The design features of Ampliwire ECI 1
After the Electrocompaniet 25 watt amplifier had established a new standard for
transistor amplifiers, research was undertaken to find ways to make the amplifier
even better, and to extend its highly musical sound quality to more powerful amplifier
designs. The engineers at Electrocompaniet were not satisfied by only reducing the
commonly recognised types of distortion to low levels. They recognised that distort-
ion appears in many forms, and that distortion was still audible in listening tests even
when conventional categories of distortion were at astonishingly low levels.
Traditionally, designers increased feedback to make a larger portion of the output
signal control the amplifiers response. Our listening tests showed us that simply
applying more feedback was not the answer. In fact, as one kind of distortion went
down, other parameters would be adversely affected, leading to an overall
degradation of sound quality. We knew that the other conventional design approach
of eliminating feedback completely was not the answer either, because this would
cause high distortion levels, and as a result would produce a “woolly” sound.
The answer to the dilemma was found in a novel approach to feedback theory. We
developed a feedback concept that allowed local feedback to be applied around
individual stages of the amplifier circuit. This approach allowed us to avoid the sonic
disadvantages of overall feedback from output to input. The concept was further
developed to reduce phase- and interphase distortion between stages of the
amplifier as well. We were able to concentrate the loop feedback on the stages of the
amplifier where it resulted in audible improvement.
Stability margins were also expanded because feedback no longer affected the fre-
quency response. The use of this concept of individual gain blocks - complex in
design but simple in function - allowed us to reduce distortion to minute values in all
the products.
The amplifier is divided into two separate sections or gain blocks. The input block is
a transconductance amplifier without overall feedback. This avoids large output
current being fed back to the input, and mixed with the minute input signal. The out-
put block is a transresistance amplifier with parallel feedback. This is done to prevent
higher frequencies than the feedback loop can handle, from entering the loop. An
approach like this will prevent Transient Inter modulation Distortion (TIM) and
Slewing Induced Distortion (SID), eliminating the need for an extremely wide
bandwidth.
All stages work in Class A with an efficiency of less than 0,1%. The power supply of
the ECI 1 consists of two 500 VA toroidal transformer. Furthermore, the power
supply consists of a 40.000 micro farad reservoir divided into four 10.000 micro farad
capacitors in parallel with 4,7 and 0,1 micro farad polycarbonate- and polypropylene
capacitors.
