Interfacing and Processing 249required to handle just one frequency band alone,^8 the signal was split among up to 10
line drivers, all daisy chained off 1 line driver. This method is far preferable to having
multiple crossovers, which might superfi cially simplify the signal path, but would also
introduce near impossible set-up and band-matching demands.
8.1.2.9 Multiconnection
When one signal has to feed many amplifi ers, it is normal to connect the amplifi ers by
daisy chaining. To permit this, amplifi ers made for professional use have both female
(input) and also male (output) XLR (or other, gendered or ungendered in/out) connectors,
linked together in parallel. “ Daisy chaining ” means physically, as the name suggests,
that a short cable “ tail ” carrying the input signal loops from one amplifi er to the next
in the rack or array. The signal being passed on is not really entering each amplifi ers ’
input stage, but merely using the input sockets and case-work as a durable and shielded
Y-splitting node. An alternative would be to make up a hydra-headed cable, that is, one
splitting inton separate feeds. This would take up far more space and is far less fl exible,
but might prove the next best method if amplifi ers without input “ link-out ” sockets have
to be used.
8.1.2.10 Ramifi cations
Professional power amplifi ers, which are the sort most likely to have long cables
connected to their inputs and to reside in electrically noisy environments, mainly eschew
impedances much above 10 k. However, if they’re to be usable for live sound, their
makers also can’t welcome any much lower impedance, as this would further limit the
number of channels that can be daisy chained off a given line driver. In most multi-
amp setups, the source that is being loaded is usually one of the band outputs of an
active crossover, rated for 600 ohms with the NE5534 or 5532, 1977 IC technology that
remains a de facto standard. In this common case, depending on the allowance for cable
capacitance, between 10 and 15 amplifi er channels (at most) should be driven.
8.1.2.11 Variables
As with other electronic equipment, input impedance is a function of electronic parts
whose behavior almost inevitably varies with frequency and almost always depends on
temperature. With unbalanced inputs, input impedance will also usually vary somewhat
with the setting of the gain control (attenuator), if fi tted.