7
X2.5 Owner’s Manual
2) The characteristic of gain devices and their specific use is
important. Individual variations in performance between like
devices are important, as are differences in topological usage. All
signal bearing devices contribute to the degradation, but there are
some different characteristics that are worthy of attention. For
example, smooth low order nonlinearities are additive in quality,
bringing false warmth and coloration, while abrupt high order
nonlinearities add harshness and false brightness.
3) Maximum intrinsic linearity is desired. This is the performance
of the gain stages before feedback is applied. Experience suggests
that feedback is a subtractive process; it removes information from
the signal. In many older designs, poor intrinsic linearity has been
corrected out by large application of feedback, resulting in loss of
warmth, space, and detail. The trick is to get good performance
without this excessive reliance on feedback.
The art of high end audio design lies in the approach to combining
these elements to get high reliability and simplicity, high quality
measured performance, and high quality subjective performance. It
takes imagination and hard work to get as much of these as possible
at once without trading them off against each other.
We recommend the use of the balanced output mode where
possible. It will retain the character of the input mode, but offers
less distortion, less noise, more gain, and more voltage swing,
without compromising the sound.
With balanced operation, the common mode rejection of the
preamp reflects the intrinsic common mode rejection of the
topology, the matching of the gain devices, and the matching of
the attenuator channels. In this case we have been able to keep
the total mismatch to about .1%, for a common mode rejection of
approximately -60 dB.
The input system of the preamplifier will exhibit full common mode
noise rejection with passive balanced sources, where the negative
input is connected to ground at the source through the appropriate
source impedance. This allows adaptation of unbalanced sources to
balanced operation with passive cable connections in a manner that
achieves the noise rejection of active balanced sources.
The use of a micro-controller allows all of the preamplifier
functions to be repeatable and accurately controlled. The micro
processor only controls the functions of the preamplifier. At no
Other Design Comments
