The layout

Here is how the frontpanel will look like. I've never been a big graphic designer so the design is kept quite simple. Each blue field contains the knobs for one sound module. The sound modules are intentionally not labeled since the modules are (or should be) designed flexible enough to to create sounds which are beyond the scope each separate module was designed for. Still the intended use is (from left to right): bass drum, snare drum, high-hats (open and closed), tom and crash. The bottom part is the step sequencer with red leds showing the pattern of a single instrument and green leds which show the position in the sequence. Two rotary knobs select the intrument which should be edited. Apart from the six internal modules an external channel (there's an accent and trigger out for this channel) and a digital sample player (a future project) can be programmed. Four patterns can be stored, the pattern to be edited is selected using the second rotary switch. The rest is self-explanatory i think.
Oops, i forgot to say: the case will be an plastic toolbox, so the size is adapted to this box.

Digital Part: Concept and schematics

For the digital part i chose to use atmega8 microcontroller to do all the tasks related to the sequencer control. These are mainly handling the buttons (start, stop, running mode, load/save pattern etc.), controlling the led's and generating the trigger pulses and accent switches to control the analog sound modules. When starting i thought that one atmega8 will be sufficient to do all the task but i soon realized that i needed a second one.
I decided to split the two controllers into a 'master' controller and a slave controller. The idea behind this is that the master processes all the incoming information (buttons and sequencer clock) and the slave controller is used to control the output (the leds and interface to soundmodules). Communication between master and slave is done via i2c.
Here is the schematic (not tested yet) for the master partHere is the one for the slave part

How it all started...

The first time i came in touch with music electronics or electronics in general was roghly six years ago. I was playing the electric guitar for a while and wanted to buy some cool distortion pedals, so that i'm able to play heavy rock and metal. I realized that i couldnt really afford them. While surfing on he internet i found out that it's not that difficult to make them myself so i gave myself a try on building some effect. I started with building some designs found on net, later i tried to design some pedals myself. But since i didn't know how the things inside work it wasn't that successful. Also because of financial issues i never used good quality switches and boxes. It ended up by putting the ~7 effects is had in a huge box. So in the end i had a huge, humming box with 7 strange sounding distortion effects in it. Because of several reasons i didn't toucha soldering iron for a while.

Renewed Interest
About a year ago i was looking for a midi controller keyboard to used with pc-based software instruments. By chance i found one at a local flea market in berne, switzerland. This flea market is organized by a alternative culture center 'Reitschule' (b.t.w. its a great place to visit), so a lot dubious sellers are around there. Maybe thats the case for all flea market but anyway... So i found this controller keyboard which looked totally new. After some negociations i bought is for 80 Swiss francs which is ~50 eur0s. Back at home i quickly found out the keyboard wasnt working at all. After nearly throwing it from the balcony i rememembered that i once wanted to start building a synthesizer. After some days of investigation i came to the decision that i'm gonna try to put the keyboard back to life by constructing an analog synthesizer around it.
Since i haven't really worked on electronics for a long time i started with very simple projects. By that time i discovered ray wilson's excellent music from outer space site. Without the invaluable information on this site i probably wouldn't have been able get into analog synthesizer technology. Thanks to ray wilson for building and supporting this excellent site!.
The first 'real' project built is the weird sound generator from MFOS. Due to a lack of an appropriate enclosure i mounted it into a a folder.
The folder gained some popularity amolng my bandmates and friend. So i offered them to build the same circuit in an specific enclosure which they could choose on their own. By the time i already biult three copies of WSG, one is mounted in a plastic case (see the myspace site dedicated to it) another one in a wooden box and the last one in a former model airplane remote control. By the time i planned my next project: the MFOS mini synth. After building three WSG's i felt sure enough to modify the mini synth slightly to fit my needs. In order to use it with the keyboard i added the scanning matrix encoder (also from the mfos site, your guessed it, right?). I also added an external (guitar) input which routes the external signal to the filter and vca section, beside that it has an envelope follower and a signal to gate converter. Another major change compared to the original sound lab is that it can be patched beside the switches that do the signal/cv routing. Below are some photos of the synth and the keyboard.
There are already enough not-so-musical soundlab demos on the net so i decided not to make a 'raw' soundlab demos yet, once i have time i'll add a video. You can hear my soundlab in a musical context (well that always a matter of taste i guess) on my myspace site. The sound lab can be heard in the songs 'the funky chicken', 'a word' and 'drifting'. In 'the funky chicked' the bass is done with the soundlab, the horns in the band (not in the intro, these are samples), and in the keyboard solo in the middle. The playing of this is lousy but the sound is quite decent i think. In 'a word' the bass and all the synths are done with the soundlab (except drums). The wah-wah guitar well heard during the first verse is the acoustic guitar processed by the soundlab. In 'drifting all the synths except drums are made with the soundlab.
After the soundlab was finished is built three guitar effect boxes, a little guitar practice amp and a midi to control voltage converter. More on these, especially the midi-to-cv converter later.

