Designing a TR-808 style snare drum from scratch

no draw machine is really complete without a Punchy Snappy snare together with the kick it creates the rhythmic backbone for most grooves so in my ongoing quest for creating a Roland inspired modular drum machine I knew I had to come up with a snare circuit that would complement the kick and high hat I've already designed after a lot of fine-tuning here's what I landed [Music] on [Music] [Music] as always when designing a drum voice I'll start by mapping out the functional blocks we need for a classic analog snare there are two main components to the sound the drum that is a pitched oscillation and the snare wires that is the noisy rattling we'll tackle the drum first for that we'll rely on the same percussive sine wave oscillator I used in my kick drum circuit to give it a Punchy attack will then modulate its pitch with a simple envelope for the snare wire sound we'll start off with a standard White Noise generator next we'll use a VCA coupled with another envelope generator to shape the noise into a percussive burst because this is very bottom heavy we'll want to fill out a lot of the low end so that the noise doesn't muddy up the drum sound later for that we'll add a rather aggressive highpass filter to the signal chain finally we just need to mix the two signals together sounds like a pretty decent snare drum to me so let's try and implement this in an actual circuit we'll start with the percussive oscillator as I said before we'll simply repurpose the oscillator I used in my kick drum for this you can check that video for an in-depth explanation but here's the basic gist by plugging a bridged T Network consisting of two capacitors and two resistors into the feedback path of an op amp we create a highly resonant filter if we then excite or ping this filter with a quick voltage pulse it will oscillate for a little bit before eventually settling down that's why I called this a percussive oscillator it creates a pitched percussive hit all by itself without the need for a VCA and an envelope generator great now to set the oscillation frequency we'll have to pick specific values for the resistors and capacitors for a snare something in the 100 to 200 Hertz range should work fine using a 910k bridge resistor two 33 Nanz capacitors and a 470 ohms resistor to ground combined with a 1K potentiometer should allow us to roughly cover the that range now to actually test this we'll need a quick voltage pulse also called a trigger thankfully we can reuse the gate to trigger converter I've come up with in my kick drum video for this you can find an in-depth explanation in that video but essentially the circuit takes a gate signal coming from a sequencer for example transforms it into a quick voltage pulse and then allows you to cap that voltage pulse's height to a given control voltage via the accent CV in since even the accented pulse is too hot for our oscillator and would cause it to distort we'll scale it down using a simple 10K 1K voltage divider to test our circuit I'll use a new project I'm currently working on with my friends at Erica syns we call it labor it's supposed to make breadboarding synthesizer circuits less of a hassle in our case I'm using the internal dual Supply to power the circuit the modular IND facing section to connect the potentiometer to the breadboard the manual gate button to trigger the drum sound the variable CV source to control the accent level and the output amplifier to connect the circuit to my audio interface at some point we'll also have a little oscilloscope expansion module up here unfortunately that's still in development so we'll have to make do with a simulated version for now [Music] as expected we get a short blip every time I push the button and we can tune it using the potentiometer also we can vary the output volume via the accent CV input great depending on your use case you might want to extend the decay of this a little though for that we'll borrow another idea from my kick drum video forcing the oscillation to keep going for longer by applying positive feedback to the system and we do that with an opamp set up as an inverting amplifier with variable gain by using a 100K potentiometer in parallel with the 47k feedback resistor we can dial in any amount of gain between zero and about 6 which should give us a decently long tail on the drum sound and yeah that seems like a solid range to me if you want to get more Decay out of this you can simply increase the value of the potentiometer but for me this is plenty next I want to add a Punchy attack to the drum sound via a pitch envelope for that we'll take another cue from my kick drum circuit Bridging the resistance to ground in the oscillator with an npn transistor it works like this if we apply voltage to the transistor's base it will allow current to bypass the potentiometer and 470 ohms resistor heavily reducing the effective resistance to ground and thereby increasing the oscillation frequency to keep the pitch from going through the roof we then add a small 330 ohm series resistor so the effective resistance doesn't drop straight to zero when the transistor is fully open this will also shift the pitch range downwards a bit but I prefer lower pitch snares anyway so I'm okay with that next we'll set up a simple envelope generator that will control the transistor it works like this if we apply a trigger to the diode current will flow into the capacitor filling it up since I want the attack to be consistent at different accent levels we'll use the full size trigger instead of