mki x es.EDU VCO

[patternmusic]

So I built out the the VCO kit.

I started by following the manual building out the breadboard. That was working to some degree, but I was having some trouble with connection jacks and power. I built up a BOM from the manual and checked each part against the PCB drawings. So I jumped to building out the PCB. I mostly followed the video by Synth DIY Guy on YouTube https://youtu.be/MMif8sz_6Cc and double checked with manual.

But my assembled board doesn't make any sound or output any signal. I've double checked for any bad or missing solder joints. I've been double checking the parts against the PCB, and I don't see anything. No wrong polarity. I assume I can't tests resistors or capacitors in situ on an unpowered board. But I can look up the colors.

When I test continuity from the +12V pin on the power supply (pin 9 or 10) to the pad TP11 marked +12V in the array of pads on the PCB I get no connect. +12V pin on power supply to the diode lead next to it connects. That seems odd.

A continuity test from the -12V power supply pin (1 or 2) to the TP18 pad reports a 0.18V diode. Is this to be expected?

p.s. I ordered the VCA kit this morning. So I've got to get this one working first!

[charlieDN]

Hey all! Total, total noob here hoping to learn with this kit.

I've had this kit for a while. I've mostly been building, taking it apart and rebuilding on a breadboard whilst following along to the manual and videos as they use slightly different approaches, but bit by bit I'm getting a better understanding of how everything works and what everything is doing in the context of a VCO. But I think I might have screwed up along the way as I'm now not getting the results I'm used to. I was wondering if someone might have the knowhow to help me make sense of where things might be going wrong. I don't have an oscilloscope yet.

I'm at the stage where the OP AMP is integrated to reduce the volume of the signal for playback. In my previous run-throughs I've gotten that unpleasant high pitched signal that we get before adjusting the frequency. However now I am only hearing a slow clicking sound, almost like an LFO. When I go a bit further and include the potentiometer in the circuit adjusting the pot gives me 3 results; no sound, a slow clicking sound and an even slower clicking sound. I have turned the pot very slowly to try and catch the correct frequencies but no joy.

In terms of trouble shooting I've tested all the components (except the IC chips, which I don't know how to test, leading me to think this could be the issue), the breadboard appears to be working fine, I've double and triple checked the orientation and positioning of the components and I THINK my dual power supply using 2 9v batteries is set up correctly. The batteries have been tested on a multimeter and are fully charged.

This is how I'm using the batteries: (I have the + from one connected to the breadboard rail marked + that is powering the 40106 and TL047, the - from the other connected to the rail marked + on the opposite side acting as the negative rail for the TL047 and the remaining + and - acting as the ground by connecting them to the 2 rails marked - and connecting them via a jumper cable stretching across the breadboard. Hope that made sense.)

So where do I go from here? Erica Synths and Thonk have included this lovely message on their respective pages which scares me from contacting them: "All kits in these series are simple and come with extensive user manuals, therefore we will not provide customer support in case your DIY build fails to function or similar..." I can't blame them if people like me exist.

Is there a way to test the IC chips? If not, I'm tempted to buy more just to completely rule out this being the issue. Could I have short circuited them somehow? Accidentally attaching the dual power supply incorrectly and not realising, touching them with static build-up?

I truly, truly hope these don't seem like ridiculous questions, but the videos and manuals are only getting me so far in terms of my understanding, searching for answers on electronics blogs and forums is difficult for me and my limited terminology and only seem to bring up more questions.

Hope everyone is doing well

Cheers

[Elahrairah]

A slow click is sensible if the whole thing is set to too low a frequency. Maybe +/-9 is not enough for a circuit designed to run +/-12. Can you add a volt or two to the CV input and raise the octave?

[patternmusic]

I'm at the stage where the OP AMP is integrated to reduce the volume of the signal for playback. In my previous run-throughs I've gotten that unpleasant high pitched signal that we get before adjusting the frequency. However now I am only hearing a slow clicking sound, almost like an LFO. When I go a bit further and include the potentiometer in the circuit adjusting the pot gives me 3 results; no sound, a slow clicking sound and an even slower clicking sound. I have turned the pot very slowly to try and catch the correct frequencies but no joy.

My breadboard version got to a similar place in my build. So I decided to move to the PCB build. But I've obviously run into problems on that track.

