MIDI IN resistor change value?

[ris8_allo_zen0]

Hi all,

for some unknown reasons, my master keyboard only works (i.e. no timeouts, no hanging notes) when the receiver's optocoupler has a ca.700ohm pullup resistor instead of 1.2kohm. I did this on my home-made midi/gameport adapter and now I need to do the same on the core of my MBSID. The component I'm talking about is R6 in the Core schematic.

I don't know the electrical effects of this mod, so I'm asking you if I risk something or what else...

However, it still reads data from PC correctly.

Many thanks!!!

Enrico

[TK.]

Hi Enrico,

I don't see a risk here --- but which master keyboard are you using? It could be interesting to know for the case that somebody owns the same

Best Regards, Thorsten.

[ris8_allo_zen0]

The keyboard is a Roland PC-160A bought via eBay. The buyer said he had no problems using it...

I didn't notice anything because the adaptor was built using the PC-160A for testing; the only strange thing was, as I said, the different resistor value.

[TK.]

Yes, the required adaption of the resistor value is strange. My assumption is, that the MIDI output of the keyboard somehow doesn't comply with the MIDI spec (5mA current loop), so that depending on which kind of optocouplers (or circuitry around the optocoupler) is used, the MIDI signal can be received properly or not.

I would start with some current/voltage level measurements, but without a scope this is too difficult... however, as you found a solution, it's fine :)

Best Regards, Thorsten.

[ris8_allo_zen0]

I just changed R6 in the Core as I said, and it works perfectly! Now I can play freely from the PC (which I used as a bridge)...

But the problem is simply postponed until I want to use a device not built by me... maybe in the next weeks I'll ask your help trying to fix the keyboard (that's what I tried to do these days, without success).

Best regards,

Enrico