KOSMO 1222 Tuner VCO Build Series

Here is the KOSMO 1222 Tuner VCO Build Series

Part 1: The Performance VCO Parts & Starting the Build

Part 2: Building the Performance VCO

Part 3: Tuning the Performance VCO

I started assembling the PCB, and when I got to the precision 10K resistors, I noticed something strange at point A in the picture below.

I first thought the trace had been cut because it was routed too close to the side of the board, but it looks like there is another trace on the other side of the board that completes the connection. The stub should probably be removed in another revision of the PCB to avoid unnecessary worries.
When I started inspecting the PCB more closely I noticed a few more weird things. For example the long trace to nowhere that ends in point B, and the ground plane stub at point C. At audio frequencies these stubs don’t matter much, but it is good design practice to avoid them.
Sam will find that a lot of PCB designers are artists in their heart and while Sam’s silkscreens are pretty and amusing, the functional part of the PCB may attract criticism. E.g. too many unnecessary vias, trace stubs, traces that change width half way through, sub-optimal ground planes, as seen in the following picture.

These are not just for esthetics, they affect the quality of the signals (no so much at audio frequencies, but still).

1 Like

The current limiting resistors for the LEDs and the 7-segment display are listed as 2K which is not the most common value.
If you don’t have resistors of that value, it is completely safe to replace them by more common 2K2 resistors, the display and LEDs will just be slightly dimmer.


The “JACKS SOLDERED ON THIS SIDE” note on the daughter PCB is a bit confusing. Based on the front panel and PCB silkscreen (see picture below) the jacks actually have to be mounted on that side (as the box around the FM input jack also indicates) and thus soldered on the other side.

yes regarding the jack daughterboard. it could be mis interpreted to put the solder on this side! luckily the jacks dont fit the other way round without quite a squeeze!!

also the small trace to nowhere, yes I noticed that. It didn’t make a difference, I removed it for later batches, but yes indeed it is there! But like you say, no effect in this instance. :).

also yeah good sight on the ground plane to that connector, I could make a better connection. thanks for that. I did not question it as the proof was in the pudding and it functions more than adequately. but yes good eye on the ground plain.

1 Like

yeah that is a good shout also.

the ground plane comment is a good shout, like I said above the proof was in the pudding and its functioning nicely however yes I will improve that for the next ones! regarding VIA’s and that wire, yes I sorted out that scragglier, imagine the amount of cross talk on stripboard! I hadn’t been overly fussed and gone for more style as its luckily very tolerant of things with modular synths, it adds to the fun, and yes ill be constantly improving on these things so thank you for the pointer.


Speaking of ground planes, why didn’t you connect all the holes in the front panel together with a plane?
It would have made it more like a metal front panel and grounded all the jacks together.

FYI, the jack sockets that I got fit equally well on either side.

thanks Antoine, I includede the picture you put up and a note mentioning you on the site about this as yes its a fair point thanks. interesting the ones I use need a bit of a squeeze to get them in but fair enough! noted. thanks for this. learning lots on how to improve these modules as I get more done In my modular. thanks again Antoine.


Cool. I’m glad you’re taking my comments positively - as they are meant. I love what you do and I am only trying to help where I can. We have experience in different areas and I am also learning as I watch your videos and build your modules.

1 Like

yes Antoine all great! its a great learning experience. thanks. im glad your delving into it! its a big subject field! what do you do? sam.

1 Like

I’m wondering if anyone can enlighten me to what i’m doing stupidly. I build 2 of the stand alone tuners now. One rack mount, one not. The display i’m using isn’t the same one as the stripboard, but does have the exact same pinout. They work, but the display is all jumbled. Any ideas? Where would I start to troubleshoot this?

This is the display I have… 5161AS

Specified display - SC56-11EWA

My guess would be that you wired the display incorrectly, the pinout of looking at the display from the front is like this:

1 Like

So right now, I’m enjoying life in early retirement.
For me that means going back to electronics as a hobby, which it was before it became my career, trying to keep up with your various channels, building some of your modules and designing my own.
I am also slowly learning Spanish with Duolingo, studying music theory on Udemy (not the greatest course but OK for the reduced price I got it for), and snowboarding when I can find someone to go with.
I occasionally post updates on Instagram https://www.instagram.com/antoine.pasde2/
I also have a web site: pasde2.com. I haven’t updated it in years but intend to get back into it.
I did a little FM based synthesizer project that I presented at the Bay Area Maker Faire in 2014. If you are curious, this is a good starting point http://pasde2.com/pasde2_original/RTFM/rtfm.html#RTFM you can scroll up from there for the rest of the project.


Grats on the retirement man!

I think I deserved it. :grin:

1 Like

That’s where my mind gets boggled. That is exactly the sane pinout as the display i’m using. Made 2…both are messed up.

Then it could be that the Arduino is not driving the pins you think it’s driving with the polarity you want.
Are you familiar enough with Arduino to write a test program that would light up only one segment at a time?

Haha! Not even close. I may be able to stumble my way through editing some existing code.