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Gakken SX 150 Mark 2 (mods)
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Gakken SX 150 Mark 2 (mods)

julien

Hi,

Can't find schematics for the Gakken SX 150 Mark 2 seriously, i just don't get it
Have you tried some mods on this synth? CV/gate input or anything else?

A+


galine

Hello,

I looking for shematics to for apply some mods on it.

From my side I connect my CV/gate to R15 & R44 it works but maybe it's not the better point for this.

I make a lot of try to sync 3 gakken (2 sx 150 an 1 mkII) and they didn't have the same octave value the gakken II seems 2 octave higer than the first edition.


galine

some pics of my goddzikken work in progress:

http://www.casimages.com/i/150124082210103597.jpg

http://www.casimages.com/i/150124082209223122.jpg

http://www.casimages.com/i/150124082208956075.jpg


heapish

I don't know the differences between 1 and 2 but
http://onlymission.blogspot.co.uk/2010/12/modified-gakken-sx-150.html? m=1


galine

heapish it's your job? if yes I will have some question for you ^^.


okelk

I just got a sx150 mark II and it seems to be quite different from the older model.
here's a picture of the circuit board:



It seems to have a transistor ladder filter!


okelk

so, I've been looking at this circuit board for a while now and thought I share my thoughts on what may be happening here. hoping to get some reverse engineering/ modding started.
Its mostly assumptions, so please correct me if I'm wrong...

    The whole thing runs on regulated 5V. with a 2.5V virtual ground (tl431 voltage reference on the other side of the board)

    The big array of npn transistors (LY=NPN, ZY=PNP) and half of IC1 (lm358) form a classic transistor ladder filter. I think q23/q24 (right from the transistor ladder) form a exponential converter for the cutoff CV. C19 and R31 form the audio input section.

    The VCO is located right of the VCF. The big white pot is for the pitch. I don't really understand how it is working, but I'm pretty sure that c13 is the timing capacitor and I think that the lower half of IC3 (lm358) is used as the cv input mixer. R10,R59 and R61 (180k) are the CV input resistors. (...so it would be possible to add a cv input by adding a resistor to pin2 of IC3.)

    The LFO is a build around IC5 ('7096', japanese low power rail-to-rail opamp) in the lower right corner of the picture. It is a pretty standard square/triangle dual opamp design. C24 is the timing cap.

    the section left of the LFO seems to be the AR envelope generator, it is build around a 74HC02 (Quad 2-input NOR gate, IC2) ...can't tell you much more about that...

    IC4 on the left side is just a lm386 working as an amplifier for the internal speaker.


haven't figured out yet how the gate signal is generated and how it switches the sound on/of...If somebody could figure out where to introduce a external gate signal, that would be awesome!

I'm pretty confident that this little synth has a lot of modding potential but it's a bit sad that it won't be possible to operate the circuit on higher voltages/a bipolar supply because of the 74hc02 and the 7096...


galine

From my side I connect my CV/ gate to legs 2 of IC2 and south of R15.

okelk did you think it will be possible to separate all synth part (LFO, EG, and other for eventualy work as an verry cheap modular?


okelk

galine wrote:
From my side I connect my CV/ gate to legs 2 of IC2 and south of R15.


That works for triggering the EG, but what I was wondering is how to switch the VCO on permanently without loosing the ability to trigger the EG ( which would be necessary for a modular ex-150).
I suspect that somewhere there is a gate generated if there is a voltage on the stylus and that this gate somehow mutes the VCO...haven't found it yet...

galine wrote:

okelk did you think it will be possible to separate all synth part (LFO, EG, and other for eventualy work as an verry cheap modular?


I'm pretty confident that this would work. thumbs up

separate square/triangle LFO outputs are already marked on the pcb. then you can separate the the LFO from the VCO by removing the LFO waveform selection switch. then you can use the middle pin of the switch as a cv input for the VCO (using the 'lfo amount' pot an a input attenuated, or add one or more resistors to pin 2 of IC3)
A VCO output is already marked on the pcb (this is only a saw-wave, I'm pretty sure you can find a square-wave somewhere in the VCO too...)
To separate the VCO from the VCF I would remove C19 and solder a wire with a new input capacitor to the left pad (new audio input for the VCF)
I think it should be possible to add a cv input for the filter via a resistor in parallel to r49 (not 100% sure, haven't tried it yet...)
A output for the Envelope generator is already marked on the pcb too, but it may be a bit easier to solder if you tap it of the 'pitch envelope' pot (which really only is a cv input attenuator for the VCO)

I think such a modular sx150 would be pretty cool! applause
especially if you combine it with a second sx150 or modded monotrons!

