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, 8-ohm load, unbalanced input, 1k-ohm 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

• 8-ohm load at 1% THD: 42W
• 8-ohm load at 10% THD: 110W
  
  
• 4-ohm load at 1% THD: 13W
• 4-ohm load at 10% THD: 130W
  
  
• 16-ohm load at 1% THD: 62W
• 16-ohm 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 8-ohm load on the 8-ohm output connectors. Performance using the balanced XLR input was the same. Frequency response, as seen in Chart 1, is beautifully controlled in the high-frequency end as a function of load. The low-frequency 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 plus-and-minus 1dB frequency-response 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 8-ohm load. Total harmonic distortion plus noise as a function of frequency at several power levels is plotted in Chart 3 for an 8-ohm 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 8-ohm 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 8-ohm load on the 8-ohm output, the signal distortion components are dominated by the second and third harmonics with higher-order harmonics at reduced and decreasing amplitude with frequency. Although the main hum components are very low in this amplifier, there are some 120Hz power-supply ripple component sidebands around the surpressed 1kHz fundamental test frequency.

Magenta line: open circuit
Red line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load

(line up at 5W to determine lines)
Top line: 8-ohm SMPTE IM
Second line: 4-ohm THD+N
Third line: 8-ohm THD+N
Bottom line: 16-ohm THD+N

8-ohm output loading
Cyan line: 80W
Blue line: 30W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

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