Reviewed by: Richard , Audio Enthusiast, from San Bernardino
Product Model Year:
I have owned several tube amplifiers, and listened to many
more. I have always enjoyed the 'warmer' sound of tubes, but they have always
been far from perfect. Transistor amps have great, clean bass with sharp, harsh
highs and mildly unpleasant mids (remember, we are talking affordable amps - I
am NOT saying that top of the line transistor amps sound bad, just that ones I
can afford sound harsh and unpleasant).
For instance, while a Dynaco ST70
has very clean mid-range and decent high frequency sound, the bass has always
sounded bloated and imprecise. The Mk IIIs, have a much cleaner bass, but the
tubes are incredibly expensive. My solution in the past has been to bi-amp ST70
systems so the tube amp carried mid and upper end frequencies while a nice,
clean transistor amp took care of the bass.
This form of bi-amping,
however, has created more problems than it solved. While all frequencies are
delivered to the speakers more 'cleanly' than with one amp, I found that I was
dissatisfied with the overall sound; the sounds were there but they didn't sound
So, I decided to try single-ended amplifiers. I started by
looking at prices and was astonished to find that 8 watts of single-ended,
stereo power started at $1,600 and went up from there. In addition, many used
tubes that made the KT88s from the Mk IIIs seem cheap by
Then, I stumbled across a little single-ended amp made by
Asusa, the K2003. This is a 4 watt per channel amp that uses three tubes, and
all are inexpensive. When I hooked up the K2003, I was soon struck by several
* it didn't sound like 'only' 4 watts;
* it had stronger and
better bass then my ST70, at only 1/10 the power;
* the mids and highs were
so sweet and musical that I was truly amazed.
* at $550 list, it was a
I was sold. THEN, I stumbled across Steve Deckart's website at
www.decware.com and started reading his papers about amplifier design.
Rechecking the K2003, I found that it used negative feedback and transistor
rectification - both big problems according to Steve.
So, I decided to
make my own comparison. I ordered a Zen Triode from Steve.
extensive, back-to-back comparisons, I can say that he is right; his Zen amp is
almost as far above the K2003 as the K2003 is above an old Dynaco. It is simply
amazing. Sounds that have always been there, but muddied, or somehow masked so
they weren't noticeable, suddenly stood out and grabbed my attention. A perfect
example is a recording that has extensive use of a steel guitar. It sounded
great on K2003, but on the Zen, all the odd sounds of a steel guitar were
rendered so clearly that it sounded as though it was in the same room with
Vocals, especially female vocals, had a new richness and timbre that
I didn't think was possible in a mid-priced stereo system such as mine.
Acoustical instruments often sounded as though they were live, not
My only objection is that the power output is so low, that my
system now has difficulty reproducing orchestral music. My speakers, at 90db,
are simply not efficient enough to do the music justice. This amp should have
speaker efficiency of at least 93db to really function well.
solution: I am going to sell the K2003 and my last ST70, purchase a second Zen
Triode, and use one per speaker as monoblocs. Wired this way, they will have
more than enough power to deliver any music I want to play.
As an aside,
my source is a Rotel RCD-955AX cd-player used as a transport, a California Audio
Sigma tube DAC, a Conrad-Johnson PV-2a preamplifier, and my speakers are B&W
I give my heartiest recommendation to this amp; it compromises
only power, but it delivers fabulous sound at a bargain-basement price, list
$550, same as the K2003, and uses tubes that are in current manufacture and are
very cheap (the power tubes are only about $7 each, compared to $15 dollars each
for ST70 tubes, $65 each for MkIII tubes, and $150 each for 300B tubes used in
all the 'best' single-ended amps you can buy.
Have a small budget but
want the best sound for your dollar? If you have the speakers for it, this is
Musical reproduction, sound stage
Similar Products Used:
Asusa K2003, Dynaco ST70, Eico ST70, Dynaco