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

[Rykhaard D.A.M.I.A.N.]

On 1/7/06, harrybissell <harrybissell at prodigy.net> wrote:
>
> OK lets say... you have ONE LM329... driving an
> opamp buffer. This suppies voltage to the top of each switch.
>
> The wipers of each switch go to the 4051 (with say 200 ohms
> on resistance when selected... 10^12 off).  The output of the 4051
> goes to the non-inverting input of a TL072 opamp (so with THAT
> high of an input impedance... the extra 200 ohms doesn't do a damn
> thing).
>
> If all the resistors in ONE switch are matched to each other... the next
> switch just needs to be CLOSE in resistance... they could be all 100
> ohms or 110 ohms, or all 90 ohms...  With the high impedance of the buffer
> they could be 10K ohms...  (but usually you want some 'real' current going
> through a switch contact)
>
> I suspecting that the tuning error you have is some small, but very real
> loading on the circuit.  Probably mr Ohm would tell you why its
> happening...
> There is some non-accounted for load, somewhere...
>
> Isn't design fun ??? :^P
>
> H^) harry
>

Ahhh!  Then, with such a high impedance, I only have to have 1 set of
resistors external to the rotaries, for the proper voltage range.  (To make
sure that I have the rotary changing the input voltage, the proper 1V/octave
amount).

With the setup as you say - that would make the entire thing MUCH simpler.
:O  I'm trying to picture it mentally right now - to see if I could
breadboard a test of it, with say - 2 rotaries. :)
If that would work, I'd scrap the entire portion that I have now (for the
rotaries - keeping the Clock / etc.) and do the rest on a daughter board. :)

Wonder if I have enough brains left tonight, to try breadboarding it. :)

Thank you muchlee for that idea, Harry! :D

--
Take care,
Warmth and Peace,
Ryk

http://deathlehem.bravehost.com/damian.html - D.A.M.I.A.N.;s webpage - Jan.
0406 update
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