If someone wanted to use it with another modular it would be a bit more work to protect it from being damaged by the higher voltages...also I think the gakken works with approximately 0.6V/octave...


galine

Quote:

galine wrote:
From my side I connect my CV/ gate to legs 2 of IC2 and south of R15.


That works for triggering the EG, but what I was wondering is how to switch the VCO on permanently without loosing the ability to trigger the EG ( which would be necessary for a modular ex-150).
I suspect that somewhere there is a gate generated if there is a voltage on the stylus and that this gate somehow mutes the VCO...haven't found it yet...


Verry strange it doesen't work from your side hre with my beatstep and my midi-if it's work but maybe I make a mistake I'm a verry beginer in analog synth DIY -_-.


A little "blog where I will try to explain all mods I make on my godzikken...

https://sites.google.com/site/godzikkenororigazmi/home.




galine

yes I saw TP10 & TP12 and I think all the other TP will be interesting to test (it's look verry similar monotron hack points ^^.)


okelk

I just found this page, by the guy who designed the sx150 mk2:

http://gaje.jp/2011/10/09/2384/

it's all in japanese ( which I don't understand...)
here's a very badly translated link:

https://translate.google.com/translate?sl=auto&tl=en&js=y&prev=_t&hl=e n&ie=UTF-8&u=http%3A%2F%2Fgaje.jp%2F2011%2F10%2F09%2F2384%2F&edit-text =&act=url

I find this picture of the prototype quite interesting! :

http://gaje.jp/blog/wp-content/uploads/2011/10/IMG_0435.jpg


galine

on the site of the guy they have some interesting things like the synth called analog 2.0

I found a little A.D.S.R. who seems verry simple to build ^^.

http://gaje.jp/analog20/resources/07_eg/eg_doc.pdf

I began to check the tp point and the TP3 point go to the R15 it's more safe to use this point cause solder directely on CMS resistor isn't not secure.


heapish

galine wrote:
heapish it's your job? if yes I will have some question for you ^^.


No, just found it on the internet.


galine

yesterday I have send a mail to beatnik.jp for ask them some advice and the answer seems verry interesting I put a copy here.

"Gakken had already published SX-150's schematics on the net.
But mk2 is not yet, I think that they don't do that.
Gakken's SX-150 and SX-150mkII are designed by my friend. I've heard so many stories about them.
About mk2, he said that he checked out the moog's 921B's schematic. and it's not transistor ladder filter. it's diode ladder using diode connected transistor.
anyway mk2 is another synth from normal, I think.

you want drive 3 gakken with one pitch CV from MIDI-IF. and 2 normal sx-150 can drive with out any trouble.
but when you add one more synth, then there should be trouble.

SX-150's vco's range is around 0.5V/oct and MK2 is around 0.25V/oct or so.
you may need buffer amp with range converter for each synth CV input of vco.
Now, I'm writing issue for "range converter" as my notes. it's about the monotron's cv schematics. you may find good example to design your own converter, I think."


heapish

http://beatnic.jp/manuals/SX-mk2/index-e.html


galine

Just a small try to drive 3 gakken with CV/gate (CV only for the MKII)

https://www.youtube.com/watch?v=5N5iLZE9Mls&feature=youtu.be


ununseptium

okelk wrote:
If someone wanted to use it with another modular it would be a bit more work to protect it from being damaged by the higher voltages...also I think the gakken works with approximately 0.6V/octave...


Okelk, do you think it would run safely on the +5V from a TipTop uZeus?


okelk

ununseptium wrote:

Okelk, do you think it would run safely on the +5V from a TipTop uZeus?


I'm pretty sure that It will work. Just remember to use the marked '5V' and 'GND' points on the pcb and not the battery connectors (to circumvent the 5V regulator)
It might even be possible to power it off the 12v rail via the battery connectors. The voltage regulator should be able to take it, but it might get pretty hot...

my concerns regarding the combination of a modularized sx150 with a modular system is that you'd need attenuators (and buffers ideally...) and some protection from too high and negative voltages (5v zener should do the trick...) on the inputs.Also and you'd need to amplify the outputs to modular levels and ideally also apply a offset to balance it around gnd...


ununseptium

Ah! I'm with you now. That's good news, since I've just received the to that I ordered :-)
I might even have some 5v zener diodes left over from other projects. I'm a bit of a neophyte in the DIY & modding side of things, so if you have any advice on amplifying the outputs and balancing it around the ground, I'd be very grateful.
Cheers


galine

A little link to my little blog about my gakken mod.

With the help of Julien now we have gakken mark II shematics you can found this last on this link https://sites.google.com/site/godzikkenororigazmi/modification-cv-gate With the shematic Julien have recive this message about the CV/gate mod.