the accented one then when the trigger disappears current slowly flows from the capacitor through the voltage divider opening up the transistor in the process why do we need the voltage divider though wouldn't a single bigger resistor connecting the cap and transistor have the same effect not quite since the transistor wouldn't allow the capacitor to fully discharge that's because at voltages below 300 to 400 molts barely any current is going to flow into the base and this would prevent the oscillator from settling on its base pitch by introducing a dedicated path the ground we fix this allowing the cap to discharge steadily and completely and while this works just fine I feel like the added punch is a little too intense and dominant to deal with this we can insert a relatively small resistance after the input diode this way charging the capacitor takes a bit longer and it doesn't get charged up as much which should result in a smoother less intense attack to be able to vary the effect we combine a 1K resistor with a 5k potentiomet here as expected we can now vary the attack's intensity from pretty Punchy to really subtle great right now our circuit sounds more like a 606 style Tom than a snare that's because we're missing the second main component of the sound the snare wires to implement it we'll first need to set up a white noise generator here we can again reuse part of a circuit I already designed in my video covering a white pink and blue noise generator I came up with this transistor-based white noise core I recommend checking that video for an in-depth explanation but here's a quick rundown we wire up a transistor backwards blasting its emitter with 12 volts which causes it to break down this allows for randomly fluctuating amounts of current to flow through the transistor which causes the voltage below the resistor to fluctuate randomly as well the rest of the circuit is then simply processing the noise signal we first center it around the Z volts line via AC coupling and then we amplify it by a factor of 45 since the original signal is extremely low in volume as expected we get a pretty uniform white noise signal out of the generator great next we'll need to shape the noise into a percussive burst for that we'll go with the swing type VCA that Roland used all over the 606 and 808 drum voices again I did a thorough analysis of this little circuit in my previous video about a 606 style high hat but here's a quick summary at its core the VCA is a simple npn transistor-based amplifier and like in a regular amplifier we first bias the input signal upwards so that the transistor is forward active when the signal is idling at ground level then when that signal starts to slightly fluctuate the transistor oscillates between cut off and saturation since its gain is extremely high this adds a lot of distortion but it also allows us to reduce the overall volume of the output by lowering the control voltage we apply to the collector resistor that's because that control voltage is the output voltage we get when the transistor is in the cutoff state for good measure we add a diode to keep the VCA quiet when the control voltage is very low and a small filtering cap to remove some of the high-end added by the Distortion to test this I I've connected the laboris variable CV source to the vca's control voltage input as expected this allows us to reduce the volume of our noise signal but I'm noticing some unpleasant high-end hiss still present in our output despite the filtering cap I suspect that this is a byproduct of our diode rapidly and and randomly opening and closing in sync with a noise signal so we'll slow that down a touch with yet another 2.2 nanofarads filtering cap on the other side seems to work just fine great with the VCA done we'll now want to add another envelope generator so we can make our noise match the volume Contour of the drum sound we'll deviate a little from the attack stage envelope design for this though first we don't want the noise to come in gradually but rather hit at full volume so we'll omit the resistance between the diode and capacitor and second we'll want to control the speed with which the noise Fades away to simulate tighter or looser snare wires for that we'll put a 100K potentiometer between the capacitor and the vca's CV in input this way that potentiometer is working double duty as the resistance that converts the current flowing through the vca's transistor into a voltage and as the discharging path for the envelope capacitor to test this I'm applying our trigger to the envelope we'll listen to the noise path in isolation for now and indeed we're able to Mor of the constant noise into percussive bursts of varying lengths we can even kill it completely great to hear how this would sound mixed together with a drum signal I'll set up a simple passive mixer using two resistors to me that sounds more like a weird combination of a Tom and a terrible hand clap the noise is just way too bottom heavy to pass as snare wires so let's get rid of that low end by routing the processed noise through an aggressive high pass for that we'll use a salent key highpass filter you might recognize this topology from my high head video though I used an op amp instead of a transistor as the active element there essentially a salent key filter consists of two passive filter stages and an amplifier chain together then the Amplified output is routed back into the first filter stage adding the amplifier and the feedback does two things first it decouples the two filter stages preventing them from loading