[sdiy] differential subtractor vs summer with an inverted input

[David G. Dixon]

I'm currently working on a matrix keyboard circuit for salvaged organ
keyboards with matrices arranged by octaves, which I hope will eventually be
of use to more than just me.  I will be finished shortly, and will share all
the details then.

However, as part of this design, I have arrived at the need to subtract 1/4
of one voltage source from another voltage source, and I may also wish to
apply gain to the result.  In other words, given E1 and E2, I want:

EO = G(E1 - E2/4)

Presuming both voltages are being buffered to eliminate input impedance
concerns, I think I basically have two options:

1.  Feed the sources through an opamp arranged as a differential subtractor
with feedback resistor R, (-) input resistor 4R feeding E1, (+) input
resistor R feeding E2, and (+) resistor to ground 4R.  Thus,

EO = (4/5)(1 + 1/4)E1 + (-1/4)E2 = E1 - E2/4

Then send the result through a non-inverting amplifier stage with gain G.

2.  Invert E1 with a unity-gain inverter, then sum -E1 through resistor R
and +E2 through resistor 4R into an inverting summer with feedback resistor
GR.

With the two required buffers, either circuit requires one quad opamp IC.

My question is: is either option to be preferred over the other for this
application?  I'm trending towards option 2, because it seems to me that
option 1 is somewhat more sensitive to precise resistor value ratios, but
perhaps there's something I'm overlooking.