to be at 2.38 watts just
before clipping. When the sign wave starts to flatten to a point
where the listener can detect unpleasant distortion the unit reads
around 3.40 watts RMS.
DIFFERENT RESULTS FROM DIFFERENT PEOPLE?
you have been enjoying measuring the RMS power of Zen amps in this
way, please be aware that output tubes (all of them) vary in emission.
A matched pair of tubes simply means they match each other. It doesn't
indicate if the tubes tested strong or weak. The difference between
a weak and a strong tube in the case of the 6Bq5's and or SV83's
can be enough to vary the reading by almost a watt.
For the RMS tests pictured on this page, we used a matched pair
of tubes (only one of which is measured at a time during the RMS
testing) that tested at 7500 micromhos. This is done on our Hickok
model 539a tube tester with the bias setting at 2 volts. We match
all our tubes here in direct micromhos using this classic military
tester. 7500 is about ave. for the SV83's that we've tested
(around 750). Some are as low as 4840 and some as high as 9750.
you can see just the tubes themselves can account for large differences
in RMS power figures of a Zen Triode Amp, as well as hours on the
tubes. We bias our Zens hard into class A at the expense of tube
life because A) it sounds better and B) the SV83 tubes are inexpensive.
If you test one after several hundred hours of use we estimate up
to a 20 % loss in power is possible from tube wear alone in extreme
SPEAKER LOADS ~ IMPEDANCE and SET's
are some stereotypes of how an amplifier drives a loudspeaker that
relate specifically to the impedance curve of the speaker. The stereotype
is that most amplifiers, especially low power single ended tube
amps, have difficulty driving low impedance loads. In fact this
has gotten so overblown that speaker manufactures are now listing
the minimum impedance right on the specs. Without fail everyone
that calls me about possible speaker prospects is concerned that
they're speaker selection may not have a friendly impedance curve.
Well, friendly to who? The Zen Triode amplifier is not like other
amplifiers, if it was it wouldn't carry the name Zen in the title.
The Zen Triode is perfectly happy with low impedance loads and will
drive a dead short.
is certainly against the grain, especially for single ended tube
gear, but was by no means an accident. Since one of the biggest
problems with low power single ended amplifiers is their ability
to drive difficult or moderately difficult loads, it's no wonder
that the SET market is so small and overlooked. It would seem to
me that when you have only small amounts of power to work with,
you certainly wouldn't want to handicap yourself further by having
the amplifier's power curve match speaker impedance. Doing so would
mean that at a speakers resonance, where the impedance is high,
the amplifier would have no problems or even put out more power.
So where your speaker is it's weakest from a fidelity standpoint,
at resonance, most amps are at there strongest further aggravating
the resonance's. Then where the speaker takes a good dive in impedance,
the amplifiers put out less power.
the amp would put the same power at any given frequency and the
speaker would have the same impedance at any given frequency but
this is impossible. Industry has focused on this for many years
creating high power amplifiers with lots of negative feedback and
high damping factors to make them "NOT FEEL" the speaker
and thereby not be so effected by its impedance. Speaker manufactures
have also focused on this by creating complex crossovers with Zobel
impedance matching networks that yield a flatter impedance over
the frequency bandwidth of the speaker. The problem with this is
POWER. To do it requires lots of power. We already know that high
power amplifiers are not as pure on the fidelity line and have more
coloration's. and less detail. Speakers with overly complex networks
become grossly inefficient and thereby require lots of power just
to sound good. If you throw only 1 watt at these units, most of
it is spent as heat in the crossover before it even gets to the
voice coil of the speakers.
the world of Single Ended Triodes, it's all about the first watt,
and the magic that lies there. This is why when used with conventional
speakers most SET amps fall short of delivering a good performance.
The pairing is not unlike trying to ask your car to start after
pouring orange juice into the gas tank instead of gasoline. My solution
to this problem was to do things backwards and design an amplifier
that put out more power into low impedance than into high impedance's.
