The soundbox is an external device used to support peripherals on a
NeXT computer. The internal circuit board is identical to the one found
inside next MegaPixel monitor. As an important side note, if your
MegaPixel has died DO NOT throw it out (if you must) without first
removing this board. Two versions of the sound box were created. A
non-ADB and an ADB version. ADB stands for Apple Desktop Bus and is
fully compatible with apple peripherals of the same type.
The non-ADB came first and is compatible with all next hardware. The
ADB version came later and is ONLY compatible with Turbo models which
have a ROM revision greater than v74. Despite the limited
compatibility, the ADB sound boxes are much easier to find. As such
there have been many discussions about converting the ADB version to be
compatible with non-ADB devices and systems. Another important thing to
mention is that you must have a 983 model power supply to use a cube
without further modification with a sound box. The 152 model needs a
minimum load (previously provided by the monitor) to function.
The NeXT 19 pin connector:
It was previously thought that the ADB soundbox had the same connection
to the 19 pin DSub connector as the non-adb version. This has been
proven to be incorrect. Previously pin 7 was unused on this connector,
but in the case of ADB is designated for the ADB bus. By providing 5V
for the keyboard it is possible to bypass the sound box entirely and
hook the ADB data line directly to the next system. You will of course
lose the ability to produce sound with this configuration.
View from the back of a Next System
\ o o o o o o o o o o /
\ o o o o o o o o o /
3. MON CLK
4. MON DATA OUT
5. MON DATA IN
6. MON PWR SWITCH
The non-ADB keyboard interface:
Figure 1: Non-ADB View From the Soundbox
Figure 2: The ADB Interface
The ADB soundbox Modification:
The modification of the soundbox is not too difficult if you have a good soldering iron and a steady hand.
Figure 3: An Annotated View of the ADB Sound Board:
1) Locate the ASIC near the large capacitor. Use a utility knife to
sever the annotated connection. We will be soldering to it later, so
Figure 4: ASIC Trace to Cut
Figure 5: ASIC Trace Cut
2) Use the schematic below to rework the board
￼Figure 6: Schematic
3) Connect VGA
Figure 7: VGA Pinout
Connect a 150ohm resistor across pins 1,2, and 3 (Red, Green, Blue).
Use an RCA connector and connect signal to the 150ohm resistor and
ground across pins 5 -10 on the vga connector. Connect V-SYNC to pin 2
on the SoundboxVGA connector. Connect H-SYNC to pin 4 on the soundbox
VGA connector. As a side note it is important to use properly shielded
cabling from the Next computer to the soundbox. Inferior cabling will
produce poor image results.
4) (Optional) Create a dummy load for Revision 152 Cube Power Supplies:
The early version of cube power supplies (part number 152) requires a load of ~400mA on the -12V power rail in order to function. The easiest way to provide this is by using a power resistor ~30ohms from -12V to GND.
This resistor will get very hot so we need a fan and heatsink to remove heat from the enclosure. I use two 5W, 68 ohm resistors in parallel to split the current between them, and lower the effective resistance to 34ohm.
Using a pentium style cooler, remove some of the fins to allow the resistors to fit inside. Then bend the remaining fins over to secure the resistors in place. Connect the fan and the resistors across the -12V and GND connection on the
Resistors embedded in the heatsink:
Modification tested on both a nextstation color turbo and an 030 cube
with no problems in the firmware or OS. Use at your own risk. Please do
not sell these to collectors without disclosing there has been a
modification. Distribute this information freely, but my ego does enjoy
credit. I can be reached at: archer174 at gmail if you have questions.