Wednesday, October 24, 2012

Korg Poly800 Joystick module

UPDATE 5/10/13!!!  This project is due for a rebuild.  Since I built this module, I've learned a bunch more cool/useful stuff about circuits.  I except a redesign in the next month. It will be even better!  Please stay tuned for my better KORG POLY800 joystick module in the near future.....

The first real synthesizer I ever owned was a Korg Poly800.  I must admit that I am partial to them--specifically the joystick, which controls Pitch bend, pitch Modulation, and VCF Modulation. I've gone through five of them over the years. I broke two and I sold three, and now I have none. But, I do still have some parts from the broken ones laying around and I thought it would be a fun/challenging project to build a module around a salvaged Poly800 joystick.


In the modular world, modules are all controlled by CV or Control Voltage. Control voltage ranges from around -5vdc to around +5vdc depending on the type of signal, gate or pitch. Joysticks work by affixing two potentiometers to the joystick, as you move the joystick, you change the values of each potentiometer.



 Above is a diagram of a potentiometer. A potentiometer can be wired as a voltage divider if you attach a negative voltage to lug A and postive voltage to lug B.  When the potentiometer is in the center most postion, Lug W will be 0 volts.  As you turn the Pot counter-clockwise, towards A, the voltage at lug W will become more negative.  As you turn the Pot clockwise toward B, the voltage at W will be come more positive.

This basic principle is what the schematic I found on Music From Outer space is based on.


And this will work without any major modifications on the pitch bend aspect of the joystick.  but this will not work for the pitch modulation and VCF modulation aspect of the poly800 joystick I am trying to duplicate.  

I think it will be easiest to describe the movement of the Joystick in terms of North, South, East, and West.

PITCH BEND
For pitch bend, with the joystick in it's center spring loaded position, the output is 0 volts.  As we move the joystick west, we start to get a negative voltage at our output, which when attached to the linear frequency input of an oscillator will cause the pitch (frequency) to decrease.  If we move the joystick east, passed the center position, we start to get a positive voltage which causes the pitch(frequency) to increase. done deal.

MODULATION VCF/PITCH
The first thing to realize about the how the joystick works on the Poly800, is that when you move the joystick north of its spring loaded default position, it affects Pitch Modulation, but if you move it south of its original position, it affects the VCF modulation.

This roughly translates into this idea, We want a way to separate the positive(north) and negative(south) values into two different signals which we could assign to two different modules.

I know, from building power supplies, a way to do this. when turning AC current into DC current, we can separate the positive side of the wave from the negative side of the wave with 2 diodes.

I breaded my ideas up on a breadboard and this is what I came up with.



R3 represents the Potentiometer inside the joystick.  R6 is a multiplier, it allows you to adjust the amount of voltage produced by the joysticks movements.  You may be wondering why one diode is before the op amp buffer and why the other is after.  It's was the only way I found would work.  The diode for the positive side of the joystick adversely affected the buffer when it was placed before the op amp, so I moved it after.

also I used an inverting buffer for the south movement of the joystick to convert the negative voltage into a positive, which I thought would be more useful than just a separated negative voltage.

something not included in the schematic was a tiny 1k trimmer pot I used in between R1 and R3 to "tune" the center joystick postion to 0 volts.

This schematic needs to be duplicated twice.  One for the X axis (east,west) and one for the Y axis (north,south).


Below is the actual build of the module.






Now I can control different modules using positive and negative voltage via North and South, or East and west movement (Ideal for pitch bend).  I can also divide all 4 directions into 4 different positive voltages (idea for whatever).  pretty wild.

This was one of my more complex designs attempts.  Most the stuff up to this point was designed by someone else and then I modified it.  This one was mostly all my ideas beyond the original voltage dividing potentiometer schematic from MFOS.  I don't believe that this method was how Korg set up the abilities of the joystick in the original poly800.  It's also not a perfect system.  It bends Slightly farther north than south, and slight farther east than west, making precise pitch bends rely on your ear more than the position of the joystick, but I would still call the module a success, and adds to the overall "rawness" of my Modular Synthesizer.





DC Voltage Distributor

The more you learn about electronics, the more you can figure out how to modify a circuit to suite your needs.  I'm beginning to understand what an amazing resource Music from outer space is.  Although the circuits are all designed around ±12v, some of them work with ±15v without modification and others can easily be modified to work with ±15v (what my system is).

