6

Precision preamplifier ’96, Part II

Morgan Jones raised the excellent point of crosstalk in the input-select switching in a recent article (Valve Preamplifiers, Electronics World, March/ April 1996). If the source impedance is significant then this may be a serious problem.

While I agree that Morgan’s rotary switch with every other contact grounded may be slightly superior to conventional rotary switches, measuring a popular Lorlin switch type showed the improvement to be only 5 dB. I am also unhappy with all those redundant ‘mute’ positions between input selections, so I instead chose interlocked push-switches rather than a rotary. A four-pole-changeover format can then be used to reduce crosstalk.

The problem with conventional input select systems ...

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