It sounds like your battery power rail setup is correct. I was using a +/- 12V Eurorack power supply with my breadboard similarly and got similar results -- no sound, clicks and slow clicks.

Tomorrow I will try some other troubleshooting. Any pointers to general DIY module troubleshooting tips are welcome.

[charlieDN]

A slow click is sensible if the whole thing is set to too low a frequency. Maybe +/-9 is not enough for a circuit designed to run +/-12. Can you add a volt or two to the CV input and raise the octave?

Thanks for your reply! Is that as simple as, say, introducing 1v from the CV out of an SQ-1 to the positive rail? How would I achieve -9v on the negative rail in that respect, or would it even matter?

My breadboard version got to a similar place in my build. So I decided to move to the PCB build. But I've obviously run into problems on that track.

It sounds like your battery power rail setup is correct. I was using a +/- 12V Eurorack power supply with my breadboard similarly and got similar results -- no sound, clicks and slow clicks.

Tomorrow I will try some other troubleshooting. Any pointers to general DIY module troubleshooting tips are welcome.

And then this could suggest that power isn't the issue. If I am running +/-9V and we're getting a similar result would we be able to rue out power being the issue? Of course I haven't tried with +/- 12V myself yet so will see if I can get that set up and see if the issue continues. But any tips on how to do that would be appreciated. How are you connecting your +/-12V Eurorack power supply to the breadboard if you don't mind me asking?

I'll continue trouble shooting myself. I've ordered some spare 40106 and TL074 chips so will let you know the results when I swap them out. If I'm wrong, at least I can make 2-3 more VCOs.

[Elahrairah]

Oh I’m sorry I didn’t mean to mess with the power rails, the sq-1 cc should go to the normal input location for note. The theory is the clicking noise is just a sub audio saw wave and you need to listen to a few octaves higher by adding 2V at the cv input.
When the power rails are different, say 9 instead of 12, then many resistor values could be wrong in comparison. The only harm should be tuning and volume. I wouldn’t try adjusting a bunch of resistors though since as soon as you’ve got it in tune, the batteries will have fallen to 8.9 …

[charlieDN]

Oh I’m sorry I didn’t mean to mess with the power rails, the sq-1 cc should go to the normal input location for note. The theory is the clicking noise is just a sub audio saw wave and you need to listen to a few octaves higher by adding 2V at the cv input.

Ah, no I'm sorry, you did say that originally. Okay, I'll give that a go!

When the power rails are different, say 9 instead of 12, then many resistor values could be wrong in comparison. The only harm should be tuning and volume. I wouldn’t try adjusting a bunch of resistors though since as soon as you’ve got it in tune, the batteries will have fallen to 8.9 …

I see, I think that makes sense. Thank you, you've given me a springboard to delve further and see if I can resolve the issue! Will report back with progress

Cheers,
Charlie

[patternmusic]

How are you connecting your +/-12V Eurorack power supply to the breadboard if you don't mind me asking?

The power supply I have is a Tiptop uZeus. I just plugged the module's ribbon cable in to the uZeus flying busboard which gives me a 10 pin header. The Eurorack 10 pin header is just -12V on the two pins at the red wire end (pin 1), +12 at the other end, and GND (0V) on the 6 others. Then just 3 jumper wires to the breadboard busses.
https://www.davidhaillant.com/how-to-li ... connector/

[charlieDN]

Oh I’m sorry I didn’t mean to mess with the power rails, the sq-1 cc should go to the normal input location for note. The theory is the clicking noise is just a sub audio saw wave and you need to listen to a few octaves higher by adding 2V at the cv input.

When the power rails are different, say 9 instead of 12, then many resistor values could be wrong in comparison. The only harm should be tuning and volume. I wouldn’t try adjusting a bunch of resistors though since as soon as you’ve got it in tune, the batteries will have fallen to 8.9 …

This has worked a treat, thank you! You were right on the resistor values too. Specifically the 100k resistor connecting the potentiometer to the NPN which needed to be much lower than recommended in the manual. I can't remember which one I used now but around 20k gave me a good range. Thank you Elahrairah.

