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The SCR pad on the PCB has been provided to allow the ground tags of the jack sockets to be
connected to the power supply ground without using the module’s 0V supply. Earth loops
cannot occur through patch leads this way, although screening is maintained. Of course, this
can only work if all your modules follow this principle.
If you have used Switchcraft 112 sockets you will see that they have three connections. One is
the earth tag which is connected to the metal barrel of the socket. One is the signal tag which
will be connected to the tip of the jack plug when it is inserted. The third tag is the normalised
tag, or NC (normally closed) tag. The NC tag is internally connected to the signal tag when a
jack is not connected. This connection is automatically broken when you insert a jack. In the
OMS-820, we have no use for the NC lugs.
The ground tags of each socket can be connected together with solid wire. A single piece of
insulated wire can then be used to connect both the tags to the SCR pad on the PCB. Do not
connect these ground tags to any other ground.
The suggested layout uses just two sockets, and wiring them up is straightforward enough.
Use multistrand hook up wire to connect each socket’s signal lug to the relevant pad on the
PCB. There is no need to use screened cable for such short runs. Keep the wires short but not
taut. If you do insist on using screened cable then connect the screen to the socket’s ground
lug. Leave the screen unconnected at the PCB end. Use a bit of heatshrink tube to keep the
end from fraying.
The GATE socket’s signal lug goes to the pad marked GATE. And the RESET socket’s
signal lug goes to the pad marked RESET.
Now the OMS-820 has five switches. Wiring these can be confusing, so take your time. The
first switch to wire up is the EG/LFO one. This is connected to the three pads labelled MODE.
The SPDT toggle switch has three pins. The top pin of the switch should be wired so that it
goes into the bottom pad of MODE. The middle pin goes to the middle pad of MODE. The
bottom pin goes to the top pad. The two end wires therefore cross on their journey from
switch to the board.
The next switch to wire up is the GATED/RESETABLE switch. This is wired to the AUTO
pad. Again you need three wires to connect this switch, and again it is the top pin of the
switch that goes to the bottom pad. The middle pin goes to the middle pad, and the bottom pin
goes to the top pad.
The next switch is the final toggle switch, the AD/AR switch. This again has three pins, but
only two are connected to the board at pads labelled AD/R. The middle pin of the switch is
connected to the top pad of the AD/R pads. The bottom pin is connected to the bottom pad.
The next two switches are the push switches. They have only two pins. The RESET switch
needs to be connected to the R-S pads. Wire one pin to either of the two pads, and the other
pin to the remaining pad. The GATE switch can be wired similarly to the G-S pads.
Right you have now completed the OMS-820 and it may be a good idea to check the board
again for any shorts or wrong components. You could also try applying power to it. It won’t
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