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.
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.
I just finished building the ultimate. Everything seems to work properly but I would like to have confirmation on a point.
On the output line out, there is a superimposed DC voltage of 2.5V dc so at the output of the echo module, so present on the cursor of R504.
While the output of the VCA can exactly adjust to 0.1mV.
on the output of the echo module there is no chemical capacitor to cut off the DC voltage.
I've been seeing on the MFOS Rockit diagrams, there's a non-polarized chemical capacitor that cuts off any DC voltage present at the output, but not on this ultimate.
While all the amp have an input capacity to cut any DC voltage, but there is still a problem, it causes some spitting of the VR504 potentiometer on the output line out.
And it's audible on the amp connected output.
The potentiometer works perfectly.
I think it's due to the fact that there is a superimposed continuous voltage that because of the variation of the cursor when moved causes it. The presence of a DC voltage on a potentiometer is indeed strongly discouraged.
What do you think?
excuse my bad English.
yannick dutauzia06/10/2019, 16:44
Sorry it has taken so long to reply. C5 is a tantalum capacitor and does not tolerate any reverse voltages. Check C5 was soldered in the right way around and also check D1 is the right way around. When you say it is dead, is the negative rail giving -12V? When a tantalum capacitor fails, it tends to fail short circuit so may well have caused D1 to fail. Check your voltages around the circuit, check for 12Vac at J1, around 15Vdc or more at the inputs to the volage regulators. Let us know your findings.
Help! Just finished building the PSU. Plugged in the 12vAC wall wart (that also came from yourselves) and C5 popped - all is dead now. Any clues?
Martin Wallace03/09/2019, 20:46
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.