The only other issue that became apparent was the noise being generated at this stage in the build. I located the source of the noise to be the jumper connecting the audio out jack to the ground rail. When I put my finger on the connection the noise would go away. I fixed the issue by moving the jumper connected from the jack to ground further up the rail towards the battery, the other side of the ground connections from the 40106, NPN and CV in jack as laid out in the manual. This didn't make the noise go away entirely but it was much less audible. Does anyone have any idea why this might have worked and produced less noise? This is one of those things I've tried to determine myself but can't find much info online.

[fosimoor]

The only other issue that became apparent was the noise being generated at this stage in the build. I located the source of the noise to be the jumper connecting the audio out jack to the ground rail. When I put my finger on the connection the noise would go away. I fixed the issue by moving the jumper connected from the jack to ground further up the rail towards the battery, the other side of the ground connections from the 40106, NPN and CV in jack as laid out in the manual. This didn't make the noise go away entirely but it was much less audible. Does anyone have any idea why this might have worked and produced less noise? This is one of those things I've tried to determine myself but can't find much info online.

Hard to say without hearing the noise levels, but generally, breadboards can be really noisy. Some are better, some are worse. I wouldn’t give it too much thought, the noise will most likely disappear once you switch to the PCB.

[fosimoor]

Also, all the bb layouts should work with +/-9V - I’ve specifically tested this when writing the manual. If they don‘t, I’d strongly suggest reading the chapter again and checking for any mistakes you could‘ve made. I will upload an updated version of the manual that extends the initial osc core setup section soon. Hopefully this will clear things up a bit!

[charlieDN]

Hard to say without hearing the noise levels, but generally, breadboards can be really noisy. Some are better, some are worse. I wouldn’t give it too much thought, the noise will most likely disappear once you switch to the PCB.

Good to know, thanks!

Also, all the bb layouts should work with +/-9V - I’ve specifically tested this when writing the manual. If they don‘t, I’d strongly suggest reading the chapter again and checking for any mistakes you could‘ve made. I will upload an updated version of the manual that extends the initial osc core setup section soon. Hopefully this will clear things up a bit!

Fair enough! I'll be sure to go back a few steps to make sure everything's in it's right place and I'm definitely understanding the core concepts. I'm a slow learner! Thanks for replying and for the kit. Really looking forward to getting the VCA

[charlieDN]

Also, all the bb layouts should work with +/-9V - I’ve specifically tested this when writing the manual. If they don‘t, I’d strongly suggest reading the chapter again and checking for any mistakes you could‘ve made. I will upload an updated version of the manual that extends the initial osc core setup section soon. Hopefully this will clear things up a bit!

Quick update. I swapped out the breadboard itself and have had a lot more luck when following along to the manual. The signal is clean and clear with a +/-9V power supply. I must have bought a really cheap one the first time around.

[patternmusic]

Well in trying to troubleshoot my VCO build I managed to lose the 40106 chip. It was on my desk and then it wasn't. (I think it maybe went to an alternate universe.)

So I ordered a couple on eBay... meanwhile the project is on hold.

[TheAnswerIsYes]

I'm currently building the VCO on a breadboard - accompanied by Molten Music Technology you tube. As a total beginner, I've gotta say Robin's doing it and asking all the questions I'm asking is tremendously helpful. Just ordered the VCA! Enjoying the journey - and finding (hopefully) a way on ... Thanks Erica Synths, Moritz Klein and Thonk! Really great project.

[patternmusic]

I got a replacement for the 40106 chip I lost. In the meantime, while waiting for the replacement, I tested all the solder points. There were a few cold joints, and I resoldered them. So I popped in the new chip and fired it up. Happily, everything is now working fine.
Tuning took a little trial and error, but I got it tracking. (I kind of cheated. I used an oscilloscope with a frequency counter.)
Voila! DIY VCO build accomplished.
Now I await the VCA.

[BenCutlan]

Hey,

I recently built this as a first time project. I really enjoyed it and didn't find it too difficult. I powered it up... no smoke! Plugged the Saw output in to my mixer and amazingly, to my surprise, it worked perfectly! No tuning issues et. and sounded how it should. However, I then plugged into the Pulse output and was far less surprised... nothing but a very quiet, high pitched squeak. Does any kind person on here have any idea where I can start to troubleshoot, and what it is most likely to be? I don't want to just go adding more solder to all the joints in hope that that will fix the problem, you know?!

Thanks a lo tin advance!

