From haines@cloverleaf.comThu Jun 22 15:03:12 1995 Date: Thu, 1 Jun 1995 20:22:46 -0800 From: Matt Haines To: analogue@hyperreal.com Subject: CS-5 mods (long) Can someone please archive this for me? Thanks. Modifications to the Yamaha CS-5 included in this document: - add control-voltage input for filter cutoff control - add control-voltage input for resonance control - add gate/control-voltage input for VCA Tools needed (individual electronic parts listed below): - soldering iron - solder - phillps-head screw driver (for opening the unit) - drill with metal-drillbit (for installing jacks) - needlenose pliers WARNING AND DISCLAIMER: THE CREATOR OF THESE DOC'S ASSUMES NO RESPONSIBILITY FOR THE SUITABILITY OR ACCURACY OF THE INSTRUCTIONS LISTED BELOW. TO TEST THE MODIFICATIONS, IT INVOLVES POWERING UP THE UNIT. WHILE RELATIVELY SAFE AS MODIFICATIONS GO, IF YOU'RE A BONEHEAD THEN DON'T DO ANY OF THESE MOD'S. IF YOU ELECTRICUTE YOURSELF TO DEATH, DON'T COME CRYING TO ME. AND DON'T STICK YOUR FINGER IN THE POWER SUPPLY. (phew!) To take unit apart: Remove both end-panels. Remove three phillips screws on back along the bottom. Top half of the synth (the bit with the knobs) will now rotate backwards to expose the innards. The following removes the righthand PC board, containing the circuitry for the VCF, VCA and EG. It's conceivable that you could solder the wires in place without removing the board. However I don't recommend it, and removal and installation are relatively simple. Disconnect the power-on LED leads that attach to the righthand circuit board (as you look into the unit, at the circuit side of the PC board). They attach to the board in the upper-righthand corner and the attach-points are marked "BL" and "RE". It is not necessary to use a desoldering device as the wires are only surface-mounted and come away easily when solder is heated. Remove all knobs pertinent to the PC board, i.e. the VCF, VCA and EG-related knobs. Remove the (not sure what you call these) screw-on washer-type things that keep the pots attached to the front panel. These are on the front of the unit and can be removed with a needlenose pliers. The board should now be loose but attached with various wires. There are three connectors attached to the unit that need to be removed: C8, C9 (both on the left edge) and C10 (in the VCA section). C10 is a bit difficult to remove but if you flip it over you can pry up the lip of the connector and it comes away easily. The board can now be removed to work with. CONTROL-VOLTAGE EXTERNAL INPUT FOR FILTER CUTOFF parts needed: - 1/8" minijack (1/4" will work too, but the former is easier to drill and matches with Kenton MIDI/cv interfaces, and also some other synths). - 33k resistor - about 1 foot of wire Solder the resistor to the tip (hot) connector of the 1/8" jack. Solder the wire to the other end of the resistor. Provide appropriate strain-relief with electrical tape. The other end of the wire is attached to the PC board. Make sure the exposed wire on that end is quite short, say 1/8" long. Pre-solder the end liberally. The extra solder means you won't need three hands when holding the soldering gun and the wire, as no extra solder is needed. The point being soldered to is on the circuit side of the PC board (the green side without all the knobs and parts). In the lower lefthand corner you'll see a vertical line printed on the board, with a circle in the middle. To the right of that is another vertical line with no circle. The solder point at the top of that line is where the wire is to be attached. Apply a little extra solder to this point, and then solder the end of the wire to the point. This adds an extra input to the VCF, in parallel with the VCF-mod, VCF-EG and initial filter cutoff pots. Make sure the join is securely attached. You might want to check for continuity at this point with a multimeter. Tape down the wire to the side of the board for strain relief. Test the jack with your cv source to make sure it controls the filter. Turn the EG depth and modulation knobs down, and also the cutoff frequency knob (most of the way). Turn up the Initial Level knob in the VCA section for a continuous sound. Then apply a varying cv to the input and marvel at the magic of electricity. Drill a hole in the back of the synth at your favorite location. For 1/8" jacks you'll probably need a 3/16" hole. Install the jack and you're done. CONTROL-VOLTAGE EXTERNAL INPUT FOR RESONANCE Note that this external control with LOWER the resonance as more voltage is applied. So for playing purposes you'd most likely crank the front-panel reosnance knob to full, and then use cv to lower it the necessary amount. Maybe it's possible to have it work the other way around but I couldn't figure it out. parts needed: - 1/8" minijack - 22k resistor - about 1 foot of wire This is very similar to the filter-cutoff mod. Repeat all steps, substituting the 22k resistor for the one above. The point to attach is thus: in the lower left corner, there are vertical lines looking like this... | | | | | | | | O | | | [ IC5 ] | | | | | | | | | | | | O | | | ^ this is where the resonance control is attached, which is the | | 5th vertical line over from the lower left corner. Or second one to the left of IC5. ^ (this is where you attached the filter-cutoff control) To test, turn the resonance up full and the filter frequency to about 10 o'clock. The effect is a bit subtle but it's there. GATE/CONTROL-VOLTAGE EXTERNAL INPUT TO VCA The thing that bugged me about the CS-5 was that it only had one envelope generator, and it was required to control the VCA as well. Many other one-EG synths have the option of using a simple gate on/off to control the VCA. Not so the CS-5. My initial plan was to allow the user to toggle between EG- and gate-control, using either the internal or external trigger as a gate. Alas, this was not to be. Instead, it works like this. Be advised that this isn't practical for everyone. If you've got a Kenton Pro-2 or Pro-4, you're all set. The CS-5 and CS-15 use a retarded gate (i.e. trigger) system wherein the note-ons are negative voltages, and the note-offs are positive. This is reversed from most synths. Luckily, an s-trigger will work here (I *think* that's ok for the synth). Since the Kenton MIDI/cv converters output voltage-trigger and s-trigger at the same time, you can connect the s-trigger to the normal input of the CS-5, and the voltage-trigger to the new input you're about to build. This can also be a variable control voltage inputted, but since this will act like the Initial Level knob, that has limited usefullness. It won't act like a volume control where the notes turn on off but get louder or softer when they're on. Rather they'll always be on (but at different levels) unless the cv inputted is 0. Parts needed: - 1/8" minijack - 100k resistor - about 1 foot of wire - 1-uF capacitor (for eliminating the click of the gate on/off) Solder the resistor to the tip (hot) connector of the 1/8" jack. Solder the capacitor to the ring (ground) connector of the 1/8" jack. Twist the two free ends together and with one end of the wire, then solder. Apply strain relief. It should look like this: input for 1/8" jack _______ _| |_ | | ------------- | |_| |_| contact for--> | ^ ^ tip of cable \_/ | | | | _ _ capacitor connected | | | | resistor connected top end to hot (tip) top end to ground |_| |_| | | \ / ^ bottom end of capacitor and resistor connected | to wire. | The capacitor shorts high-frequency AC signals to ground (in this case, the gate attack and decay), thus smoothing out the DC that continues on into your synth. (No apologies for that decidedly unprofessional description!) Provide appropriate strain-relief with electrical tape. The other end of the wire is attached to the PC board. Make sure the exposed wire on that end is quite short, say 1/8" long. Pre-solder the end liberally. The extra solder means you won't need three hands when holding the soldering gun and the wire, as no extra solder is needed. The point being soldered to is on the circuit side of the PC board (the green side without all the knobs and parts). At the bottom of the section marked "VCA" is "IC6". Below is a single line of solder points.below that are four vertical printed lines, leading almost to the bottom edge of the board. The point to connect to is the top point of the line second from the right (which corresponds to pin 2 of the chip, but we're soldering to point just below where pin 2 enters the PC board, and is connected to pin 2). Make sure the join is securely attached. You might want to check for continuity at this point with a multimeter. Tape down the wire to the side of the board for strain relief. Test the jack with your cv source to make sure it controls the VCA. Warning: the ground of the jack must be connected to the ground of the synth for proper functioning. You can test by sending the voltage gate or cv to the jack, but you will hear extraneous noise most likely. Once the jack is secured in the chassis of the synth, this will not be a problem. As a temporary test, run an alligator-clip lead from the ground connector of the jack to the synth ground. My personal favorite would be to connect it to the reverse side (i.e. with the resistors, capacitors, pots and pans and such). Find the VCA EG Depth pot, which is on the left when reading the writing the PROPER WAY UP. Connect the clip to the right of the three posts at the top (assuming you've got it around the proper way). That's a ground, and the hi-freq buzzing should go away. Drill a hole in the back of the synth at your favorite location. For 1/8" jacks you'll probably need a 3/16" hole. Install the jack and you're done. You're done! Don't forget to resolder the power LED leads back in place, and also connect the three connectors back. Also, there are washer-type things that go on the pot-stems UNDER the front panel...make sure you haven't lost any. Any questions, contact Matt Haines at haines@cloverleaf.com and I'll attempt with my limited knowledge to answer questions. Matt Haines haines@cloverleaf.com \co/ntrol-X \to /\abort / \transmission.