[Amps] Tetrode Boards Grounding Scheme

[Jim Brown]

On Tue, 6 Jan 2009 12:28:10 -0600, Dugas, Jason A. (JSC-EP) wrote:

>In doing so I noticed that I will have many pins connected to 
>"CHASSIS GROUND" but potentially only one wire coming from CHASSIS
>GROUND to the connector, internal to the power supply.

In most interconnect wiring, the concern is NOT IR drop (or IZ drop) 
for the signal, but rather for NOISE current induced onto signal 
wiring. In general, the signal is a voltage from a low Z source 
working into a high-Z load, so there's usually very little signal 
current. The correct analysis, then, is based on asking, "Where does 
the NOISE current want to flow?" In general, most NOISE current on 
external wiring is trying to return to the power system green wire 
(the chassis). This is also where most RF noise induced on external 
wiring is trying to go. 

Thus, the best termination point for the shields of external wiring 
is the chassis. If shields of external wiring comes inside the box, 
current on the shield still wants to get to the chassis, so it 
creates an IZ drop (remember that XL is nearly always greater than R) 
in the wiring between wherever it hits signal common and the chassis. 
This IZ drop is introduced at various points in the signal flow and 
can cause grief at various points in the circuit, depending on PCB 
layout. You can read more about this on my website. Click the links 
about "the pin 1 problem" or the link for RFI for Hams. 

http://audiosystemsgroup.com/publish

Bottom line -- a star connection to the chassis can be very good 
scheme for connection of signal returns. Note that I didn't say 
"grounding," because this has nothing to do with the EARTH. :) 

73,

Jim Brown K9YC