analog sequencers (Penfold or any DIY)

[Rob01]

----------
From: Jeremy N Bradbeer <Jeremy_N_Bradbeer at sbphrd.com>
To: 'Synth DIY' <synth-diy at horus.sara.nl>
Subject: analog sequencers (Penfold or any DIY)
Date: Wednesday, May 07, 1997 8:51 AM

I didn't really get much response to the questions below. In case this was
due 
to the 'loose connection' people have been reporting, here goes again. 

If nothing else, I would be interested in hearing from anyone re.
experience 
building analog sequencers.

Jeremy





Previous posting:
I have just looked through the Penfold book and am thinking of rigging up
the 
sequencers. The circuits look very simple (good thing) but I have a number
of 
questions mainly relating to ganging or otherwise combining these circuits
to 
get more sophisticated configurations.

So here goes:

1. Are the Penfold sequencers any good?
2. Do they have any inherent problems in their design and if so are there 
simple fixes?
3. Can switches be added (eg ahead of the diodes) in the note-sequencers to
get 
rhythmic effects by omitting notes in the sequence?
why not??
4. Can the diodes be replaced with LEDs to display the sequence (like
Doepfer 
etc) progression?
prolly!
5. Can several note-sequencers be run from a single 555 to get different 
control voltages for e.g. filter parameters etc in addition to pitch and
etc?
yep.
6. Can the percussion-sequencer and the note-sequencers be run from the
same 
555 to get e.g. accents by using the voltages output by the note sequencer
to 
alter e.g. filter/env. characteristics of the perc. sounds?
dont know..
7. Can 2 or more sequencers, running at different tempi, be synced i.e. to 
produce polyrhythms etc?
yep, divide-by-N circuit added to the input of the counter.
8. Can the frequency of the 555 be voltage controllable - imagine the fun
of 
having tempo controlled by an LFO or EG?
yep.
9. What would it take to convert the analogue voltage outputs into MIDI
data to 
allow control of MIDI devices and to record into a standard MIDI sequencer 
(like the Doepfer sequencer does)?
An ADC and a microprocessor.. prolly more trouble than its worth, but
possible :)

Read below for more evil deeds... ;)



Well, it seems as though you found the right guy for the job!! I just got
the prototype of my analog sequencer working.. ITs REALLY simple and is WAY
expandable.. I even built in a 556 VCO chip into it with a little cheezy
moog like filter, and the silly thing actually sounded pretty damn good! I
even went so far as to mess a little with a PLL chip to keep it in tune :)
BAsically, the sequencer part of it is a 555 timer connected to a bcd
counter, which counts off to a 74154 1-16 multiplexer chip. i found this
configuration more convenient that the 2*8 mux system in the ETI schemes.
It saved me a few extra parts too...i hooked the outputs of the mux to FETs
first, then realized i could just use optoisolators, and the optos i could
get in quad configuration. then, i could switch the different steps off
using switches. I used an op-amp to drive the output of the CV. I would
really prolly be better off sending you the schemes i made in circuitmaker.
Maybe ill send you the demo of circuitmaker and then you could see it work
for yourself! 
BAsically, it has two rows of leds, ONE row shows what step is currently
being played, and the one under it, closest to the step on/off shows if the
step will be played or not..Using a PLL to do a divide-by-N circuit, you
could switch them around to different divisions of the 4 bar scale. No
biggie, but not really neccessary.
My analog sequencer also has 12 step break-before-make dial switches so i
can choose a particular note. I also figgered out a way to only have to use
12 resistors in a voltage divider matrix cuz there is only one step on at a
time. saved me a lot of $$$ compared to buying 16 seperate pots and never
knowing WHAT note would be played..Well, actually, the 12 step switches
were a little more, but it wasnt much and was WAY worth the effort! I also
have octave switches that will change the octave, and the 12 step dial
switches choose the note in the octave.. 
ONe cool thing i messed with is that, the way i have it set up, it can
cycle a pattern forward, reverse, and back and forth.. Really cool, but i
didnt implement it.. it just need a couple of switches though to do it..
you could even sync it to midi by using a UART, then mask off pulses and
use a divide-by-n circuit to change the resolution.. To do it straight
sync, i figgered out you have to do a divide-by-6. You could come up with
added craziness by making the division a variable... scary!
ill talk with you later on this.. im pretty bogged down by finals and
trying to get a job! cya brother! :)
if you can, also send me a copy or point me to where i can look at the
penfold schemes.. i could prolly help you better then..
                  Rob01
             Zeros & Ones
The Mind Controls the Machine 
The Machine Controls the Body

Sorry bout the big mailing everyone! :))