15.6 What about Phono Interconnects:
Description
This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
15.6 What about Phono Interconnects:
Phono interconnects are part of the link between a cartridge on
a turntable and a preamp (or head amp or receiver). They are a
special case of line-level interconnects because the signal is
much lower, typically 1 to 50 millivolts. They are also
intended to operate into a higher impedance, typically 47K ohms,
and form part of the capacitive load for the cartridge.
The low signal levels mean that the shielding of the cable, and
the presence of a separate drain/shield are more important, as
is a good ground. A separate solid ground should come along
with the cable as a separate lead co-routed with the cable.
In addition, the low signal levels make a good solid connection
to and through the connectors MUCH more important, because of
the greater sensitivity to low-level nonlinearities.
Wire capacitance is often ignored in line-level interconnects;
however, in a phono interconnect, it may constitute half of the
total capacitive load of the cartridge. Obviously, then, two
cables with significantly different capacitances should sound
differently. In this sense, the "right" cable for one cartridge
may be too low or high in capacitance for another cartridge.
For low-impedance cartridges (most moving coil cartridges),
the wire must have low resistance to prevent cartridge unloading
and frequency-dependent signal loss. In addition, as the
signal levels are quite low, shielding is important.
Unfortunately, copper shields do not block stray magnetic
fields, so in the case of phono cables, careful routing may be
even more effective at reducing hum than special wire.
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