On the Bench
I set the gain at +18 dB and used an XLR input and output for the bench
tests.
At 1 kHz input and 2 volts output, THD+N was a very low 0.003%. There are
no significant AC peaks (60 Hz and its harmonics), indicating a very clean power supply.
The standardized SMPTE/DIN IMD test, using 2 kHz and 60 Hz input signals,
yielded less than 0.001% IMD. There are only a couple of peaks immediately
on either side of the 2 kHz fundamental (the SMPTE/DIN test includes the
peaks within a region ± 250 Hz on either side of the
principal fundamental, in this case, 2 kHz, for the calculations). This is really fine performance. It means a
minimum of congestion, so you hear lots of detail.
Using 5 kHz and 6 kHz input signals, the A+B peak at 11 kHz was 111 dB
below the fundamental, and the B-A peak at 1 kHz was - 110 dB.
For 10 kHz and 11 kHz, the A+B peak at 21 kHz was at - 115 dB, and the
B-A peak at 1 kHz was at - 114 dB. Truly excellent.
The THD+N vs. Frequency test shows that the 326S is flat from 10 Hz to 50
kHz. This will deliver a very neutral sound, since no frequency is
colored by harmonics any more than any other frequency. This kind of
performance is very tough (and expensive) to achieve.
I used the +18 dB gain setting for all the tests, and for THD+N vs.
Output Voltage, the 326S delivered a maximum of 16.44 volts before clipping.
Input was 2 volts at this point. That is a lot of output!
Measured frequency response was 10 Hz - 100 kHz
± 0.15 dB.
Conclusions
Fortunately, I can write this conclusion and don't
have to speak it, because the Mark Levinson No 326S
preamplifier took my breath away. Its looks, build quality, and sound are
unconditionally superb.
- John E. Johnson, Jr. -