[sdiy] 5v ADV Bass / AD EG Question.

[Jay Schwichtenberg]

Bill,

2)

Another issue is that the attack, decay and release pots on envelope
generators are typically log pots, a non-linear scale. So if the digital
pots you use are not log they may not give you the timing resolution that
you are use to. One techinque to do that is buffer the pot and add a
resistor. Picking the right resistor and placing it between the wiper and
the other ends of the pot (assuming using pot as attenuator between signal
and gnd) can give you log or expo curves. Try
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm for that info.

Good luck.
Jay S.
  -----Original Message-----
  From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Bill Berzinskas
  Sent: Thursday, March 17, 2005 7:36 AM
  To: synth-diy at dropmix.xs4all.nl
  Subject: [sdiy] 5v ADV Bass / AD EG Question.


  Hello everybody..  just woke up to a crazy little burst of snow here in
NC..  wierd..

  Anyhow..   As you probably know i'm modding the bejezzus out of my
adv-bass..   In my quest to make it digitally controlled, i've hit a few
snags..  so maybe you can help me out..

  1) I am converting it to digital control..  mostly thru digital pots..   a
few things with DAC..  so.. for the digital pots, i have to use 5v input,
and rather then use way more opamps then i want to deal with, i would like
to make it operate on 5v possibly with a bipolar or just 12v output stage if
necessary..   So..

  I've done some crude experiments with the Trigger section just to see how
it reacts to switching from +/-12v to just +5v..    I've tried with tl082s..
and i just can't get the trigger ratio right.. and it always triggers.. so..
since i broke down and got a few lm324s, i tried those.. and it seems to be
working correctly..   i then went on and built the impact part using the
digital potentiometers..   all good so far..   if i just switch all my
opamps in the design, will it carry through the rest of the circuit
properly?

  2)  I plan to use a digital potentiometer to control the decay time..
but the highest value i can come up with is 100k.. so i'm thinking i can
change the capacitor and get about the same decay time?   any
recommendations for a value?

  thanks guys!  :-)
  --billie
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