April 2009
JE Audio VS70
Stereo Amplifier: Measurements
All amplifier measurements are performed
independently by BHK Labs. Please click to learn
more about how we test amplifiers there. All measurement data and graphical
information displayed below are the property of SoundStage! and Schneider
Publishing Inc. Reproduction in any format is not permitted.
 Measurements were made at 120V AC line voltage with both
channels being driven. Measurements made on the 8ohm outputs of the left channel and
balanced inputs unless otherwise noted.
 Input/output polarity: noninverting
 AC line current draw at idle: 1.67A
 Input sensitivity for 1W output into 8 ohms, volume at
maximum, Lch/Rch
 Unbalanced inputs: 82.4mV / 81.9mV
 Balanced inputs: 117.3mV / 116.9mV
 Input impedance @ 1kHz
 Unbalanced inputs: 52.0k ohms
 Balanced inputs: 95.0k ohms
 Output impedance at 50Hz: 2.76 ohms
 Gain, output voltage divided by input voltage, volume at
maximum, Lch/Rch
 Unbalanced inputs: 34.3X, 30.7 dB / 34.5X, 30.8 dB
 Balanced inputs: 24.1X, 27.6dB / 24.2X, 27.7dB
 Output noise, unbalanced inputs, 8ohm load, 1kohm input
termination, Lch/Rch
 Volume control at maximum
 wideband: 2.49mV, 61.1dBW / 1.20mV, 67.5dBW
 A weighted: 0.46mV, 75.6dBW / 0.33mV, 78.7dBW
 Volume control at reference setting
 wideband: 2.06mV, 62.8dBW / 1.07mV, 68.4dBW
 A weighted: 0.40mV, 77.0dBW / 0.27mV, 80.4dBW
 Volume control full counterclockwise
 wideband: 2.32mV, 61.7dBW / 1.19mV, 67.5dBW
 A weighted: 0.38mV, 77.4dBW / 0.25mV, 81.1dBW
 Output noise, balanced inputs, 8ohm load, 1kohm input
termination, Lch/Rch
 Volume control at maximum
 wideband: 2.59mV, 60.8dBW / 1.39mV, 66.2dBW
 A weighted: 0.48mV, 75.4dBW / 0.34mV, 78.4dBW
 Volume control at reference setting
 wideband: 2.22mV, 62.1dBW / 1.20mV, 67.5dBW
 A weighted: 0.42mV, 76.6dBW / 0.30mV, 79.5dBW
 Volume control full counterclockwise
 wideband: 2.35mV, 61.6dBW / 1.24mV, 67.2dBW
 A weighted: 0.40mV, 77.0dBW / 0.26mV, 80.7dBW
Power output with 1kHz test signal
 8ohm load at 1% THD: 35.9W
 8ohm load at 10% THD: 45.5W
 4ohm load at 1% THD: 24.0W
 4ohm load at 10% THD: 38.9W
General
The JE Audio VS70 is a mediumpower stereo tube power
amplifier. Although not an integrated amplifier per se, its frontpanel volume control
allows adjustment with a single source.
Chart 1 shows the frequency response of the amp with
varying loads. This plot was made with the reference volumecontrol position set for 0.5V
input to produce 5W output into an 8ohm load. The highfrequency response is moderately
wide with an approximate 3dB point of about 40kHz. Highfrequency rolloff is nicely
controlled for all loading conditions. Output impedance as judged by the closeness of
spacing between the curves of opencircuit, 8ohm, and 4ohm loading is typical of many
tube amplifiers. Variation in output as a function of frequency with the NHT dummy speaker
load is a little less than +/ 2dB  an amount that could be quite audible with some
speakers. The frequency response of this unit was little affected by volumecontrol
setting. Tracking between channels was within about 0.5dB from full up to 50dB of
attenuation.
Chart 2 illustrates how total harmonic distortion plus
noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. This
design is optimized for an impedance close to the output terminal value (i.e., 8
ohms on the 8ohm output and 4 ohms on the 4ohm output), as half loading reduces the
power output at 1% THD+N considerably. Distortion is not particularly low with this design
despite the owner’s manual claims about "unique balanced circuitry."
Total harmonic distortion plus noise as a function of
frequency at several different power levels is plotted in Chart 3 for 4ohm loading. The
amount of rise in distortion at high frequencies is moderate and a good thing, but there
is quite a rise at low frequencies at powers much greater than a few watts.
Damping factor vs. frequency is shown in Chart 4 and is of
a value and nature typical of many tube power amplifiers, being relatively low and uniform
over most of the audio range.
A spectrum of the harmonic distortion and noise residue of
a 10W 1kHz test signal into 8 ohms is plotted in Chart 5. The magnitudes of the ACline
harmonics are fairly high and complex in nature. Further, intermodulation components of
line harmonics with signal harmonics are also moderately prominent. Signal harmonics
consist of a complex spectrum of even and odd harmonics, but with the second and third
harmonics being dominant.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Cyan line: NHT dummy speaker load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 10W to determine lines)
Top line: 8ohm SMPTE IM
Second line: 4ohm SMPTE IM
Third line: 8ohm THD+N
Bottom line: 4ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
4ohm output loading
Green line: 35W
Cyan: 25W
Blue line: 15W
Magenta line: 5W
Red line: 1W
Chart 4  Damping Factor
as a Function of Frequency 
Damping factor = output impedance divided into 8
Chart 5  Distortion and
Noise Spectrum 
1kHz signal at 10W into an 8ohm load