"If you put external CV and gate, the easiest way is to put them to the
stylus. The stylus input signal is basically CV, but the voltage is
also used for triggering gate. Gate turns on at around 2.5V of CV input
or higher up to 5V.

Valid CV range is between 2.5V to 5V which is mapped to approximately 4
octave range.

So when you put control voltage to the stylus input:
When you turn off sound: put 0V.
When you turn on sound: put from 2.5V to 5V.

The stylus input is at left bottom corner of the PCB.

If you want to control CV and gate separately, I would suggest to remove
R15 and R13, and put gate signal to pins 2 and 3 of IC2A. By doing so, you
should be able to use CV ranging from 0V to 5V. However, please note
that I myself have not tried this, so there is a risk that behavior is
not as expected."

I haven't try this mod yet.


EarlJemmings

So what I want to do is add a switch monotron-style to have the LFO modulate pitch and/or filter. I suppose this would be as simple as cutting a trace and tapping after the Lfo switch with a 3 position switch, but where would the control input to the filter be?


okelk

Thanks galine!
That info about the cv/gate is quite useful.

EarlJemmings wrote:
So what I want to do is add a switch monotron-style to have the LFO modulate pitch and/or filter. I suppose this would be as simple as cutting a trace and tapping after the Lfo switch with a 3 position switch, but where would the control input to the filter be?


I already tried that. The lfo modulates the filter if you connect the lfo output to the middle contact of the filter cutoff pot. but the proper way to do it would be to input the signal via a resistor in parallel to R49 (same value. 47k, I think). the leg of R23 or R24 seems to be a good solder point. (As I said before, those transistors seem to be a exponential converter for the filter cv...).
For the mod you're describing I would desolder the middle led of the 'lfo depth' pot, and switch the middle leg to either the original solder pad or to the filter via a resistor as described above.
Or just tap the signal from the lfo waveform switch and add a input attenuator to the filter cv input. (so you can modulate both at the same time.)

ununseptium wrote:
Ah! I'm with you now. That's good news, since I've just received the to that I ordered :-)
I might even have some 5v zener diodes left over from other projects. I'm a bit of a neophyte in the DIY & modding side of things, so if you have any advice on amplifying the outputs and balancing it around the ground, I'd be very grateful.
Cheers


At first you need to measure the maximal peak-to-peak signal levels on the sx-150 to determine the gain you need ( I think it was around 2.5V, that would mean that you need a gain of 4 for max. +/-5V and maybe more (8) for the LFO and EG)
then you need a simple opamp circuit to amplify the signal and mix the output with a negative offset voltage.
something like this:

This might be a better protection for the input than the 5v zener:

have a look here for a description:
http://www.doepfer.de/DIY/a100_diy.htm

for the VCO, VCF and LFO you can omit O2 if you don't care that the signal is inverted. don't forget that you have to power those opamps from +/-12V and to add some decoupling caps.

If that information isn't enough, I'm sure I'm gonna do that mod sooner or later and then post the schematics here.


okelk

galine wrote:

With the help of Julien now we have gakken mark II shematics you can found this last on this link https://sites.google.com/site/godzikkenororigazmi/modification-cv-gate With the shematic Julien have recive this message about the CV/gate mod.


But the linked schematic is for the old version of the sx150.

but thanks anyway!

I think the info about the seperate cv/gate inputs for might be for the mark II.


galine

The link for the schematic of the MKII is on the bottom of the page.

I post a direct link here: https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnx nb2R6aWtrZW5vcm9yaWdhem1pfGd4OjM0ZjQ1ZTNhZmM5ZWUwZjg


okelk

d'oh!

Awesome. this is great.
even the part designators are correct!
applause


galine

It's not me at the origine it's Julien who have win to have this schematics.

Now I really hope this lasc can help everyone to mod the MKII more simply.


galine

Now My question is how can I separate all parts of the gakken mkI and mkII I would like know by exemple how I can remplace the original AD by a complete ADSR like on a modular synth?


ununseptium

okelk wrote:
At first you need to measure the maximal peak-to-peak signal levels on the sx-150 to determine the gain you need ( I think it was around 2.5V, that would mean that you need a gain of 4 for max. +/-5V and maybe more (8) for the LFO and EG)
then you need a simple opamp circuit to amplify the signal and mix the output with a negative offset voltage.
something like this:

This might be a better protection for the input than the 5v zener:

have a look here for a description:
http://www.doepfer.de/DIY/a100_diy.htm

for the VCO, VCF and LFO you can omit O2 if you don't care that the signal is inverted. don't forget that you have to power those opamps from +/-12V and to add some decoupling caps.

If that information isn't enough, I'm sure I'm gonna do that mod sooner or later and then post the schematics here.

