MIDI Ultimate Support Blog

26/02/2019
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.
 

Comments

Hi Chris,

The grey wire is the aux output and will give a voltage depending on what mode the aux switch is set to, i.e. velocity, pitch bend or modulation. The brown wire is the CV output so best to use that for your tests. Make sure the blue LED flashed on keydown and key release, if so then the MIDI comms is working. After that, it is the DAC and opamp to check. As it worked before, you are best looking at any construction faults such as failure to solder all of the pins on the chips (my most common mistake). Let us know how you get on.
Hi Gareth,

V1.1 is the version documented in the PE magazine. The difference between the PCB and the correct version is just some text and does not make a difference if following the described wiring colour code.
The MIDI sockets did cause me some confusion as I did initially solder the sockets to the wrong side, they should be soldered to the side with the two circle outlines indicating the sockets. So, fig 82 was the first effort that was corrected in fig 80. The consequence is as you suggested, swapping over pins 4 & 5.
Apoogies for the confuson.
Hi Paul

I'm wondering if you could help me troubleshoot an issue with the MIDI interface. I assembled this last month in when part five of of the build guide came out. At the time I tested it and it all worked fine, however since then and assembling the synth in the case the interface appears to have stopped working. I'm using a KeyStep midi controller on Channel 1 and have the channel on the synth set to Channel 1.

Currently when I power up the synth I get a steady drone from the oscillators and nothing changes when I press keys on the KeyStep. I've checked the voltages on the grey wire from J902 and I'm only seeing 0.035V and on the violet cable I'm seeing 0V even when the mod is set to max on the KeyStep.

I've checked the reference voltage on PIN 13 of U907 and I'm seeing 4.26V as expected.

I'm not sure how best to proceed with this, any advice would be greatly appreciated.

Kind regards
Chris
I'm just finishing off the construction in Part 5 of the PE series of articles and I think I've noticed a couple of discrepancies.

Firstly the caption for figure 82 mentions that the silk screen for J901 is incorrect and you provide a photo of the corrected version. However, the board I have shows it the same as the photo. My board is version 1.1 so can we assume that this error has been corrected in v1.1? I've checked the circuit and it does seem to be correct now.

Secondly, I soldered the sockets to the MIDI board (7210-790, no version number) on the side with text on as shown in figure 82. However, I then noticed that figure 80 is different - the sockets have been installed on the opposite side, i.e. the track side. I've studied the circuitry and the board and come to the conclusion that I've done it correctly, i.e. as in figure 82. If the sockets are soldered onto the track side of the board then pins 4 and 5 are reversed and the wiring would have to be changed. Can you confirm my conclusions?
We have just added a zipped file containing all of the MIDI Ultimate circuit schematics to the PCB product page (7215-074). These are easier to read as they are generally larger than even the magazine print versions.
Hi Richard,

They are quite readable in the paper version. It is out intention now the articles have been published is to also add selected info to our website. So, I have just uploaded the drawings to the product page for the case 7250-015, see the 'Downloads' tab.
Hi, I’ve purchased the July 2019 edition of Practical Electronics in Pocketmags. I’m making a mock-up case before I get my expert woodworker brother in law to make a case out of black walnut for me. The dimensions in the magazine are very blurred in Pocketmags. Is there any chance of obtaining higher quality files please? Otherwise I’ll have to track down a print copy and hope they’re better. Thank you.
Hi Richard,

No problem at all, happy to help. Good news that you have also resolved the white noise source as well.
The last part of the magazine article comes out within the next 10-14 days as it has just gone to print. That will explain the remaining calibrations including the oscillators.
Enjoy.
Paul
Hi Paul....so, how embarrassed do I feel now? I have quite a lot of experience with analog synths, although not necessarily modular. The bit that caught me out was the VCA Level. I thought that was simply the volume of the VCA output. What I now realise is that it's the volume of the VCA when it is unmodulated. If I turn it down so I hear silence when the sequencer is stopped, then start the sequencer, the ADSR envelope is applied to it because I have the ADSR Mod pot on the VCA turned up. Apologies for wasting your time, I understand it now. In fact I also resolved the noise issue by reflowing a few solder joints in that module and it is working fine now.

Thanks again, looking forward to getting this cased up and in use in my studio now!

Richard
Hi Richard,

I'm not sure that we actually have a fault here. The VCA looks to be working from what you describe. Not sure of what experience you have with analogue synths but there are two fundamental considerations, pitch and signal level. The MIDI interface outputs a voltage that directly relates to the pitch of the note and that seems to be working fine and a gate signal that is on whilst a note is being played. A MIDI interface to an analogue synth always outputs the voltage of the last note played which yours is doing.
Now comes the signal amplitude which uses the MIDI gate signal, there are two ways of doing this, one is to use the VCA and the other is the VCF. Both need a voltage envelope which comes from an ADSR. Switch ADSR1 to MIDI Gate and set the attack to 1, decay to 1, sustain to 7, release to 5, time to Short. Now, each time a key down command is received from the MIDI, it will trigger the ADSR to create a voltage envelope. Let's now route that voltage envelope to the VCA by switching the VCA to 'ADSR1 Mod'. On the VCA, set the initial level to 10, ADSR modulation to 10. Run your sequence and gradually turn down the VCA initial level pot until you start to hear the note played varying in volume. With the sequence stopped, if you can still hear a note playing, turn down the VCA initial level until it just goes silent. You can vary the ADSR mod pot to vary the peak amplitude of the note and the ADSR timing pots to get the profile best suited to the sequence.
You can do something similar with the VCF, set the VCA initial level to 10 but this time we are going to vary the amplitude of the note by using the filter cut-off. Switch the VCF to ADSR1 Mod, set the VCF ADSR Modulation pot to 100% and run your sequence again. Adjusting the VCF Freq cut-off and ADSR modulation pots will give amplitude modulation like the VCA but with a harmonic change as well. As with the VCA, if you can still hear the note at the end of the sequence, turn down the VCF Freq cut-off.
Let us know how you get on. Hopefully I have not made a mistake as I am describing it without a synth in front of me!
Paul
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