All measurements taken using an Audio Precision APx555 B Series analyzer.
The Meitner Audio DS-EQ2 was conditioned for 30 minutes at 1Vrms at the output before any measurements were taken.
The DS-EQ2 phono preamp is designed to operate with DS Audio optical cartridges, and therefore operates differently from a conventional phono preamp designed for moving-magnet (MM) or moving-coil (MC) cartridges. As per DS Audio’s technical information page, these optical cartridges are an “amplitude proportional type” transducer, as opposed to a “velocity proportional type” transducer found in record cutting heads and both MM and MC cartridges, which operate on electromagnetic induction.
In terms of measuring the DS-EQ2 phono preamp with the APx555 analyzer, certain issues needed to be overcome. For a detailed description of these issues, along with test set-up configurations, as well as an explanation of how our DS Audio inverted EQ curve was derived, please see our measurements of the DS Audio DS 003 phono preamp.
The DS-EQ2 offers one pair of unbalanced RCA inputs, and one pair of unbalanced (RCA) outputs. There is a switch on the front panel that will enable a high-pass filter. Unless otherwise stated, all measurements were taken with the high-pass filter disabled. Using these settings, to achieve the reference output voltage of 1Vrms at 1kHz at the DS-EQ2 outputs, 125mVrms was required at the output of the APx555.
Our primary measurements revealed the following (unless specified, assume a 1kHz sinewave, 1Vrms output into a 100k ohms load, 10Hz to 90kHz bandwidth):
|Parameter||Left channel||Right channel|
|Crosstalk, one channel driven (10kHz)||-106.8dB||-108.0dB|
|IMD ratio (18kHz and 19kHz stimulus tones)||<-93dB||<-93dB|
|IMD ratio (3kHz and 4kHz stimulus tones)||<-93dB||<-93dB|
|Maximum output voltage (at clipping 1% THD+N)||9.5Vrms||9.5Vrms|
|Noise level (A-weighted)||<85uVrms||<85uVrms|
|Noise level (unweighted)||<229uVrms||<241uVrms|
|Output impedance||151 ohms||151 ohms|
|Signal-to-noise ratio (A-weighted)||81.3dB||81.3dB|
|Signal-to-noise ratio (unweighted)||72.8dB||72.5dB|
In our measured frequency-response (relative to 1kHz) plots above measured at the left and right outputs, the blue/red traces are with the high-pass filter (HPF) disabled, while the purple and green are with the HPF enabled. The DS Audio inverted EQ is applied to the input sweep to emulate the output of the DS Audio optical cartridge. With the DS-EQ2, we find an exceptionally flat response from 20Hz to 20kHz, with only a small bass lift of about 0.5dB at 20Hz with the HPF disabled. With the HPF enabled, we are at -3dB at 20Hz. In the graph above and some of the graphs below, we see two visible traces; the left channel (blue or purple) and the right channel (red or green). On other graphs, only one trace may be visible, this is because the left and right channels are tracking extremely closely, so as not to show a difference with the chosen axis scales.
Frequency response (absolute gain with no EQ applied)
Above is the frequency response plot in terms of absolute gain with no EQ applied. In terms of the shape of the response curve, we find as expected, roughly the mirror image of our DS Audio inverted EQ curve. Absolute gain ranges from about 4dB at 20Hz, to 18dB at 1kHz, and about 24dB at 20kHz with the HPF disabled. With the HPF enabled, we are at 0dB at 20Hz.
Above is the phase response of the DS-EQ2, from 20Hz to 20kHz. The right channel has inverted polarity; however, this is intentional, to match the behavior of the optical cartridge, which has its polarity inversed on one channel. Since the phono preamp must implement a combination of the RIAA equalization curve and a compensation curve for the inherent behavior of the optical cartridge, phase shift at the output is inevitable. Here we find the worst deviations in the left channel between -110 degrees at 20Hz, down to about -150 degrees at 200Hz and 5kHz.
THD ratio (unweighted) vs. frequency
The chart above shows THD ratios as a function of frequency, where the input sweep is EQ’d with our DS Audio inverted EQ curve. The unbalanced output voltage is maintained at the refrence 1Vrms. THD values are relatively flat, hovering between 0.001 and 0.002%, down to as low as 0.0006% at 20kHz.
THD ratio (unweighted) vs output voltage at 1kHz
The chart above shows THD ratios as a function of output voltages at 1kHz. THD values at 100mVrms are around 0.01%, then dip as low as 0.0006% between 2 and 3Vrms, then a rise to the “knee” just above 8Vrms, then up to the 1% THD value for both inputs at 9.5Vrms. It’s important to mention that anything above 1-2Vrms is not typically required for most line-level preamps or integrated amps.
THD+N ratio (unweighted) vs output voltage at 1kHz
Above we can see a plot of THD+N ratios as a function of output voltages at 1kHz. THD+N values at 100mVrms are at 0.2%, then dip as low as 0.003% at the “knee” at 8Vrms, then a steady rise up to the 1% mark at 9.5Vrms.
THD+N ratio (A-weighted) vs output voltage at 1kHz
Above we can see a plot of THD+N ratios as a function of output voltages at 1kHz. THD+N (A-weighted) values at 100mVrms are just below 0.1%, then dip as low as 0.002% at 5Vrms to the “knee” at 8Vrms, then a steady rise up to the 1% mark at 9.5Vrms.
FFT spectrum, 1kHz
Shown above is a fast Fourier Transform (FFT) of a 1kHz input sinewave stimulus, which results in the reference voltage of 1Vrms (0dBrA). We find an exceptionally clean FFT, with only the second signal harmonic (2kHz) barely visible above the noise floor at -110dBrA, or 0.0003%. On the left side of the signal peak, the 60Hz power-supply fundamental is visible at a very low -110dBRa, or 0.0003%.
FFT spectrum, 50Hz
Shown above is the FFT for a 50Hz input sinewave stimulus measured at the left and right outputs. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. We find an exceptionally clean FFT, with only the second signal harmonic barely visible above the noise floor at -115dBrA, or 0.0002%. On the left side of the signal peak, the 60Hz power-supply fundamental is visible at a very low -110dBRa, or 0.0003%.
Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)
The last graph is an FFT of the IMD products for an 18kHz and 19kHz summed sinewave stimulus tone at at the outputs. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 1Vrms (0dBrA) at the output. Once again we see a squeaky clean FFT, this time, with no visible peaks above the -120dBrA noise floor at the second-order (1kHz) or third-order (17 and 20kHz) IMD locations.
Electronics Measurement Specialist