Mark Levinson Reference Preamplifier N32 - Manual (Page 8)

8
able from our balanced circuitry by including a balanced XLR input
connector version of the phono preamplifier modules.
1 2
3
NC
1 2
3
NC
LEFT +
LEFT -
TONE ARM GROUND
RIGHT +
RIGHT -
No32 XLR phono module
recommended wiring
Combined with a shielded, twisted pair cable from cartridge to preamp,
the XLR input phono preamp offers the ultimate in noise rejection and
low level signal resolultion. (An RCA-equipped version is also available
for wider compatibility with existing phono cables.)
Madrigal uses a fully balanced implementation in its phono preampli-
fier. The gain stage produces a perfectly symmetrical pair of opposite-
polarity signals, based solely on the difference voltage appearing at the
amplifier input. Each half of the balanced signal sees identical signal
path and circuitry from input to output. The RIAA equalization stage
and even the DC servo is duplicated for each signal half. (A single resis-
tor change on the input amplifier would let each channel operate as a
stereo pair of phono preamplifiers.)
The balanced output signal from the phono preamp is received on the
Nº32 audio input selector board with the same treatment as a line level
balanced input.
instrumentation
amplifier topology
The classic method of resolving tiny electrical signals from potentially
noisy environments is called an “instrumentation amplifier.” The fully
balanced, input to output instrumentation amp—first pioneered in the
high end audio business in the Nº38 family of line-level preamplifi-
ers—is the ideal foundation on which to build a high performance
phono preamp.
The industry’s lowest noise amplifiers implement the input side of the
phono circuit. Gain is distributed over two stages with ample band-