#1007 midimuso midi-cv

ChristianBloch · 2020-09-05T05:58:07.038Z

Mine did what sounds like the exact same thing. Bad optocoupler.

twinturbo · 2020-09-05T06:10:23.413Z

It’s been a couple of weeks since i looked at mine, but I swear it did some sort of POST?

Yet to calibrate and test… so no midi as yet.

Farabide · 2020-09-05T14:20:50.405Z

Does anyone like me earth the circuits before putting the ic into the socket? You do get the odd bad one but they are far more likely to die when handled.

ChristianBloch · 2020-09-05T17:10:21.113Z

I use an anti static mat and I also have a wrist strap that I must admit I stopped using. An optocoupler doesn’t seem like it would be the most sensitive to static, but maybe I’m wrong?

Farabide · 2020-09-05T20:02:27.339Z

I too use a mat and strap but earthing and even draining caps was something I was shown when I did a job for ferranti many years ago along with leg prep and working with an open window… but then ic’s were a lot more expensive then.
Can’t hurt can it?

fluxpavilion · 2020-09-14T15:47:21.942Z

guys apologies if this has already been asked in the thread, quick question

how do we wire up the midi ports to the molex?

pins to pins etc

heckseven · 2020-09-14T17:02:32.454Z

I still haven’t got mine working, but Sam goes over it here:

ChristianBloch · 2020-09-14T17:15:29.755Z

You can see it in this picture:

image1000×750 212 KB

lookmumnocomputer · 2020-09-14T17:26:26.601Z

yes! you could even just solder the wires and skip the molex if you havent got them! but yeah in the image. if the midi sockets are pointing the right way. blue is to the top of the midi socket, and pink is to the bottom, hope the images help. Very dusty this module of mine! I grabbed the prototype from off the shelf

WhatsApp Image 2020-09-14 at 18.25.491200×1600 155 KB

WhatsApp Image 2020-09-14 at 18.25.541600×1200 184 KB

lookmumnocomputer · 2020-09-14T17:28:59.706Z

was I right in thinking you got it working then the problem came back?

heckseven · 2020-09-14T17:32:52.309Z

No. I haven’t given up. I’m starting by swapping out a couple ICs, which means waiting on the post. I looked pretty thoroughly at the connections. I don’t see any shorts. I rewet many of the solder points just to try something. I even tried swapping the midi connections even though they’re connected as shown. I did some connectivity tests and some voltage tests. About the only other thing I haven’t tried is the oscilloscope (because I have a pretty cheap DIY version that’s mediocre for this type of work), which I’ll break out in the next evening or two. I think I’m going to have to be patient with this one.

fluxpavilion · 2020-09-14T18:57:23.742Z

ace i feel like a lucky little boy and mine worked on first boot

few snags, channels 5 and 6 dont work but the rest do

and when im calibrating im jsut getting a reading of 11.6v no matter how far i turn the trimmer

Jos · 2020-09-14T19:13:56.568Z

Has anyone connected their midimuso to an oscilloscope and made a ramp with midi messages and checked whether the voltages produced form a neatly rising ramp?

I build a midimuso CV12 two years ago (this was an original kit, so it is not Sam’s version) and I saw that some of the outputs showed a neat ramp, some were quite wavery and some even jumped up and down between values. So not all outputs showed a linearly rising output value. I gathered this had something to do with the pwm and the type / value of the capacitor I used and how that is loaded by the following circuitry.

What type and value of capacitors do you use?

ps. I modified my midimuso version because I wanted -5V … +5V outputs next to the standard 0V … 10V outputs, so I made this switchable. If anyone is interested I can explain the details.

ChristianBloch · 2020-09-14T19:37:21.796Z

Jos:

If anyone is interested I can explain the details.

Definitely!………………………

ChristianBloch · 2020-09-14T19:39:24.209Z

fluxpavilion:

im jsut getting a reading of 11.6v no matter how far i turn the trimmer

Are you sure the voltage from your power supply isn’t low?

sebastian · 2020-09-14T19:52:42.267Z

Mine is still strange… When I want to use it, I need to reheat the solder joints of the quartz and the capacitors next to it. It then works for about 3 hours (no difference if it is on or off, I think) and then stops working again

Jos · 2020-09-14T19:54:32.140Z

What I did is connect an opamp to each output which was configured as a subtractor. On one input the original 0 … 10 V is connected, on the other either 5 V from a LT1021 (voltage reference) or GND via a switch. That gives a -5 V to +5V range and a 0 … 10 V range respectively. I piggy backed a circuit board on top of the original PCB. This subtracting op-amp needs a negative power supply b.t.w. but that is no rarity in a euro rack, so that is added easily.

P91206782592×1944 1.02 MB

I mailed the makers of the midimuso cv12 that it would be relatively simple to change the buffering op-amps that are in the original schematic to this configuration so that with the same amount of components, one voltage reference (could be the 7805 that is already in the design) and one added switch they could make their product more usable. This was the response (18 Sept 2019):

Jos, this is the best email I've ever received from a customer!

And, yes, the ORAC reference is from the beloved Blake's 7.

There are plans for a bipolar CV-12 and an easier way to customise it.

Those plans still need to be implemented as far as I know.

fredrik · 2020-09-14T20:03:35.471Z

Heat issues? Instead of soldering, have you tried warming up the oscillator/caps with, say, a hair dryer?

(could be a crystal/cap mismatch and warming things up is enough to get things in range)

fluxpavilion · 2020-09-14T20:22:50.951Z

was talking about calibration, the point where im looking for a 10.6v im getting 11.6v whatever i do with the trimmer

ChristianBloch · 2020-09-14T20:32:45.753Z

Right, got it. Reflow the trimmer perhaps?