Updating MIDI interface

The following steps detail the method involved in upgrading the original Antonus 2600 monophonic MIDI interface to the all new Duophonic MIDI interface.

Please remove the AC power chord along with all patch cables and audio leads from the synthesiser before commencing with the installation.
Once removed, ensure that your working environment is suitable, comfortable, and clean, as in order for you to update the MIDI interface, the synthesiser will require being opened up via its front panel. You must also ensure that your working area can provide adequate protection for the front panel once it is removed, thereby ensuring no damage will occur to both the exposed panel and its sliders.

Gaining access into the Antonus 2600, will require the removal of the 3 nuts which are located on the left and right hand sides of the front panel. In order to avoid damage, we strongly recommend the use of a 5.5mm wrench whilst removing these nuts. Alternatively, flat pliers can be used, but do take extra care not to mark or damage the exposed panel. Fig 1

Step 1: Insert a jack cable or headphone connector into the headphone socket. Then, using your right hand, grasp the inserted connector and with your left hand grasp the circular ‘GAIN’ potentiometer. Gently lift and remove the front panel away from the cabinet, resting it carefully upon a suitably soft surface within your working area. With the panel now removed, you will see the exposed circuit boards within the synthesiser. Fig 2


Step 2: Looking carefully at the exposed boards, locate ‘Board A’– it is clearly marked with text and situated on the inner right hand side. Now locate the MIDI Board (Fig 3) along with its side panel connectors 3 in total. Fig 4 and Fig 5 (If you discover a small deposit of glue on the board and/or its connectors, please gently remove using your finger nail before uninstalling).
Remove the old interface along with all of its connectors as indicated in the photographs. The monophonic Midi board is a MIDIMPLANT board.  


This midi board can be used to add MIDI into many analog synthesizers, so don’t throw it away. You can contact Antonus if you don’t know what to do with it. 


Step 3: Remove the connector that leads directly from the power socket of the side panel to the internal transformer. It is a larger 3-pin connector, locate it and remove it. Fig 6
During this process, you might discover that some of the cables are joined together via cable ties, in which case, it will be necessary to cut these – please use a suitable tool, but be careful not to damage any of the surrounding cables. Fig 7


Step 4: By this stage, you should have all the connectors from the side panel disconnected. Now proceed to remove the 4 wood screws that retain the side panel. Assuming that Steps 1- 4 have been followed correctly, the panel along with its cables can be safely removed without problem. Fig 8 and Fig 9


Step 5: Now mark the location for the screws of the new duophonic board. This plate is larger than the original monophonic model and as a result, cannot be installed in the same socket or in place of plate A. We recommend that you install the board inside the cabinet, close to the side panel opening as shown. Fig 10.
From inside the cabinet, place the board in position as shown, and mark the location points for the wood screws. Use a drill of no greater diameter than 3mm to create small pilot holes for the screws, thereby, ensuring that a good grip will be established within the cabinet. Now fix the board in place with the supplied screws. Fig 11

FIG 10
FIG 11

Step 6: Looking at ‘Board B’, (situated on the inner left hand side of the panel and labelled with appropriate text) locate the cable that connects the power supply of ‘Board B and Board C’ (Board C is the lower of the 3 panels). Disconnect both sides and remove the cable. (These sockets will be replaced with new cables during step 7) Fig 12 and Fig 13. Once again, if there is a deposit of glue on the connectors, gently remove this using your finger nail before removal. Likewise, if the cable is strapped together via a cable tie, this must be cut.

FIG 12
FIG 13

Step 7: Locate the 2 supplied 3-pin power cables (Fig 14) and plug them into the new interface as shown Fig 15. The order that these are fitted to the interface board is of no consequence. Now, connect the end of the longer 3-pin connector to ‘Board B’ and the shorter one to ‘Board C’ (these cables replace the one removed from boards B & C at Step 6).

FIG 14
FIG 15

Step 8: Now install the side panel. Note: If the cabinet opening is too narrow and the panel’s circuit board does not fit securely, the installer will need to sand the wood a little until the board is able to pass through safely.
Once the side panel is installed, you can then connect the included 8-pin cable (Fig 16) one end to the side panel and the other end to the MIDI board. Now connect the 2-pin Midi connector cable Fig 17.

Next connect the larger 3-pin cable from the new side panel to the transformer AC input.

FIG 16
FIG 17

Step 9: Locate the supplied grey cable fitted with 2-pins on one end and 3-pins on the other Fig 18. Connect the 2-pin end of the cable to the 2-pin socket on the Midi board – this socket is situated close to the long 8-pin connector Fig 19. The 3-pin end of the cable plugs into the CVS OUT connection on ‘Board A’ Fig 20.

Step 10: Next using the supplied cable Fig 21 – the one fitted with a 4-pin connector at one end and a 2-pin and 3-pin connector at the other. Fit the 4-pin end on to the Side Panel Board. Then fit the 2-pin connector to the EXT CV socket on ‘Board A’ and the 3-pin connector to the Gate Out socket on ‘Board A’. (See Fig 20)

Finish off the installation by organising the cables using cable ties. This completes the Duophonic Midi Interface installation procedure.

FIG 18
FIG 19
FIG 20
FIG 21

Step 11: Refit the front panel of the synthesiser and tighten the nuts again using the 5.5mm wrench, but do not over tighten. We do not recommend using an electric screwdriver during this operation as this could damage the internal fittings. We simply recommend tightening the nuts to the point that you cannot loosen them using your fingers, but please do not tighten them beyond this point. Remove the cable or jack connector from the headphone socket.

Well that’s it. The installation is complete. You can now reconnect the AC cord and repower the Antonus synthesiser. First check that the CV and GATE inputs work. Next connect a MIDI device to check that the CV outputs and internal functions are working correctly. It is normal to notice a blue light flash through the left side speaker grill as you trigger the device via Midi.

For more information, download the manual for the Duophonic MIDI Interface.


Important, if you have any questions before, during or after the process, it is better to contact the Antonus team using any of the different ways of contact available.

Remember: This old MIDIMPLANT interface can be used to add MIDI to many analog synthesizers, so don’t throw it away. You can contact Antonus if you don’t know what to do with it.

Many thanks to Mike Smith for additional help creating this guide.