This approach certainly won't solve all the obstacles of pairing
single ended triode amps with speakers, but it will make it possible
for most anyone to find out what single ended is all about.
marketing the Zen Triode for 2 years, 90% of our 250 customers were
able to use a Zen amp with their existing speakers. Speakers that
were designed for today's solid state power houses. And while I'm
sure none of them get LOUD like a big amplifier, I do know that
I was successful in letting these people not only hear what single
ended triodes were like, but gave them one that sounded better than
similar units at ten times the price. That by the way, is what gives
me the most pleasure, and why I enjoy my work so much!
I said I wanted to "Design an amp for the masses",
this was what I meant.
DOES IT WORK?
primary thing that makes the SE84B unique is that it was not designed
with a calculator to effect the max. power. In other words there
was no greed involved when balancing power output against fidelity.
A math guy will always match the output transformer's primary impedance
against the plate resistance of the output tube. The closer the
match, the more power the tube will emit. The bad side to this is
that it also will put out more distortion. I can be fairly certain
of this because we had to make our own power transformers to come
up with the right impedance for our needs. Our custom hand wound
air-gapped grain oriented silicon steel output transformers have
a primary impedance of 9800 ohms and the EL84 / SV83 output tubes
would rather see 1/2 to 1/3 of that. This combined with a single
6 ohm tap gives ideal clipping characteristics. on the average speaker
load. Lets face it, 8 ohm speakers are often closer to 6 ohm and
with a six ohm tap the Zen can drive either 8 or 4 ohm speakers.
The clipping characteristics. of this design are so graceful that
you can't hear when the amp is soft clipping. It takes a hard flat
line clip before you can actually hear it.
is this gracious clipping and lower distortion from the output transformer
that makes it hard to give a power rating that means the same thing
to everyone. If you were to measure it like a solid state amplifier
at .001 % distortion, you would have below a watt. When the engineer
measures the amp, it is his interpretation of the wave form on the
scope and or the distortion threshold he sets that determines the
RMS output. Consumers used to hearing that distortion is a bad thing
from large solid state manufactures have been grossly mislead to
assume that this would apply also to tube gear. I would guess that
most people who listen to a good SET amp, Zen included, are pushing
between 5 and 10% distortion and don't know it. Reason: Even order
harmonic distortion sounds good, is natural, and preserves if not
enhances the harmonics of room acoustics. Odd order harmonic distortion
(the type solid state circuits generate when clipping) is the exact
opposite. Nothing good or pleasing about it. In fact it rather sounds
like sandpaper going through a meat grinder. It creates ear fatigue
by it's very design because nothing God created on this earth that
I can find creates odd order harmonic distortion naturally.
the tests above, using the same output tube, the Zen Triode amp
performed with higher RMS output into low impedance loads. For example,
a 16 ohm load yielded just under or at 1 watt RMS before measurable
(not audible) distortion. (The waveform shown in the picture) An
8 ohm load yielded around 1.5 to 1.9 watts RMS. A 4 ohm load gave
us around 2.38 watts RMS and a 2 ohm load gave us around 3.21 watts
RMS. In the same tests, the amplifier was bridged using our series
bridging technique made possible by floating the outputs. In this
configuration the now mono amplifier exactly doubled all the figures
are overdone. Specs for solid state amps and the procedures for
measuring should not be the same as the procedures for measuring
tube amps. RMS to the end user i.e.. the consumer of tube gear means
"Real Meaningless Spec" and worse than that is THD, and
worse than that is DAMPING factor. Please don't let the math guys
trip you up with rigid specifications because the slightest tweak
of the knob on our test gear (and theirs) can change the readings
- making it largely open to interpretation. Remember RMS does not
account for Peak Power, Clipping characteristics, and the distortion
level where RMS is measured is open to the guy doing the measurements.
If people are telling you the Zen amp is only a watt, smile and
remember that you know better and remember that if you have a speaker
load that only coaxes one watt out of your each channel of your
Zen, that just means more headroom and besides that's where the
magic is, the first watt.