Tuesday, December 7, 2010

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

Sunday, December 5, 2010

Gakken-based 6V (transistor) Filter

Here's a cheap and Lo-Fi filter I made in about 6 hours. That includes picking up parts too. I still need a knob for the gain pot.

I got the schematics from here:


As you can see (if you've looked at the Gakken schematic), this is almost identical to the Gakken filter section, with a few resistor sizes altered and different routing for input through that 100k resistor - I experimented reversing the CV and filter inputs, as the Gakken has the filter pot going through the 100k resistor instead of CV, but it worked less well.
This is a proper lo-fi filter, so your not going to get all those big juicy filter sweeps with it. And, unless I wired something wrong in mine, you'll lose the signal (in slightly different ways) at high and low gain settings. It sounds like a bit crusher or decimator effect - which is cool.
You can adjust the input levels along with the gain trimmer to tune in certain sounds. In fact, I found that this can fatten dry character-less sounds quite a bit.
The way I've been using it is somewhere between distortion and tape saturation, but without the hiss. You will get the characteristic 'droning' sound identical to the Gakken SX-150 (so that must also be the source of the drone in that unit too!!!), especially when there's no sound running through it. So gating is in order. But I've made bass-sounds, etc, sound much hotter and oversaturated, and I've run some drums through it - to get that fat borderline-distorted 1997-2000 drum sound.
Will put up sounds later.

Friday, December 3, 2010

Modified Korg Monotron

Here's my modified Korg Monotron:

As you can see, I removed the speaker and made an enclosure from an old minidisk adapter (kept the Sony logo) with the 'stop' button from a minidisk remote, and super-glued it all together. I probably won't do it this way again, since its pretty tight in that box for the 3 jacks, the keyboard tracking switch and the trim pot (which you can see in the front). All the required resistors are "floating" inside. I did use some heat shrink to wrap 'em up. These mods are exactly as shown here:

This is well worth the work to get some CV and Gate in there.

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

Thursday, December 2, 2010

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:

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

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

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:

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