[sdiy] Sequencer tuning update. Good & bad news.

[harrybissell]

Hi Ryk

"Rykhaard D.A.M.I.A.N." wrote:
>
> The result?  3 or 4 of the notes within the 12 notes around that
> rotary switch, are STILL out of tune, by a few cents.  ????  I'm
> really confused about this.  It couldn't require picking the resistors
> to 0.01 or 0.001% could it??  Maybe ...... my wonderings here:

Well it depends on how fussy you are...

Another way to do the whole thing (little late for this :^) is to have
the
switch send a binary representation of its value to a bus (we talking
tons
of diodes here... and have just ONE DAC at the end...

This is how we made 'sequencers' in industry many years ago, before
micros...

> - LM329 6.9V reference into an
> - LF353 Voltage follower into the
> - input of a CD4051 1:8 multiplexer with each step into a
> - 5K6 resistor into a
> - 1K 20 turn trimmer into the
> - 12 position rotary switch, with 12 x 121 ohm 1% resistors around it,
> finally into a
> - 1K resistor
> 
> The control voltage from each step, is taken from the point between
> the trimmer and the rotary switch.  (Changed from the previous string
> setup.)

With voltage, why would you not take the outputs from the wipers... and
go
into a high impedance at that point (voltage follower opamp). ???

H^) harry