Ben

[BenCutlan]

Hey,

I recently built this as a first time project. I really enjoyed it and didn't find it too difficult. I powered it up... no smoke! Plugged the Saw output in to my mixer and amazingly, to my surprise, it worked perfectly! No tuning issues et. and sounded how it should. However, I then plugged into the Pulse output and was far less surprised... nothing but a very quiet, high pitched squeak. Does any kind person on here have any idea where I can start to troubleshoot, and what it is most likely to be? I don't want to just go adding more solder to all the joints in hope that that will fix the problem, you know?!

Thanks a lo tin advance!

Ben

Ignore this... has suddenly just started working! Horraar!!

[Whatthevolt]

Hello everyone.

Sorry if this is a really silly question. Very new to this.

I’m on page 21 of the guide.

When I add a 4k resistor between the middle leg of the transistor and ground, I simply lose all sound.

I’ve tried other value resistors and have the same result.

While the 4k resistor is attached to the transistor, but not yet to ground, the sound is altered as I touch them and their leg.

I’ve completed all the steps at this point (added the jack etc) and there is still no sound.And put a sequence into it from an SQ1. Removing the 4k resistor reinstates the noise.

Does anyone have any ideas? Fully prepared to hear that I’m doing something silly.

[patternmusic]

I don't remember what happened for me at that point. First I would just experiment with different values which your finger clearly is. But the manual is just trying to demonstrate a principle at this point. The design moves on from there. I would move to the next step, and see if you can pick it up from there. And if you feel the need, go back and try to recreate what was being demonstrated on page 21. Most of the manual is just an experimentation laboratory.

[fosimoor]

When I add a 4k resistor between the middle leg of the transistor and ground, I simply lose all sound.

Can you post a picture of your breadboard? That would make troubleshooting much easier.
When you say you "lose all sound", you mean that you've tried fiddling with the potentiometer, but can't get any audible oscillation at the output, right? So you don't get any clicking noises?

[thecrimpmaster]

Hi

Very first time builder here, and a bit lost. Apologies for the basic questions. I'm trying to put together the very first step on a breadboard but I can't hear any sound at all. Are there any tips on how to trouble shoot a circuit, where/what/how should I test with a multimeter?

Also I think it's possible i blew one of the ICs (TL074). I thought I heard a pop, and it got really hot. Is there a way of testing if it's still good?

Any help or pointers would be appreciated

[msegarra]

Does a standard Eurorack power supply work with these modules?

[KSS]

Welcome to ModWiggler, thecrimpmaster!

Very first time builder here, and a bit lost. Apologies for the basic questions. I'm trying to put together the very first step on a breadboard but I can't hear any sound at all. Are there any tips on how to trouble shoot a circuit, where/what/how should I test with a multimeter?

First make sure the power pins are correct and the voltages are also correct. Some whiteboards are crap. Try moving the circuit to a different part of the breadboard.

Also I think it's possible i blew one of the ICs (TL074). I thought I heard a pop, and it got really hot. Is there a way of testing if it's still good?

Look online for the pinout of the '074. What you'll find are power pins in the middle of each row, with the remaining 12 pins grouped so each 3 pin 'corner' group has an op amp with positive input, negative input and output pin.

The simplest circuit to test is a buffer. That means you connect the minus and output pins together. Then you put some voltage or signal on the positive input pin. What you put in should be what you see-hear at the output. 1V in, 1V out. 5V in 5V out. Saw in, saw out. Audio signal in, audio signal out. Since there is no external IC pin for GND in this setup you get the GND-0V for your meter and inputs, outputs from your dual power supply.

Do this for each group of three pins and you'll know if the part is still working!

Be sure you have the power supply -pins 4 and 11- connected according to the pinput-drawing you saw on the net or in the 074 datasheet.

Dual and single op amps can be tested the same way. Identify the power pins. Identify the three -primary- pins of the op amp or op amps in the package.

Dual op amps will have two power pins and two groups of three pins.
Single op amps will have the three pins and power pins, but not in the same locations.

The 'extra' pins -beyond the 3+2- are used in various ways depending on the actual type of op amp. They are not needed for a basic functional test.

[patternmusic]

> Does a standard Eurorack power supply work with these modules?

Yes. They only require the 10 pin connector. So +12V, -12V and GND/0V.

The case/power supply kit does not build out the +5V option.