Drumulator : how to switch between two banks of sound?

Originally, the Drumulator has a basic sound bank. Over the time, some people wanted to replace the original sounds. The operation was not very difficult since it was enough to replace the four basic EPROMs with four others containing the new sounds.

The original mother board.

Replacing the original sounds was a good idea, but in this case, the basic sounds were lost. Then additional printed circuits board appeared, which allowed to switch between two or more banks of sound :

or the more famous JL Cooper board:

Why not! But these boards have the disadvantage of being large and must contain a large number of EPROM. 2 x 4 EPROMs for two sound banks plus possibly two EPROMs for the system if Digidrum sounds are used for a total of 10 EPROMs, just for two banks of sound!

So I thought it might be better to concatenate four 16K byte EPROMs into one 64K byte. This makes it possible to propose two banks of sounds in only two EPROMs. So I developed an electronic board that contains two banks of sound that can be selected with a simple switch.

The result is a small circuit board :

The switch in not yet connected...

Well. The problem is that if you want to have a Digidrum sound bank, you also need a modified system EPROM.

In the same way, I decided to develop a circuit board allowing to select two system EPROMs.

Here too, the principle has been to concatenate two system EPROMs into a single EPROM. This requires some file manipulations to be programmed in the final EPROM, but this makes it possible to build a small printed circuit board :

Not bad, isn't it?

But that's not all. On this circuit board I added the following features :

• Two banks of RAM selectable by switch.
• 20CR32 battery backup with socket, instead of the original big battery.
• Better RAM protection when turning the machine on / off (nerver more the 'Bad' message).
• Implementing the MIDI interface.
• Control of the EEPROM sounds board if necessary (in case of one Digidrum sound bank).
• And, obviously, the selection of two system EPROMs. 

And voilà!

Only two small and easy modifications are to be made on the motherboard for the power good function (juste one wire to be soldered), and for the MIDI function (two pin to be soldered together on the IC13F as the 'normal' MIDI extension).

Therefore, it is also possible to remove the 'DIY' MIDI interface of this kind :

Hum!!!

And now, an expanded Drumulator :

Sérial  #1477 :

Enjoy!