Thanks for this. I'm in the middle of trying to hack something together now. I'll post the results here. I'm sure it'll be pretty ropey though!


julien

galine wrote:
It's not me at the origine it's Julien who have win to have this schematics.

Now I really hope this lasc can help everyone to mod the MKII more simply.


thumbs up
Big thanks go to Mister Naoki Iwakami the designer of the Gakken SX150MK2


ununseptium

I'm having trouble powering it from a Eurorack rail. I tried +5v into the 5v TP and I tried +12v via the battery terminals. With each I get the LED on but no sound. When I switch back to the batteries it's working fine again. Any suggestions?


okelk

ununseptium wrote:
I'm having trouble powering it from a Eurorack rail. I tried +5v into the 5v TP and I tried +12v via the battery terminals. With each I get the LED on but no sound. When I switch back to the batteries it's working fine again. Any suggestions?


weird...I don't see any reason why it shouldn't work...
You did connect your ground from the eurorack supply to ground on the sx150, not to 'Vref', right?


galine

Did you think this cut point will be good for divide the sx-150 mkI?

https://sites.google.com/site/godzikkenororigazmi/separer-pour-mieux-r egner/gakken_schematic%20semi%20modular%20cut.jpg

https://sites.google.com/site/godzikkenororigazmi/separer-pour-mieux-r egner/sx150_cv_modular_cut1.5.jpg

https://sites.google.com/site/godzikkenororigazmi/_/rsrc/1423525610458  /separer-pour-mieux-regner/gakken_sx150_MKII_cut1.jpg

and if yes did you think I need to connect some cuted point to ground via resistor for didn't have pitch troubles?

on my matrice mod I would like small cables like arduino wires no jack I hope it's not a problem.


ununseptium

okelk wrote:
ununseptium wrote:
I'm having trouble powering it from a Eurorack rail. I tried +5v into the 5v TP and I tried +12v via the battery terminals. With each I get the LED on but no sound. When I switch back to the batteries it's working fine again. Any suggestions?


weird...I don't see any reason why it shouldn't work...
You did connect your ground from the eurorack supply to ground on the sx150, not to 'Vref', right?


Ah, here's my inexperience showing! I was having difficulty in getting solder to stick to the Earth TP so I've got the power Earth and all the Earths from the Jacks that I've fitted going to the Earth connection side of the Stylus, which I think shares a track with Vref. Guess I did a boo-boo?


okelk

ununseptium wrote:

Ah, here's my inexperience showing! I was having difficulty in getting solder to stick to the Earth TP so I've got the power Earth and all the Earths from the Jacks that I've fitted going to the Earth connection side of the Stylus, which I think shares a track with Vref. Guess I did a boo-boo?


The resistive strip is connected between 5V and 2.5V (Vref)
I'm sure you find another point that's easier to solder, like the black battery connector cable for instance...
Yeah...It can be a bit confusing when you have a "real" ground and a voltage reference which you think of as ground when you try to figure out how a circuit works...


ununseptium

okelk wrote:
The resistive strip is connected between 5V and 2.5V (Vref)
I'm sure you find another point that's easier to solder, like the black battery connector cable for instance...
Yeah...It can be a bit confusing when you have a "real" ground and a voltage reference which you think of as ground when you try to figure out how a circuit works...


Thanks okelk, I'll try that next!


ununseptium

ununseptium wrote:
okelk wrote:
The resistive strip is connected between 5V and 2.5V (Vref)
I'm sure you find another point that's easier to solder, like the black battery connector cable for instance...
Yeah...It can be a bit confusing when you have a "real" ground and a voltage reference which you think of as ground when you try to figure out how a circuit works...


Thanks okelk, I'll try that next!

Aha! Yes, this worked (of course).
I'm not sure whether everything's doing what it should yet. I've not tried any of the additional circuits described above yet, I've simply attached a jack socket to each of the TP's (Osc, Env, 2 x LFO out and VCF and CV in) to see how it works. The CV in is all I've tested so far (from a Minibrute). It seems to respond well, although the tracking may take a bit of tweaking. With no envelope or gate however, each note played continues to hang after key up. I assume this is how it should be - as it is on any modular osc without using an env.


