MIDI Ultimate Support Blog

by Admin Admin

Please use this blog to post support questions for the MIDI Ultimate or just to say hi and how you are getting on with your build.


Hello again! The power supply is a success. Put the new cap in correctly and it fired right up as expected. I plugged in J3 and no smoke! Also, I had good meter readings on the main PCB so, I inserted all the chips for the VCOs, VCF and Mixer. I think I'm getting all the readings on my scope I'm supposed to. They're not exactly stable or clean looking square and sign waves, but the frequency changes with the pot and so does the PW. Cool. Onto April.

(Full disclosure, I had to wait a while for my transformer to arrive so, I went ahead and populated the rest of the main PCB with the passive components before going back to begin testing. I did not install any of the ICs, but all the switches, pots, LEDs and the rest.)

Having built the back panel already, I plugged it in via J902 along with my headphones and that's kind of where my success ends. I adjust all pots as directed (March2019/EPE) but get very very faint sound. All the controls seem to be doing what they should, but very, very quietly. There's a bunch of "hiss" (not buzz), but it doesn't go up or down with changes to the master volume. Side note, if I touch a couple of the parts right under the master volume pot, I get a couple local radio stations really loud and clear. So, something is working with the amp, but again, the radio doesn't change in volume with the pot.

From there, I began writing this note and thought, "maybe because I installed all the other parts, I have to install all the other ICs to make anything else work." So, I did that as well. I've built it all and connected it on the bench as in fig. 82 - June2019/EPE. I still get only super faint sound from the unit.

With continued thanks, any ideas?

Hi Gino, good to hear you have found the problem, easy mistake to make. We have all done it at least once, at least it didn't explode which they can do!
Hello! Upon further inspection, you are correct, I had put it in backwards. Replacements ordered. I'll post back with my results.

Hi Gino,

The spec of your power supply sound just fine. Don't worry about the current rating, the MIDI Ultimate will only draw what it needs so having a little extra capacity will not be the cause of your problem.
Electrolytic capacitors burning usually indicates a reverse polarity so check that the capacitor has been soldered in the right way around. Also check your diodes for being the correct way around. I assume you didn't have the synth connected to the power supply at the time you were testing the power supply. Assuming not, then you are simply looking at the power supply board for any potential damage. Check those component polarities first and then come back to us with your findings.

Just plugged in my power supply and fried C6. I think I'm a stupid American that used the wrong wall wort. So my questions are...

1. Transformer specs: INPUT: 120VAC 60hz 15VA OUTPUT: 12VAC 1A MAX - Is that wrong? Is the 1A MAX draw too much? What's a transformer you'd recommend for the USA?
2. C6 on the PSU PCB smoked and has a nice little burn mark on the top. Do you think anything else got fried?

Thank you,
Hi Richard,

Great to hear you are enjoying the MIDI Ultimate.
Modifying the LFO circuit for a sync input is not so easy because it has a tri-core with no actual reset circuit (no FET across the integrator capacitor).

It can be done and this link may give you some ideas on how to do it http://electro-music.com/forum/topic-49081-25.html
Sorry I can't be of more help than that at this time. If you do manage to do it, happy to share your solution here for other builders.

Loving my MIDI Ultimate. One thing I keep finding myself needing is a way to sync the LFO to an incoming midi or gate signal...is there any way to make a mod to do that?


Hi Mic,

The MIDI ultimate is based on the MFOS Soundlab Ultimate which also does not have a triangle waveform output. Both have pulse and saw waveforms.

It will require modifications to work on +/-15V, easier to use some voltage regulators and regulate down from 15V to 12V.

It is already available as a kit, ready built is not a commercial option because it has been designed for the hobbysit to assemble using through hole components. We have had lots of interest in an assembled version but we are more likely to design a new synth from scratch rather than re-work the MIDI Ultimate.

To digitise the output to plug into a USB port is too complex, simply plug the line output into the soundcard line input. One less level of conversion.

Hope that helps.

hi paul recieved order next day many thanks
why no tri out from vco like in mfos design will it work on +15V/-15V what about a kit/ fully built to allow synth output into usb to pug into pc to play thu soundcard
regaurds mic
Hi Yannick,

The scratching noise when the volume pot was adjusted was brought to our attention a couple of weeks ago by a customer. The level of scratching noise seems to vary from board to board but we agree we need a blocking capacitor there. We will be publishing a small optional hack on how to fit the capacitor for existing users that are experiencing this problem.

Thank you for also bring this to our attention.
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