White paper
February 2006
Cambridge Audio 840A Class XD™ integrated amplifier
Matthew Bramble – Technical Director, Cambridge Audio
Douglas Self – Electronic Engineer, Cambridge Audio
Cambridge Audio made a significant leap forward
with the introduction of the Azur range in 2003 by
pushing the boundaries of what was possible in
the budget audiophile segment of the market.
However, we were also keen to produce a high-end
product range which allowed us to flex our engineering muscles and show what we can do with
fewer constraints. A number of development programmes burgeoned while working on the original
and V2 Azur ranges of which the 840A Class XD
TM
integrated amplifier was one, part of our new 8-
Series.
A number of ideas came to the fore, including the implementation of full microprocessor control for
all functions, nameable inputs and AV mode, custom install features such as RS232 and outputs
for our own Incognito multi-room system. But above all, the unit had to be a true audiophile product
in that sound quality was paramount.
We decided the 840A should in fact be a pre-amplifier and dual-mono power amplifier all in one
chassis. It should also have a balanced input for the matching CD player (of which more in a
separate white paper), two pairs of very high current output transistors per channel so it could drive
any speaker, a new acoustically damped casework and relay switching for input selection. A
relay/resistor ladder volume control scheme for excellent channel balance and low distortion was
also designed.
