I’ve built a couple of the Kosmo Modules already and they all work great but I’m running into issues wit the VCO. I’ve bought two but have assembled only one so far and it doesn’t work as in: no sound comes from the outputs and the display and LEDs are unresposive.
When I use the Code from SAM the LEDs and Display just stay blank when connected to my power source. When I use the updated Code from Jos Bouten the LEDs just light up constantly and so does the whole display. So at least I know those components are working and I guess the Arduino isn’t the problem as well.
I’ve reflowed every single component as that was a problem with an earlier build I had. I also turned the Potentiometers all they way in every direction (as that was the problem with my LFO build) but to no avail.
I’ve used a multimeter at the test point where it says “4V” but I only get some very small mv number there.
As I’m a beginner when it comes to electronics and haven’t had to troubleshoot anything serious yet I’m a bit stumped and could use some guidance as to what might be wrong / which components I should test and how.
If you don’t have ~4V at the test point, you can start with this comment a few posts above, replacing “3.3V” by “a few mV”
Until you get that 4V fixed, at best your oscillator will be stuck at the lowest octave setting. You can try feeding some control voltage on the 1V/oct input, to determine if the rest of the oscillator is alive.
You should get at least some very low oscillations (possibly even sub audio).
Until the oscillator works properly in the audio range, there is no point in trying to debug the tuner circuit.
Thank you for your help mate!
I now got my ~4V at the test point but I still can’t get any audio to play. I tried the trimpot “ctrl” (RV6) and also the octave and fine tune knobs but nothing changed at all. If it’s too low of a sound I think I might just not hear anything as I currently only have a very shitty speaker connected to it. What should I test next to see where the problem might lie?
Thanks again for the next steps, but I’m a bit stumped now as to what the hell is going on. Here is what I’ve done:
I’ve changed the Resistor on R42 from a 220R to a 4,7k as recommended in the other thread.
I’ve tested the resistor values from the trimpots to pin 15 and found out that it’s all measuring around 50-60k instead of 100k but I don’t understand why. If I measure the 100k resistors on R23 & R24 I get 55k / 58k
The 100k resistors on R25 & R19 measure the correct 100k
But they’re all from the same batch. Does this mean those two are just faulty? Or does it measure something else with it as they are already on the board (heard something like that a while back but not sure about it)
So now I’m wondering if I should swap out those 2 resistors or the ICs to proceed. Sorry for being kind of high maintenance but I’m really eager to get this thing running. I’ve built 6 other modules (LFO, Mixer, MIDI to CV, Splashback Delay, Filter, Envelope Generator) and they all work fine, but I was really looking forward to finally generate some actual sound with my box -_-
EDIT: Forgot to add: I’ve hooked it up to my audio interface and could confirm that there is zero sound coming out of the module unfortunately
Yes, it’s problematic measuring resistors in a circuit. R23 is in parallel with R24 plus the lower parts of pots RV6 and RV7, and vice versa, so you’d expect to measure something less than 100k for either of them. They’re almost certainly fine. They’re certainly within the right ballpark so would not cause the problems you’re seeing. Move on to checking the voltages as described.
The voltages are for the centre almost nothing (a couple of mv), -1V for the “trk” one and almost nothing for the “HF”.
If I turn the centre note trimmer I get no change in voltage, I’ve also just resoldered it again just the be sure but no dice. So I assume the trimpot might be busted and I need to swap it?
Yes red probe on the points, black is on ground (I use the jack connector part of it as it’s easy to hold it in place there - jacks are disconnected at the moment)
I get 12V on the “left” or “down” point of the center note trimmer (seen from the back, so the one where there is no screw to change the trimmer)
And I just realized that the one in the middle is changing, so I’ve been measuring the wrong one? I assumed “on the trimmer/knob side of the 100k.” means on the pin where the screw is
EDIT: Sorry forgot the values. I had ~0.8V, turned the trimmer a good amount and got it to ~3V next
As I have a second PCB and enough components I’m thinking about just building a second one for now. Can I just build the Oscillator parts and keep the tuner parts (especially the Arduino) out? If so, what components would I need to solder on to get just the Oscillator going?
My thinking is - if I can get the second one going I can check each values / components to troubleshoot the first one
hey ben!!! sorry your having such troubles! to answer your question I have highlighted the bits you can miss out to just get the oscillator going . you can even skip the octave switch if you want (highlighted in green) to see if it will actually work. (all tuner things are in grey you can skip them all)
also another thing!!! and this is a problem that has been mentioned before if you have accidentally plugged the power input into the link and left it plugged in for a little while it will break the opamps. I did indeed test it, if you plug the power into the link input for about 10 seconds and realise your mistake they still work (I checked after finding people had problems) but if you leave it in and sit about for a bit they will eventually die.
so maybe have a think about if you plugged into the right socket!
the man himself!
Yeah I’ve been very, very careful to not plug it in the Link port so that is not it. Thank you for the markings on the schematics though that is very helpful! I’ll start building the second one in the next couple of days and that will hopefully work!
I’m pretty sure I either made a very stupid mistake which I will realize some time and be ashamed about it - or some component is faulty. We’ll see.
I’ll post here when the second VCO is done
If you got spare OpAmps, you could try popping them in to see. I remember when i built a few things i made some simple mistakes and before i knew it those opamps got blazing hot and silently failed. Careful, dont touch them, these things can be hot enough to burn you if you blunder like i did.
Hello everyone! So yesterday i MIGHT have plugged power into the link socket of one of my VCO. I say might because i was checking power consumption and was only focused on my ampère meter… Anyway when i replugged everything in my case, this VCO was behaving strange:
The arduino is starting up (blinks behind), and the screen is showing the q »starting sequence » i added in the code.but then nothing is showed on the screen.
i have output signal from triangle and square outputs but not from saW. The signal i have from triangle and square might be weak i havent checked…
I reflowed some connections but didnt change anyacomponents. I did not find any burnt component (or it seems) but this morning reading u guys i thought i might have plugged power into Link… I am at work so i cant test to replace the opamps right now but i wonder if it could be the solution, what do you think ?
