April 2008
JAS Audio Bravo
2.3 Integrated 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.
 This integrated amplifier does not invert polarity.
 AC line current draw: 2.5A.
 Input impedance @ 1kHz: 35.0k ohms
 Output impedance at 50Hz (8ohm output)
 Minimum feedback: 5 ohms
 Maximum feedback: 1.7 ohms
 Gain, output voltage divided by input voltage, volume at
maximum, Lch/Rch
 Minimum feedback: 14.5mV, 23.2dBW / 17.3mV, 24.8 dBW
 Maximum feedback: 6.64mV, 16.4dBW / 7.03mV, 16.9 dB
 Output noise, 8ohm load, 1kohm input termination, Lch/Rch
Minimum feedback
 Volume control at reference position
 wideband: 3.36mV, 58.5dBW / 4.29mV, 56.4dBW
 A weighted: 0.858mV, 70.4dBW / 1.17mV, 67.7dBW
 Volume control full clockwise
 wideband: 1.72mV, 64.3dBW / 2.29mV, 61.8dBW
 A weighted: 0.479mV, 75.4dBW / 0.606mV, 73.4dBW
 Volume control full counterclockwise
 wideband: 1.06mV, 68.5dBW / 1.37mV, 66.3dBW
 A weighted: 0.264mV, 80.9dBW / 0.320mV, 78.9dBW
Maximum feedback
 Volume control at reference position
 wideband: 1.51mV, 65.5dBW / 1.81mV, 63.9dBW
 A weighted: 0.383mV, 77.4dBW / 0.473mV, 75.5dBW
 Volume control full clockwise
 wideband: 0.549mV, 74.2dBW / 0.612mV, 73.3dBW
 A weighted: 0.185mV, 83.7dBW / 0.204mV, 82.8dBW
 Volume control full counterclockwise
 wideband: 0.515mV, 74.8dBW / 0.573mV, 73.9dBW
 A weighted: 0.123mV, 87.2dBW / 0.130mV, 86.8dBW
Power output with 1kHz test signal  minimum
feedback
 8ohm load at 1% THD: 0.94W
 8ohm load at 10% THD: 17.3W
 4ohm load at 1% THD: 120mW
 4ohm load at 10% THD: 5.3W
Power output with 1kHz test signal  maximum
feedback
 8ohm load at 1% THD: 5.0W
 8ohm load at 10% THD: 19.3W
 4ohm load at 1% THD: 0.21W
 4ohm load at 10% THD: 6.9W
General
The Bravo 2.3 is a singleended, tubebased design
utilizing one of the large Russian 6C33 carbonplate triodes for the output tube in each
channel. The firststage tube looks to be an octalbased pentode type that I haven’t
seen before. A GZ34 rectifier is used for each channel. Since the design has a frontpanel
negativefeedback control, measurements were made for the extreme positions of this
control  minimum and maximum feedback.
Charts 1A and 1B show the frequency response of the amp
with varying loads. As can be seen in chart 1A, with minimum feedback the output
impedance, as judged by the distance of spacing between the curves of opencircuit, 8ohm,
and 4ohm loading, is fairly high, with the result that there is likely to be significant
coloration with speakers with widely varying impedance curves. The variation with the NHT
dummy speaker load is in the range of +2dB to 3dB over the audio range. With the feedback
control set to counterclockwise (maximum feedback), the measurements in chart 1B are more
reasonable and more in line with the measurements of many tube amplifiers. Frequency
response as a function of volumecontrol setting was essentially unchanged from full up to
50dB of attenuation. Volumecontrol tracking between channels was within 1dB down to 60dB
of attenuation.
Charts 2A and 2B illustrate how total harmonic distortion
plus noise vs. power varies for 1kHz and SMPTE IM test signals at 4 and 8ohm loads. The
attainable maximum power, generally rated at 10% distortion, is greatest with an 8ohm
load on the 8ohm output connection. The reduced power and higher distortion with 4ohm
loading on the 8ohm output would not be the case when a 4ohm load is driven from the
4ohm output. Then the performance would be essentially like the 8ohm loading on the
8ohm output. Not tested, 16ohm loading on the 8ohm output would likely yield less power
but with lower distortion than either 8 or 4ohm loading.
Total harmonic distortion plus noise as a function of
frequency at several different power levels for 8ohm loading on the 8ohm output is
plotted in Charts 3A and 3B. As is typical, distortion rises at both ends of the audio
range and noticeably more so with maximum negative feedback, as in Chart 3B.
Damping factor vs. frequency as measured on the 8ohm
output is shown in Chart 4. Here, with maximum feedback, the damping factor is highest but
with more variation over the audio range.
A spectrum of the harmonic distortion and noise residue of
a 10W 1kHz test signal is plotted in Charts 5A and 5B. The amount of ACline harmonics,
especially the 120Hz component, are rather high. As shown in the outputnoise
measurements, hum would likely be audible with highsensitivity speakers. The decay of the
signal harmonics with increasing order is more uniform in Chart 5B with the
maximumfeedback condition.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
A  Minimum Feedback
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Cyan line: NHT dummyspeaker load
B  Maximum Feedback
Red line: open circuit
Magenta line: 8ohm load
Blue line: 4ohm load
Cyan line: NHT dummyspeaker load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
A  Minimum Feedback
(line up at 1W to determine lines)
Top line: 4ohm SMPTE IM
Second line: 8ohm SMPTE IM
Third line: 4ohm THD+N
Bottom line: 8ohm THD+N
B  Maximum Feedback
(line up at 1W to determine lines)
Top line: 4ohm SMPTE IM
Second line: 8ohm SMPTE IM
Third line: 4ohm THD+N
Bottom line: 8ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
A  Minimum Feedback
8ohm output loading
Green line: 15W
Cyan line: 10W
Blue line: 3W
Magenta line: 1W
Red line: 0.3W
B  Maximum Feedback
8ohm output loading
Green line: 15W
Cyan line: 10W
Blue line: 3W
Magenta line: 1W
Red line: 0.3W
Chart 4  Damping Factor
as a Function of Frequency 
Damping factor = output impedance divided into 8
Red line: maximum feedback
Magenta line: minimum feedback
Chart 5  Distortion and
Noise Spectrum 
A  Minimum Feedback
1kHz signal at 10W into an 8ohm load
B  Maximum Feedback
1kHz signal at 10W into an 8ohm load
