Wednesday 15 December 2021

Synthesizer Build part-46: 808 KICK for EURORACK. (Juanito Moore circuit).

The kickdrum from the famous Roland 808 drummachine. With four controls and a print small enough for Eurorack (although a bit deep). Naturally you can just as well build it in a Kosmo size if that's the size you're using to build your modular synth. 

Now that I've started to play the modular synth I built more and more, I felt the need for some percussive action so I started out with this famous kick drum sound using a schematic from Juanito Moore who is famous for building his modular system without using any circuitboards at all just 'dead bug' soldering and he's really good at it too. A real inspiration for DIY synth builders like me. 

The layout I made worked flawlessly right from the get go. This is quite a straight forward build. It requires 4 panel potmeters of different values and you must keep to these values too. You need a 5K, 10K, 100K and 500K panel potmeter. (470K instead of 500K and 4K7 instead of 5K will be fine too.)  
You can modify the T-filter by changing the 15nF caps. Smaller values will give you higher tones but it will disrupt the balance of the filter and cause the Decay function to stop working correctly. Also there's no CV control for this module because it's not practical to implement. Here's what Juanito himself had to say about that:
"The decay not working right with different cap values is due to the properties of a bridged-T filter that oscillates with a ping of voltage. I gave up on voltage-controlling an 808 kick because the decay, dictated by the laws of physics, changes with pitch. Also, if you use a fancy voltage-controlled resistor (LM13700 datasheet) when you change the CV, the kick will trigger. A Vactrol was the best I managed to get."
So you can get away with putting a Vactrol over the 'Pitch' potmeter but that's about it. I personally didn't bother with CV control.

Here are the verified layouts I made for this module. I marked two screwholes on the layout but I didn't use them. I just hot-glued the print straight to the back of the potmeters once I had the panel ready and this works just fine. I glued the topside of the print with the eurorack power connector pointing downwards (see pictures below). Beware that this does make the overall depth of this panel 7.5cm which won't fit some eurorack cases!
Wiring Diagram:

Print only. Pay extra attention to the connection of the transistor in the upper left. The emitter leg skips one copper strip and is soldered directly to the ground strip of the power rails. Strips B,C and D are all ground and I connected them together on the print by putting extra solder under the power connector so it bridged the middle three ground pins, shorting them together. Make sure to use polystyrene, polyester or silver mica type capacitors for all but the de-coupling caps (if you choose to include de-coupling caps. They're not on this layout). It's important not to use ceramic caps in the filter section because of various reasons. If you want to include de-coupling caps then solder some small ceramic 100nF caps over pins 4 and 5 and pins 10 and 11 of the TL074:

Here's an overview of the cuts and the wirebridges seen from the component side. As always; mark the cuts on the component side with a sharpy marker pen, then stick a pin through the marked holes and mark them again on the copper side and then cut the copper at the marked holes. Do this and the wirebridges first and check the cuts and wirebridges by measuring with your multimeter for continuïty. Then solder in the rest of the components.
Cuts and Wirebridges seen from the component side:

Here's the schematic I used to make the layouts, drawn by Juanito Moore in his distinctive cool style. There are two versions of this schematic in circulation and one of them has the clipper section wrongly connected but this is the correct schematic:

Here's a Falstad simulation of this circuit which allows you to test different component values and see what the result is on the output. I put an audio output at the end that allows you to play the result and listen to it. It comes really close to the real thing.

The 'Clipper' switch increases the amplitude of the drum sound extra (when the switch is open) and provides a little bit of distortion which makes the sound more audible. The low frequency of this kick drum can be so low that you can hardly hear it but through a good PA system you will feel it in your stomach because of the extreme low frequencies. It shakes the windows in my attic and makes the dust fall from the beams LOL. It really is an exact replica of the original 808 kick drum sound. I have the Behringer version, the RD-8 drummachine in my little studio and the kick sounds just the same.
I soldered the 33µF electrolytic cap for the Decay straight to the potmeter to save space. There was one opamp left over as you can see in the schematic. I used that opamp to drive a little LED connected to the output so we have a visual reference of the output without pulling any current from the output to drive the LED. It's always handy to have a visual indicator to see if the circuit is triggered correctly. Plus a LED always looks cool in a module.  The 1K current limiting resistor for that LED is soldered directly to one of the legs and reinforced with some heat-shrink tubing. 