ununseptium

Okay, I've this thing sorta modded...
All the main TP's now have jacks and I used that diode idea to protect the input on the VCF. I haven't done any of the more involved amplification circuits on the out going signals yet, so it's all pretty low by eurorack standards, but there's still stuff happening...
I've put a little synopsis along with a few test demo videos up on my synth blog. You can have a look here if you're curious. Please ask questions and/or offer advice. I should add that it looks a bit wobbly just now as I haven't secured it properly in the case yet.
Thanks for all the help in getting it this far.
applause


okelk

just looked at your videos. Nice! thumbs up


ununseptium

okelk wrote:
just looked at your videos. Nice! thumbs up

Thanks okelk. It's still a bit of a work in progress, and I don't think it'll be replacing my Verbos Composition system just yet, but it certainly has it's own charm ;-)


zodiak

Thanks for the info, I have three of them, well at £15 it seemed rude not to, but have been waiting to find a schematic , but maybe I will just press on now hihi


ununseptium

zodiak wrote:
Thanks for the info, I have three of them, well at £15 it seemed rude not to, but have been waiting to find a schematic , but maybe I will just press on now hihi

Yeah, it's really not rocket salad, Zodiak. ;-) All the information you should need is in the posts above. That said, some of it was a little too complicated for my puny brain, but I've ended up with something that works for me anyway. Just don't expect a £45 Minimoog. This is fun!


zodiak

Arghh.. I just spent 20 minutes in posting a reply, hit submit and nothing!
..
So.. thanks, I have played with them for a bit so I know what to expect (ish) hihi
The plan is to mount then on a panel along with a MIDI/CV I/F , simple mixer, stomp box graphic EQ and a stomp box delay unit (that can also do chorus) .
There will also be a "click" box which provides a short hit of noise when a note is played. This sounds crude, and it is, just a switch for blue/ white/ pink noise and a decay pot. It has an incredibly fast attack and can add aggression to almost any patch, but especially brassy/organy type sounds.
There will be a breakout box for each SX-150, with bannanas to connect to my modular, VCO square wave out (inc PWM from LFO or AR), and a kill switch for the internal VCO output.
Two of the SX-150s will have dual sub-octave, while the third will have a feed from the noise source.
I already have all the extra bits, apart from the breakout boxes, and it can certainly produce sounds I never heard elsewhere. I didn't say good, just very, very unique hihi
Before I can really get into this though I need to finish the similar project for my monotrons hihi


galine

ununseptium Verry funy mod.

I have some question about your mod:

"There will be a breakout box for each SX-150, with bannanas to connect to my modular, VCO square wave out (inc PWM from LFO or AR), and a kill switch for the internal VCO output."

Where did you instal kill switch on the MKII (at just before VCO out TP?) and did you think this mod need a resistor?

Did you know a simple and cheap ADRS who will work with the gakken MKI & MKII?


zodiak

galine wrote:
Where did you instal kill switch on the MKII (at just before VCO out TP?) and did you think this mod need a resistor?


I know its weird but I try not to make any permanent changes to a circuit I am modifying just in case I want to put it back to original and sell it, or if I come up with something better that means undoing a previous mod.

This mod works by taking a feed from the VCO output, inverting it and mixing it back into the VCF, along with the original signal so that they cancel out. All of this can normally be done by soldering wires onto exiting pads and doesn't require cutting tracks.

I have modified several monotrons like this and although its not perfect it works well enough. I only just got the schematic from this post so I haven't tried it on SX-150mk2, but I will be starting by taking a feed from Q9/R37, feeding that through an op-amp inverter (47k resistors). The output of this will go to a 1uF cap (like C19), then a 47K resistor (like R31) and then to the base of R20. Assuming that this diagram is correct and all being well that should cancel out the sawtooth.

If you want to get it completely cancelled then replace the feedback resistor on the opamp with a series combination of a 39K+4K7 fixed resistors and a 10K trim pot. This should allow you to trim out most of the signal, but some high frequency harmonics will probably still get through. In practice you would be hard pushed to notice this in the mix.

As for the envelope generator, I can't help, I mainly use AR generators with a one shot switch or a simple percussive envelope for most mods, or full blown ADSRs on my modular.

However my first stop for all things DIY synth is always http://www.musicfromouterspace.com/index.php?page=HOME, its brilliant hihi


okelk

Does anybody understand what Q27/Q28/D7/D8/D9 do?

As I understand it the darlington pair detects if there is a voltage coming from the stylus, and if so it adds a voltage (dropped by the diodes) to the filter vc...but if so, why? what for? hmmm.....

Also,What do D3,D10 and D1 do?
I assume that they stop the lfo and the vco from oscillating if the voltage on the cathode is low ( the gate is high)
Is that thrue?


zodiak

okelk wrote:
Does anybody understand what Q27/Q28/D7/D8/D9 do?

As I understand it the darlington pair detects if there is a voltage coming from the stylus, and if so it adds a voltage (dropped by the diodes) to the filter vc...but if so, why? what for? hmmm.....


