ytsestef
Well-known member
Hey guys, long time no see!
I haven't been around for quite some time, I have gotten myself into a different project
I am building a MBSID synthesizer ( http://ucapps.de/ ), but I am using a keyboard I have vandalized out of a MIDI Controller (It was 5 octaves long, I cut it down to 3), along with its own controller (just a small PCB with +12V input, a ribbon cable input for the keyboard and a MIDI out).
Now, check this out:
The midi controller of the keyboard does not send MIDI data at all (or so it seems) when connected directly from the midi out of the keyboard controller PCB to the midi in of the synthesizer, but when I connect it via an m-audio 2x2 midi interface that I have lying around (in THRU mode, not USB), tadaaaa it sends midi messages and mid SIDs sing...
I guess the m-audio midi interface buffers the signal and/or gets rid of noise or ground loops? I'm not sure. I know midi is strange and prone to noise and hum issues due to the optoisolators used and I highly suspect grounding issues here, but I am not sure how to wire it up. So far, my grounding scheme is as follows:
Mains ground is connected directly from the IEC connector of the synth to a large metal bar underneath the keyboard, where the jack from the output also connects. Also 0vdc from the master keyboard controller is connected to the same bar (I saw this on the original master keyboard enclosure, so I just moved it over to my design.
Also different midi pinouts confuse me (where pin2 is NC at IN, but connected to shield at OUT etc), but I guess this is only important when using midi cables (as opposed to wires for 5-6cm from pcb to pcb, which is what I'm doing).
To confuse you even more, before I get the PSU I connected them using different PSUs for each device (C64 for mbsid, generic wall-wart for master keyboard controller) and it worked, which only makes it more obvious that there is noise/ground loop introduced when using a single PSU.
Any thoughts? Any help would be much appreciated! I'm pretty much at a loss, how do I troubleshoot such stuff? I can't trace or measure the MIDI signal (I think), because it is a 5mA current loop (which means the current is modulated/switched, not the voltage).
The PSU is a switching Meanwell RPT-60B (+12, -12, +5, GND), 60W.
BONUS: Pics of my build so far
I haven't been around for quite some time, I have gotten myself into a different project
I am building a MBSID synthesizer ( http://ucapps.de/ ), but I am using a keyboard I have vandalized out of a MIDI Controller (It was 5 octaves long, I cut it down to 3), along with its own controller (just a small PCB with +12V input, a ribbon cable input for the keyboard and a MIDI out).
Now, check this out:
The midi controller of the keyboard does not send MIDI data at all (or so it seems) when connected directly from the midi out of the keyboard controller PCB to the midi in of the synthesizer, but when I connect it via an m-audio 2x2 midi interface that I have lying around (in THRU mode, not USB), tadaaaa it sends midi messages and mid SIDs sing...
I guess the m-audio midi interface buffers the signal and/or gets rid of noise or ground loops? I'm not sure. I know midi is strange and prone to noise and hum issues due to the optoisolators used and I highly suspect grounding issues here, but I am not sure how to wire it up. So far, my grounding scheme is as follows:
Mains ground is connected directly from the IEC connector of the synth to a large metal bar underneath the keyboard, where the jack from the output also connects. Also 0vdc from the master keyboard controller is connected to the same bar (I saw this on the original master keyboard enclosure, so I just moved it over to my design.
Also different midi pinouts confuse me (where pin2 is NC at IN, but connected to shield at OUT etc), but I guess this is only important when using midi cables (as opposed to wires for 5-6cm from pcb to pcb, which is what I'm doing).
To confuse you even more, before I get the PSU I connected them using different PSUs for each device (C64 for mbsid, generic wall-wart for master keyboard controller) and it worked, which only makes it more obvious that there is noise/ground loop introduced when using a single PSU.
Any thoughts? Any help would be much appreciated! I'm pretty much at a loss, how do I troubleshoot such stuff? I can't trace or measure the MIDI signal (I think), because it is a 5mA current loop (which means the current is modulated/switched, not the voltage).
The PSU is a switching Meanwell RPT-60B (+12, -12, +5, GND), 60W.
BONUS: Pics of my build so far
