A DIY EEPROM Cartridge Design for the Ensoniq ESQ-1
A friend was recently interested in getting an EEPROM voice cartridge for his Ensoniq ESQ-1. The design of this kind of cartridge is complicated by the fact that later ESQ-1's had an extra signal added to the cartridge slot which can be used with newer style EEPROM chips. This signal is not present on older model ESQ-1's, like the one my friend has, so the cartridge needed to be a little different for his unit. The design presented here uses a 74LS14 IC to modify the ESQ-1 cartridge slot WRITE signal to work with the newer EEPROMs that did not exist when the ESQ-1 was designed. It should work in earlier or later production ESQ-1's. The specific part that this design uses is AT28C256 or X28C256, depending on the manufacturer. These chips are not easy to find, but they are out there. This part holds four "banks", selectable using the two switches. Each bank has Cartridges A and B. The cartridge must be inserted into the ESQ-1 with the switches and chips facing the front of the keyboard. Do not insert or remove the cartridge with the synthesizer powered on.
Here are the parts needed to build it:
1) 28C256 EEPROM (28C64 could probably be used for just one "bank", with no switch, but has not been tested)
2) U2, 74LS14 (do not use 74HC14, 74C14, or 7414)
3) RN2, 7-pin, 6 resistor, resistor network, 3.3K (4.7K also works), pin 1 common to all 6 resistors (Dot shows pin 1, must be installed properly)
4) C3, 0.1 uF 50V ceramic cap
5) C1, 330 pf 5% NPO ceramic cap
6) 2.2 uF 16V electrolytic cap (square pad is positive end)
7) SW1, 2-position DIP switch
8) 1K 1/4W 5% resistor
9) 2.7K 1/4W 5% resistor
10) Sockets for both IC's
I will not be offering pc boards for this cartridge. Instead, I am sharing the Gerber files, so that anyone who wants can order boards for themselves. The boards shown at the top were ordered from JLCPCB in China and have gold plating on the edge fingers. The price was very reasonable. Here are the Gerber files. The pcb is 2.243" x 1.577". This pcb was not designed to fit into any specific plastic case.
Something to watch out for:
The 28C256 EEPROM has a special mode called "Software protection mode". When the chip has this mode enabled, the CPU must write special bytes to the chip before each write operation to "unlock" it, temporarily, and enable the write to take place. The ESQ-1 firmware doesn't know anything about this mode, and does not do the special unlocking operation, so if the EEPROM has the software protection mode enabled, any ESQ-1 copy operation to the cartridge will fail. It seems that many 28C256 chips currently being sold have this special mode enabled. In order to use one of these in the ESQ-1, it is necessary to first turn off this mode, which can be done using most modern EPROM programmers. The TL-866 definitely can turn off this mode, as well as the GQ-3X and GQ-4X programmers.
Please note: The design presented here has been tested in several ESQ-1's, but is not guaranteed to work properly or be useful. Use it at your own risk. I will not be responsible for any damage to any instrument caused by either proper or improper use of the design offered here.