I thought it was the CV to exponential convertor for the VCF, and I think its the IC2a/b part that acts as the detector as it feeds the ARG.

okelk wrote:

Also,What do D3,D10 and D1 do?
I assume that they stop the lfo and the vco from oscillating if the voltage on the cathode is low ( the gate is high)
Is that thue?
I think that's right, and the LFO is reset so that it always starts at the same place everytime you trigger a note.


okelk

zodiak wrote:

I thought it was the CV to exponential convertor for the VCF, and I think its the IC2a/b part that acts as the detector as it feeds the ARG.

I think you're right about IC2, but I'm pretty sure that Q23/Q24 are the exponential converter for the VCF. (simple npn/pnp exponential current sink)

But Q27/Q28 are arranged as a darlington-pair. As far as I understand it, If a voltage is applied to the base of Q27, they switch the 5v from their collectors down to the emitter of Q28.
...and I just don't get what for...

zodiak wrote:

I think that's right, and the LFO is reset so that it always starts at the same place everytime you trigger a note.


I wonder If it's better to remove them, or to permanently switch them to 5v if I want the oscillator not to stop oscillating...I guess I'll just try...


zodiak

okelk wrote:
But Q27/Q28 are arranged as a darlington-pair. As far as I understand it, If a voltage is applied to the base of Q27, they switch the 5v from their collectors down to the emitter of Q28.
...and I just don't get what for...


You are right that is a darlington pair, but that just means it is like a very high gain transistor, not necessarily for switching, although that is their most common use.

The exponential response only happens for a small part of the transistor curve, and I assumed this was just a way of making the response part wider.


galine

Hello,

Some pics of my work in progress.





As you can see ther is a lot of new:

I decide to cancel one of the 2 step 16 sequencer for ad a 32 key keyboad
I also install a joystick without spring for control modulation and pitch.

In realy soon future I will remplace the micro CV/gates/etc matrice by a more classical 3,5 jack matrice.

On the upper side you can see they have a few change to. I'm work in to the modifications implantation.

I have order electronic parts for began the "serious work" I hope all of that will arrive soon.

In wainting I continue to work on the external box.


zodiak

That looks really nice, and I hope it sounds as good. thumbs up What wood are you using for that? I also like the keyboard did you buy it like that or was it taken from something else? Mr. Green


galine

All I use in the build of this synth is recycled keyboard is a old edriol pcm r30 I will remake contact of the keyboard.

The wood is just fir from rest of my father new car garage the white medium plate is from pallets.

Only potentiometers, knobs, switch, led holder, are new.

About the sound for the momment it's the first stage the 3 gakken at unison but in future i will have more flexibility (VCO mixer, system X adsr, for the MKI cause for the MKII I didn't know exactely how separate all parts of the synth...

If all be good I will ad an arpegiator (built with a arduino.)

a little technical question: I whant add a "transpose fonction to my CV/gate 16 step sequencer) I imagine it's juste a CV amp it is possible to setup with a potentiometer for have the needed range but I need confirmation.


zodiak

galine wrote:
I whant add a "transpose fonction to my CV/gate 16 step sequencer) I imagine it's juste a CV amp it is possible to setup with a potentiometer for have the needed range but I need confirmation.

You are correct, you could use a potentiometer, but will have to be very careful setting the values. You might find it easier to use a chain of resistors and a multi-way switch.


galine

zodiak wrote:
galine wrote:
I whant add a "transpose fonction to my CV/gate 16 step sequencer) I imagine it's juste a CV amp it is possible to setup with a potentiometer for have the needed range but I need confirmation.

You are correct, you could use a potentiometer, but will have to be very careful setting the values. You might find it easier to use a chain of resistors and a multi-way switch.


Its a great idea, with this system I can only transpose down or I need found a "neutral position" and always keep it mind or better forgot as the range is divided ^^.

I'm sorry for my bad english and my very low level in analog synth, the gakken is my verry first analog synth and I have to many things to learn before understand all I need to know.

I realy hope some interesting mod will be found on the gakken sx-150 MKII cause for the moment the mkII mod panel look empty ^^.

About Effects I think instal some simple guitare effect kit like this

http://www.ebay.fr/itm/Chorus-CE2-Kit-/151579957331?pt=Altro_per_Chita rra_e_Basso&var=&hash=item234ade9853

and a simple passive ring modulator like that

http://www.ebay.fr/itm/261528191457?ssPageName=STRK:MEWAX:IT&_trksid=p 3984.m1423.l2649

what did you think about that? Maybe it's to cheaper?


zodiak

A chorus is always useful, I use them a lot, and that seem like a good price for a kit. Ring modulators can be fun too, and I love that circuit, but don't use it too often as it can make the music sound mechanical.


galine

In waiting the switch and pots I instal my modulation joystick ^^.




galine

I have a stupide question:

Yesterday evening I make some try on my goddzikken and I asked me how can I sync the ocylator? when I put a key on the keyboard CV are sended to eatch gakken but that's not for that they are sync that's right?

the idea is to make the gakken sound more fat.


galine

I'm always waiting for a lot of part for my Goddzikken and during this time I began my second project based on Gakken the Origami.