Here's the Bill of Materials. Make sure not to use ceramic caps, except for the 100nF de-coupling caps for the chip if you want to include those, but they are not included in the layout or this BOM. 100nF de-coupling caps can be soldered directly on the copper side from the plus pin of the TL074 to ground and from the minus pin of the TL074 to ground. Make sure the legs have some heat-shrink tubing on them so they don't cause short circuits:

Here are some pictures from the build proces and the finished panel:



Like I mentioned before, the depth of the module as you see it here is 75mm (7.5cm) so it might not fit in some Eurorack cases. Keep that in mind. The width of the module is 6hp. (3 cm). You could save some depth by rearranging the potmeters to be directly underneath eachother and then hot-glueing the print straight to the back of the panel instead of on top of the potmeters. 

Instead of making my own demo I thought I'd embed Juanito's own video here. This video is over two hours long because he shows the complete build process but this link will start the video at the end where he demonstrates the functions. It should start at 2:23:36 If not, then just jump to that time manually.

If you can't see the video on your mobile device then CLICK HERE to view on YouTube directly.

Here's a link to Juanito's YouTube channel. Subscribe to his channel while you're there :)

Okay that's if for this one, with grateful thanks to Juanito Moore for his reactions and for just being awesome :). 
If you have any questions or remarks please put them in the comments below of post them on the Eddy Bergman Facebook group where we have an awesome little community willing to help you with any problems you may encounter.

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  1. Hi Eddy,
    Thanks for the tutorial. The module sounds awesome and was straight forward to build. :)

    1. Hi Jens, thank you very much! I'm glad it worked so well. Good work :)

  2. I've just finished a breadboard circuit of this and after spending a couple of hours fixing my two stupid wiring errors I got it working and it's brilliant! I found the 500K pot to be too large and most of the range results in self resonating (which is maybe useful?) and replacing with a 220K pot seems to provide almost perfect control through the decay range through to self resonating at the extreme. Thanks for sharing this circuit, although I'd stumbled on his video before I forgot about it!

    1. Hi James. Excellent that you got such good results. I feel you really should thank Juanito Moore because he's the one who designed it. I just made it and made a project of it but anyway I'm glad you got it working so well.

    2. Oh absolutely I will, I was just watching his video again (mesmerizing the way he does things) and considering my comment and word of thanks. But thanks to you for curating such a great selection of circuits. It's far too easy to be lost in a sea of amazing possibilities - you're a lighthouse in the fog! I sometimes feel overwhelmed at the choice of what to build next - what I *should* build or what I'd *like* to build. Then I find this website - - and I get blown away by the possibilities. That's when I know I have to try to limit my choices again :)

    3. Oh yes, I should also add a thank you for idea of adding an LED. I was looking at that spare OpAmp and thinking... I need to use that for something. Getting some visual feedback is always useful, so I'll be adding another nice orange LED on my panel :)

    4. Haha yes I always try to add a LED to a module if it hasn't got one. Like you say it's always good to have some visual feedback and leaving an opamp unused is just criminal in my opinion ^___^ And this LED actually has a useful function because you can see the length of the Decay with it.

    5. Also thanks for the kind words. I'm really happy so many people see my website as their main go to website for starting with DIY modular. I wanted to create a website that I wish that I had found when I first started out. So I thought I'd make my own since I already had this website plus the domain name and wasn't really using it much. It has grown into something so much bigger than I had anticipated. I don't think much more projects will be added in the future since I now started with Eurorack but you never know. At least it's already a great archive of projects and also a source for education. I'm not certain but I think my website is also used in classrooms sometimes because every now and then I see huge spikes in visitors. That is amazing especially because I myself am by no means an electronics expert. I just like helping others :) I'm glad you're finding it so useful too. :)

    6. I sourced some bi-colour LEDs because I wanted to give them a try (an LFO being the obvious place to use one) and so popped one into this circuit; pretty cool to see the +ve and -ve parts of the wave in light form, but a bit too muddled to be useful really. It does highlight the effect of the clipper switch though (without looking at the 'scope). I'll most likely stick with one of my standard orange LEDs and you're right it does give a good indication of the length of decay.

