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Midi In Problem and solution
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Please be positive and constructive with your questions and comments.

Midi In Problem and solution

by Localboy on Thu Jun 07, 2007 5:47 pm

My box was near complete. (A Kiwi box based in London) But Midi In did not work. Midi Out did, and it would even respond to Midi coming in from the thru port...not recommended.

Signals were passing through the circuit onto the uC Midi in, but at too low a level. So R16 was increased from 100R to 125R, driving Q50 a little harder. IC24 or Q50 a bit far from typical I guess.

This did the job and it now works.

Maybe this will help somebody.

X0X 494 fully operational!

EDIT: In the latest bill of materials R16 has been changed to 150 Ohms.
Last edited by Localboy on Tue Sep 04, 2007 4:40 am, edited 1 time in total.
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by mixhard on Mon Jun 11, 2007 1:11 pm

mine doesnt respond to the midi in as well but in keyboard mode it responds to the midi thru. So i assume if i do the same, mine should work. My x0x is 493. weird. I had my IC 24 in backwards, so i have a replacement on its way. So im going to try a new IC24 and Q50 and see if that solves it without upping the restance on R16

And does your x0x respond to midi start stop messages after your fix?

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by Localboy on Tue Jun 12, 2007 4:03 am

Yes it does, it syncs up nicely to banned. Most likely your Ic24 has gone.
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by c0nsumer on Sun Jun 17, 2007 8:23 pm

Just FYI, #496 also had this problem. I replaced R16 with a 120Ω part (closest I had to what you did) and things are better. I've only tried controlling it from a P3, but it actually works now.

Now my second x0xb0x is done. :D

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by Cyanid on Thu Jul 12, 2007 4:56 am

I used a 120Ohm and now midi in works.
Still midi thru works as midi in anyway.

It's X0X #509
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Re: Midi In Problem and solution

by digitalwank on Thu Jul 12, 2007 1:38 pm

Huh, I just posted about having the exact same problem. I didn't even think to try the thru port, but I'll test that tonight. If it's the same thing I'll try your fix.

Anyone know why this sometimes happens?

Thanks,
Corey

Localboy wrote:My box was near complete. (A Kiwi box based in London) But Midi In did not work. Midi Out did, and it would even respond to Midi coming in from the thru port...not recommended.

Signals were passing through the circuit onto the uC Midi in, but at too low a level. So R16 was increased from 100R to 125R, driving Q50 a little harder. IC24 or Q50 a bit far from typical I guess.

This did the job and it now works.

Maybe this will help somebody.

X0X 494 fully operational!
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by jbdiver on Thu Jul 12, 2007 2:12 pm

I had the exact same problem with midi-in on #608. I replaced it with a 120R at first but then I had to add another 5R to bump it up to 125. It was barely triggering at 120.
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by rumba on Fri Jul 13, 2007 1:21 am

Same here. x0x # 576. Changed R16 to 120 ohm and MIDI IN works...

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by BONSAI_PINE on Fri Jul 13, 2007 11:41 am

Hmm, I'll have to try that out tonight as I'm having the same problems, although I havn't even checked the midi out, but it's box 6hundred something(i'm at work right now and cant think of the exact #) but maybe like said before there were some funny IC's or Q's...I know my square wave shaper is really low beta and isn't all that squareish too.

Note:just to make sure I opened it up here at work to see if I put IC24 in backwards, but all looks good there so hopefully the resistance will fix it up.
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by guest on Fri Jul 13, 2007 6:42 pm

i just did some tests on my x0x
and it seems you can increase that resistor
to about 4k before there are any noticeable effects
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by guest on Fri Jul 13, 2007 7:28 pm

disregard previous post
it seems 220ohms is the max id go with
but this is with tests on an old optoisolator
so i cant guarantee anything for a newer one
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by BONSAI_PINE on Sat Jul 14, 2007 12:05 am

Well, I've gotta give up for tonight or I'm gonna blow something out I think, but so far I've gon from 120ohm to 150ohm and now I've got an 220ohm and still nothing goin' with the midi IN. THe midi thru and midi out work fine, but midi in isn't doing anything. Any sugestions would be much appreciated!
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by guest on Sat Jul 14, 2007 4:59 am

check the line to your microcontroller
midithru is just a copy of midi in
so your optoisloator must be working
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by BONSAI_PINE on Sat Jul 14, 2007 12:20 pm

Oh Jesus! It's been set on midi channel 16this hole damn time!!! It all seems to work fine afterall! Should I bother to go back and swap the 220ohm resistor at R16 to a lower one or would it be fine to just leave it as is? Is the optoisolator basically a bunch of vactrols in chip form? I found an exTremely basic PDF manual somewhere on the site and thought that was all the instructions I was gonna get on how to use this thing...if only I'd have just looked to the side and clicked the other tabs below the "USE" tab on the main x0x page!
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Re: Midi In Problem and solution

by Localboy on Fri Jul 20, 2007 10:53 am

digitalwank wrote:Huh, I just posted about having the exact same problem. I didn't even think to try the thru port, but I'll test that tonight. If it's the same thing I'll try your fix.

Anyone know why this sometimes happens?

Thanks,
Corey

Localboy wrote:My box was near complete. (A Kiwi box based in London) But Midi In did not work. Midi Out did, and it would even respond to Midi coming in from the thru port...not recommended.

Signals were passing through the circuit onto the uC Midi in, but at too low a level. So R16 was increased from 100R to 125R, driving Q50 a little harder. IC24 or Q50 a bit far from typical I guess.

This did the job and it now works.

Maybe this will help somebody.

X0X 494 fully operational!


This is a guess... The current transfer ratio (CTR) of IC24 in recent batches is low. Because when saturated 4N37 should drop around 0.5V? and Q50 about 0.7V?, with only these two devices between 5V and 0V this means current is being limited by 4N37, as the Q50 base won't... because it is like a diode (needs current limiting externally). R16 will be bleeding away too much current from the Q50 base making it fail to switch.
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Please be positive and constructive with your questions and comments.