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 know where we are if you need any further help.
Much microscopic review and found a poor joint. Thanks so much for your help - onwards and upwards!
Do you have the 'initial level' pot set fully clockwise when checking for an output of the VCA?
Assuming you do, I have never had a customer have a faulty LM13700 so I would look elsewhere first. The VCA will only give an output if the CV to Expo converter is also functioning correctly. Make sure you have a CV at the output of U502.1 pin 1, it increases by 18mV for every 1V increase in CV.
Just commenced testing at stage 3. No headphone output. Good square wave at c504 and attenuated at r517/518. Nothing at pin8 of u501.1 (echo in). Suggests faulty lm13700? Reviewed all surrounding joints and they look fine - could it be something else?
Ian Shepherd03/08/2019, 15:00
U502 getting hot means it is now most likely failed. The most common cause for a low current op-amp getting hot is that it has been inserted the wrong way around either now or at some time in the past. Make sure the IC socket has been soldered in the right way first. If that is all correct, then you are looking for a solder joint problem, check Q501 is the correct way around as well. Let us know what you find.
Hi - I hope you can point me in the right direction. The VCA module dissent work. Non of the pots have a effect and the U502 gets pretty hot. Do you have a idea where to look after a error I have double check and wound no errors on the board. The rest of the board seams to work as it should. Hope you chan help.
Mikkel Ørsted08/07/2019, 14:56
Pleased to hear that you have sorted the problem. Yes, I have seen the videofrom Torsten and it is indeed very good. I have shared it through the Soundtronics Facebook page. Looking forward to seeing more from Torsten and hopefully other builders as well.
I did eventually figure out my mistake in the way I built the MIDI socket board and adjusted the wiring accordingly. That's all working fine now:-).
By the way if you haven't already seen it you should definitely check out Torsten Spiller on YouTube - his demo of the MIDI Ultimate Synth is very good - https://www.youtube.com/watch?v=Tlg9BXiYan0
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.
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.