AW: To earth, or not to earth...

Don Tillman don at
Tue Dec 2 20:15:57 CET 1997

   Date: Tue,  2 Dec 97 09:47:52 PST
   From: Tim Cockram <tim at>

   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.

  -- Don

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