OK, so here is my (relatively) straightforward mod to the A-155 to
allow for permanent Trig and CV outputs to turn it into a simple 16-
step sequencer, thus removing the need for external modules A-160 and
A-150, as shown in Fig 6 in the manual. I deliberately don't want to
be too 'prescriptive', as what *I* have done is quite a lot more than
really needs to be (for several reasons: I move my modules around a
lot, so a separate 4hp plate with 10-way IDC + ribbon fits the bill;
I was too lazy to consider pulling various boards off the 155 to
drill extra holes etc.). I used a piece of stripboard because I had
some, and I more-or-less just added the wires as I needed to, cutting
tracks where needed - the mod could be done by sticking the IC on its
back and soldering directly onto its legs.
The gif file shows the schematic: the chip is a CD4053 or something
equivalent, such as an HEF/HCF4053 etc. Resistors could be 2k2 for
use with 5mA LEDs (I used 5k1 as the LEDs I had were low-current 2mA
types, left over from some kit I built).
The pictures:
155_16_step_gen - a general view of the back, showing the ribbon
cable I used. Note that the blue wire is a factory-fitted mod, and
not part of this one!
155_16_step_mod - my new panel on the right of the 155: the top
socket is the combined trigger rows, the bottom one is the CV; the
LEDs are in line with the pots on the row that is active.
155_16_step_outs - location of the row 'post outs', these are the
legs of 100ohm resistors, which can be traced directly to the 'post
out' sockets.
155_16_step_strip - shows how little there is, most of the
complication arises because of my use of the 10-way IDC header. It
should be easy enough to wire point-to-point straight from the
schematic.
155_16_step_trig_etc - shows the other outputs:
+12V taken from the top pair of pins on the back of the power
connector on the 'controller board'
GND taken from any of the middle 3 pairs (I used the pair second from
bottom).
Pin 6 on the '4024 is just that. There is no other connection to this
pin on the board (the 4024 is right next to the other connector).
Trig 1 is the second pin _down_ on the back of the connector on
the 'trigger/gate adapter board'
Trig 3 is the second pin _up_ on this connector (you can easily trace
tracks to the sockets to be sure)
There's no need for any sort of switch: when not in use there are no
loading effects on the normal 8-step circuitry - when you want to go
16-step, just plug in!
The only thing I haven't catered for is if _negative_ voltages are
input to the bottom row external inputs. Since I have taken Vee, pin
7 to ground, the 4053 will not be happy with such voltages (it's
highly unlikely I will ever want to do this). If bothered about this,
there are two 79L05s (one on each potentiometer board), and the -5V
from either could be taken to pin 7 (the 4053s already in the 155 are
wired that way).
That's about all I can think of (its enough to be going on with!).
Tim