Coda Stereo Amplifier 15.5 - Manual (Page 10)

I. Design Philosophy and Approach
The subtlety of the design process at this level of performance makes it impossible to easily
explain all of the advantages inherent in the 15.0. However, we present here an overview to
give you an understanding of some of its unique features and an idea of the listening experi-
ence you can expect. Often a particular technique has numerous unrelated advantages and
possibilities. We make every effort to exploit these advantages with the final result being an
amplifier that performs better than the sum of its individual features suggest.
The topology and component selection is built on the foundation established by the Coda
System 100. Balanced interconnections are provided to take advantage of their greater noise
rejection. Differential voltage gain throughout provides exceptional rejection of external noise
and contributes to the inherent DC stability of the circuit. This allows direct coupling without
servo circuitry. The unit also uses output followers operating without feedback.
Excellent high frequency design insures linear operation at high speed, and translates into a
sonic reproduction which is extremely transparent in character. The power supply takes a very
direct approach to high performance. First, top quality toroidal transformers and over 144,000uf
of capacitance with very low ESR and inductance are used. For optimum performance and
reliability all circuitry remains continuously powered.
The specifications are consistent with what would be expected in a high current amplifier design.
In this design , however , an unusual degree of attention has been paid to sonically meaningful
parameters.
For example, the current stage is capable of producing peak currents in excess of 100
Amperes with a degree of linearity and speed unmatched by other designs producing only a
fraction of of this current. This is achieved by the implementation of several distinct circuit
features.
Extremely wide bandwidth transistors are used in the output stage instead of the usual TO3
devices used in other output designs. Each channel uses 30 individual output transistors with
a combined power rating of 1500 Watts and 120 Amperes with a bandwidth of 50 Mhz.
The 15.0 uses bias voltages and component values which have been specifically selected 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
impedance and is particularly effective at eliminating IM distortion which often occurs in these
instances.
DESIGN PHILOSOPHY 9