LA4 - Bench Test
"Benchmark's LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered."
- John Atkinson
"I measured the Benchmark LA4's performance with my Audio Precision SYS2722 system (see the January 2008 "As We See It")."
Frequency Response
"The preamplifier's frequency response in both balanced and unbalanced modes was flat from 10Hz to 200kHz both into the high 100k ohm load and into 600 ohms was taken with the LA4's volume control at its maximum setting; both the response and the superb channel matching were identical at lower settings of the control."
Gain Accuracy
"The gain for the balanced inputs to the balanced output with the volume control set to "+15" was exactly 15dB, and reducing the control to "0.0" resulted in a gain of 0dB—ie, the output voltage was the same as the input voltage."
Input and Output Impedance
"The LA4's balanced input impedance was both usefully high and higher than the specified >50k ohms, measuring 80k ohms (40k ohms per phase) at 20Hz and 1kHz and still 75k ohms at 20kHz."
"The balanced output impedance was a low 61.5 ohms, the unbalanced impedance 201 ohms, both values consistent across the audio band."
Channel Separation
"Channel separation was simply superb, at >140dB, R–L, and >132dB, R–L, below 2kHz, respectively decreasing to 130dB and 112dB at 20kHz."
"The superb separation measurement is a testament to excellent circuit-board layout, something I have commented on before with Benchmark D/A processors."
Noise
"From balanced inputs to balanced output, the Benchmark preamp offered extremely low noise, with virtually no power-supply–related spuriae in its output."
Headroom
"The LA4's balanced output doesn't clip (ie, when the THD+N reaches 1%) until a very high 24V."
THD
"I looked at the spectrum of the distortion at a similarly high output level; while the second and third harmonics can be seen, these are still at astonishingly low levels: each harmonic is at or below –120dB (0.0001%) and is close to the residual level of these harmonics in my Audio Precision SYS2722's signal generator."
IMD
"Tested for intermodulation distortion in balanced mode with an equal mix of 19 and 20kHz tones at peak level of 5V, the second-order difference product at 1kHz was effectively absent, and the higher-order products all lay at or below –114dB."
Conclusion
"Benchmark's LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered."
- John Atkinson, Stereophile Magazine
The above is just a brief summary of John Atkinson's independent lab tests. Please follow the link below to read his entire test report which includes 9 high-resolution test plots (including the two shown above).