The Beginning

Today I'm starting the blog which is dedicated to the development of an analog drum synthesizer. I was asking myself for a long time if I really should start this since there are already too many blogs out-there (in my opinion) with doubtful content sometimes. Anyway, this is about building a analog drum computer. A drum computer is a device on which rhythms can be programmed, it is one of the basic ingredients for all sorts of electronic music. There are some famous examples of drum computers such as the tr-808 from roland which is unfortunately not produced anymore. My own design will be heavily influenced by the tr-808 although i never had an example in my hands. I'm mainly doing this because the tr-808 is considered to be a classic and it looks cool too. And i've player around with the virtual version of it (Propellerheads rebirth). So whats my motivation for building a drum computer? If you just want to create beats then you probably use a pc and a software drum machine. There are some good ones out there for free (for instance propellereads rebirth. Thats not a i want to do with is. I'm rooted in 'live played' music and i'm a guitar and piano player for a long time so i don't really get along well with creating music by clicking on virtual buttons on a computer screen. I'm happier with a hardware instrument which is quickly started and easy to use (one button - one function, no menus). Well in this case a hardware groovebox could do the job so why still build a drum computer myself?
First: building an instrument is fun, and, once finished, a deeply satisfying experience.
Second: There are almost no drum computer diy projects on the web. With this project i hope some give something back to the synth diy community of which i benefitted a lot during my first synth diy projects. I will post some information on these later on.
Third: A self-built instrument is very easy to use is the since you built it the way you want to have it.

Basic Concept

Before starting the first sketch of a schematic i put up a list of general features the drum synth should have. The basic concept is a step sequencer based drum computer with analog sound generator circuitry. The pattern control and programming is done with atmega8 microcontrollers. These are chosen because they are relatively cheap and they can be programmed with very little extra hardware required. The following sound modules will be built:
->Bass Drum
->Snare Drum
->Open and Closed Hi-Hat
->Tom
->Crash
The sequencer should have 16 steps, it should support 4 running modes:
->forward (the standard one)
->backward
-> forward followed by backward
-> random
Beside a clock is supports also a manual advance mode. A 'swing'-mode which enlarges every second note period is not planned currently. The sequencer will be able to control eight instruments whereof six are integrated in the drum synth. The sequencer will have a trigger output to control external equipment. One instrument control line is reserved for a digital sample player which might be added later on. Each trigger pulse will have a normal and an accentuated mode, the amount of accent will be tunable for each sound module separately.

There will be the possibility to store 4 patterns in the internal eeprom of the atmega8's. It won't feature a 'song-mode', i.e. the ability to store a sequence of patterns since it is designed as simple instrument which will be played as 'life' as possible. But we'll see, maybe i add that later on. However it supports playing one pattern while programming another one, as many things else this is shamelessly copied from the tr-808. Thats it so far. Next i will some sound clips of the prototypes of the snare and bass drum modules since i already built as well as some information on my finished synth projects, schematics etc. Beside electronics i play music solo and in a band.