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Service Manual A85
Issue 2.0
DiVA A85, P85 & P85/3
Amplifiers
ARCAM
Contents List
! Contents list
! Circuit description
! Service guide
! Circuit diagrams
! Component overlays
! Circuit board parts list
! General assembly parts list
Pre-amplifier circuit description The digital pots Z108D and Z108A control the bass and treble
respectively. This is done by moving the wiper connected to the
frequency-sensitive impedance between the non-inverting and
inverting terminals of Z112A, effectively changing the ratio of
The A85 preamplifier is a high-performance, DC coupled design feedback boost and feed-forward attenuation of the circuit at the
with microprocessor control of input select, two independent tape desired frequencies, thus providing a EQ gain control that is
loops, electronic volume control, tone bypass and electronic tone symmetrical on a logarithmic scale, with the use of a linear pot.
control.
Z112B provides the 6dB of gain necessary to bring the nominal
It features a discrete power supply and low-noise linear circuitry to signal level back to unity. C116 and C117 remove the 2.5VDC
obtain very good distortion and noise performance, suitable for offset from the output, to prevent clunks when the tone controls
high quality source material such as CD or DVD-A. are activated.
Z108 is controlled by a simple 3-wire serial interface from the
Input switching microprocessor. Each of the digital lines has its own ground return
to minimise electromagnetic interference. They are connected
Each of the inputs has a pair of diodes to the