Real World Interfaces modifications
to the original DX7 from about 1987 to the late 1990s
Robin Whittle contact details
11 February 2021
To the main
Real World Interfaces page. To the index
page of this site, for all sorts of
things . . .
- Mod 7.1 firmware. This was a 27128 EPROM with a modified
version of the DX7 firmware, with a few features missing and many new
features. One feature was the control of 16 banks of 32 voice
memory. Some of the features only worked with the sound
Some of these I sent as EPROMs in the post to customers, mainly in
Australia. In other cases I installed it the DX7 myself - and for
these machines I often did the sound mods and sometimes the 16 bank
- 16 banks of 32 voice memory, with a lithium battery for battery
backup. This was generally, or always, a cylindrical Panasonic BR
2/3 AE battery which should last for decades. Its voltage should
be about 3 volts. You can replace it with a cylindrical BR 1/2 AA
battery, or a 2032 coin cell soldered in or in a holder, though these
coin cell batteries rarely last more than 10 years. The
cylindrical batteries should last for decades.
- Sound improvement mods. These were some fancy modifications
to the analogue circuit following the DAC which increased signal level
and reduced background noise and distortion. Overall the SNR was
improved by 12 or 14 dBm, I recall, though this was not weighted for
our ear's response to low level signals (https://realfield.com/anm/).
The DX7 converts one voice signal at at time, 16 times over, per
sampling period. With the standard patches, the new DAC
arrangement worked linearly. With the Mod 7.1 firmware it was
possible to make patch which put out twice the ordinary signal level to
the DAC. The top and bottom 25% ranges of these signals were
handled in the modified DAC circuit with half the gain of normal.
So this constitutes a soft clip distortion, of each individual voice
independently, without mashing them together by distorting the sum of
all 16 voices. More information on this is in the Mod 7.1
- DX7 MemPacs. I also modified some ROM carts with a large box, two
pushbuttons and a 7 segment display, to be a 16 bank RAM cart.
Originally these had NiCad rechargeable batteries, but this turned out
to be a really bad idea since they leaked. I later used (and
upgraded older MemPacs) with lithium, non-rechargeable, BR 1/2 AA
batteries. These should last a few decades. All those have
"Li" inscribed on the bottom part of the box.
The wooden boxes were made to my design from cedar, by Kim Devenish http://members.dcsi.net.au/kimjulie/ .
Documentation for the Mod 7.1 firmware - and the memory and sound improvement mods