CEM3340 Oscillator Help

A little foreword before the main topic. I have been looking to get into modular for a while now and I’ve been taking steps to start building my own. I am a music production student in the US and am hoping to work on eventually putting together my own DIY rack as a thesis project over the next 2 years or so. I am looking to do it in eurorack specs just so they can be used with modules I may buy as well, but I’m taking Kosmo designs and modifying them. I am very new to DIY electronics, however, and am in need of some help broadly speaking.

Around 6 months ago, I was working with somebody local who had experience with these sorts of projects and they were helping me redesign the schematics and making the PCB. We got up to the part where I needed to start ordering parts and due to a number of circumstances, it had to get put off and eventually, we lost contact, leaving me feeling somewhat dead in the water.

I have the Gerber file, the BoM, and all the other parts as far as I am aware that I would need. I was going to order the PCBs through JLC and then grab the remaining parts through ebay and other similar sites. My main concern at the moment is messing something up in the ordering process and ending up with defective PCBs or getting the wrong parts. If anyone would be interested in looking over what I have before I place the orders so I’m sure I’ve got everything I need to make it work.

I should note, I’m not expecting these to be perfect by any means, but I also want to make sure I’m giving it the best shot I can and I figured this would be the best place to ask. Thank you all in advance.

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I recommend Tayda for the parts shopping. It’s hard to tell on eBay which vendors are good and which aren’t, and buying one component from one and the next from another and so on adds up in postage and complexity. Tayda will have most if not all of what you need and if you don’t mind waiting a week to two, the shipping costs will be very low. If Tayda doesn’t have everything there’s Digi-Key. Huge selection, more expensive than Tayda but fast and reliable. Or Mouser, but their shipping rates are higher. The CEM3340 will have to come from somewhere else, maybe there’s a good eBay vendor for that, or there’s SynthCube or Thonk. That’ll be a big chunk of your expense right there. The AS3340 is cheaper, but it’s your call.


The person helping me suggested a lot of parts from Thonk so I was definitely planning to look there. I’m unsure if there’s anything about that AS3340 that would require me to change my PCBs or not. My main question is regarding the PCBs if there’s anything specific I would have to do while placing the order to make sure they function for this specific project or as long as the schematics and PCB layouts are sound, it won’t really matter.

I would breadboard (or stripboard) the circuit first just to make sure it works before you start losing your head about it. If you go stripboard, be sure to buy the IC chip sockets so you dont have to have it permanent! Feel free to share pics of that if you have any issues with getting it up and running. Do you have a modular power supply yet? i would start there first, so you can test modules and actually have something working!

Here is a thread for the Frequency Central Microbus Power supply. I include Sam’s vid on the case, and a link to the builder’s livestream on his patreon. It also has the build doc and a BOM which includes links to tayda so you can easily get the parts you need!

The AS3340 should be a pin for pin drop-in replacement. Its been said that there are some quirky stuff to keep in mind with resistor values and the square output, but its all i use, and yeah they work fine.

See this thread for a discussion about the weird stuff.

I got mine from Electric Druid.

As far as common components, i made a post in the Cheap Components Thread a while back that might prove useful:

You definitely want to buy op amps. They are used a bunch in many different types of projects.


I will definitely take this into account. I appreciate all your advice. The one thing I want to mention is that as far as I understand, the PCB that is designed will function as the person who helped me modify it has built many themselves. In the future I will very likely be using strip board as I will be working on my own.

The other thing I want to mention is since I lack the ability to build my own case, and I am still very new to DIY electronics, I decided it would be safer to buy a powered case. Likely going to get a 4MS case, as I can get them small, but I have been looking at a few others.

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If you plan to go eurorack, i think getting a powered case should be the way to go.

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Most of what I’m concerned about is making sure this order is doable. I don’t want to order the PCB and have it be borked. Not sure anyone would be able to let me know just from these screenshots if it would work, but this is really where I’m at.

