[sdiy] Guard Rings

[David G. Dixon]

> > The junctions between the emitters of Q5 and Q6, resistors R16 and
> > R18, and
> > the drains of Q11 and Q12, respectively, are emphatically NOT high
> > impedance.  In fact, their impedances are about 2.2k.
> 
> These are outputs of emitter followers, so their impedances are even
> lower.

Ah yes, of course, you are right.  The impedance of those traces will
actually be less than 50 ohms!  All the more reason not to include them
inside the "island".