TB303 quickie question and EG findings...

[Byron Jacquot]

>I am wondering why the TB's accent control signal is controlled by the
>slide control. The accent logic signal comes from the output of a D-type
>flip flop, the rising edge triggered CLK is the slide control (high to
>slide), and the DATA IN is coming off the control board. Anyone know why
>there should be a d-type there??

>From what I can tell, it was done in order to conserve lines from the
processor.    The line being used to clock the flip flop (IC 9, the basis of
an R2R Digital to analog converter), and also switch on the slide circuit.

I've never analyzed a 303 using a scope, but here my guess what happens:

If a note is to be triggered, but without slide, the clock line will pulse
high for a very short moment, then go low again very quickly.  The data will
hit the flip-flop and generate the proper CV voltage.  The slide circuit
will be switched in for a breif moment, but switched right back out, so the
CV may have a tiny portamento, but probably not enough for us to hear.

For a slid note, the clock line will go high, clock in the note bits on its
rising edge, then stay high, leaving the portamento cap in the circuit,
inducing glide.

Incidentally, the same clock line also latches the accent information to IC13.

It's actually a pretty ingenious way to conserve processor lines.  If you
have lines to spare, you might make things a bit more flexible by using more
lines and handling things in software...or stick with the classic!


Byron