First post, by t9999clint
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We have a growing community of Soundfont nerds here. (never expected that to happen)
This project is a multipurpose synthesizer platform for the raspberry pi. Complete with automatic profile switching using sysex messages to allow the raspberry pi to be controlled from the machine sending the midi data.
This is to act either as a MT-32/CM-32L replacement, or as a soundfont powered synth to use with your old computer, or MIDI Keyboard.
There will be a number of ways to connect this to a old pc, through MIDI cable to gameport adapter, through a serial port, or to the wavetable header like the one on a soundblaster 16.
So far I've only finished the standard MIDI cable in software *edit, serial is done now*, but the others are coming. Serial is probably the cheapest way to connect it to a old PC, but it won't support any game that you can't use with softmpu.
Regarding the wavetable header...
I was looking at some schematics and it looks like it should be fairly simple, (not super easy though) to make a adapter that converts the pinout on a soundblaster wavetable header to something that you can plugin to the GPIO on a raspberry pi.
The current plan is to workout something on a breadboard that converts the MIDI to Serial (at 3.3v) and plug that into the gpio pins on the raspberry pi.
From my testing, the 5v rail from most computer power-supplies isn't stable enough to use with the Ras Pi and might damage the Pi or even worse the computer. To get around this, and to still allow the WavePi to be internally powered it has to go through a 12v to 5v buck converter like the LM2596 (calibrated for about 5.5v).
The Midi data will be converted by a optocoupler like the 6N138 and a few resistors. This should bring everything to the levels that the Pi is expecting, while also hopefully limit the noise from the computer's hardware.
The biggest roadblock is the Raspberry Pi 3's built in DAC, which is basically unusable. The cheapest good quality DAC I was able to find was the Sabarant USB one for about $8.
The goal is for the circuitry to only cost about $2-5 USD in parts, (not including the Pi) but so far the project's BOM will probably be around $20 depending on features. The biggest cost is the DAC.
Youtube demo of a WavePi installed inside a PC directly connected to the wavetable header, ZERO EXTERNAL CABLES!.
here's a draft diagram based off of one from samplerbox, some reference documents and another from serdashop...
I'll replace this with a proper schematic when I get to that stage. I'm just at the software stage right now...
BOM (sort of) for wavetable adapter... rough guess is $20 USD total, I need to find a way to make this cheaper...
- $8 - 1 x USB Audio DAC (Sabrent USB)
- $1.50 - 1 x LM2596 DC to DC Buck converter (12v to 5v to power pi, 5v from soundblaster is too unstable/unsafe)
- $0.80 - 1 x 6N138 Optocoupler (MIDI to TTY signal stripping/voltage stepdown)
- $??? - 1 x diode 1N4148
- $??? - 1 x 220ohm resistor
- $??? - 1 x 40 kohm resistor
- $??? - 1 x 4 kohm resistor
- $??? - 1 x Aux stereo cable (connect DAC to soundcard, either internal or external)
- $??? - 1 x ribbon cable, eg. floppy cable (connect midi and audio to wavetable header on soundcard)
- $??? - 1 x molex, female connector (for 12v)