MOD: Casio VL1 Gate inputs

[playthatbeat]

picked up a Modified Casio VL-1 on eBay recently.. It had been Modified by S-Cat (spacecat)

Check it out here:

http://www.youtube.com/watch?v=8BRkjPDJ9DA

So.. It's a crazy piece of kit.. Even the original non-circuitbent version is kinda neat..

Check it out here: http://www.unhacker.com/maximumcheesecore.html

Thre is an interesting function on it, where you can input a series of notes, and then play them back again by hitting a button - ONE KEY PLAY.. You can do this in normal playing mode as you play the keyboard too. So, imagine banging in 3 notes into the memory (REC mode), then playing the keyboard but being able to cut off the not you are playing with the next note in the sequence you put in in REC mode - you can effectively play extremely fast, making for a unique playing style and sound.. I first saw LEO KELLY (aka Leo O'Kelly of Tir na n'og) do this. He would pre-prepare a sequence of sympathetic notes and jam while ONE KEYing to blind with an onslaught of notes in a live set.. Like a FURIOUS violin solo! The trick was, once the list of notes has been played through, it would go back to the start of the list again - allbeit with one tap of the key that would NOT trigger a note, cos the list was finished.. So, if you think about it - if you were to click on every kickdrum, thats 4 triggers.. if your list of notes is 3 long, then every 4 kicks it would cycle! So, all you need is a trigger in to advance the ONE KEY PLAY, and you have a basic but awesome Sequencer!

So, how to do?

You need to allow the switch/button for ONE KEY PLAY to be controlled by an external switch. If you just wanted to use a footswitch, or a button to do it, you need ONLY tap the 2 points on the control board that would be joined (shorted) by the ONE KEY PLAY button(s) (either will do) and pass them out to the switch, or to a socket - easy once you know where to tap..

For pro use, i needed a GATE input, as used on 95% of all analogue synths and available on most MIDI/CV converters. This was a little tricky. I had to make an S-trigger convertor, using a transistor and 2 resistors (see attached diagram) to allow me to hook up the GATE from my drummachine and CV/GATE gear to fire the ONE KEY PLAY.

I ended up making 3 circuits. The first was external with an adjustable Resistor built in to a lead, because the circuit DOES NOT WORK on the VL1 and needed testing. It turns out it needs a resistor (6.63k) added to the common (negative) of the whole thing to load properly. I then built 2 on 1 small circuit board to fit inside the unit with fixed resistance added to the - rail to match the VL1, 1 for ONE KEY PLAY trigger, and one for the RESET button..

Pics to follow, but the mod DOES work - and now i can step the sequencer from a gate (or rimshot on the TR909) and reset the sequence to the start (or cut off long notes) with the RESET trigger in.

The Picture (below) is from the Doepfer website, and shows how to make a lead with an s-trigger output from a GATE input. I found this would not work, and needed a resistance (6.63k) on the shield of the lead (the common) to get it in any way predictable.

Converting Gate to Switched Trigger (S-Trigger)

In some devices only gate outputs are available (e.g. Doepfer MAQ16/3, Schaltwerk, Regelwerk, MCV24). This means that a positive voltage (e.g. +5V or +8V) is used to trigger the device controlled by the gate output. Some devices (especially Moog synthesizers) require instead of this a so-called switched trigger or S-trigger. This means that a short circuit (connection to GND) is used to trigger the unit (example: a foot switch making a short circuit when actuated).

A simple electronic circuit made of a 10k resistor and a standard npn transistor is used to convert a gate signal to S-trigger. The sketch below shows this circuit. The resistor and transistor can be built e.g. into the case of the 1/4" jack. If you have problems to assemble yourself the cable described above please ask your local dealer. We offer such a special cable at a price of about Euro 20.00 - 25.00 (depends upon cable length and connector type). Please specify if you need a 3.5 mm or 1/4" jack on the input side and the length of the cable. E.g. for A-100, MAQ16/3, Schaltwerk, Regelwerk or MCV24 outputs 3.5mm jacks are used. For other applications a 1/4" jack on both sides may be required.

I adopted this design for the little board i made for the inside of the VL1..

[playthatbeat]

Here's a picture of the Layout of the Gate to S-trigger circuit on a breadboard.. The Input (from a gate) is the orange & white, the output (s-trig to the tap points in the VL1) is on the green & white..

You can of coarse, just run wires from the tap points on the CPU (see picture for pins) to a Jack-socket, and then use and EXTERNAL convertor - built into a wire (see picture 2 attached) or from a proper midi-CV box that supports Positive S-trigger, but i wanted to be able to use the TRIG out from my equipment with no fuc*ing about, so i made 2 and hid them inside the case..

The pins on the cpu are tapped like this:

OKP (advance the sequencer): Pins 5 & either 13 or 11
RESET (kill note & restart sequence): Pins 10 & 16

If you were to just attach wires to these points, and touch them together, you would get the same effect as pressing the buttons on the machine itself - er, yeh, so that makes sense innit..

You can try soldering wires to the pins, or scraping off some of the coating on the tracks below the pins, but fuc* that, just follow the tracks from the pins until You find a nice easy place to attach a wire.. Trying to tap onto the chip itself or it's legs is a stupid idea - best scratch into the track somewhere further down the line a bit. I'll add pics of where i tapped later..