November 2002
Manley
Laboratories Snapper Mono Amplifiers: 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 with 120V AC line voltage.
 Output tube plate current adjusted to 30mA per tube when
warmed up.
 Power output and distortion plotted with both channels
driven.
 Gain, unbalanced input/balanced input: 36.4x, 31.2dB/19.2x,
25.7dB.
 Output noise, 8ohm load, unbalanced input, 1kohm input
termination: wideband 0.6mV, 73.5dBW; A weighted 0.13mV, 86.7dBW.
 AC line current draw at idle: 1.4A.
 Output impedance at 50Hz: 1.8 ohms.
 This amplifier does not invert polarity.
Power output with 1kHz test signal
 8ohm load at 1% THD: 60W
 8ohm load at 10% THD: 120W
 4ohm load at 1% THD: 10W
 4ohm load at 10% THD: 150W
 16ohm load at 1% THD: 53W
 16ohm load at 10% THD: 82W
General
This amp is a pushpull design rated at a nominal 100W.
Bias is set by convenient test points and adjustable controls on the top part of the
chassis. The idling current as received when warmed up was quite uniform between the four
output tubes at about 30mA (0.3V across assumed 10ohm resistors) and was not adjusted for
the measurements.
Measurements were made using the unbalanced input. It was
found that results with the balanced inputs were virtually the same. Frequency response,
as seen in Chart 1, is beautifully controlled in the highfrequency end as a function of
load. The lowfrequency response holds up down to 10Hz nicely at the 1W level of the test.
Output impedance is typical of many tube amplifiers giving an approximate +/1dB
frequencyresponse variation with the NHT dummyspeaker load. Total Harmonic distortion
plus noise as a function of power output and load for a test frequency of 1kHz is plotted
in Chart 2. Also shown in this chart is the SMPTE IM distortion for an 8ohm load. Not
having separate 4 and 8ohm outputs available, this amp is clearly designed for an
optimum load lower than 8 ohm, most likely around 6 ohms. This can be seen as the
attainable output power is more like 140150W into 4 ohms. As a result of this,
considerably less power is available into 16ohm loads. Total harmonic distortion plus
noise as a function of frequency at several power levels is plotted in Chart 3 for an
8ohm load. Amount of distortion over the main midrange energy band is less than 1% for
power outputs of 30W or less. Admirable is the relatively low amount of distortion
increase at the higher frequencies. However, distortion does rise considerably below 20Hz
at higher power levels. Still, this is very good performance indicating a good output
transformer design (as was the nicely controlled highfrequency response). Damping factor
vs. frequency referred to an 8ohm load is plotted in Chart 4 and is approximately 4.5
over most of the audio range. In the spectral plot of distortion and noise for a 10W 1kHz
signal into an 8ohm load on the 8ohm output, the signal distortion components are
dominated by the second and third harmonics with higherorder harmonics at reduced and
decreasing amplitude with frequency. There is quite a bit of hum modulation around the
suppressed fundamental 1kHz test frequency.
Chart 1
 Frequency Response of Output Voltage as a Function of Output Loading 
Magenta line: open circuit
Red line: 8ohm load
Blue line: 4ohm load
Cyan line: NHT dummyspeaker load
Chart 2  Distortion as a Function
of Power Output and Output Loading 
(line up at 5W to determine lines)
Top line: 8ohm SMPTE IM
Second line: 4ohm THD+N
Third line: 8ohm THD+N
Bottom line: 16ohm THD+N
Chart 3  Distortion
as a Function of Power Output and Frequency 
8ohm output loading
Cyan line: 100W
Blue line: 30W
Magenta line: 10W
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
