Building a DIY Eurorack TR-808 Kick
Few sounds in electronic music are as instantly recognisable as the TR-808 kick drum. From its deep, booming bass in hip-hop and techno to its punchy, resonant thump in house and electro, the 808 kick has been a staple in music production for over four decades. Initially introduced in 1980 with Roland’s legendary TR-808 Rhythm Composer, this analogue drum machine was initially overlooked in favour of more “realistic” digital drum machines. However, as producers and artists began to experiment, the 808 kick’s unique sound found a home in countless genres, forever changing the sound of modern music.
Today, the 808 kick remains a core sonic component of genres ranging from trap and drum & bass to pop and industrial. This simple circuit has transcended its humble origins to become an iconic sound and Eurorack essential.
In this guide, we’ll use the N8 Synth’s 8HP Eurorack Prototype kit to build a DIY Eurorack 808 kick module that captures the magic of the original, adapted for modular synthesis and modern performance needs.
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808 Kick Schematic & Module Layout
808 Kick Circuit Overview
Our take on the 808 kick follows the overall topology of the original circuit, but we’ve added a Eurorack compatible trigger section. We’ve tweaked the values of components, both to adapt the circuit for Eurorack, and dial in a sound that we find pleasing. We’ll note these changes below and suggest where you can swap out components to tailor the sound to your liking. Helpfully the original Roland TR-808 service manual explains the 808’s architecture in some detail and is worth checking out.
Trigger & Accent Input
Our Eurorack 808 kick module has both Trigger and Accent inputs, and both expect a 5V trigger of > 2mS duration or a 5V gate. You’ll note that with the exception of the Accent Level, both input circuits have identical topologies and are ultimately summed by U3B and then inverted by U3A to provide a single trigger pulse to the oscillator. As the inputs could be a gate CV ( or longer than the required trigger pulse ), R27, C8, R28, R12, C6, and R17 shape the inputs to generate the required 2mS trigger pulse. The two diodes, D2 & D4, protect transistors Q4 & Q7 from any negative voltage that may appear across the inputs.
At rest, Q2 and Q6 are in a cutoff state. The incoming trigger causes Q7 or Q4 to saturate, grounding the base of Q6 or Q2 and causing them to saturate. Now fully open, the voltage present at the emitters of Q2 and Q6 is dropped across R18 and R20, respectively. In the case of Q6, this voltage is fixed, but for Q2, it is adjustable and gives us our accent. Also, note that J1 is normalised to J2, so if a jack isn’t inserted into J1, the trigger CV at J2 will also trigger the accent circuit.
In operation, we can either:
- Provide a trigger to Trigger Input (J2), in which case the Accent Level is used to boost or trim the trigger and change the overall output level of our kick.
- Provide a trigger to the Trigger Input (J2) and a second trigger to the Accent Input (J1). In this case, the output level is louder ( accented ) when the triggers coincide and quieter when they don’t. The Accent Level pot adjusts the difference.
To increase the dynamic range, you could reduce the value of R18, which will increase the effect of the accent; note this also increases the overall output level.
We picked this approach for the accent circuit because it matches that of the TR-808 and works well with trigger sequencers; however, an alternative approach is to have a single trigger with its level set by CV. This would allow continuous adjustment of the kick’s level with each hit. The velocity output of a keyboard, drum pad, or sequencer could potentially drive the accent CV.
Bridged -T Oscillator
We’ll skip over the Pitch Envelope and Trigger Shaping temporarily and look at the Oscillator. These preceding stages modify the oscillator’s frequency, so it makes sense to understand how it works without them first.
A Bridged-T oscillator, like the one in the TR-808 kick, is a simple yet effective circuit for generating self-damping sine wave oscillations. As the oscillator is self-damping, it doesn’t require a separate envelope generator and VCA to shape the sound. The Bridged-T oscillator is a type of twin-T oscillator modified to be self-oscillating when excited by an external trigger.
A trigger pulse arriving at the non-inverting input of U2A momentarily disrupts the balance of the oscillator, “kicking” it into motion. C4, C5, R21, R10 & R13 in U2A’s feedback loop form a resonant filter, setting the oscillator to a frequency of ~45Hz, with the specified components. The amplitude of the oscillation starts strong and naturally decays over time, like a real drum skin vibrating after being struck. The natural decay of a bridged-T oscillator is exponential, however, U2B adds positive feedback, allowing us to increase the decay. It is this feedback that gives the 808 its signature boom.
The Bridged-T oscillator's frequency is given by:
Where R1 is the total resistance to ground from the junction of the two capacitors and R2 is the feedback resistance.