So I built this DC voltage distributor. 
This circuit actually requires no modifications to work with ±15v.  A DC distributor circuit is ideal for using a single control voltage source to control multiple modules without loading the incoming signal.

when a signal is split into separate paths, the voltage stays the same but the current is divided.  A buffer circuit relays the voltage through an op amp, but the current is supplied from the power source, rather than the signal source.

 It's basically an input with 4 buffer op amp circuits.   I assembled the circuit on a breadboard first--tested it with my modular power supply, then assembled 2 of them on perf boards and finally mounted them for my module.

Here's the module in my system (3rd from left on bottom row).  I can now send a single gate signal to my ADSR module to shape my VCA in addition to sending the gate signal to my slew limiter circuit and then on to my VCF.  (in a pinch, a slew limiter can be used as a minimal envelope generator.)


I also found this module to be helpful when I was testing the module I made after this, my joystick controller.  having a buffer circuit that you can plug into immediately, helped me diagnose the problems with my joystick circuit. I needed buffers to keep the joystick circuit isolated from the loads I was plugging into it.  



Thursday, September 6, 2012

MFOS Noise Cornucopia Module (white noise generator)

I bought two PCB's from MFOS.  The one I'm holding is the Noise Cornucopia PCB.  They primarily gear stuff towards 12v+/- systems but they usually explain which components to change out for a 15v+/-, which is what I've got running.

For the most part, putting these kits together is like building legos,  I ordered all the parts from Jameco and waited patiently for them to arrive.  I did all the careful stuff like heat sinking my transistors as I soldered them and so on.

I used those chip saddle things to be safe. 

As you can see in this picture, I didn't have any 43k resistors--so I made some by twister 2 resistors together.

I got creative with mounting the circuit board.  usually I mount the board parallel with the panal--with a couple of stand-off screws but this board was wider then the ones I use for my DIY stuff.  I decided to use that piece of walnut as a bracket--it also stiffened the panel up, which was nice. 



 Besides generating a few different kinds of noise, it also has a random gate generator. There's a little blip on the MFOS page about setting multi-turn trimmer pot (R8) on the board. You need an oscilloscope for that, which I don't have, so I just kind of turned it until I liked what it was doing.  I am fairly certain it adjusted how the Random gate generator operated.

The noise modules is the 4th from the left.  I kind of like how my synths is mostly unlabeled--making it almost inaccessible to anyone but myself.

Next up, I'm gonna redo my Ring Modulator module and build a slightly more complex mixer circuit.  

Friday, August 10, 2012

Exponential Portamento (Slew Limiter) Module


My friend Joel--a fellow synth geek--built this circuit for his Roland Modular System and I thought I'd give it a try.  Basically, this is what's called an RC Lag Circuit.  I played around with a few different combinations of potentiometers and capacitors to see what worked best for me.  This circuit is for exponential portamento--meaning it is time constant no mater the distance between notes--and the potentiometer determines the length time.  I ended up with a 10K pot and a 10uF cap--it fit the range and sensitivity I liked.

There's almost nothing to the circuit.  I breaded it up in about 2 minutes and spent about 10 minutes changing out the values of the 2 variable components to see what I liked.  I'm using and LM324 which is a quad op amp IC.  The circuit only uses 2 op amps so I figured I might as well double it and create 2 portamento circuits--maximizing my space and moving towards my eventual goal of having the ability to have 4 separate synthesizers paths in one modular rack.
LM324 -->

I put it all together on a perf board and tested both circuits out.  They seemed to work well but there's something I wasn't noticing, that will come into play later...

I got a drill press about a month back and it's really made panel production much cleaner, easier and faster.  I drilled my holes for my 1/4" jacks, potentiometers, and mounting screws.  Something you can't see in this pictures is a stepper bit for cutting holes in metal, it's very handy.

So, after I got this thing all mounted up and plugged into my system, I noticed something I hadn't noticed when I breaded it--there is a small amount of portamento--even when the knob is all the way left. I asked Joel about it, and he said his does the same thing and that's why he built in a "true bypass switch"--something I had overlooked.  So I went ahead and wired one of those in for each circuit.  I used 2 DPDT switches in a way to disconnect the circuit completely from the signal path.


Here it is all racked up in my case.  The portamento is the 3rd module from the left.  The bypass switches are above the potentiometers. An interesting artifact happens when you switch on the portamento while sound is coming out, there's this cool little ping sound, like a ray gun charging or something.  These sort of cool anomalies, I guess is why it's fun to build your own stuff.

