PROJECTS

A-141 Bus Link

This is a modification to the A-141 envelope module to connect it to the system bus.

 

 

Here, is presented a modification that can be done to the A-141 so that it is connected to the system bus, with front panel override in the same way as the A-141 module works. Although a simple modification, it does involve dismantling the A-141 and anyone inexperienced in soldering may want to avoid this one. The modification requires that a socket is removed from a pcb and the pcb track under it cut, and then a new IDC ribbon cable is needed with an extra wire that connects the Gate socket to the bus board.

In order to carry out this modification you will need just a soldering iron, a knife and a spanner (to remove the sockets and pots). It is all quite straight forward really, just a little care is needed in places.

 

STEP 1: REMOVING PCB FROM PANEL.

Having removed the module from the system, disconnect the IDC ribbon cable from the module - you actually will not need to use this again (but don't throw this away, you will need it later on to verify the orientation of the plugs when making the new cable). The A-141 has two pcb's, one larger one with the ADSR pots on and one smaller board with the control input sockets and CV pots on, this is the board that needs to be removed. Pull off the CV knobs (CVA, CVD, CVS and CVR knobs), although this sounds simple enough, you may find that the knobs do not always come off very easily. If the knobs are tight and cannot be pulled off, you will need to give them a little extra leverage, your prime concern is not to scratch the front panel and not to damage the knob itself. There are two ways to remove a stubborn knob, either use a flat blade screwdriver by resting it's shaft on the adjacent socket and prizing the blade under the edge of the knob whilst pulling the knob up, trying to get the blade of the screwdriver as far under the knob as possible - using this method be very careful that you do not dig the screwdriver into the knob base, as a metal screwdriver is somewhat tougher than the plastic knob, and too much force will dig into the knob. An alternative is to get a piece of thin nylon string (or a piece of insulated wire), wrap it around under the knob, so that it goes around the shaft of the pot under the knob, and pull upwards.

Once the knobs are off, remove the nuts from the pots and also from the CV sockets CVA, CVD, CVS, CVR and the Gate socket. Again, be very careful removing the nuts, a spanner will scratch the panel very easily, try to hold the spanner at right angles to the panel and try to grip the nut just in the upper half so that the spanner is not in contact with the panel. Try removing the pot nuts first, as if you do scratch the panel around the nut, the knob will cover up the marks anyway, there is no leeway with the sockets. You can use a spanner or shifter spanner, but if you must use a pair of pliers to do it, just make sure they are at a right angle to the panel, and if they slip off, remember it's your panel at stake here! You do not need to remove the Retrigger socket. Having removed the 9 nuts, the pcb will come out of the panel, note that there are some trailing wires, so don't expect to move the pcb far from the module.

STEP 2: REMOVING THE GATE SOCKET

Unfortunately the single pcb track that needs to be cut, is under the gate socket itself, unlike most pcb assemblies the A-141 has components both sides of the pcb - pots on one side and sockets on the other, So, the Gate socket has to be taken off the board to expose the pcb track to be cut. Removing the socket is perhaps not as easy as it may seem. A desolder tool is not very useful in this instance as the socket is on the track side, and trying to use a desolder tool will probably just result in a melted pot - don't damage the socket, as you have to put it back on afterwards.

The best way to remove the socket on this pcb is to put the soldering iron across the two pins of one side and then pull the socket up on that side. Don't try and get it all the way out yet, once it has moved up a little, move to the other side of the socket and repeat the operation, Eventually by hovering betwen the two sides the socket will become free. Be careful not to lift the pcb track by getting the joint too hot or simply pulling too hard on the socket. You may wish to use a desolder tool or desolder braid to remove the solder over the track pads once the socket is removed.

Having removed the socket, the pcb track should now be exposed, the track that needs to be cut is the line that goes from each side of the tip of the socket (nearest the centre of the pcb), do not cut the earth track nearest the edge of the pcb. Using a knife cut the track in the middle, this is best done using a knife such as a Stanley knife of similar. Try to get the cut about 1mm wide, score two lines 1mm apart on the track and then point the knife blade towards the centre of the planned cut and slice a piece of track away, and then repeat with the other side. Double check that there is a perfect breack in the pcb.

STEP 3: RE-ASSEMBLY

Next, resolder the socket back to where it came from on the pcb, make sure the pins do not end up shorting together with a soldering blob, and try not to melt the socket! Next, put the pcb back into the panel and refit the nuts, then turn all the pots fully anti-clockwise and put the knobs back on making sure they are all pointing to 0.

STEP 4: MAKING THE NEW IDC CABLE

Finally, a new ribbon cable is required, this has to have a 10-way connector one end and a 16-way the other, but it has to have a 16-way cable with one of the spare wires longer, this is the gate connection and will be soldered directly to the Gate socket. To make up this cable you really need the special tool for assembling IDC cable, but it can be done by feeding the IDC cable into the socket and clamping it together in a vice. You must use a 16-way IDC cable, though you only need a piece 200mm long. Fit the 16-way connector to the cable, then measure off 125mm from this connector and cut through the first 10 wires (this must include the RED lined wire), peel off the unconnected edge - this part of the cable is not needed. This leaves 6 wires, seperate these from the main cable by a further 30mm, then seperate the end 2 (this is the Gate connection), the middle 4 wires are not needed and can be cut off where they come out of the attached ribbon cable. Then attach the 10-way IDC connector to the remaining 10 wires, note the orientation of the connector, when laid flat down, the connectors face opposite directions, check with the original cable that was removed for confirmation of the way it is connected

The 2 wires left must be soldered together and then soldered to the tip of the socket that had been removed, at the edge of the pcb side. See pic for comfirmation. When reconnecting the 10-way connector to the A-141, make sure the red wire is towards the edge of the board.