Gakken sx-150

[Kenneth]

I tried the F-V converter some more, it seems the amplitude has got more to do with it than the pich. I fed it with a fixed frequency sinus (440 Hz), nothing happen until I raised the volume, the higer I turned it up the higer the pich of the GAKKEN becamed, I could use the volume knob of my source to tune the GAKKEN. I tried a diffrent frequency for the sinus, same thing happend but it was responding diffrently to the volume. The higer the pitch of the sinus, the easier the GAKKEN responds.

It does not even have to be a clear wave, I also fed it with white noise and the same reaction occured.

An easy sequencer would be like use any sound for source and vary the output volume. (sequncer that controls a VCA that controls the volume of the source sound).

[Kenneth]

When talking about sequencers:

Here
Specially here

I'm trying to learn some basics first, then I will start to collect parts for building one of those ("SQ-150").

Here is a demo from the tube of the two together

(the SX he's using has got a square wave mod so it is not only the sequencer, and of course the effects, but it's great anyway)

[reve]

[Kenneth]

OK, thank's, I try a square next time

Yea, I know, it is CV/gate and yes, wery cool and intresting project for a begginer like me

[Kenneth]

I think I got it now, the F-V input is digital, you feed it with a series of on/off like this: 10101010.... = a serial digital stream and depending on the BAUD rate you get diffrent voltages out!

[Kenneth]

I just made my first mod to my GAKKEN, a very simple one, no soldering or anything complicated, just a simple wire job

What I did was to put a jack to the resonace switch so I can connect a pot to it that gives me control over the amount

I have to get a better pot though, this one is far too large = 470K Ohms so it only gives me about 5-10 degrees of action but for this test it works.

EDIT: this leads me to a futher qestion, this is probably complicated but what do I need to control the amount of resonance using let's say a LFO?

Or, how is a automated potentiometer constructed, ("VCR"? (voltage controled resistor))

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Description:	A; the underside of the resonance switch B; a mono jack C; end of wires of the jack D; wires wired to the legs of the switch E; Ready to rock!
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[NerveJam]

[Kenneth]

I'm planning to do this:

Take any keyboard from a toy that has got a one, like these (BTW, dig the sequencer =) Normaly they got batterys so there is voltage on board, take that and put a switch for it under each of the keys so the key toggles voltage on/off and followed by that a pot that you can use to set the pitch for the key. A sequence of resistors or a restor for each key makes it simpler but you won't get perfect harmony from that, pots is the way to go (not wery cheap but there are some brands less than a dollar a piece, for 2 octaves this makes around $20, the switches you can get for free or really cheap from used or old elecrtonics, like telephone keyboards and such).

Now, if you connect a line with no current to the GAKKEN, + to the top of the stylus and - to ground and then put a current on = switch, any voltage between 0> and +5 then the GAKKEN will automaticly generate a trig signal!! The voltage is CV strait!

So there is no need to make modifications to the synth, you can connect and deconnect the keyboard at any time. Currently I have a bicycle rear ligth LED blinker, GAKKEN ground to battery connector and the stylus to one of the legs of the diode. I blinks in about 160 BPM and the voltage is pretty low = low feqency, with a bit of pich envelope, short AD and low filter setting I got a 808 kick/tom drum comming out from the synth

[v-un-v]

[Kenneth]

Here is a vid of my LED blinker trigger

http://www.youtube.com/watch?v=quhclEU7Khc

The blinker makes a bit of noise

The signal is both trig and pitch.

So now I'm considering taking the printer port, it has got 8 separate lines, put a pot on each of them and I can play 8 diffrent notes just by outputting one bit at the time, a 8 step sequencer with variable gate time.

BTW; the easiest way to do this is to turn your GAKKEN upside down, put the tip of the stylus to where the square from the LFO goes into the LFO switch, use speed knob for tempo

Problem is that it is 5V = high pitch, it will go ping ping ping... if you don't put a resistor or a pot on the line, a 1 meg pot gives full range.

[NerveJam]

I'd be more interested in adding a keyboard.
I have a couple of dead VL-1s kicking about.. (and an Excel-O-tone..)
How wide is the bit between the speaker and the rhs of the stylus track?

[Kenneth]

Around 10 cm, but you can also ommit the speaker, then you got near 15 cm.

But... this is related to the LED blinker, it shows how you can use a keyboard with 1v/oct, just connect to gnd and the tip of the stylus and go ahead, that's it! (hopefully your keyboard cuts the connection when no key is pressed, else you have to solve the trig somehowe, like use the keyboard gate out to turn the CV on/off)

Someone said the GAKKEN does not use 1v/oct but I think it does, maybe the confusion comes from the fact that the topmost position of the track does not give the higest pitch possible, you can still add full pitch envelop on top of it. I think it is about 1/3 missing, it can also go lower than on the track but not much...

