KR Enterprise VT8000 MK monoblock power amplifier Manufacturer's Comment
Editor: First of all, I would like to take this opportunity to thank Stereophile for permitting Mr. Michael Fremer to review our "top-of-the-line" monoblock amplifier, the VT8000 MK, and to visit our factory in Prague, Czech Republic.
Second, if I may, I would like to respond to a number of inexplicable points that have been raised by your test-bench results that may give erroneous ideas of our sound quality and design philosophy, despite Mr. Fremer's very enthusiastic audition.
My primary duty is to answer, point by point, the results of the curves comprising the testing report you have sent me that will accompany the article:
Fig.1: This graph could be interpreted as valid if the amplifier was loaded with a noted impedance, not with a load that has not been established. [The load referred to was the simulated loudspeaker load Stereophile uses in all its amplifier reviews.Ed.]
Fig.2: This graph conforms to normal values.
Fig.3: It is impossible to measure this amplifier with a value of 4W, 2 ohms, in that no value of 2 ohms exists in this amp. Furthermore, for the graph at 2W with the simulated load the above also holds true.
Fig.4: This measurement is not valid for KR amplifiers, because none of our units have 2 ohm values. [As a loudspeaker with a nominal impedance of 4 ohms will always have an impedance that drops below 4 ohms at some frequencies, it is legitimate to test a tube amplifier's behavior into a load less than the nominal output transformer tap value.Ed.]
Fig.5: We do not understand the value you are testing or the results.
Fig.6: With regard to the testing of the odd-harmonic values, this is normal for tube amplifiers that are using directly heated triodes. Therefore, we cannot understand your comments.
Fig.7: The intermodulation spectrum at 19 and 20kHz has a very rapid drop, which is absolutely normal. What is confusing is that, at the beginning of the graph at 1000Hz, there is an interference whose origin our engineers cannot determine. [The spectral component at 1kHz is the second-order intermodulation product derived from the 19kHz and 20kHz tones. The interference at the far left of this graph is the residual DC component of the FFT analysis.Ed.]
Fig.8: Again, your laboratory has measured a 2 ohm value, which does not exist in our amps. No one understands why you persist in measuring a value that has no meaning.
Fig.9: The values appearing in fig.9 are not valid because we have only 4 and 8 ohms.
At this juncture, what remains fairly obvious is that no one in your testing department has asked us how our amplifiers work and what principle the Vacuum Transducer represents. In fact, with a static input, the amplifier can never give the maximum potential of the frequency response and the output power. Just to give you a simple way of measuring our new technology: If you feed a signal of 1kHz to the amplifier and calibrate the output at 1W on an oscilloscope screen without touching anything else, you will be introducing a musical signal reaching peaks of over 50W. Naturally, it was amusing to read that one of your contributing editors, Mr. Sam Tellig, in "Sam's Space," discovered this wonderful phenomenon on his own (Stereophile, September 1999, p.33). Allow me to quote Mr. Tellig: " 'FIVE watts,' I exulted. My friend Marc and I were listening to the latest version of the Audio Electronic Supply SE-1 power amplifier with upgraded transformers and the KR 2A3 output tubes. Much to Marc's amazement, this little 5W dynamo was driving the B&W 805 Nautilus speakers to reasonable sound-pressure levels. So much for B&W's suggested minimum amplification of 50W." He continues by saying, on p.37, "The SE-1 'works' okay with the B&W Nautilus 805, even though B&W recommends a minimum of 50W, not 5W."
To clarify how our sophisticated tube technology with extremely high vacuum functions, KR was forced to apply our tubes to circuitsie, build amplifiersto demonstrate what could be achieved in audio by using our new tube technology. It is only now that the various OEMs have found our KB 300B tube models to give 25W.
Surely, it was the first time these gentlemen found themselves in front of the raw power of the new KR technology, where the dynamics and, consequently, the music drive our tubes at output powers never achieved before, either with normal/traditional tubes or transistors. Therefore, using standard values for all test-bench measurements is completely invalid, bordering on shortsightedness and engineering incompetence.
To declare a generic instability is incorrect in that your laboratory neglected to say or state "What is potential instability?" Mr. Norton should elaborate exactly what he means by this comment, in that no bench test was tied to his statement. We believe Mr. Norton might have been in good faith, but, given his repetitive testing errors at 2 ohms (not existing), we would be happy to come to Santa Fe at our expense and organize refresher courses on tube amps in general and our KR design philosophy in particular.
This logically brings us to the conclusion that your testing criteria cannot be applied to all amplifiers. Every amplifier must be measured according to its characteristics. Another point is that the preamp you use in your testing might not be compatible in obtaining the best bench results for our amplifiers. [No preamplifier is used in our bench testing.Ed.]
After receiving your 22-page galley proof including the test-bench report, with...a six-day deadline [for our answer], I called a number of engineers, some residing in America, some in Asia, and some in Europe. The answer was the same: You cannot apply the same method of measurement to all amplifiers. Unfortunately, your laboratory did not contact us for ulterior information and amp characteristics. If someone had called us, you would have been spared the extra work of measuring [the] nonexistent 2 ohms [setting].
With regard to your well-taken point about the sufficient replacement and warranty parts, I believe Stereophile ignores the international law that every manufacturer must guarantee the existence of available spare parts for the duration of five years, starting from the first date of production of the model in question. KR has supplied its distributors with these parts and is compliant with the law.
If your laboratory has really opened the amplifier to examine the quality construction, you could easily have noted that [its] resistors, capacitors, and solid-state devices are available all over the world, being that they are of standard production. Except for the output power devices, future or potential KR customers should feel reassured that the company has the [pieces] necessary to make the amplifier whole/working. Repairs can easily be carried out wherever a KR Service Center or distributor/importer exists.
Although someone thought it very funny to call the units "boat anchors" if they were not serviced with our designer parts, we feel that this sense of humor is misplaced, and thought it to be malicious in that it is untrue.
The same goes for your test-bench procedures, which throw an unflattering light on our product, misrepresenting our technology to the industry and the public. It is natural for anyone who has not physically auditioned our amplifiers to come to the conclusion that Mr. Atkinson did: "We reserve the right to withhold unconditional recommendation of the KR amplifier due to the unfavorable test results."
We would like to ask in the future, if Stereophile is of the same mind, to retest our products using our standards, and then reserve a second opinion not only after our excellent bench reports, but the marvelous sound.
KR cordially extends an open invitation to our next public audition in the States, at CES 2000, Alexis Park Hotel, January 69, 2000, Rooms 1707 and 2607.Dr. Riccardo Kron, KR Enterprise