Input Connectors; Output Connectors; Matching - Audio Research Reference 750 SE Manual

Input Connectors

The Reference 750 SE uses a fully balanced
circuit topology and has a balanced XLR
input connector on the rear panel. It
therefore requires a balanced preamplifier
output, as provided by most Audio Research
preamplifiers. Connect your preamplifier's
output to the Reference 750 SE before turning
on the amplifier.

Output Connectors

Heavy-duty output terminals are provided
on the rear panel for 4, 8, or 16-ohm speaker
impedance loads. Using high-quality speaker
cables, securely fasten the (-) speaker lead to
the appropriate (black) terminal, then the (+)
lead to the matching (red) terminal. Follow
your speaker manufacturer's impedance
specification.
The Reference 750 SE puts out the same
amount of power whether the 4, 8, or 16-
ohm terminals are used.

Matching

It is important to use as close as possible an
impedance match between the amplifier and
speaker for optimum transfer of power to the
speaker with minimum distortion. In the case
of speaker systems with significant variations
in impedance throughout the frequency
spectrum, such as most electrostatic types,
determine the best impedance match
empirically for best overall sonic results.
Connect the Reference 750 SE input to the
preamplifier or electronic crossover, using
only the highest grade of audio interconnect
cables. To avoid sonic degradation use the
shortest practical length of cables.
Connections
Important
Use the best available speaker wires and
interconnects.
emphasize this enough. As better components
and systems are developed, it becomes
increasingly important to avoid the limitations
of inferior system interconnections.
It is important sonically that your entire
system be connected so that the audio
signal arriving at the speakers has correct, or
"absolute polarity" (i.e., non-inverted). Unlike
most other Audio Research vacuum tube
amplifiers, the Reference 750SE does not use
the "conventional" 0, 4,8,16 Ω (ohm) speaker
connection terminals. Due to the special
output winding configuration, the Reference
750SE's output transformer is fully balanced
and therefore has no speaker "ground" 0 Ω
terminal. Correct speaker connections will be
to use the vertically- arranged + and – taps
for the impedance that most closely matches
your speaker's impedance. For example: for a
4 Ω speaker, connect the red or " +" speaker
terminal to the wire that connects to the
upper 4 Ω + terminal, and the black or "-"
speaker terminal to the wire that connects to
the 4 Ω – terminal just below it. Do likewise
for 8 Ω and 16 Ω speakers.
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