April 2003
Lamm Industries
ML1.1 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.
 Power output and distortion plotted with one channel driven
(this is a mono amplifier).
 Gain: 21.2x, 26.5dB.
 Output noise, 8ohm load, unbalanced input, 1kohm input
termination: wideband 0.122mV, 87.3dBW; A weighted 0.045mV, 96.0dBW.
 AC line current draw at idle: 1.9A.
 Output impedance at 50Hz: 1.08 ohms.
 This amplifier does not invert polarity.
Power output with 1kHz test signal
 8ohm load at 1% THD: 42W
 8ohm load at 10% THD: 110W
 4ohm load at 1% THD: 13W
 4ohm load at 10% THD: 130W
 16ohm load at 1% THD: 62W
 16ohm load at 10% THD: 72W
General
The Lamm ML1.1 is an upgraded version of the ML1, with
simplified bias and balance adjustments. Two meters and associated screwdriver controls
are used to set the total plate current and balance. The idling current as received, set
up, and warmed up, was the nominal design 300mA and the balance was zero. Neither control
was adjusted during the measurement period.
Measurements were made using the unbalanced RCA input and
an 8ohm load on the 8ohm output connectors. Performance using the balanced XLR input was
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 less than plusandminus 1dB frequencyresponse variation with the NHT dummy
speaker 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. Total harmonic distortion plus noise as a function of
frequency at several power levels is plotted in Chart 3 for an 8ohm load. Admirable is
the relatively low amount of distortion increase at the higher frequencies, which is a
hallmark of Vladimir Lamm’s design philsophy. Damping factor vs. frequency referred
to an 8ohm load is plotted in Chart 4, and is between 7 and 8 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. Although the main hum components are very low in this amplifier, there are some
120Hz powersupply ripple component sidebands around the surpressed 1kHz fundamental 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: 80W
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
