808 clones

TR-808 Snare DIY Project - a version of the TR808 Snare, designed for hand-wiring on perfboard.  PDF graphics; CAD software not required.

808 HiHat DIY Project (revised Dec 2009) - as above, but a more complex project.  This is the revised version as of Dec 2009.  Thanks to Marco Rossi for pointing out an overlapping wire issue on the PWR page.  It is corrected in this version.  If you built the previous version and it doesnt work, look on the PWR page and identify the wire that connects T13 to T1.  It looks like it says to connect it to C20, but that is a mistake.  This wire does not connect to C20; it just goes straight from T13 to T1.  Check out a track recorded by Marco using his 808 Bass Drum clone w/ mods via this link.

TR-808 Bass Drum DIY Project  - simplest project of the three.

TR-808 Service Manual   … bask in the full knowledge of original Roland schematics and technical data!

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I was curious about how those smart engineers at Roland made the TR-808 sound so cool. I found the schematics online and decided to build some of the drum oscillators as individual modules. I started with the kick, snare, and hi-hats, copying them as faithfully as possible to these original schematics.  But instead of the old transitors and diodes, I substituted currently available stuff whenever obsolete ones were called for; BC546B and BC556B transistors seem to work fine.

You’ll need a split power supply to make these circuits work.   You can use +/-12VDC or +/-15VDC.   In a pinch you can make a +/-9VDC supply with two 9V batteries and a pair of battery snaps.  Or you can adapt an old PC power supply to make a +/-12VDC “bench power supply”.  Look for instructions on how to hack a PC supply on the net.

Or do what I did: I found that the miniature muRata NDTD0515C DC-DC converter works nicely, boosting juice from a cheap wallwart up to nice +/- 15VDC bipolar power.

I put together PDF guides for you to hand-build the kick, snare, and hihats on perfboard.  These are at the top of this page.

Since then, I started making some sense of how it all works; take a look at my modified TR808 Cowbell for an analysis.

I also designed a modified 808 CP, and called it the Clap-Raca.  I’ve done the RS/CL (rimshot / clave), MT (mid tom), and LT (low tom) with mods, but haven’t written about them yet.  That pretty much leaves the cymbal and maraca…  The 808 cymbal circuit is complex and pretty remarkable, you can read about it more in this Sound on Sound article.

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If you’re interested in modeling the 808 sound in sofware such as PureData, Reaktor, etc. here are a few points not to overlook:

Swing VCA.  This is a cool invention: a voltage-controlled amplifier (VCA) made from a single transistor.  It is not typical of the VCA/mixer blocks in software though.  It is much more lo-fi.  Thats because thanks to the fact it only has one transistor, it only passes audio of one polarity.  Look at the following illustration and notice that the output waveform is missing the lower half of what is fed into it from the SIG input.

swing vca

This rudimentary synth building block adds harmonics and a distorted edgy tone wherever it is used.  In the 808, we find this invention applied to the hi-hats, cymbal, snare (noise portion only), toms (for the poof of filtered noise that simulates reverb), clap, rimshot, and maracas.  If you’re all espresso’d up and feel like looking at schematics, open up the 808 Service Manual at the top of this page, and see if you can find the swing VCAs.  Look at the maraca first, its simplest.

ENVELOPE is the control voltage that sets the amplitude of the output.  This is a simple Decay-type envelope in many of the 808’s sounds.  In other cases, the envelope is the sum of two Decay envelopes with different time constants (cowbell).

My point about the swing VCA is that you should use a half-wave rectifier element in your models to get close to the 808 sound.   Imagine an oscillating waveform with its center at zero, max amplitude of +/- 1.  A half-wave rectifier function returns zero for anything that is equal to or less than zero.  But what do you get if you apply this function to noise?  It is still noise but the frequency content changes.. (?)

Block Diagrams

The 808 service manual kindly includes block diagrams of how all the analog voices work.  Although its not something you can directly import into software.  The circular symbols with arrows inside are front panel knobs.

808 voice diagram 1   808 voice diagram 2

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More info here: Big Box o’ Techno

clone TR808 modules

From front to back - 808 hihats, snare, and kick

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Trigger and Accent inputs - Each drum has a TRIGGER and ACCENT input. In the 808, the accent input is a global signal that boosts the level of all drums when requested (TTBOMK). In my clone, I just have a potentiometer set up as a voltage divider to deliver a constant voltage to the ACC input. It is basically a volume control in this arrangement. The trigger inputs are a little more tricky; if you are driving the drums with a logic circuit, you’ll need a little bit of trigger generator “glue” inbetween. Basically this lets the energy of the positive transition thru to trigger the drums, and shaves off the negative edge. If you omit the trigger generator, the drums sound weird b/c they will also trigger on the negative edge, with a different and weaker tone, reduced decay time… weird.

 

808 trigger network

Trigger generator network