EEH Banana Analog Synthesizer
I was intrigued by a recent forum post, and decided to learn more about the German EEH Banana analog synthesizer from the 1980's. It seems this was designed to be similar to then-current Oberheim models, but at a lower price. Six voices were implemented, each with two oscillators. One obvious cost-cutting measure was the use of single-sided circuit boards with no silkscreen or solder mask throughout. Some other measures were not as apparent, such as not dividing the main oscillator by two to get 50% duty cycle before feeding it to the CPU, as is normally done. Total RAM memory was just 3K bytes, as opposed to 6K in an OB-8 or Sequential Six Trak. Six voice boards and one sample and hold board were mounted vertically, with connectors that mated with single-row headers on the main board. A combination of CEM 3340 oscillators, 3360 VCA's, 3310 Env Gens, and SSM2044 filter chips was used.
For schematics, it seems that only part of the design is documented, and even those drawings look more like the original plan, rather than actual production schematics. Many details are not shown. So I decided to see if I could create a more complete set of schematics for the 100-200 units that were manufactured.
Here is an archive containing the schematics that I generated for the banana synth. I did not capture the voice board schematic, but have included a scan of my copy of the original schematic, to which I have added some pin numbers and one or two corrections. Please note that I do not have a banana synth, nor do I have access to one. My schematics were made by studying many high-resolution photographs of the banana pc boards (Thank you to the people who sent them) I am sure there are at least a few mistakes in the schematics, so use them with caution. If you find any mistakes, please feel free to let me know and I will try to correct them. Also, the photographed units had a number of small cuts, jumpers, and components tacked onto the board. I have included these changes in my schematics, but it's possible that not all units are the same.
New MIDI board:
Some later units had a small MIDI board added. I have captured the schematic for this board and laid out a new pc board with the same circuit (except I changed the opto-isolator portion, and removed MIDI Thru).
Here is an archive containing the schematic for my new board, and also the original MIDI board schematic. If you are interested in getting one of the new banana MIDI boards, please contact me. Also, if there is enough interest, I may look into adding one or two new features to the MIDI firmware, such as sysex patch save and restore.
Here is a photo of the bare pcb that is now available. (It has been tested in a banana synth and worked fine)
And here is a picture of it populated with the ribbon cable (Note that in this case, the red stripe on the cable is NOT pin 1, nor is the pin called "1" on the 40-pin DIP plug:
Firmware EPROM images:
Here is an archive containing two different versions of the banana MIDI firmware, and version 4.2 of the non-MIDI firmware.
Please note: The information provided here is not guaranteed to be accurate. I will not be responsible for any damage to synthesizer circuitry caused by its use.
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