[sdiy] [SDIY] Doepfer A-151 reset modification.

[Peter Grenader]

Simple, but effective and useful as heck:

The Doepfer A-151 is a simple quad sequential switch.  It's a 2 bit binary
counter which drives a quad mulitplexer and allows the user to either:

Route a single signal out of 1 of four outs which are turned one
sequentially from an incoming pulse

-or-

Switch bewteen four independant signals out of one jack sequentially from an
incoming pulse.

Nice.  I got it because of Milton, so I can construct these humungus 32, 48
and even 64 step sequences.  Kewl.

The A-151 has an external reset jack (not a switch).  With this jack, you
can reset the four step sequence at any time. Not thinking about it clearly
enough when I bought it, I figured I would just use the NEXT step of the
A-151 to reset it to anything shorter than it's maximum range, much like you
would with a pulse sequencer.

Once I got it however, I realized how stupid this was.  In a pulse
sequencer,  you have pulses coming out of each of the outputs.  With this
baby however, you have only whatever is on the I/0 port coming out, and
unless you've arranged it to be high like a pulse at that specific moment,
it don't reset.

Blast.

But it does have LEDs.....ahhhhhh ...and they take a high signal from the
mutliplexer to turn on...ahhhhhh....so I did the obvious and it works like a
charm.

There is 1 empty space below the last I/O jack which will (barely) accept a
hole and a switch to be installed.  On the wiper, I have a diode leading
into the backside of the reset jack, to each of the other contacts of this
ON-OFF-ON three position switch I have 1Ks which connect to the step 3 and
step 4 mutliplexer outputs.  You switch it up, and a two position sequence
is selected.  You switch in downward, and a three step sequence is set.  In
the middle, you have an open through the switch and the resets are bypassed
so it counts threw to four.

Because there's diode protecting this, the external reset jack can still be
used whenever you wish.

Sorry for the long post.  I thought some of you might benefit from this.

I have a schematic posted for this on my site.  Go to:

http://www.allegrobikes.com/synth.html

and click on 'Son of Frankensynth"  scroll to you see the link on the word
modifications, and when the new page loads, scroll down to Doepfer A-151.

enjoy (or not),

Peter