each other down and thereby improving the filter's performance and second it allows us to introduce resonance here the amount of resonance added depends on the size of this resistor as a rule of thumb the smaller the resistor the more reson will get using two 1 naner capacitors with a 100K resistor to ground and a 22k feetback resistor gives us a cutter frequency of 3.4 khz and a pronounced bump at that same frequency for the amplifier I'm using a simple npn transistor set up as an emitter follower with one slight catch since our noise signal is swinging around the 0 volts line we need to give the transistor enough headro to operate if we connect the resistor down here to ground like you normally would for an emit follower the transistor wouldn't be able to reproduce some of the signal because it's already fully closed at Zer volts base voltage so instead we connect it to the negative rail that way the transistor has all the headro it needs to amplify the full signal the value of that resistor isn't super important by the way it will mostly influence the DC offset set of the output and also its volume a 22k resistor worked well for me here giving us a roughly 3 volts peak-to Peak output with an offset of about minus one volt to get rid of the latter we'll simply AC couple the output using a 10 nanofarad capacitor we can use such a small coupling cap here since the signal barely has any low end left anyway and yeah our filter does remove a big chunk of the Signal's low end while also introducing a bit of bite via the added resonance great almost done now all that's left to do is properly mix both signal paths together for that we'll first set up an opamp in the inverting configuration this configuration is great for mixing audio signals since it isolates the different inputs from each other you can learn more about this in my video on designing an audio mixer from scratch next we'll need to pick values for our three resistors the one in the opm's feedback path determines the overall gain of the mixer while the other two resistors in the input path set the individual gain for the two signals with this in mind I settled on using a 100K resistor for the drum sound a 10K resistor for the noise and a 33k resistor in the feedback path giving me an approximately 10 Vols peak-to Peak signal at the output with a nice balance between drum and snare wires I'm pretty happy with how this sounds but there are two bonus features I'd like to implement first a CV input for the drum sound space pitch and second one for controlling the snare wire sound for the pitch CV input there's a super simple solution keeping the attack stage transistor open to varying degrees because remember if that transistor is open the oscillator's frequency increases to open it we can simply connect our control voltage to the 47k resistor at the transistor's base instead of connecting it to ground then the oscillator's behavior will be unchanged at Z volt CV but the pitch will increase as we push it [Music] up seems to work just fine we can set the drum space pitch using the tune potentiometer and then increase it from there via the control voltage great ideally I'd also like to adjust the intensity with which the CV is affecting the pitch to do that you might be tempted to Simply put a variable voltage divider between the CV input and the 47k resistor unfortunately this would mess with the capacitor's discharging process slowing it down significantly which would in turn affect the sound of the attack so we need to make sure that the impedance here stays the same and we can achieve that by buffering the attenuated CV with a simple upam buffer that way the impedance between the transition base and the buffer CV is independent of the attenuation we apply sounds great to me the attenuator allows us to manipulate the drum's pitch in a much more subtle way next we'll add a CV input for the snare wire sound this is thankfully super simple we only need to adjust the decay of the envelope that is controlling the swing type VCA to do that we'll simply establish a second path for that envelope capacitor to discharge through if we combine a 22k resistor with a PNP transistor to create this path we can open or close it via a voltage we apply to the P&P space at Z volt CV the transistor is fully open allowing the cap to quickly discharge via the 22k resistor and if we increase it from there the transistor will gradually close down slowing the Cap's discharging [Music] process and yeah this does allow us to adjust the amount of snare wire sound we add great with this final feature implemented let's hear what kinds of snares we can get out of our Circuit by tweaking all of the controls together and with this we've now got a pretty versatile analog snare drum in a straightforward little circuit if you try building it for yourself let me know how it went in the comments ideas for how to improve the circuit are very welcome too if you'd like to support the channel consider becoming a member of on my patreon page or check out the lineup of your DIY kits I develop in collaboration with Eric since you can get most of my designs as complete bundles containing a set of components a pcbn panel and an extensive write up in the ARA sin's web shop the snare is now available too links are in the description anyway thanks for watching and until next time see you for

Channel: Moritz Klein

Views: 87,297

Keywords: mortiz klein, moritz klein, DIY synth, DIY snare, electronics tutorial, DIY synth tutorial

Id: hULEn2_4Unw

Length: 22min 44sec (1364 seconds)

Published: Fri Apr 19 2024