ARP 2500, DG 2500, ARP 2500 copy synth built from scratch with unique matrix to replace the Cherry switches. Synthesiser, Synth, Synth build, cherry matrix switches

Building a Synthesiser
Based on the ARP2500

The "DG2500" synthesiser

When I was in my teens I had the privilege of using and demonstrating some of the world's most fabulous music synthesisers. This synth build is my attempt to recreate one of my favourite synths of all time.

The ARP 2500 modular synthesiser was a wonderful design and it should have been, it cost as much as two houses! It was futuristic looking and very well thought out. It was also a bit quirky in places and suffered from breakthrough, a kind of noise interference where one part of the synth picks up noise from nearby sources. There was however, an upside to this in the form of added richness which often enlivened the the final sound patch.


Above: Phil Dodds (M.I.T.) using an ARP 2500 with additional side wings during the filming of "Close Encounters of the Third Kind". The synth was mounted in a unique housing to make it look even more massive on the set.

The "DG 2500" project from the beginning

Not made from a kit
The first stage

1. The proposed idea for the layout of the cabinet. Notice two rows of modules instead of the one row of the original ARP 2500. This is because the Behringer modules are only Eurorack size. A shame but understandable as they are a popular size. This would mean that my version would have double the modules but only 25% of the matrix connectivity of the original. However, the modules each have their own sockets so flexibility would not be a problem.

Later, I designed two keyboards to complete the synthesiser. The wood chosen for the cabinet is solid sapele.

The first stage

2. The first pieces. Aluminium extrusions are bolted onto pieces of wood which will make up the inner module housing. These extrusions will eventually form rails to which the modules are attached. A small but very important start of a huge project. This synthesiser is being built outwards from the very centre.



Inner module housing

3. The inner module housing (I.M.H.) starts to take shape. It's a cabinet which no one will see when the synthesiser is complete. The picture shows one of the temporary formers which hold the wooden sides to the top and bottom of the I.M.H. at an angle of 90 degrees while the glue sets.

The first stage

4. The I.M.H. on it's side. It is now a long rectangular box with a closed back secured by brass screws for future access. The wood has been carefully trimmed, sanded and sprayed with a protective finish.



Inner module housing

5. The inner module housing is now almost complete. It only requires a long oak mounting platform for the power distribution arrays and some wiring. You can see the aluminium extrusions fixed at the bottom, top and half way point of the housing. The blank panels at either end are just resting in place to help keep the shape of the structure as true as possible until it's populated with modules.

The mounting board

6.This long piece of oak is the mounting for the power distribution arrays. There will be 4 of them fitted along the length of the mounting. The whole unit will then be fitted inside the I.M.H. at the back so there will still be plenty of space for module circuitry.



Inner module housing

7. The power distribution board is now complete with its four arrays. At this point I have yet to make the wiring looms and connect them to power supply and the arrays but this will soon be done. I can then test the three modules I already have.

The first panel

8. Sapele is a beautiful wood. Shown here is the top piece of the main cabinet. It has been finished with Danish oil to bring out the natural grain of the wood.



Cutting aluminium

9. Precision cutting for the module front panels. The angle had to be exactly 90 degrees to make a good fit.

All cut to size

10. The aluminium sheet ready to cut to size for the matrix panels. There are 12 needed for the synth. As you can see, it's not a kit.

The first panel

11. An etching undercoat was used underneath the authentic 1970s control-panel grey paint. The picture shows the panel being washed after the application of the legend.

Finished panel

12. The finished module panel with components fitted. There is nothing like a large red light-up button to indicate power! Next to it, the spare plain panel just in case a disaster should happen.





Power panel

13. The power module resting in place at the right hand side of the internal module housing ready for hookup.

Finished woodwork

14. The wood of the main cabinet, fully assembled with the inner module housing in place ready for lots of wiring!



Mains

15. Power in and several outs for the keyboards and also just in case the system expands in future.

Switch modules

16. A couple of switch modules for the matrix. These will allow me to run busses the entire length of the cabinet or split them, one for each half.

Keyboard

17. Fitting the upper keyboard which has space for the main cabinet to sit on top.

Keyboard

18. Low profile for a sleek side view.





Keyboard

19. The left hand end blocks with holes cut for the analogue and digital controls and display

Keyboard

20. The right hand end blocks with cutouts for the pitch and scaling controls.





Keyboard

21. Meanwhile the two keyboards have taken their place underneath the main cabinet. This picture was taken before the matrix modules were more than just sheets of metal with holes in.



Keyboard

22. In this picture you can see the digital controls on the endblock for MIDI channel as well as pitch bend and modulation controls.





Keyboard

23. Sanding the transfer paper very lightly on a matrix panel ensures that the fix underneath can dry fully before removal.



Keyboard

24. Washing the transfer paper off the module front panel.





Keyboard

25. After installing 120 miniature jack sockets to the panel the completed module is ready for testing. It's far easier to fix a problem at this stage rather than after wiring it into the synth cabinet.



Keyboard

26. The matrix module is finally installed. Wiring it in requires 6 multi-sockets and 24 single wires soldered onto the internal loom.





Keyboard

27. The first matrix modules in place. I can now use the modules above them but there is no keyboard control yet.



Keyboard

28. A wider view of the synth so far with the internal wiring for the matrix clearly visible.