Following the publication of a Youtube video from SynthMania concerning the installation of ZIP sockets in a Drumulator, I will discuss an even more interesting modification than the one presented by him. You can find his video here:
In his video, Paolo Di Nicolantonio, indicates how it is possible to place ZIF sockets in a Drumulator, in order to be able to replace the original sound bank by another sound bank. And first of all, what is ZIF support?
It is a support which allows the easy insertion and extraction of an integrated circuit. To do this, it has a lever which allows the component legs to be released or locked, without mechanical stress. This kind of support can be presented in different ways:
Now, what does a sound bank look like on a Drumulator? In fact it's quite simple ... in principle. A sound bank is made up of four read only memory. Each of these memories contains one or more sounds for a total capacity of 64k bytes. Note one very important thing: each start and end memory address of each sound is written 'hard' in the machine's system memory.
Where are these four ROMs located in the Drumulator? Inside the red rectangle:
In conclusion, each time you want to change the soundbank of a Drumulator, you have to remove these four circuits and replace them with the four new ones. However, this is not very practical!
Hence the following idea: why not have at least two banks always available inside the machine, which we could choose using a switch? In this case, the problem is that it is absolutely necessary to build a printed circuit board to receive not four, but eight ROMs. This type of extension existed at the time:
In this case, the expansion board allows the choice between three sound banks. It's interesting, but not necessarily easy to install due to the large size of the board.
Another approach is to provide only two banks, and in addition, to concatenate the four ROMs of a bank into a single ROM. In fact, two banks can be contained in two 64K byte ROMs instead of eight 16K byte ROMs like the original ones. Here is the result of such a modification :
Another approach is to provide only two banks, and in addition, to concatenate the four ROMs of a bank into a single ROM. In fact, two banks can be contained in two 64K byte ROMs instead of eight 16K byte ROMs like the original ones. Here is the result of such a modification :
However, as I mentioned above about the start and end addresses of each sound, this system works fine as long as you are working with the same types of sounds that have the same start and end memory addresses.
If you want to use different sounds with different lengths than the original ones, you must also set the system ROM with these new settings. This is not an easy task. A well-known company, Digidrums, offered various soundbanks for sale. Each soundbank consisted of five ROMs. The four containing the sounds, and the one containing the modified system.
In short, to be able to switch between two sound banks, and in the event that one is a Digidrum bank, you must also be able to switch the system. Another expansion board is therefore required to perform this task :
This board performs this task but also brings some other improvements. It allows SRAM to be backed up with a standard battery. It also offers two SRAM banks allowing the saving of two sequences that can also be selected using a switch. It improves the write protection of the SRAM, it has the MIDI input interface and finally allows to control the switch of the sound ROMs corresponding to the selected system.
The simplicity and efficiency of this board, however, requires programming a single 64K byte ROM with the two envisaged versions of the system. Likewise, this is easily done using an EPROM programmer and its software.
This is what it looks like inside the machine. The system is being assembled. The old MIDI interface has not yet been removed and the switches have not been mounted on the rear panel:
Note that by searching the Net, it is possible to find utilities that allow the creation of a complete set of four sound ROMs plus the system ROM from personal samples, in the same way as the Digidrum was doing. While remaining of course within the maximum limit of 64K bytes of samples.
More info here: 
