[sdiy] Keyboard matrix decoder

[Luís Marka]

Hi,
I got a broken Yamaha DX27, and I am planning turning the dead thing into a
CV keyboard. Besides pitch and modulation wheels, I still get two sliders
that can be turned in CV sources as well! My home brew modular is hungry for
a CV source!!
The DX's keyboard matrix is an arrange of 6 rows by 12 columns, and I am
modding it to 8 by 8, as required in the decoder circuit I am building. An
inverted Trigger signal will feed the latch IC, 74HC373, which will feed a
R/2R network. But right now, two things are puzzling me: First, I've seen
R/2R networks using almost every resistor value, from 1K/2Kohms to
100K/200Kohms. I am planning to use matched 10K metal film resistors. Does
it matter at all?
And second: Some designs use a 4050 buffer between the latch and the R/2R
network, others plug the network directly on the 74373 outputs. Is that
buffer needed?

That's it for now. All my best,
Luis Marka