Up next, I have a noise circuit and a LFO circuit I bought from MFOS.  I am also working on a buffered signal splitter type thing too.




Friday, August 3, 2012

Ring Modulator

I recently took another look at this module and did some more adjustments to it,  the following blog was written during an in between stage.  You may want to look ahead in my blog for a more current version of this build.


I bought a passive ring modulator kit from Synthrotek.

It worked ok, but I didn't like how much it attenuated the signal (decreased its volume). So I thought it would be cool to build a circuit that boost the signals going into the ring modulator.

The ring modulator kind of works like this.  There are 3 jacks--the first is the input, the second is the carrier and the third is the output.  something magical happens between the input and the carrier whilst in that ring of diodes that creates a bunch of kooky shit and it sounds cool, or at least it's supposed too. I'm not sure, it may be the transformers in there, but you loose a bunch of volume somewhere along the line, and all can hear is some crinkly ghost sounds by the end.














So, I built a signal boost circuit using two LM741 op amp chips.

Here's my super simple circuit.  It's a basic non-inverting amplifier.  Unlike the non-inverting averaging amplifier in my simple mixer, this one has a 50k potentiometer to control the the amount of amplification.  I think the spread works out to be a gain of between 2x and 51x.

I made two of these little circuits and put them on a perf board, one for Input signal and one for the carrier signal.  I forgot to take a picture of it all soldered up, but anyway...







Here's what it looks like as a module from the side.











Here's what it looks like from above. you can see my two potentiometers up there control the volume of each incoming signal, so they can also be used as a kind of mixer or controller--as volume seems to be a factor in how the two signals affect each other.

It was definitely a vast improvement, especially in the bass department. Next time around, I may even try for 100k potentiometers instead of 50k, which may result in the incoming signals clipping after a certain amount of gain, but that might sound cool too.  dig it.











Thursday, August 2, 2012

Simple mixer for my modular synthesizer

This is my schematic for my Simple Mixer.  By "my schematic", I mean I found on the internet.  There's no volume or tone control.  I wanted to start with something simple and hard to screw up.  Without getting into how op amps work, its non-inverting, which means that signals that enter, will leave in the same phase.  It's also set up as an "averaging" amp and not a "summing" amp, meaning that the volume after mixing is an average of the volumes before mixing.  That doesn't mean it mixes all volumes evenly. Things that were louder going in will be louder coming out.

I found the schematic here and modified it just a little bit by adding some Caps on the input.  From what I've come to understand, Caps will help filter out DC? I dunno,  I'm really just kind of playing around over here.  It occurs to me now that I could have put a Cap on the output too.







I built it on a breadboard first without the caps and it seemed to work fine.









So I went ahead and tried out with the caps.  It all worked so I stuck it in a perf board and soldered it up.

















Turned it into a module.














The mixer is on the Right.  just to the left of my Ring Modulator which I haven't written about because I'm still working on it.  You can see the mixer has 4 inputs above and an output below.

I build these modules with the intent, to return to them--after my knowledge has grown-- and modify them.  I will eventually add some trim pots to this circuit for volume control.

One of the cool things about building a modular synth, is being able to work in steps.  Each modules is isolated and if one doesn't work, I can still chug along trying different stuff--teaching myself all along the way. They also share a common power supply, meaning I don't have to build that circuit each time. There's nothing quite like learning by necessity, and I've learned more about electronics in the last 3 months than I did in the 8 years prior.

ps.  My portamento module worked but I'm waiting on some supplies to come from Jameco before I solder it up.

Thursday, July 26, 2012

LM386 amplifier

I was initially inspired by Hack-A-Week to build this amp kit.  I noticed while I was looking around the web that there are a lot of different version of it, but they are all basically the same, and it can be used to power a small speaker, headphones or as a pre amp of some kind too.

I wouldn't be surprised if most distortion pedals utilize the 386.  I saw 4 inside this old "boutique" pedal I had.  






You might have noticed, if you've ever tried to panel mount anything--like switches or jacks--inside a wood cabinet, the wood is usually too thick.  I've found that having a 1 1/4" paddle bit laying around is helpful for recessing the jack into the wood so the threads reach the other side.

I built the schematic on a piece of perf board and mounted inside this drawer I had.  In the Hack-A-Week video, he builds a little pedal type thing, but I opted for my "mini-amp" idea. The speaker is a 16ohms --2.5 watt.

It's actually pretty loud for a 9v battery amp. 


I decided to build a second one, but I went this this "dip" style perf board this time around.  It worked out really nice and made for a really clean soldering job.