Inserting our component values:
Trigger Shaping
In addition to kicking the oscillator into motion, the trigger pulse appears at the output via U2A. This sharp pulse replicates the high-frequency noise component of a physical drum, which is generated when the beater hits the drum skin. C7, R24 and R25 shape the ~2mS square pulse from the trigger stage, giving it a sharp transient and exponential decay. As specified, C7 with a value of 1nF adds very little “click” to the output, which is how we like it; increasing the value of C7 will increase the “clickiness” of your drum. Replacing C7 with a 10nF – 15nF component should give you a nice clicky kick.
Pitch Envelope
Along with the extended “boom”, the pitch envelope of the 808 kick is a crucial part of that iconic sound. Unlike a simple sine wave oscillator, the 808’s kick starts at a higher pitch that quickly drops, mimicking the natural characteristics of a physical drum being struck. This transient pitch drop creates a strong percussive attack, making the kick sound punchy and dynamic.
As discussed above, the capacitors and resistors in U2A’s feedback loop determine the oscillator’s frequency. The initial pitch bump is achieved by bypassing R13 with Q5. When Q5 is saturated, we’d expect the oscillator’s frequency to be ~128Hz as the effect of R13 has been nulled. In practice, the interaction is more complex, and the frequency varies over time at a rate determined by the pitch envelope.
A trigger pulse arriving at the base of Q3 via the divider R6 & R7 causes the transistor to saturate. This allows C3 to discharge, causing Q1 to cut off. With Q1 cutoff, a voltage develops across R16 at the base of Q5, allowing Q5 to saturate a short R13. When the trigger pulse ends ( after ~2mS ), Q3 cuts off, allowing C3 to charge via R4. As C3 charges, the base-emitter voltage of Q1 increases until Q1 reaches saturation. C1 discharges through Q1, progressively cutting off Q5. R4 and C3, therefore, set the attack of the pitch envelope, and C1 determines the decay rate. Adjusting the value of these is an easy way to tweak the sound of your kick.
Output Stage
The oscillator’s output is fed into an RC lowpass filter (RV2 & C10 ), which acts as a tone control, and RV1 reduces the amplitude before being buffered by U1B for output.
Bill of Materials
We’ll build the Eurorack 808 Kick using the 8HP Eurorack Prototype kit. The kit contains a Eurorack Solderable Breadboard and Eurorack Control Deck, a pre-drilled Eurorack panel, and the pin headers used to connect them. The Eurorack breadboard provides power to our module, and the Eurorack Control Deck makes mounting controls a breeze.
The 8HP Eurorack Prototype kit, jacks, and pots required for this module are available from the N8 Synth store. The remaining components are widely available and relatively inexpensive. If you are just getting started building modular synths, stock up on these components, as they are ubiquitous in the schematics you’ll find online.
A note about capacitors
The voltage rating of the ceramic capacitors is not critical. We’ve specified 50V as this is common for the cheap bulk capacitor kits you’ll find on Amazon and the like, but any voltage rating of greater than 25V will work. The type and tolerance are also not too critical except for C4 & C5, which set the oscillator’s frequency. Ideally, these should be as close to the specified values as possible if you want the maths to work.
| Type | Refs | Value | Qty | Notes | |
|---|---|---|---|---|---|
| 8HP 2x5 Eurorack Prototype Kit | - | - | 1 | Includes Eurorack Breadboard, 8HP Control Deck, 8HP Panel, 40-pin headers (PH1 & PH2), and 2x8 power header. | |
| Jack Socket | J1, J2, J3 | PJ-3001F | 3 | PJ-3001F | |
| Potentiometer | RV1 | A100K | 1 | Alpha-RV901F Style Round Shaft | |
| Potentiometer | RV2 | B10K | 1 | Alpha-RV901F Style Round Shaft | |
| Potentiometer | RV3 | B100K | 1 | Alpha-RV901F Style Round Shaft | |
| Potentiometer | RV4 | B10K | 1 | Alpha-RV09 Style | |
| Hardware | Level Knob | Davies 1900H Clone Orange Round Shaft | 1 | Davies 1900H | |
| Hardware | Tone Knob, Snappy Knob | Davies 1900H Clone White Round Shaft | 2 | Davies 1900H | |
| Hardware | 3 | DIP8 IC sockets for U1, U2 and U3 | |||
| Capacitor | C19, C20 | 10uF ±20% 25V | 2 | Radial Electrolytic 5x11mm | |
| Capacitor | C3 | 330nF ±20% 50V | 1 | Multilayer Ceramic 4mm | |
| Capacitor | C10 | 150nF ±20% 50V | 1 | Multilayer Ceramic 4mm | |
| Capacitor | C2 | 10uF ±20% 50V | 1 | Radial Electrolytic 5x11mm | |
