Internal Voltage Divider Done - now get 1V/Oct

Here's a solution to get 1V/Oct - I just used a trimmer as a variable voltage divider to replace the external test V-divider I made before. I'm still tuning it right now, and the sweet spot drives the octave range up two full octaves (So note C3 = C5).

More spaghetti!

So (for novices like myself) I took CV in to pin 1 (could have gone to pin 3, opposite operation), the line the R7-south off pin 2 (the wiper) and a wire to ground from pin 3 (could have used pin 1, opposite operation).

Still, could have saved all the trouble with Silent Way!

Febuary 6th 2011 - Additional Info:

Here's the basic circuit for the voltage divider:

Instead of using two resistors for a fixed voltage divider, a single trim pot replaces both.

Then terminal 1 (or terminal 3) is equivalent to the Vin connection above. This will be the CV input.

Then terminal 3 (or terminal 1) goes to ground.

Then terminal 2 on the potentiometer (trim pot), which is the "wiper" terminal, is Vout above. This will go to south side of R7 if you did Din Sync's mod for CV input.

The interchanging of terminals 1 and 3 does not matter; the direction of operation will just be opposite for either choice - resulting in Clockwise (CW) operation or Counter-CW operation.

This circuit is based on the ratio of Z1 and Z2 (or R1 and R2 for resistors). Because of this, using two 10k resistors is identical to using two 100k or two 1M resistors, according to the following equation:



Vout = [R2/(R1+R2)]Vin

For the list of values above you will always get that Vout = (0.5)Vin.

With a trim pot you can "tune-in" the right ratio to get Gakken on 1V/Oct.

Note that this is the simplest case. To get proper V-division, you would have to know about the impedences of the circuitry connected to it.

Gakken Mods: Basic-Basic Demo

This track is proper pants!
The demo is ultra basic to show the mods on the Gakken.
This shows the LFO ramp and saw-down waveforms applied to the pitch, filter, and pulse width modulation (PWM). There's also a demonstration of the high pass filter (not so good), the keyboard tracking knob (depth), and some resonance. Near the end I have a bit of fun with resonance and I switch the decay envelope on - its off for most of the track.
This demo only has some basic drums and the modified Gakken.
I added the points of change as comments on the player, but here's a list anyway:
0m00s: Sawtooth (original wave)
0m14s: Square wave (modification)
0m28s: Saw
0m42s: Square
0m52s: bring in triangle LFO
1m10s: Saw up LFO or Ramp (Modification)
1m17s: back to Triangle LFO
1m24s: Saw down LFO (Modification)
1m31s: Triangle LFO
1m38s: Saw down LFO, increase rate
1m55s: slow down rate
2m02s: sweep in LFO to Filter depth (Modification)
2m13s: increase rate
2m27s: increase PWM
2m42s: modulate PWM from LFO
3m02s: "tune-in" modulation via rate
3m16s: change some notes for some detuning effects
4m00s: high pass filter sweep (modification)
4m12s: switch off HPF
4m29s: deepen keyboard tracking depth (Modification)
4m54s: ...bored now...
5m08s: Some resonance fun
5m36s: Switch decay envelope back on (Modification off)

Gakken Demo: SquareWave LFOs PWM HPF KybdTrk by MickeyBoyeeee

Clip of Squarewave/PWM sounds

This clip is mostly Gakken sounds. The drums, pads, and sawtooth in the breakdown are not from the Gakken, but the main Bassline and the whirly sounds are from the Gakken. The sound effects have some delay, and the Bassline has only gating and compression. This clip has no sub-bass, and as in the header, this is the square wave mod with PWM and LFO to filter and pitch.
Mighty Gakken - clip by MickeyBoyeeee

Modified Gakken SX-150

Here's the result of several hacks and mods for the Gakken SX-150:

Top View

Power, CV in, Gate in and envelope trigger switch

External LFO input jack, internal/external LFO switch, high pass filter kill switch, and pitch envelope kill switch

Guts,... rough job, ey?!?!

The LFO input and outputs, along with pitch envelope disable switch, CV in, and resonance feedback knob were found here:

http://www.dinsync.info/2010/06/gakken-sx-150-modifications.html

This is one of the best blogs I've seen.

