JSx

Hi LyleHaze, I want to thank you for your hints, even if I think a bit different than you (both is absolutely OK, I think). This is relevent technical information. Thanks. It's not complete, because it just mentioned the drawbacks of Schotty-diodes, but it helps me. I don't agree with your conclusion, because you only mention the drawbacks, not the advantages. If there wouldn't be any advantage, I would totally agree with you. 50 V Limit is no problem for MIDI, I think. MIDI is 5 volts. Maybe for this reason I overlooked that part in wikipedia. If you put more than 50 volts through the optocouplers LED will be damaged anyway, won't it? The leakage seems to be much smaller than the current through the Optocoupler-LED, so it doesn't affect operation in normal cases. (OK, no new discussion about going beyond specification, please!) If I would have found out this kind of problems 20 years ago, I would have talked to the MMA about it. After 20 years I doubt, that they would change anything. But indeed a good suggestion to contact the MMA. I don't want you (all) to adopt my ideas, just give a hint that those who want for the reasons I mentioned or for their own reasons be able to choose which way they want to go. to stryd_one: Sorry, I won't discuss any further with you. This is simply stupid. I know my attitude is OK, but yours seems rather strange to me. I know some people have problems to recognize correctly what read, for cultural or educational reasons. Of course this is even true for me, but probably to a different degree than in your case.

Unfortunately you missed the point. MIDI devices are part of a larger system and this whole system of MIDI devices is made to be able to change them. This might happen more or less often. In my case very often. I want EVERY device to be able to communicate at least with ANY of my MIDI Interfaces. In your citation I asked for electrotechnical advice, not for your general personal opinion. And even this missed the point, because it was not MY implementation that was bad. Sometimes you have to live with equipment with bad implementations. It is not always possible to throw any device with bad technical design in the trashcan. I know that I often work in unusual environments. So I might have more experience in situations where the specifications MUST be violated (very long MIDI cables, more than 10m long) or where I need to use specific devices/interfaces. (In 1988 we didn't have MIDI repeaters or they would have been much too expensive to connect more than 10 studios in the presentation.) I NEVER told anyone that the diode MUST be changed, just gave an idea and reasons why it might make sense in certain situations. AND IT DOESN'T HURT in normal situations if you use the schotty-type, so you can just have a more reliable MIDI In in critical cases with the Schottky-Diode. After some reading and with my experiments in mind it seems that with a standard pn-diode the signal edges at the optocoupler are not as steep as without a diode at all (I checked this too) or with the Schotty-diode. After some reading about the function of schottky-diodes and pn-diodes the leakage of schottky-diodes seems to have a lot less impact on the signal than the discharging of the pn-area for this kind of application. For those who read until here: I'm not completely sure, because I couldn't find the rest of my diodes I used, but I'm rather sure that I used 1N 6263 schottky-diodes in the successful tests with my MIDI interfaces. BTW, my masterkeyboard uses standard TTL-signals for MIDI out, not open collector as in the reference implementation and this causes trouble with MIDI cables longer than a few meters and if you make heavy use of continuous controllers. I'm rather sure this was done to save a chip and I'm almost sure this wouldn't be the only device where this engineers/marketing decided to hurt the standard to save a few cents. Since this gets more and more off-topic and I didn't got any useful replies yet, I will stop now. You got the information. Use it or don't use it, it's up to you.

Hi folks, If you look at the schematics of a MIDI Interface, you see that the diode is in parallel with the phototransistor of the receiving optocoupler. More than 10 years ago I tried to build a MIDI adappter for a soundblaster with spare components in my little lab (Using a 1N... optocoupler, because it was a bit difficult at that time to get the PC900 from my preferred distributor). At that time I also thought that the optocoupler was problematic, but it was not the culprit. After changing the 1N4148-diode to a schottky-type, it worked very well. I know that my AKAI MX73 Masterkeyboard has a badly designed MIDI out circuit, but sometimes you don't want to change the electronics inside an industry-manufactured MIDI device. (Probably not to loose guarantee if it is a new one or not to damage it by accident.) But even with a PC900 (on my Mac interface) I got better results (with problematic devices or very long MIDI cables) with the schottky-diode than with the 1N4148. It seemed to me that the signal was degraded by the 1N4148, because when I desolderd the diode, all problems went away. (The diode is present only for security purposes and not needed if the cabling is correct if I read the schematic correctly.) BTW, the old serial mac interface is basically a RS422 to 5mA current loop conversion interface which also feeds one pin on the RS422 with a 1 MHz clock signal (independent of the voltage-current signal conversion). Why not make a schematic better if it doesn't hurt? BTW, I used a different type of Schottky-diode in my original tests than the one I mentioned in my last post, but I need to get home in a few days to check which type it was. (But I'm almost sure, that the type of Schottky-diode is not so much important.) I don't wanted to provoke a discussion if you like the idea or not or somebody thinks that there might be no need for changing a standard schematic, but would be happy to get feedback if somebody with more knowledge than me thinks it would be a bad idea (probably because the schottky diode may be killed (?) if the MIDI input lines are reversed by accident or something similar) to replace the 1N4148 with a schottky-diode. I'm not familiar with the drawbacks when using schottky-diodes instead of normal ones. Build your interface as you like. I just thought some of you might want to order the schottkys and the 1N4148 and then check them out instead of reorder them afterwards. BTW, I still know a event on the last day of International Computer Music Conference 1988 at Cologne where we needed MIDI-cables more than 15m long to network several studios who wanted to jam with their software through MIDI and we had problems with some devices, but not all of them. JSx

Hi, in my own old serial MIDI interfaces for my Macs I could solve receiving problems with some devices or rather long MIDI cables (more than 5 m) by using a Schottky-diode rather than the normal 1N4148 at the input of the optocoupler. One problematic device is my AKAI MX73 master keyboard. OK with short good cables, but not with longer or low quality cables. For me it seems this is a principal design flaw in the MIDI specification. I can't remember the ones I tested on my heavily used MIDI interface (it's a bit delicate to open it up), but I'm sure it was a BAT-type. The last ones I solered in have been BAT47 (I also have ordered BAT46 which I might have used in my first interface), but I have not checked them with long cables or problematic devices. Since I'm mostly a software guy, some more electronic oriented people may want to comment my suggestion. Maybe you want to order them instead of the 1N4148 or together to try it out. It's just a few cents from Reichelt. I hope this helps, JSx