AW: To earth, or not to earth...
don at till.com
Tue Dec 2 20:15:57 CET 1997
Date: Tue, 2 Dec 97 09:47:52 PST
From: Tim Cockram <tim at redragon.demon.co.uk>
If the modules are star eathed i.e. a separate earth lead from each
module to the central earth point, there should be no increase in
crosstalk. As a general point good earthing is essential. My
personal preference is a star earthed Technical earth and a dirty
earth for leds etc, logic is run @ +-7V5.
Yes, creating seperate ground paths for low-noise audio signals and
for more robust circuitry is a very good approach.
The earth "dustbin approach is also quite usefull (use an op-amp
unity gain buffer with the non-inverting input connected to ground,
the output is a goood solid ground (limited by the outputs
(I've never heard it called a "dustbin" before!)
It also suffers from other opamp problems; noise, rising output
impedance with frequency, offset voltage, etc. 'Sounds like it makes
any grounding problem several times worse!
Right now I'm trying to decide weather to use 1/4" jacks or Banana
sockets. The only down side that I have come up with so far for
the banana route is that in order to reduce interference the signal
levels must be high (I'm allready using +-5v for audio) and driven
from a low (ish) source impedance.
Other problems with banana plugs:
They're a pain to interface to external pieces of equipment.
They can't do input or output normalizing. (Or shorting an unused
input to ground.)
They can't accommodate balanced or stereo signals.
You can't borrow spare cables from your guitar player.
Personally I think it's a high price to pay for stacking.
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