The LFO to filter switch and envelope trigger switch were found here:

http://www.flickr.com/photos/matt_the_modulator/3375768994/

I later chaged the LFO to filter switch tap points in order to install a separate LFO-VCF depth knob, since I wanted it to be independent of the LFO-VCO depth (see below). Instead of tapping right to the filter knob I went to the north side of R33. I kept the switch as a LFO-VCF disable switch. This works very well. If you want a more squibbly and unstable sound, you can go off of the south side of this resistor (or north of R32 - same thing).

The envelope trigger switch is an (on)-off-on type, as I found some wierd sounds with trigger held on. Well, what really happened was I soldered for too long with an (on)-off switch and melted something inside! Then I found it useful to install said type.

The Square wave with Pulse Width Modulation, LFO saw-up and saw-down wave shapes and selector switch, LFO depth (to VCO, or rather pitch), and decay kill switch were from this dude:

http://userdisk.webry.biglobe.ne.jp/000/024/65/N000/000/000/SX150_Mod7.PNG

This schematic is pretty awesome. I did try the temperature compensation, but couldn't get it to work. And I tried the filter on the carbon panel section, and that also did not work. I think I was using the wrong Schottkey diodes (over-rated). Because of these trials, I had to replace a few of the resistors (as they're SMD), so that's why there's a few extra wires inside...

Anyway, I added a PWM master switch, as this circuit still affected the original sawtooth wave - which is cool, but the original wave is so fat that I wanted the option. The kill switch is DPDT, in order to kill the 5V feed and 2.5V reference connections, thus killing the LED too. I'd recommend this mod to anyone seeking a cheap and very fat square wave/PWM sound. This really does "smash it proper!"

The LFO depth pot was used to control all LFO effects - to VCF and VCO - and it also controls the input LFO (total fluke), which is nice. I later added a separate LFO-VCF knob (see above) which also controls the input LFO to VCF (again, a total fluke!). The decay kill is nice, but the synth will hold the pitch at the position determined by the pitch env depth - again this is pretty cool - and if you disable the pitch envelope, it just holds the filter envelope open.

Though my favourite mod from Hoshu is the square wave/PWM, the Saw Up/Saw Down LFO wave shapes is a close second. This is very easy to do, and only requires a few parts. You could even let them float, although I did install them on a tiny piece of PCB. What makes these really cool is actually a consequence of them being a bit rough. I'll explain: These wave shapes actually oscillate at a highr rate (faster) then the origunal waves, so you can actually tune in some serious ring modulation/FM effects. Furthermore, these shapes also get sent to the PWM section, so you can imagine the possibilities...

I will probably put a bigger knob in for the LFO rate, as I heard that you can really slow the rate down (one meg VR, apparantly), which will be nice for the extra wavesahpes, as they have higher rates, right?! I'll try this and post results.

The VCF tracking switch is nice too, can't remember where I got this??!! Anyway, I added a knob to adjust this, so you can tune it in a bit better. I just installed a 100k pot in parallel with a large resistor (and through a kill switch) between R31 west and R5 south. I also put a resistor in line so that a minimum VCF tracking cannot overcome a threshold - I did not want to get a dead short for obvious reasons. This actually ended up being really good for filter tweaks, since the original filter knob is a bit cheesy.

The high pass filter was an accidental outcome from mucking around, touching a resistor to different points - fun!  I installed a 10k pot to ground and the east side of R40. I could only get this to work with a logarithmic (audio tapered) pot, as the signal gets a bit 'quantized' (steppy) as you reduce this. Also, I had to install it reverse operation; that is, it works as a high pass filter counterclockwise, instead of clockwise - a bit counter intuitive. I added a kill switch here also, as there was a tiny bit of leakage with 10k pot. A bigger pot would do too. This is by no means a real HPF, but it does the trick - especially for tuning in some sounds with PWM on either the square wave or the saw wave. Not so great for real-time tweaks, especially since it doesn't have its "own" resonance feedback control (suggestions?).

This whole process started with DinSync's blog (above link), where he posted a great vid displaying how fat this machine can sound. I will be adding some sounds of the Gakken in the near future.

January 25th 2011: Pic's for Anonymous hacker:



LFO to Filter attached to North side of R33
(See pointer - East of R39)



LFO Mod - See two diodes on mini PCB

Hope this helps, Mick