| Capacitor | C17, C18, C15, C16, C12, C11, C13, C14 | 100nF ±20% 50V | 8 | Multilayer Ceramic 4mm | |
| Capacitor | C6, C8 | 10nF ±20% 50V | 2 | Multilayer Ceramic 4mm | |
| Capacitor | C1 | 33nF ±20% 50V | 1 | Multilayer Ceramic 4mm | |
| Capacitor | C7 | 1nF ±20% 50V | 1 | Multilayer Ceramic 4mm | |
| Capacitor | C9 | 1uF ±20% 50V | 1 | Multilayer Ceramic 4mm | |
| Capacitor | C5, C4 | 15nF ±5% 50V | 2 | Polyester Mylar Film Capacitor | |
| Diode | D2, D4, D1, D3 | 1N4148 | 4 | Switching Diode, 300mA 100V | |
| IC | U3, U2, U1 | TL072 | 3 | DIP8 | |
| Resistor | R10 | 6K8 | 1 | Metal Film 1/4W | |
| Resistor | R7 | 2K7 | 1 | Metal Film 1/4W | |
| Resistor | R21, R4, R2 | 1M | 3 | Metal Film 1/4W | |
| Resistor | R3 | 470K | 1 | Metal Film 1/4W | |
| Resistor | R22, R5, R20, R18, R13 | 47K | 5 | Metal Film 1/4W | |
| Resistor | R17, R28 | 33K | 2 | Metal Film 1/4W | |
| Resistor | R30 | 20K | 1 | Metal Film 1/4W | |
| Resistor | R32 | 1K | 1 | Metal Film 1/4W | |
| Resistor | R23 | 220R | 1 | Metal Film 1/4W | |
| Resistor | R6 | 8K2 | 1 | Metal Film 1/4W | |
| Resistor | R12, R8, R27, R26, R1, R16, R24 | 100K | 7 | Metal Film 1/4W | |
| Resistor | R14, R19, R15, R33, R9, R11, R31, R25 | 10K | 8 | Metal Film 1/4W | |
| Transistor | Q6, Q2 | 2N3906 | 2 | PNP Transistor | |
| Transistor | Q4, Q7, Q3, Q1, Q5 | 2N3904 | 5 | NPN Transistor |
Constructing the Eurorack 808 Kick
Building the breadboard 808 Kick circuit
Our 808 kick module is built on an N8 Eurorack breadboard. If you’ve used a sprung breadboard before, you should be right at home, as the layout is basically the same. The product page provides a diagram of the layout and connections and an overview of the breadboard’s design and features.
As with any PCB construction, we want to build low to high, starting with the wires and then adding components in reverse order of height. Beginning with the lower-profile components makes our life easier by giving us more room to manoeuvre without the taller parts getting in the way. This design has several longer wires, and it may be easier to route these after the other components have been positioned, as indicated below.
1. First up, we add the shorter wires indicated in the “step 1” diagram. Strip around 3mm of insulation from each end of the wire and feed the conductor through the appropriate holes. It can be helpful to work in sections and use masking tape to hold several wires in place before flipping the breadboard for soldering.
2. With the wires in place, solder in the three DIL chip holders. Soldering one pin first and checking that the part is flat to the board before soldering the rest is good practice.
3. Add flat resistors to the breadboard, for example, R2, R16, R19, etc.
4. Add the remaining resistors and the four diodes.
5. Capacitors. Solder in the small ones and then the big ones! The three electrolytic caps, C2, C19 and C20, are polarized, so make sure to mount them with the correct orientation.
6. Add the seven transistors. Remember that Q2 and Q6 are PNP devices while the others are NPN, and check their orientation is correct.
7. Solder in the 2×8 pin header (J5), our power connector. The power connector can be mounted on either side of the breadboard, but we mount it on the front (component side) for an 8HP module like this.
8. Solder the single-row, 90-degree, 40-pin male header to the left edge connector. Because we are using an 8HP Eurorack Control Deck, the pin header is mounted on the breadboard’s rear (non-component side).
9. With the components in place, we now tackle the longer wires indicated in the “step 2” diagram to complete the breadboard.
Top Tip: It can be tough to strip the insulation from the short wires, like the ones connecting the power rails to the TL072 op-amp. Instead of stripping 3mm of insulation from each end, remove 6mm from one end of the wire and then cut the wire to length. You should then be able to slide the short piece of insulation along the conductor, leaving 3mm at each end.
The 808 Kick Control Deck
N8 Eurorack Control Decks have logical front and rear sides. The front has screen-printed boxes indicating where pots, jacks, and switches are mounted, while the rear doesn’t have these boxes. Components can be mounted on either the front or the rear.
For the 808 Kick module, we mount our jack sockets and pots on the front of the Control Deck, the side with screen-printed boxes, and add a number of wires to the rear.
Check out these guides for further details on mounting components on your Control Deck.