This is a more compact, and simple project for keep the portable side of the original gakken.

In the began I would like use one MKI and one MKII for this project but I have to mutch difficulties for tune MKI and MKII together.

Finaly D decide to remplace the MKI of the Origami by the MKII of the Goddzikken.

As you know now I use Midi-if in my Goddzikken project I didn't whant explore the same way and I decide me to build me a analotg 32 key keyboard.

For that I use a old yamaha PSS 30 (my realy first noise instrument) and I hack it with 32 2,2 k resistor but it doesn't work correctely I decide to remplace all resistor by 32 1,5k and now all my 32k worls like a charme.

For guive a nice sound to my gakken I plug the output of the gakken 2 in the input of the gakken one.

Then the souns look more fat with some nice resonance and EG effects.

Since then I have a little problem my gakken n°1 automodulate and EG seems doesn't work. Something is wrong on it but I didn't found what for the moment.

As soon as I fix the problem I will post a little video for show you how the Origami sounds.

In waiting some pics of the build process.







As you can see this project is verry tinny next to the goddzikken.

I will add soon the pitch/modulation joystick on the place of the speaker of the yamaha. this las take place on the underthe structure of the Origami like the korg volca series.


astrosound

I snagged a SX-150 MK II the other day and started modifying it, so seeing as this thread isn't too old and was the most helpful resource I could find I figured I'd post my results here. While I don't see the point in making this thing totally modular, I want to make it a little more compatible with other equipment. I hate working inside cramped enclosures so additional jacks and circuitry inside will be limited. Anything that would need extra (active) circuitry can just get sent to an external euro module via some kind of multi-pin connector (haven't decided what kind yet though).

Something that might be helpful for those wanting a gate input: I found that the proposed gate input modification (removing R15 and R13 and sending the gate directly to IC2 pins 2 & 3) did not work. Q12 was still chugging down my (admittedly flimsy) gate signal. So instead of removing the resistors, I cut the trace between Q12 and R13, just to the right of the "C16" marking on the PCB. Gate input still at IC2 pins 2 & 3. I used a small value resistor and 5.1V zener to protect the chip from gates over 5V. Scrape both sides of the cut trace down to bare copper and wire a switch between these two points if you still want to gate with the stylus. If you don't care to use the stylus to gate, I'd suggest removing R13. Since it is connected to the stylus input, the gate signal will bleed through and shift tuning a bit.

Added a switch to send the LFO to either the VCO (stock) or to the VCF. Cut trace between wiper of VR5 (LFO depth pot) and R61. These two points wired to a two-position switch to re-enable LFO pitch modulation. The other switch position connects VR5 wiper to junction of R42, R49, R50, R52, R74, and Q24 via a ~150K resistor. Lower values allow more LFO depth, but adds more positive offset to filter CV which limits lowest cutoff frequency. I kinda half-assed this one cause it was quick and easy.

I was able to approximate a 1V/oct response on the VCO by running CV through a 200k resistor + 100k trimmer connected to the stylus tip. Didn't actually modify this part yet, just quickly tested. The filter tracking kinda pisses me off , so I might cut the trace between the stylus tip and Q27 and add a switch to re-enable it. Oh, and I added a VCO direct output. Removed C19, put a new 1uF cap between TP7 and a 3.5mm output jack. It is normalled (normalized?) to R31, so with nothing plugged into the jack it functions normally, but with the plug inserted the VCO is removed from the VCF input.

I think the line input might be clipping a little too easily, and in a not-so-pleasing way. If it's not a hassle I might replace R56 with something a little bigger.

I'm considering adding an EG output jack, pulling the signal right off TP9. It only has a 0-2.5V range though, so in order to be more "modular friendly" it should have an external amplifier. Might be more trouble than it's worth. The Attack/Decay pots are kind of finicky anyways.

No doubt this would all be much easier to interpret with a schematic showing what I've done. Maybe I'll document it more clearly with a few photos once I'm finished. In the meantime I hope this will be of some help.

edit: the VCF is gated on (IC2 pin 1 LOW) and off (IC2 pin 1 HIGH) via R65 and it made an annoying click when being gated on. Removing R65 and replacing it with a same value resistor going to ground keeps the VCF permanently enabled so it can be used as a standalone filter and eliminates the annoying click. Alternatively you could cut the trace between R65 and IC2 pin 1 and ground the R65 side, but I couldn't find a convenient enough place to do that so I replaced it altogether.

also, I can still hear the VCO bleeding through to the filter a tiny bit when the VCO is disabled (using the method described above). Haven't looked into it really. Just thought it was worth mentioning. Not finished dicking around with this little thing just yet!



robman84

Some useful tips there! So I don't fry my 2-day old Gakken, can you describe the Zener circuit some more please? Is it Gate->Zener->pins 2&3? Or is there one diode per pin? Where would the small resister go? Sorry if these are noob questions.

