VAC Vintage Mk II User Manual
Page 14
SPECIFICATIONS
The VAC System has been developed with the critical ear as the major arbiter of quality,
with both conventional and unique measurements providing insight and guidance as
necessary. The lack of emphasis on measurements is due to the fact that engineering's
arsenal of equipment and techniques do not operate on the pattern recognition principals that
control human perception of sound.
In the immortal words of Daniel von Recklinghausen, if it measures good and sounds bad
it is bad. If it measures bad and sounds good you've measured the wrong things.
For those concerned with test bench performance, the following describes typical measured
performance of a Vintage Williamson operated at 120 VAC, 60 Hz.
Power Output:
37 watts continuous average power at 1 kHz with less than 1%
THD into 8 ohms connected to the 4-8 ohm tap, both channels
driven.
Frequency Response:
down 0.5 dB at 6 Hz and 55 kHz, ref 0 dB = 1 watt @ 1 kHz.
(Note: response peaks will be observed at approximately 68 kHz and 190 kHz. Such peaks
are present in all tube type transformer coupled power amplifiers, and are normally
suppressed by the use of a phase compensation network in the negative feedback loop. VAC
has deliberately avoided this technique, finding that it is sonically inferior to the slight
ultrasonic peaks encountered with an excellent output transformer. The compensation
technique looks good into a resistive load, but falters in the real world. Interested
audiophiles should see Some Defects in Amplifier Performance Not Covered by Standard
Specifications by Norman H. Crowhurst, published in the October 1957 Journal of the
Audio Engineering Society.)
Power Bandwidth: down 0.5 dB at 15 Hz and 33 kHz, ref 0 dB = 35 watts @ 1 kHz.
down 3.0 dB at 11 Hz and 55 kHz, ref 0 dB = 35 watts @ 1 kHz.
Distortion:
< .2% THD at 1 kHz 10 watts
Noise:
S/N ratio > 84 dB
Sensitivity:
.8 volts input for full power output
Negative Feedback: Loop feedback is fixed at approximately 8 dB regardless of output tap
selected.
Absolute Polarity:
Does not invert signal polarity.
Fuse:
Slo-Blow type, 3.15A for 100 & 120 Volt configuration.