15.5 What about interconnects, such as the cable between tuner and amp?
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This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
15.5 What about interconnects, such as the cable between tuner and amp?
Line-level interconnects conduct smaller signals than speaker
cables; the typical signal ranges from -2V to +2V (the CD
output standard) with currents in the microamps (the
corresponding values for speaker cables attached to a largish
power amp might be -70V to +70V and currents of many amps).
Line-level interconnects can be divided into single-ended (or
unbalanced), and balanced interconnects. Home audio is almost
always single-ended interconnects.
Single-ended interconnects almost always use a form of the
RCA connector (or phono plug). RCA plugs form fair to poor
connections that degrade with time as corrosion works into the
metal-metal contact and as the spring tension of the connectors
relax. Gold-plating reduces the effect of corrosion and locking
RCA connectors solve most of the mechanical problems. However,
these premium phono connectors are rare and expensive. For
example, a gold-plated Vampire locking RCA plug costs
approximately $23/pair. If RCA connectors weren't a de facto
standard, we'd recommend against them.
Unbalanced interconnect wires vary in geometry, material and
price. Cheaper wires have a single conductor (normally
stranded) and a shield and cost $.20-$2/ft. Medium (complexity
and price) wires have two conductors (often arranged as a
twisted pair) surrounded by a shield and cost from about
$3-$20/ft. Exotic wires have all sorts of geometries and
materials (such as stranded silver conductors, or ribbon cable
braided around a core, or in one extreme case, a tube filled
with mercury!). Prices may be as high as $200-$300/ft.
Balanced interconnects have three conductors: two for the signal
one for ground, and additionally a shield. The standard
connector for balanced cable is the ITT/Cannon XLR connector,
which is quite good mechanically (they lock). Equivalent
connectors are also available from Switchcraft, Neutrik, and
other vendors. If you have to run cables longer than 12 feet or
4 meters, the greater noise immunity of balanced interconnects
is often a good idea. For this reason, balanced connectors are
standard equipment in professional installations such as
studios, public address systems, and broadcast stations. There
is not much variation in balanced cables. The three brands
mentioned above are known to be rugged, high quality and
moderately priced. Slightly weaker imported connectors are
available, but they aren't dramatically cheaper. Better
connectors are also easier to assemble and have a more durable
cord strain-relief.
For most systems, the most important aspect of a cable are
the mechanical reliability of the connectors; in particular,
the joint between connector and wire, and the joint between
connector and socket. Typically, interconnect cables are
short. It is worth getting just the right length; cables
often come in .5 meter increments. With quite good systems,
some people observe differences in sound between various
interconnects. This is quite system-specific and the same
advice as given above applies: try several brands. Most
good dealers will loan interconnects for home evaluation.
In cables where the shield does not carry the signal or ground,
the shield is normally only connected to ground at one end.
In systems where there are significant differences between
ground levels on various components, it may make a difference
which way such cables are connected. Typically, the end where
the shield is grounded should be at the source of the signal.
Often, such cable has arrows on it pointing in the direction of
the signal flow. In any case, try both orientations.
There are many objective reasons why cables might cause
differences in sound by interacting with the drivers in the
signal sources as well as by providing non-linear effects in the
RCA connector. Most of these effects are again related to
interconductor capacitance and resistance, and the quality of
the shielding provided by the "shield" conductor. In balanced
cables the quality of the "twisted pair" inside the shield is
also important. One might note that a shield protects from only
capacitively coupled interference, and not from any magnetic
field interference. The twisted pair in a balanced line provide
some magnetic rejection, as does steel conduit. However, steel
conduit has other characteristics which make it undesirable for
audio in general.
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