Important: The wires on the rear of the Control Deck should be added first.
1. On the rear of the Control Deck, position the short (black) wires connecting the “d-bus” to the spare horizontal C pad of each JPS cell, where a 3.5mm jack socket will be mounted. These are JPS7, JPS9 & JPS10. Flip the control deck over to solder these wires in place from the front.
We are using the d-bus to create a common ground on the control deck, saving space on the breadboard for our core circuit.
2. The schematic shows that Pin 1 of RV4 is also grounded. Pin 1 corresponds to the A pads of JPS8. Make this connection on the rear of the Control Deck by connecting a black wire from JPS8’s vertical A pad to the “d-bus”.
3. Similarly, the schematic shows that Pin 1 of RV1 is grounded. Make this connection on the rear of the Control Deck by connecting a black wire from JPS1’s vertical A pad to the “d-bus”.
4. The tip (T) of J2 is connected to the switch of J1 (TN). We can make this connection on the rear of the Control Deck by connecting JPS7’s horizontal B pad to JPS9’s horizontal A pad. This is the yellow wire on the diagram.
5. On the rear of the Control Deck, connect the vertical B & C pads of JPS5, again soldering from the front. This is the short orange wire on the diagram.
6. Connect the vertical A & B pads of JPS4 and then the vertical C pad of JPS1 to the vertical C pad of JPS1—the two pink wires on the diagram.
7. Take a moment, make coffee, and check that all the wires are on the rear of the Control Deck and match the diagram. They can be corrected after the pots and jack sockets are added, but you’ll save time if they are correct before the pots and jacks are added.
8. Dry-fit the potentiometers on the front of the Control Deck. If the pots have metal support tabs on their top and bottom edges, they should be tucked under the pot’s body, as illustrated here.
9. Dry-fit the jacks on the front side of the Control Deck. If in doubt, check out this guide for correctly positioning jacks on the Control Deck.
10. Attach the pre-drilled Eurorack panel using the hex nuts provided with the jacks and pots, checking that the jacks are centred in the holes and that each component is seated on the Control Deck.
11. Leaving the panel attached, flip the Control Deck over and solder the pots and jacks into position from the rear. The trigger input jack (J2) needs its switch pin connected to ground. We achieve this with a solder blob, connecting the switch and ground pins of JPS9 on the rear of the Control Deck.
12. Remove the panel, position the 40-pin female header on the rear and solder it into place from the front. If needed, hold it in place with masking tape. Solder a pin at either end and check that it is perpendicular before soldering the other pads.
13. Connect the finished Control Deck to the breadboard using the pin headers.
14. Insert the three TL072 op amps in their sockets, being careful to orient them correctly.
Testing, Testing, check one two.
Before you power up your kick module for the first time, you should do some basic tests. While not extensive, these help keep the magic smoke in the components where it belongs.
Visual inspection
- Compare your module to the diagrams and schematic on this page. Do all the components and wires look like they are in the right place? Anything missing?
- Inspect the solder side of the Eurorack Breadboard and Control Deck.
- Are any of the pads shorted by solder splashes or untrimmed component leads?
- Are all the component leads soldered?
- Have solder bridges indicated on the diagrams been made?
Continuity
We want to ensure there is no continuity between +12v, ground and -12v rails. We’ll do this using a multimeter.
Put your multimeter in continuity test mode, then, with your module unpowered, check the continuity between the following points on the circuit:
- Connect one of the multimeter’s test leads to the +12V rail and the other to ground. There should be no continuity
- Connect one of the multimeter’s test leads to the -12V rail and the other to ground. There should be no continuity
- Connect one of the multimeter’s test leads to the -12V rail and the other to +12V. There should be no continuity
Power Up
If your new module passed the continuity tests and visual inspection, it’s time to power it up. If you have a bench power supply, it is good practice to use it for the first power up of a DIY synth module so that it is a minimum safe distance from your other modules.
The Eurorack power connector format is sadly a little open to interpretation, and many a module has lost its life to the specification’s vagueries.
N8 Eurorack prototype boards follow the most common convention. A white stripe is printed next to the -12V end of the power connector. Typically this is where the red stripe of the power cable should be aligned. BUT not every manufacturer follows this convention, and this is a DIY synth tutorial, so chances are you made your cables, right?
Always check that your power supply is supplying -12V at the red stripe before connecting power to your synth module and that the red stripe is connected to the -12V pin on the module.
Making your 808 Kick look beautiful
The final step is to make your shiny new DIY 808 kick look the part next to those expensive commercial Eurorack modules. The good news is you can do this with nothing fancier than an inkjet printer and some sticky-back plastic.
We have a complete guide to making labels for Eurorack panels here. If black and orange are your thing, you can download our finished label, ready for printing.
Download the N808K label template.
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