      Your website certainly is a great resource for those starting out; there is so much choice out there on the web and also no guarantee of success. Also when starting out you don't always know what circuits you'll need. I think you've most likely reached a natural end point to it now, but once someone has exhausted the projects you've covered they'll know what they'll be looking for when researching elsewhere. That's great to hear your site has been so successful. Thanks again!

    7. Ah that's interesting because I haven't actually checked the output signal of this module on my scope so I have no idea how far it goes into the negative and what exactly the exact effect of the clipper switch is. I might have a go at testing and post some screenshots in the article. I think you're better of sticking to a normal type LED like you suggested.

      Yes if people went through a lot of my projects I think they will have formed a clearer view of where they want to go with this hobby and take it from there. It's been a real journey of exploration for me. After finishing my DIY synth I bought a load of Behringer synthesizers thinking that would be useful and more fun to play around with but I ended up with a little studio full of synths and I hardly touch those synths except for seeing if I can replicate a sound I heard in a song (mainly on the Odyssey with Kraftwerk songs). So I came to the conclusion I want to be able to perform live in the future without being a good songwriter or musician. So that brought me to Eurorack and now I'm in the direction that I feel I really want to go. It's bloody expensive though but luckily these modules keep their value pretty well. Anyway, enough of that. ^___^
      Thanks for all your feedback James! :)

  3. hi eddy, do yoi think it will work with +/- 15V ?

  4. Übersetzen
    hi eddy,
    I have a general question,
    how do you make your interruptions,
    I use a drill with a very small size,
    earlier I cut it, with the drill it is also not as clean as on your pictures

    1. I use a new (sharp) 7mm dril bit that I hold in my hand. I just rotate it and it scrapes away the copper. It works very well. I put some tape on the other end to have better grip.

  5. This is fantastic! Didn't have TL074 used LM324N no probs. Solid audition and now this guy is employed in the lowdowntown partyrack ;)
    Thank you Eddy and Juanito
    All the best!

    1. Excellent! I'm glad you're enjoying this module so much.

  6. Hi Eddy, thanks for putting this up - your site is such a great resource! I'm brand new to this and decided to build this as my first module. Unfortunately, after wiring it all up, I'm afraid it's only making a tiny click, almost inaudible when I trigger and the LED does not light either. Any troubleshooting tips? I've gone through it quite a few times but can't see any obvious issues. Any suggestions would be much appreciated, thank you!

    1. Hi Roland, I'm glad you like the website. As for troubleshooting tips, I can only suggest to use an oscilloscope to see where the circuit goes wrong. The first rule of troubleshooting is 'thow shalt measure voltages'. Are you sure the power supply is feeding it the right voltage? What are you using to trigger the circuit? A nice low frequency squarewave would be good for testing. Otherwise, if you can't find it, just take a fresh piece of stripboard and build it up again. I'm afraid troubleshooting is going to be a big part of the hobby ^____^. You will make mistakes, as I have many times, but you'll learn a lot in the proces. I hope you find the solution, it's a cool little module. Good luck!

    2. Hey, thanks for the quick reply! Made some progress this morning, now it appears to all be working except for the decay and the led - oddly the led works when I first power up but then stops working after a few triggers. When I meter the decay knob I'm seeing a steady +11.22v on it, and the trigger doesn't change anything. I'm not sure what should be there, let me know if you have any ideas otherwise I'll keep hunting.

    3. Hmm that suggest a problem with one of the capacitors. Check the 33µF cap and the 33nF. Als check if he diodes are place the correct way around. Are all ground connections good? The Decay not working could be because the cap can't discharge to ground.

  7. Alright, that did it! I had the diodes in the correct way but it looks like one of them got fried somehow and wasn't working. Swapped it out and the decay is working now! really appreciate the help - I can't believe how huge this thing sounds. Cheers!

    1. OMG! That is awesome! Well done you! Yes it's a good sounding module isn't it. Hope it'll serve you well. Cheers!


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