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.
Good to hear you are enjoying the build.
Not come across any similar reports from other builders thus we have to start on the basis that you have an assembly issue.
C513 forms part of the right side of the headphones amplifier but I am surprised you heard increased noise and radio signals. Even though C513 is connected to the input of the right amplifier, the amplifier only has a gain of 20 so not the same as touching the input of a high gain preamp or your PC speakers.
It may be that you have a missed solder joint in that area, i.e. R522. What about the left headphone, does that act the same? Even better is to try the line out and see if that has the noise on it. Also, in case you missed it, make sure that the collector lead of Q1 is snipped off because that part of the circuit is high gain and the collector lead can act as an antenna.
If you still have problems, try and narrow down the source of the noise by turning down the mixer pots for example. Let us know how you get on.
Enjoying the build so far but have hit a problem at 'Part 3' .
Started to test the VCA, Echo & Headphone amp, but noticed a lot of stray audio noise (i.e. not from the Noise generator) coming through the headphones. Despite the audio noise all the tests were OK and (other than the audio noise) everything worked as expected. However, I then accidentally touched the case of electrolytic capacitor C513 - not only did the noise through the headphones increase, but I was picking up a radio station as well!.
I reflowed the joints for C513 just in case and now have no audio at all through the headphones. Do you think C513 has now failed? If so, will it have taken out anything else?
Sorry for potentially stupid questions, but many years since I built anything at all and never something as complex.
Anthony Barker27/02/2021, 15:11
The MIDI LED will flash with any message on any of the 16 channels. The CV DAC will only update with a MIDI note on message received on the same channel as the 16 position rotary switch. So first thing to check is that the MIDI keyboard is on the same channel as the rotary switch. It is also worthwhile checking the auxiliary channel output to see if that is responding to a velocity / modulation or bend command. From your post, I assume it was working so unless inadvertent damage has occurred to the CPU or DAC, then the channel number is the thing to check.
Hi, recently finished the build and in the process of calibration, but I have hit an issue with the MIDI controller. After calibrating vco1 I hooked up the scope to the phones output, because it seemed somewhat noisy. When I went back to set up vco2, the midi keyboard seemed unresponsive. I did the usual stuff, on & off, powering up in a different order etc. But no success. The purple led flashes in response to key presses but the midi output voltage seems stuck at .25 volts. Any suggestions as to how to troubleshoot from here?
Stephen 07/08/2020, 18:47
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?
Gino Scarpino24/05/2020, 04:48
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.
Gino Scarpino19/05/2020, 20:19
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?
Gino Scarpino16/05/2020, 23:08
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.