dESCRIPTION
7
The remote controlled Coda
Control Amplifier CSi Balanced
is designed with thorough-
ness reserved only for the finest preamplifier and amplifier gain stages. Analytical design
techniques, both objective and subjective, were applied in an open-minded fashion with
musical perfection as the goal. The
CSib
features a wide range of design topologies and
components ported from both broad lineage and the most recent advances in the Coda
products and design topologies.
Unlike other integrated amplifiers, the
CSib
offers true “separates” performance. The
CSib
is, internally, essentially a Stereo Amplifier CS with a separate preamplifier section based
on the circuit topology of the Coda Preamplifier CL.
On the faceplate, the straightforward controls and display provide comprehensive func-
tionality to the user. All input selections have LEDs to show when they are in use. Buttons
control both volume and balance, with an LED display to show which channels are
being adjusted. Gain is controlled by a high performance Burr-Brown PGA2310 analog
attenuator. This digitally controlled analogue device features an improved output buffer
and increased voltage swing for high level input signals. Digitally controlled level tracking
allows 1 dB per step attenuation without error. The digitally controlled stepped resistors &
zero crossing detection circuit allow for “zipper-free” operation. Total harmonic distortion is
less than 0.004% with a signal to noise ratio approaching 130 dB.
The preamplifier section has its own separate power supply with multiple independent
transformer taps. A reference voltage is developed by delivering constant current to
zener diodes. The resulting voltage is heavily filtered and delivered through class-A fol-
lowers to provide absolutely stable power to the preamplifier section. A separate power
supply is provided for all controls and microprocessor control system.
In the amplifier section of the
CSib
, differential voltage gain throughout provides excep-
tional rejection of external noise and contributes to the inherent stability of the circuit. The
front end is designed to provide a slew rate of 50 V/us without entering class B operation
as is common in many other designs. This combined with excellent high frequency design
insures linear operation at high speed.
The amplifier’s overbuilt power supply take a very direct approach to high performance
by utilizing a top quality 2.0 kVA custom toroidal transformer, IXYS high speed rectifiers and
a 60,000µF capacitor filter bank with very low ESR and inductance.
This latest generation output stage design is capable of producing peak currents in
excess of 100 peak amperes with a degree of linearity and speed unmatched by other
designs producing only a fraction of this massive amount of current. This is achieved by
the implementation of several distinct circuit features. Each channel uses 18 individual
output transistors with a combined power rating of over 4,000 watts and 125 amperes and
a bandwidth of 30 MHz. The
CSib
operates in Class A up to approximately 20 watts. At
higher output levels, the bias section is designed to produce a precision transition with no
abrupt changes in distortion or output impedance. This “Precision Bias” technique yields
seamless performance regardless of the complexity of the load. With such linearity and
bandwidth, only 6db of feedback is used to maintain damping factor while permitting the
minimal value custom emitter resistors to provide current limiting only under extreme con-
ditions that would exceed the output stages high current capabilities. One advantage of
this is a high degree of immunity from interactions with complex speaker loads or cables.