For this one, I put in a power switch and I got these handy 9v battery clips from jameco which made for a nice touch.














I left this one in the orignal case (this is the back).  Strangely, the 2 amps sound kind of different even though I used the same schematic for both,  I'm not sure if its the case, but the first amp in the drawer case seems louder and a bit brighter.  This one on the other hand seems like it might be better for bass.





A couple weeks ago,  I went the the reuse center and bought a broken receiver for a couple bucks,  inside was a bunch of boards full of Caps.  On this board, theres about 40X 10uF caps, 10X 220uF and some others.  It's nice to have these lying around for parts on projects like this.








Yep.  building stuff.  All the schematics and stuff are on Hack-A-Week


Tuesday, July 24, 2012

THE NEW STYLE: a shift towards new skills in electronics.



In December of this year I will be turning 30.  I've spent most of my adult life playing music and customizing things for my performances.  Something happened in the last couple years that has swayed me away from my original path and eventual goal of being a godlike pop star.  It could be as simple as the fact that performing significantly improved my self-esteem and therefore, I no longer need constant affirmation of my incredible and unique talents.  Or my slow drift toward Existentialism, and with it, the truth that no mater how successful I become, I will always be the same person who will eventually die.  Or that I started to lose my hair and I can no longer impersonate an angst-y adolescent .  Or just that I am tired of doing the same thing over and over again.  probably all this crap.
Clearly its time to foster a new era of growth and instead of suddenly changing my course towards something more noble--like pursuing a career as a doctor or garbage man--I begin only a slight coarse correction.  
 I am going to teach myself electronics.
Becoming a master of electronics will allow me to pursue a slightly more useful talent than pouring glitter on myself and humping things-- and because it is still in the vein of my earlier vanity, I can continue build on whatever momentum and skills I have accrued to this point.
Interestingly enough, I feel I can continue performing as a musician with emphasis the things I create, rather than trying to sell records or make money from performances. 
shows will become demonstrations.



Among the many things I've wanted to build, but felt I didn't have the skills or time to build, is a bad ass modular synthesizers.  I choose the route of the MOTM/5U Moog or Synthesizers.com style rather than Eurorack.  I went this route because I like things to be big and expressive and I'm pretty sure I'd have a hard time making modules that fit in the smaller Eurorack format.

I chose to start with 4 modules from Synthesizers.com to get started, rather than try to build everything from scratch.  I bought an Oscillator, Amplifier, Envelope Generator or ADSR, and State Variable Filter.  I figure it would be easier to build modules knowing that these four modules worked correctly.

My goal is to build as many of my own modules are possible, and to learn stuff along the way.
Anything I come up with that seems different or cool or unique, I will probably try to sell to help fund my immersion education. 

My first module was simply a power plug with on/off switch and LED. 
The aluminum blanks were cut by a friend who works in a metal shop. As you can see from the picture, my blanks don't have folded metal on the side to stiffen them up like synthesizers.com modules, which would be nice for the next go around.
I got the plug socket thing from a broken rack mounted Behringer piece of crap. The Switch is a simple SPST from the hardware store.  And the LED is mounted in an LED socket I got from Radio Shack.  Synthesizers.com power supplies come with 4 sources.  +15v, +5v, GND, -15v.  The LED is connected  to the +5 and GND with a 100ohm resister per this thing I like to use LED WIZ.

My second module was a MIDI to CV converter.  I want to eventually be able to control 4 different semi isolated synthesizers, like 4 notes of polyphony, but less for playing chords and more for construction songs made up of 4 parts, all with different timbre.  There are a few modules out there that will do this ready made for between $559 and $1200 dollars depending on other options.  While Searching the web I discovered the Midimplant,
A very small but seemingly powerful MIDI to CV converter board.  The implant allows for 2 pitch controls and 2 gates on different midi channels.  I bought one with the future plan of adding a second later on.









The board doesn't have any holes for mounting, so I soldered it through a perf board so I could mount it.

I went ahead and put in all 8x1/4" jacks so I wouldn't have to do any drilling in the future.  I got some threaded aluminum stand-off spacers from the hardware store for mounting.

I'm not sure if you can see but I used 2 legs from some LED I had to make the power connector.  It fits nicely into the Synthesizers.com DC Harness. 






So, there it is all set up.  More to come later.  The case is an old keyboard case for my Mono/Poly which never leaves my apartment, so I certainly don't need a case for it.  More to come.  Next up is a Portamento Module.