Eric Archer TR808 modules

Hola Kosmonautas,

I just stumbled upon these drum modules laid out by Eric Archer.

TR-808 bass drum
TR-808 snare
TR-808 hihats

I haven’t tried these out but his build guide is a super detailed with awesome wiring diagrams. Leaves nothing to the imagination. The build is on protoboard for all modules, which is awesome as I just picked up a few to tinker with from Microcenter.

Looks like Tayda has stock on the 2SC945 but I cant find the 2SA733 or figure out what would be the suitable replacement [I only searched for 10mins…tho]

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Transistor Substitutions | Audiokarma Home Audio Stereo Discussion Forums suggests KSA992 which is in stock at Tayda. (And KSA733 but that seems to be obsolete now too.)

At 2SC2229 and 2SA733 replacment/substitute | diyAudio someone says

2SA733 are just general purpose transistors. BC557 will work but the pinout is different.

I haven’t verified any of the above.

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I keep finding new builds to do, and have so few parts ;-;
Great find though man, these are totally going in the backlog!

the 2SA733 is $6.95 over on Ebay , it is rare and and this is just for one, but usa buyer, not China and there are spec sheets on equivalents. Thanks for the share great circuits to build yes us thanks again .

Parts aren’t the problem, you can buy them (even if mine seems to be lost somewhere… still waiting…)
Time is the real problem :slight_smile:

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@binarymob
All the Eric Archer 808 modules have been adapted to stripboard if that is easier for you. I’ve built the kick, voice,cowbell, cymbal, hi-hats, and started the snare, though my high-hats aren’t working yet.

https://electro-music.com/forum/topic-37646.html
https://electro-music.com/forum/topic-54826.html&postorder=asc
https://electro-music.com/forum/topic-45134.html

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@EddyBergman I saw you were asking about the 808 accents in synth DIY. I thought it would be helpful to some in this group that are also interested in building these to repost some of this info.

Pete Hartman

Accent, technically, never made it all the way to the voice itself.

Here’s a thumbnail of how the 808 dealt with clocks and voicing…

There is a trigger pulse that is constant – it goes to all the voices, all the time.

There is a voice enable gate of 5 V, and the voice can’t fire without the gate being enabled. This is how they control which voices fire on a given step/trigger pulse.

The trigger pulse is conditioned after it comes out of the MCU. It is combined with the accent LEVEL, so that the trigger pulse itself is between 4V (the nominal value) and 14V (maximum accent). This is why the accent is a global parameter – all the voices that fire on an accented step get that accent.

When people started making individual drum voices, they saw that the voice input had two parts (the gate and the trigger as I’ve described) but they either didn’t look more deeply at the circuit, or they didn’t want to add the additional circuitry to make the voice fully emulate the original, so they basically called one input the trigger and the other the accent and left it at that. Depending on how you assign those, they do kind of work that way – you can set the “normal” trigger input to be an accent level and use the “gate” input as the trigger, and it will function more or less the way you expect it to.

The service manual for the 808 is out there, it’s got some good information in it, that and playing with these circuits is how I learned this.


From reading through the electro music threads, it seems like many are tying accent to trigger or accent to +12v. There is also a gate to trigger converter that you can build in this thread.
https://electro-music.com/forum/topic-45134-25.html&postdays=0&postorder=asc&highlight=

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Good idea to make this info available here. It was certainly an issue that had me puzzled.

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Archer’s schematics use BC546/556 everywhere (7/8/9 will work too), except for the noise source (where you can probably use one too, but noise transistors are a bit “try the ones you have until you find one with nice noise, throw away the others”).

(If you think he doesn’t, you’re looking at the wrong pages in these PDFs :slight_smile:)

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Confusingly, the only BOM shown is the one for the original circuit, not Archer’s version.

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