Gakken sx-150

widdly · Posted: Sun Aug 31, 2008 6:32 pm Post subject: Gakken sx-150

Someone posted this schematic on the sdiy mailing list. Looks like a nice simple project.

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andrewF · Posted: Mon Sep 01, 2008 2:43 am Post subject:

Its from Houshu - master of cmos!
The Gakkens filter looks very like the early Korg MS20 filter

Joel · Joined: Sep 12, 2006 Posts: 97 Location: London, UK

alternative link (the first linked pic wasn't showing up for me)

Looks cool!

andrewF · Posted: Mon Sep 01, 2008 3:34 am Post subject:

Houshu has also developed a pitch quantizer for it Surprised

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richardc64 · Posted: Mon Sep 01, 2008 6:34 am Post subject:

The VCO looks interesting, too. I wonder how good it is or can be made to be.

loss1234 · Posted: Mon Sep 01, 2008 9:37 am Post subject:

where is the pitch quantizer??

synthmonger · Posted: Mon Sep 01, 2008 2:27 pm Post subject:

top left F/V portion.

What voltage is the frequency converted to?

andrewF · Posted: Mon Sep 01, 2008 4:36 pm Post subject:

synthmonger · Posted: Tue Sep 02, 2008 1:02 am Post subject:

oh boo thats an EF not something like hz/v. mehmehmmeh

endif · Joined: Jul 14, 2006 Posts: 138 Location: Reno, NV

Still waiting for mine to come in the mail from Japan. =P

valis

Greetings,
First time, long time. Anyway, I've been trying to learn more about modding synths and I figured the SX-150 would be a good place to develop such skills further. I've done circuit bending, some simple mods, and a couple Ray Wilson projects but I could use some help.

I've been looking over the schematic and trying to learn how to read one at the same time so I have some serious knowledge gaps.

Anyway, I have two goals that I'd love some input on.

1. I'd like to run an audio signal through the VCF . There was some info located on the AH mailing list where the gentleman was talking about cutting the trace from C16 and reconnecting it through a resistor to the positive side of C6. I don't quite see how this would work via how I'm reading the schematic so I'd love some input (and perhaps some other users would too) on how to to a VCF-In mod on the SX-150.

2. I would also love to have a potentiometer control the resonance (instead of the switch). I'm also not quite sure how of the best way to do this.

Thanks for reading this! Sorry about my noob factor. Thanks!

Here's a link to the schematic:

http://matrixsynth.blogspot.com/2008/08/gakken-sx-150-schematic.html

Uncle Krunkus · Posted: Wed Sep 17, 2008 3:06 pm Post subject:

If it were me I'd bring an external signal into the junction of R29/R30/Q4 after going through another 4u7 and 2K2 combination. Well that's where I'd start anyway.
As for the resonance pot, the switch simply swaps between either end of a virtual pot the way it is now, so just try a 10K pot with the wiper connected to R39 and the two ends connected across where the 10K was.

valis · Posted: Wed Sep 17, 2008 8:31 pm Post subject: Thanks!

Thanks for taking the time to reply! I'll probably give your suggestions a try by the end of the weekend and report back..

Scott Stites · Posted: Fri Sep 19, 2008 1:09 pm Post subject:

Seems to me that would shunt the output signal to ground on one end of the pot. One end would be filter at resonance, the other end would be -----.....

Scott Stites · Posted: Fri Sep 19, 2008 1:10 pm Post subject:

Oh, no it wouldn't....nevermind.......

akrearke · Joined: Sep 08, 2008 Posts: 53 Location: US

I two young family members who love to play on my synths and these would be a good way to get them started in synthesis early in life. I think I'll build a couple clones . now what I'd like to know is what is a NJN2902. i would think a TL084 would work as well as gen. purpose trannies. Is this a wild assumption?

Uncle Krunkus · Posted: Mon Oct 13, 2008 3:39 pm Post subject:

The only thing I'd check is whether it's a JFET op-amp or not, this could change things a bit.

valis · Posted: Mon Oct 13, 2008 8:22 pm Post subject:

Sorry, I got some Ray Wilson projects and I haven't gotten around to modding the Gakken..

richardc64 · Posted: Tue Oct 14, 2008 5:24 am Post subject:

Haven't found info for NJN**** but, asssuming it's the same part, the NJM2902 is a quad single supply op amp. From the looks of the circuit, an LM324 should work. G.P. transistors should be fine as well.

akrearke · Joined: Sep 08, 2008 Posts: 53 Location: US

Thanks for being so helpful. i have dabbled in electronic for many years, and still learn something new everyday! I want to gives you guys a heads up, on this I am currently building a Touch Keyboard, much like the Buchla 218, I found the documentation of the japanese clone on an EM forum, and began working on a 25 note version with the VC portamento included. The only thing left is the enclosure. I will keeps everyone up to date for who ever is interested. I am thinking about trying to sell them. I would also like those interested to keep in mind that all the boards, of which there are 8, are all hand made. also i have completed the layout for a 25 note vesrion of the Touch Keyboard and Programmer found in the Synapse article. if there is anyone interested in that
Cheers to everyone!

v-un-v · Posted: Sun Feb 01, 2009 6:37 am Post subject:

You guys may like to know that I've now got three of these little beauties Cool

Two made up and one still in its box (for a pressie to someone- don't know yet!). The first one I got on eBay, and gave it to my littlest daughter, then my friend Richard, who lives in Japan sent 2 more. One I hope to mod (and I prey it doesn't end up on the stupid todo list that I still had 6 months back)

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Uncle Krunkus · Posted: Sun Feb 01, 2009 2:52 pm Post subject:

Cool,
Nice to hear from you Tom. Very Happy

reve · Joined: Feb 23, 2008 Posts: 149 Location: USA

Does anyone have a working CV/Gate mod for this fella yet? I saw this:

http://www.denhaku.com/sx150mod.jpg

... and I can get pitch to _track_ -- but not to scale.

Putting my ears and a meter together, it seems like the gakken runs on about 1/3v per octave. At least from the stylus input. Is that what you guys have come up with? Anyone come up with a clever way to run this off straight 1v/oct CV?

Kenneth · Joined: Apr 16, 2009 Posts: 43 Location: Stockholm, Sweden

http://gaje.jp/sx150e/sx150_schematic.pdf

I got one of these, real fun for almost no money (I paid $38 + shipping on ebay). This will be my way into synth DIY (I hope =)

Here is a short demo I made today:

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

For collectors, it seems there is an early version that has got a green sliding board instead of the brown one.

BTW, the F-V converter, how does that function, do I put a freqency into it to control the pitch? (I tried to use a DX-7 audio out into it but nothing happend)

reve · Joined: Feb 23, 2008 Posts: 149 Location: USA