It's a bit moot, as my current gate is 4.5v max but I'm likely to have a higher voltage source before too long (if Ebay goes in my favour for once...).

Thanks


astrosound

This is what I did (didn't draw this, found the image on google):

Your external gate signal goes to the input, the output goes to pins 2 & 3 (which are already connected together as you can see on the schematic). I used a 5.1V zener because that's what I had on hand and the IC should be able to handle the extra 0.1V. A resistor between 100 and 1k should be fine.


robman84

Great, thanks.


robman84

Hi folks, I've got a couple of questions about possible mods:

(1) How could I add a pot to adjust the amount of EG that goes to the VCF? (i.e. what points, and what spec of pot?). I see the pitch EG pot amount is 10k.

(2) Is it possible to have more of a range to the decay amount? When setting short decays it "jumps" from a short decay to no decay. At the other end, long decays deem to max out when the pot is about 1/2 way.

(3) I assume to add a volume control it would be a pot as a voltage divider, but as a noob I'm not sure where I would attach the 3 pot terminals.

(4) Ambitious here, but would there be a way of having CV control over the amp? I've messed around with a vactrol to do this with a monotron, but that was just modifying the volume in place of the volume pot, not direct CV control of the amp.

Thanks to all who have written up the mods here. I'm really enjoying my Gakken and can't wait to get it into my Eurorack this summer!


zodiak

These are all untried and untested. If you fry yours don't come back to me Mr. Green

(1) Cut track from R52 to R57/R58. Connect the ends of a 10K pot across R58, and wiper to cut end of R52. You might need to experiment with the value of the pot and R52.

(2) That sounds screwy, and I would be tempted to think that VR2 is damaged. Try replacing it with a new one and if that works then if its a LIN pot try a log one and if its LOG try a lin to see if the different law makes it nicer to use.

(3) Cut track from R24 to R22/R38. Connect the ends of a 10K Log pot across R38, and the wiper to the cut end of R24.

(4) You could try connecting a Vactrol across R38 instead of a volume control, but the range will be limited.

Let me know if you try these and how you get on. Do you need a schematic or do you have one?


astrosound

For what it's worth, the decay pot on mine also is kind of useless at the first 10% or so of its travel. I think increasing R77 to something between say, 220 and 5k would eliminate the "dead spot", the trade off being the larger R77 is, the longer the minimum decay time. You might need to experiment with different values to find the sweet spot that works for you.


robman84

Thanks zodiak and astrosound. Will give some of those mods a go. Out of interest, what do you tend to use when cutting a trace? Is a Dremel a bit too harsh?


grenert

robman84 wrote:
Thanks zodiak and astrosound. Will give some of those mods a go. Out of interest, what do you tend to use when cutting a trace? Is a Dremel a bit too harsh?

I really like some of the Dremel high-speed cutters for breaking PCB traces. The 109 and 110 are especially nice because of the right-angle edge:
http://www.dremel.com/en-us/Accessories/Pages/ProductDetail.aspx?pid=1 09

I used to use some kind of blade, but I sometimes slipped past the intended trace and damaged an adjacent one.


astrosound

robman84 wrote:
Thanks zodiak and astrosound. Will give some of those mods a go. Out of interest, what do you tend to use when cutting a trace? Is a Dremel a bit too harsh?


I've been using a small, very sharp knife. Works fine as long as you don't try to gouge out the whole trace at once. It's also handy for scraping away the silkscreen/solder mask on a spot you want to solder to. I've also used a Dremel with a very small bit for cutting traces. It works well and is a lot faster, just have to be careful not to let your hand slip and wreck a component or trace.


zodiak

I use a sharp knife, but always try and cut well away from pads, making it easier to solder flying leads to.

I also make two cuts 1mm apart and remove the track between them by heating it up with my soldering iron and lifting the track with the knife.

I always bear in mind that I might change my mind at some point and want to remake it. I do this by running a thin strand of wire along the track, and solder the ends to existing pads. You can scrape the track you cut, but bear in mind that as you solder to it the glue holding the track will soften and create a weak spot which could fail later. Pads are already soldered so will be quicker and easier to solder to which reduces the stress on the glue.

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