BTW: I have built myself a GAKKENIZER, will post a pic soon...

[Kenneth]

It is a astable using two 470u caps (from old telephones), two 546B transistors (old light organ), one 20k slider pot for PW (telephone bell volume) one 10k pot (to small, will change) for speed (bend arm of a broken guitar hero guitar), one red and one yellow LED (computer on and HD LED's). The output I take from both sides of the PW slider and I got a switch (computer turbo on/off) to choose any, the switch also breaks the connection in the middle so I get a retrig when switching, the switch is followed by a 200k pot (old VCR) that controls the end pitch a bit. "All" this is mounted on an upside down ice cream bucket, wires on the inside. To put the components there I have small metal pipes normally used for nylon fishing tackles, but I pinch one or two wires into one end and make a small hole in the buckets plastic and then push the other open end of the pipe so it goes out on the top side, two next to each other for diodes and caps, three for transistors, no soldering, you can switch to a diffrent cap (or whatever) in seconds. Power is a battery box 4*1.5 = 6V (bottom half of a telephone call logger) sitting next to the bucket

(No, I don't have any diode protection resistors (470 or so), it is only 6V so it is not a problem I think)

OK, is this on the lower end of synth DIY or what?

The sound?, Well it alters hi/low pitch, if I take the output from the side where the slider is then I get short high and long low, then I switch and get short low and long high instead, about 1-2 keys difference but it depends on the PW slider, in the middle it is only one pitch. The PW also controls the length of the two halfs (it also changes the speed, in the middle it runs fast, slower near ends and at the most ends of the slider it stops, all is on one side. The speed is also dependent on if I take the output from A or B side depending on the total resistance is changing, wery unstable =)

Well, I took my LED blinker showed in a previous post and used it to feed more power to one half of the circut but in pulses, then I also used the internal LFO + pitch envelop of the GAKKEN, then I used that sound together with chords of my electone and it sounded like Beach boys singing choruses??!! (No, I don't think a reproduction is possible =)

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[Kenneth]

Daylight so now I can take better pictures than last night, here is another view of my GAKKENIZER where you can see the constrction better:

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[reve]

[loss1234]

can anyone tell me what kind of wave the vco of this beast puts out?

is it simply a square? or a triangle? or a saw?

thanks so much

[v-un-v]

It spits out a sawtooth. It's actually quite fat sounding, but pretty limited (on/off resonance anyone?)- which is a shame. Good value for the money though!

[reve]

[reve]

[p2b]

Hey reve,
I've had my Gakken 150 for a bit and really want to make the mod for midi (I'd actually be happy to just run it through usb). I've seen a few solutions the most detailed being:
http://mrbook.org/blog/2008/11/22/controlling-a-gakken-sx-150-synth-with-arduino/

and with actual midi port:
http://mrbook.org/blog/2009/06/27/sx-150-synth-mod-schematics/

Is this the mod you did? If not do you have any instructions I could follow?

I'm pretty much a noob and had some problems. Basically every little problem led me to more areas I didn't understand...(the circuit and Processing...damn even getting the midi network on my mac working is mysterious)
I really want to understand as much as possible not just build this by following directions. Mainly so I can learn something.

[reve]

[p2b]

Thanks for the quick reply. I'm going to see if I can do it though, it's a bit beyond my experience. I most likely will have to ask for your help along the way...We'll see.
Thanks again

[alienmeatsack]

I read about the Gakken SX-150 here, and thought I needed to see what the fuss was about.

Mine arrived last night. The packaging is large and confusing, the japanese does that to my brane.

Anyway, so my first impression... Man this thing is cheap cheap cheap. My first goal is to remove it from the case, replace the cheap pots and switches, and then do some bends.

I do dig the sound, and for the money, I don't know of anything that can affect inputed sound like this.

So, why is this thing such a big deal? To me it appears to be a really cheap synth. (Cardboard back, seriously?)

I'm not bashing, I just expected something else after reading so many people talk about it.

[reve]

[alienmeatsack]

Yeah, I do that a lot... It's kind of me thinking outloud. I do like your cereal box analogy. Only problem is, the cool magazine is Japanese so it's like I got the cereal but can't eat it, so I just get the prize.

I have plans to do a few things to mine... First off I want to put it into a decent case, replace the speaker and pots and switches.

Then, I am going to try and add the VC out, put a pot on the resonance switch, do the envelope trigger and LFO to filter cut off mod, add a slider pot to go along with the strip, and a keyboard mod.

I actually have a perfect case for it, the empty body of my failed Lil Tikes Keyboard bend. It has 8 working keys I can use for set pitches. Im hoping to run a primary pot to then control these so I can ptich them all up or down.

Going to be a fun little mod I think.