Don’t really get why’s you go for this odd mix of smd and tht, especially considering its a very simple module and there’s plenty of space of tht components. If you’re scared about messing up the order, I’d consider leaving off the smd assembly

To be bluntly honest, it has been so long since I worked with the guy I mentioned at the beginning of this post that I don’t really remember why I was doing half the stuff I was doing. I was more or less following his directions with the assumption that we would go more in depth later on but that obviously didn’t happen. Pardon the stupid question but would you mind explaining what “THT” is? I’m trying my best to figure a lot of this out but I don’t have a lot of in person resources which has made this process difficult.

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THT = Through Hole technology,
as opposed to
SMT = Surface Mount Technology


Based on what I’ve read here, I’ll give you some advice at the risk of sounding ‘gatekeepy’. Please know I have no such I’ll intend.

Take a step back. It sounds to me like you’ve gotten in over your head with the help of someone, and now are a bit lost on your own. Rushing ahead can be a great way of ensuring you have an incomplete knowledge of things, which won’t do you any favours in the future. Just as an example, if one needs to ask the meaning of tht and smd, they should probably not be ordering custom pcbs. Again, not trying to sound like a tool here.

If you haven’t already, draw out the schematic of this or another simple module. Then build it on a breadboard and check if everything works as you’d expect. Then for a more permanent solution, make a stripboard or protoboard layout. If you’ve done this a few times and are comfortable with the circuit and layout design process, thén start making your own pcbs.

It’s an involved hobby with quite the learning curve, there’s no shame in taking it one step at a time. In fact, thatll probably bring you more in the long run. There’s heaps of resources and friendly people around, both on this forum and outside of it, so anything can be learned.



I appreciate the advice and I won’t pretend for a second that I’m not in over my head. It’s a little difficult to explain my situation regarding my motivations but I will be returning to university in two or so months and it being an engineering school, I will hopefully have many people who will be able to help me.

I guess at this point, it’s frustrating because I did go through the process of making the schematic and everything and it does to some extent feel like a waste to just scrap it. That being said, I also recognize that it’s a fool’s errand to jump head first into something like this with so little experience.


Nah m8, you still have the experience, and it might work you know?

This stuff can be fun to learn, and fun to take in steps.

It’s also fun to dive in!

Dont feel silly or stupid asking anything, this place is full of learning folks. Arguably most if not all of us are professional amateurs.

According to your first post you got 2 years for this project right? So dont sweat it and take it slow and take it in.

Find out what you want to learn (makin PCBs or makin basic circuits or making analog synth circuits) then, take bite sized pieces.

Im sure we can all learn together n have fun doing so.


No need to scrap anything, but breaking things up into more manageable tasks, with natural checkpoints before you move on to the next task, makes it much more likely that you end up with a good final “product”. For your first DIY build, I’d suggest:

  1. Using your schematics, build the circuit on a breadboard and make sure things work as expected. Tweak things until if does.
  2. Revise your schematics, as necessary. Design a PCB, using through-hole footprints, and order the minimal set of boards from JLCPCB or other cheap “prototype” fab.
    • If you feel confident in your soldering skills, you can use (reasonably sized) surface-mount footprints instead, but through-hole is a bit more forgiving (at least as long as someone else drills the holes for you; if you etch your own PCBs the equation is different).
  3. Populate one board, and test it. There may be mistakes. Find them and figure how to fix them.
  4. (Stretch) Fix any issues in the PCB layout (and/or the schematics), order another set of PCBs, and build a “production quality” board. Or three.
  5. (Stretch) Design another PCB, with surface-mount footprints. Consider having the fab add some components so you don’t have to.

Once you get more confident, you can skip some of the steps when you move on to other synthesizer modules…


So I built quite a few CEM 3340 circuits and I had a similar problem once. I’m not sure, but I think that my power supply wasn’t consistent or I accidentally put the wrong voltages in and probably fried my chip (more than once by the way).
Once you feel comfortable with your voltage stability overall and at each pin, do you have another chip to try?

I’m going to be ideally getting enough to make 5, so I have room for error.