Gakken SX-150

Matt the Modulator · March 22, 2009, 03:29:59 PM

Just modified a Gakken sx-150 anlog synth. Its possible to make the filter self oscilate and use the LFO to modulate the filter cut off point. the input is a frequency to voltage (high pitch = higher voltage) which can be tapped as a seperate output so a theremin or any synth can be used for volatge controll. theres probably a lot more but i gave up. click on the pick to goto my Flickr page were i have lableled the bend points and Enjoy

<a href="http://www.flickr.com/photos/matt_the_modulator/3375768994/in/pool-40324274@N00">

Bendables · March 22, 2009, 09:49:00 PM

I want one!

Matt the Modulator · March 23, 2009, 09:38:48 AM

they are getting exspensive now some are advertised on ebay for £60! i paid around £35 inculuding postage form japan. The schematic is here http://www.flickr.com/photos/matt_the_modulator/3369071990/sizes/l/in/set-72157609013413720/ looking at your webpage i think you have the parts

Gordonjcp · April 04, 2009, 10:49:49 AM

That's a really *horrible* filter design. I bet that is really properly crappy and distorted.

Hmm, I feel a bit of breadboarding coming on...

Matt the Modulator · April 04, 2009, 11:24:26 AM

Quote from: Gordonjcp on April 04, 2009, 10:49:49 AM
That's a really *horrible* filter design. I bet that is really properly crappy and distorted.

Hmm, I feel a bit of breadboarding coming on...

yeh its simple lo-fi filter but it does have quite a dramatic low pass cut of effect. i have bread-boarded and used a 9v supply, i found i had to change the resistor that feeds an inicial voltage to the base of the transitors (for less voltage i think). The output op-amp stage can be turned into a orverdrive clipper (1meg pot) well it allready is ! i cant remember what changes i made i decided to make the low pass filter by tim escobedo instead much better. let me know if find a good hack of the circuit.

Gordonjcp · April 05, 2009, 10:00:51 AM

One interesting thing is that the voltage applied to the bases of Q4 and Q5 control the current through them, and therefore the cutoff, but the voltage on the emitter (from the VCO) will *also* change Q4's conditions. So you'll get the cutoff modulated a bit by the VCO, rather like the filters in early MS20s and the like.

The big advantage of the Moog ladder design was that the control voltage and input voltage balanced, so the input signal didn't "pull" the cutoff.

Matt the Modulator · September 06, 2009, 03:57:39 PM

ive had a play about with the gaken SX-150 filter circuit and have found a rather usefull CV controlled low pass filter that runs on 6v

great for putting in Hing-hon ek-001 and all other 6v keyboard's casio SA series

anyway here's my tested and working schematic
http://www.flickr.com/photos/matt_the_modulator/3890263959/#

Tyler1144 · September 20, 2009, 06:54:53 PM

I saw a vid of one of those on youtube hooked upto a sony "my first sony" or something. it sounded pretty cool lol. Was it yours matt?

Matt the Modulator · September 21, 2009, 09:38:19 PM

Quote from: Tyler1144 on September 20, 2009, 06:54:53 PM
I saw a vid of one of those on youtube hooked upto a sony "my first sony" or something. it sounded pretty cool lol. Was it yours matt?

Nah Not mine iam waiting for PC conector for my camera then ile put some stuff up hopefully

jamiewoody · September 16, 2011, 10:52:07 PM

i got mine! ;-)

i opened the box, that is it so far. i found a magazine with nice photos, and fun to look at, even if i cannot read it!
the 'zine apperently contains nearly the whole history of the synthesizer, and almost EVERY commercial synth version! nice, framable photos of keith emerson, and other artist...articles on bob moog, devo....innovators and artists. i'll bet the magazine cost more to produce than the synth did! lol!

something which impressed upon me was a high quality printout of the pcb...as if they WANT people to copy the board and build one of these from "scratch"! ;-)

anyhow, i am PSYCHED to say the least! ;-) i may use the same keyset i am using for my stylophone keyboard. do you think i can get 3 octaves out of this thing?

i'll post my findings...

jamiewoody · October 13, 2011, 10:51:53 PM

matt the mod, did you ever take the images of your mod on this? i want to bend mine, but i thought i'd look at some examples first.

i think i'd like to get that midi kit from beatbik for both this and my monotron.

also, something i discovered...there are lots of sweetspots, just poking the stylus at the circuit board in different spots! ;-)

Matt the Modulator · October 21, 2011, 06:55:01 PM

i posted these notes up on flickR
http://www.flickr.com/photos/matt_the_modulator/3375768994/#
hope you find them usefull

there are loads bends points and different ways to bend these beasties great fun

jamiewoody · September 16, 2012, 06:30:51 PM

i might try these bends.

funny, on the box, there is a print of the circuit board pattern, like they want people to copy the boards!

personally, i think my sx-150 is lame, and i don't see what the fuss is all about. it sounds weak. also, the filter input jack does not seem to work.