wire wrap vs. high freq. attenuation

jean-charles maillet jc at lynx.bc.ca
Wed Dec 3 06:41:34 CET 1997

>I guess I should have thought about this before I wire-wrapped numerous
>modules, but I recently read something that made me think that making a
>pcb might be better than wire wrapping in circuits where high
>frequencies are involved.
>What's the relationship here?  More importantly, has anyone wire wrapped
>a VCO, VCF, VCA, etc. with no problems in the high frequency ranges?
>I know that most people probably make their own pcb's, but I really
>enjoy wire wrapping.

the problem has to do with proximity capacitance, that is from wire-to-wire
and wire-to-ground.  Wire-to-wire proximity creates a capacitance which
affords high-frequency coupling between the two conductors, resulting in
high-frequency crosstalk, and wire-to-ground proximity creates a shunting
capacitance which will dull to front edge of any upward or downward
transient waveform.  The determining factor here is circuit impedance

For supply lines this is no problem since the low-Z of the regulator can
supply extra current to any stary capacitance.  The place to watch for
potential problems is in CMOS circuits that have low drive (i.e. high ohmic
impedance).  The longer the wire, the closer it is to another wire or
ground, and larger the signal level the worse the problem becomes.  If you
lift any sensitive wire away from others you reduce the problem by the
square of the distance roughly.  In most bipolar or op-amp circuits you
don't have to worry too much.

In general audio circuits this should not pose too much of a problem unless
you've twisted wires together.  In tube amp circuits, where signal
amplitudes become very large, this can definitely be problematic when not
dealt with carefully but then you wouldn't wire warp a tube amp circuit
unless you're way into Tesla :)


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