Frequently Asked Questions
(FAQ)
Some frequently asked
questions are listed below.
Can I use more
expensive op-amps in these designs?
The OPA134 opamp was chosen
as the best product to meet the design aims, which also happens to be sensibly
priced. A more expensive op-amp may well not produce better performance of the
system as a whole. Opamps with a higher slew rate or a wider bandwidth may
suffer instability problems unless other changes are made to the designs to
compensate.
Why are relays not
used for switching the audio?
Although relays with gold or
palladium plated contacts are suitable for switching audio (and, being passive,
add no distortion), the breakthrough of audio signals when they are switched
"off" is noticeable unless more than one relay is used for each switch to
ground unwanted signals. High performance audio switch ICs were chosen in
preference as the off isolation is excellent and they take up less space on the
PCBs than a multiple relay solution. The distortion from the audio switch ICs
is slightly higher than that of the op-amps alone, but is not significant as
only two are used in the audio path from an input socket to an output socket in
a typical preamp system configuration.
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