How to build a Breadboard voltage controlled filter
This breadboard voltage-controlled filter project uses the CEM3320 Curtis Electromusic IC, you can also use an equivalent. I have in fact used the AS3320. I’ve tried to make it as similar as I can to the Sequential Circuits Pro 1 synthesizer filter because this was one of the first synthesizers I owned and I think it sounds fantastic.
Information
The Sequential Circuits Pro 1 was used for lots of the sounds on the Yazoo – Upstairs at Eric’s album.
Vince Clarke says it is his favourite synthesiser of all time.
What is a voltage-controlled filter?
A voltage-controlled filter is at the heart of an analogue synthesizer. Once the voltage controlled oscillators have generated the waveforms they head into the filter to get, well, filtered. This is something I’m not even going to attempt to describe in words. Instead, just go to the video and listen instead.
It’s worth noting that the filter on the Sequential Circuits Pro 1 synthesizer is fantastic. I know this because I was lucky enough to own a Pro 1 for several years. I’m not the only one who thinks this by the way. I’ve read many an interview with musicians who eulogise about this particular mono synths filter.
So I make no apology for trying to recreate the sound by using a similar IC.
If you want to try to build a full Pro 1 type synthesizer on a breadboard, check out my article “Breadboard synthesizer” here, which gives you full illustrated instructions on how I went about it.
The picture above shows the complete circuit diagram for the voltage controlled filter.
Components required for the breadboard voltage-controlled filter
If you haven’t got a breadboard or need some more I’ve just bought a pack of these Breadboards from Amazon.
Constructing the breadboard voltage controlled filter project
If you are a beginner you might want to check out my article, Breadboard Tips. This will help and guide the beginner to become successful in building breadboard projects. You might even learn something that helps even if you are an experienced constructor.
Also just double check your breadboard is similar to what I’ve shown in the diagrams. Some have red and blue columns opposite to those shown here. Why? I don’t know, you would have thought they would all be the same. They aren’t so if yours is backwards then you’ll have to alter the wiring accordingly or alter your breadboard.
I have altered my breadboards so that they are all the same and the same as the Fritzing diagrams. If you want detailed instructions on how I did it you’re in luck because I have them here.
I usually start by inserting the smallest components first as it’s harder to plug them in when the large ones are in the way.
Start by making and inserting the wire links. These are short and can be made with tinned copper wire. I preform all the links and components first. It significantly speeds up the construction process.
List of instructions
1. Link 1e to 1f.
2. Link 7a to blue.
3. Link 9j to red.
4. Link 21j to red.
5. Link Link 11h to 22h.
6. Link 24j to blue.
Fit the resistors
7. 3K resistor 12b to blue.
8. 100K resistor 22b to blue.
9. 100K resistor 6c to 10c.
10. 100K resistor 5d to 11d.
11. 100K resistor 6g to 8g.
12. 100K resistor 13i to 5i.
13. 68K resistor 23b to blue.
14. 150K resistor 23h to 27h.
15. 2K resistor 23j to 22j.
16. 1K5 resistor 10g to 14g.
17. 220K resistor 13d to 17d.
18. 240K resistor 1j to 6j.
19. 240K resistor 1g to 5g.
20. 240K resistor 1a to 6a.
21. 240K resistor 21b to 22c.
22. 51K resistor 12c to 21c.
23. 91K resistor 5h to 8h.
24. 91K resistor 6b to 11b.
25. 91K resistor 2d to 2f.
26. 20K resistor 21d to 25d.
27. 150K resistor 4c to 5c.
28. 200K resistor 23g to 29g.
29. 100nF capacitor 24a to blue.
30. 100nF capacitor 19i to 21i.
31. 100nf capacitor 9h to blue.
32. Link 19j to blue.
33. 150pF capacitor 8a to blue.
34. 150pF capacitor 9a to blue.
35. 150pF capacitor 12j to blue.
36. 150pF capacitor 7j to blue.
37. 2u2F capacitor 13j to 15j (positive to j13 negative to 15j).
38. 100K linear potentiometer 16a 17a 18a.
39. 100K linear potentiometer 27j 28j 29j.
40. Link 2h to 6h yellow wire.
41. Link 2c to 10a green wire.
42. Link 1i to 14i black wire.
43. Link 14f to 24c black wire.
44. Link 15g to 23c purple wire.
45. Link 26i to blue wire.
46. Link 28i to red wire.
47. Link 16b to red wire.
48. Link 18b to blue wire.
49. Link 24b to 29f black wire.
50. Wire the two blue strips together and wire the two red strips together.
Final checks
Make sure none of the wires or component leads are touching
Before plugging in the ICs you can power up the breadboard with a dual 12V supply. Plug +12V into the red strip, 0V to the blue strip and -12V to 1d.
Now check with your multimeter that you have +12V at 9f (the AS3320 pin 14) and +12V at 21f (the TL082 pin 8) and -12V at 24e (the TL082 pin 4).
If these are correct you can turn off the power to the breadboard and plug in the ICs.
Take extra care you plug these in the correct place and the correct way around. If you put them in the wrong place and power up the breadboard there is a very good chance you will damage them.
39. AS3320 pin 1 to 5e.
40. TL082 pin 1 to 21e.
The input to the filter is at 4e and the output is at 25a.
Final thoughts on the breadboard voltage controlled filter
So you’ve built this breadboard voltage-controlled filter project and you want to know what you can do with it.
Only joking, if you’ve built it you probably have a very good idea but if you don’t you can integrate it into other stuff you probably have. It makes an excellent addition to a Eurorack or you could just go to my Breadboard synthesizer project and build the complete breadboard synthesizer.
Oh, I nearly forgot to say I’ve built this breadboard voltage controlled filter and then taken it apart and rebuilt it using only the constructional list and diagrams in this article to try to find any omissions and errors. I remember the frustration of spending many hours building a project only to find it wouldn’t work.
If you have any problems getting this project to work check out my article Common Breadboard Mistakes to make sure you’ve not done anything that I’ve listed there.
Also check out my post, Breadboards – the complete guide, for everything you need to know about breadboards.
“Hi, I’m Graham Moore and I’ve been building electronic projects since I was 12. I had a fascination for old radios and taking them to pieces but when my Nan bought me an electric soldering iron, I realised with a few components I could build stuff.
Learning to solder opened up many doors for me as electronics also became a career. I hope you get as much from it as i did”.
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