Monday, December 16, 2013

quad ADSR simplified yu synth ADSR.

I am an aspiring electrical engineer. Circuit design inspires me in the same way that songwriting once inspired me.  In electronics as in songwriting, one often imitates until he can create on his own. When modifying another person's circuit, it's hard to say exactly when one can claim a circuit.  How much needs to be different?  What kind of changes are considered more than arbitrary and therefore justify claiming ownership (my circuit)?  

A majority of the circuits I've worked on for my synth started as either yu synth designs or MFOS designs.  The designers of these circuits have far more electronics knowledge than myself and clearly execute a higher level of intention in their circuits. Though I've learned a lot since I began my modular project, I still often find myself in the "shit, lets try this resistor" process. The designs available on these sites are sometimes built upon older designs in which the newer design only varies in peripherals (like input/output buffer impedance, trigger method, resistor value, LED indicator), keeping the core function identical.  In all cases, these designs are based on simple electronic processes which were discovered by someone else years ago-- a fact to which these sites openly acknowledge.  As participants, we cannot ignore this chain of influence.  

I take the postmodern view when it comes to circuit design.  No one owns the function in which these circuits are designed to perform. No one owns the function of a filter or the function of an oscillator. These simple electronic functions can be performed in a variety of ways and as we get further away from the tree trunk of an idea, the branches become thinner and closer together. The things I change about these circuits--however arbitrary--make them more suited to my purpose and therefore are as "mine" as  anyone's claim to a recipe for homemade nachos. 

That being said, I would never directly clone a person's circuit or disregard the chain of influence.  I don't believe that is in the spirit of sharing knowledge or creative engineering.  In circuit design as in songwriting, my goal is to participate, not "steal"(whatever that word even means anymore). 

That diatribe was meant to address the fact that "my" quad ADSR circuit is really nothing more than a simplified version of the yu synth ADSR.  By reducing the number of functions it performed and therefore reducing the number of components, I was able to squeeze 2 simple circuits onto a PCB using only 2 chips (quad op amp and LM556).  I have no need for an inverted ADSR output because most of the cv inputs on my synth were designed with attenuverters. This ADSR is a sort of a simpler compromise between the two yu synth designs.

This is likely one of the last PCB I will layout in photoshop.  The circuit repeats 4 times and so it made sense to do it in photoshop as eagle cad will not allow you to simply copy a section of  your PCB layout and stamp it around. 

The transistors are 3904's and the collector is the square pad.  ha ha.  except the very bottom one that controls the led. it's backwards and so the emitter is the square pad.  That kind of mistake is easier to make in photoshop. the arrows point to the negative side of the diodes.  I doubt anyone will try and build this based on my minimal instruction but posted the PCB just in case. comment any questions, I respond pretty fast. 

since I began building modules, I find myself planning more.  I like to print version of the panels and lay the components out on them in order to insure that they will fit correctly. 

a little DEVO joke for you. 

I managed to take a million pictures of my build, except for one showing all the panel wires.

Ms. Twenty module

The MS20 is a excellent beginner filter because it sounds awesome and there is tons of documentation available for those interested in how it works.  Generally when I implement a circuit, I like to find a few different version of it.  The MS20 has been cloned about a thousands times and so there are a variety of schematics in which you can compare and contrast component values.  I primarily used Tim Stinchcombe's page but I printed and consulted tons of other MS20 filter schematics available online. 

There are only a few things which need to be changed in order to switch the filter between lowpass and hi pass functions.  I implemented a switch to move between the two functions.  The lowpass filter output volume is much lower than the hi pass filter volume so I also incorporated a gain circuit which switches with the filter function.  

In retrospect, my method for switching the gain circuit is pretty sloppy and wasn't really seeing the whole circuit when I designed it.  The next version would switch the non-inverting buffer at the audio signal input to an inverting buffer, thus the gain amplifier (located at the end of the circuit) could also be inverting (returning it to the correct phase), then I would simply have it switch between two different "Rin" resistors to adjust the gain of the inverting amplifier.  There is an audible bleep when switching between filter modes. 

also, it is definitely NOT 1v/octave. 

I got the boards made at OSH Park. This was one of my first projects in eagle cad.  There are things I like about it better than photoshop and things I like less.  Unfortunately, when a circuit board has repeating parts, it's next to impossible to copy and past PCB layouts. 

Initially I was going to use a picture of Martin Sheen (MS pun) from Badlands on my panel but I couldn't find one that fit the panel layout.  In the end, this picture of young Steve Martin (Still MS but backwards) won out.  After all of the knobs and jacks are put in, it's hard to tell it Steve but it's still fun for me to know he's on there. 

 In my earlier modules, I've generally been pretty lazy and just done all my panel wiring in one color. My modules have become a lot complex and so I had to implement the multicolored "twist" method. Since doing so, I do enjoy the final "wire up" process a lot more.  less stress. 

Monday, September 16, 2013

messing with the MFOS variable state filter -- Sagittronics -- Charlie Slick

I will start this post with a modular confession.  I have yet to utilize, on any filter, the ability for it to act as a sign wave oscillator.  I mean, like in a performance, I mostly like to use filters as filters and oscillators as oscillators.  That being said, I've been questing for a nice sounding, versatile, simple filter and I don't care so much about 1v/oct tracking.

One of the really amazing things about the MFOS website is that Ray sometimes has the same circuit in 3 different stages of complexity.  As a person trying to learn as much as I can about circuits, this is an unmatched resource!  I like to look at the early versions of circuits and compare them to the later more complex circuits, to try and understand why things were changed.

Earlier this year, maybe as earlier as February, I built the 12db state variable filter from Ray's "Oldies but goodies" section, on a breadboard.  I liked the filter but the filter had some problems.  The first problem was that the filter didn't self-oscillate. The second problem is a bit harder to explain.  It seemed that when the CV input voltage and Cutoff voltage combine to more than about half a volt, the filter would self-oscillate at a full 30v spread.  I likened these problems to the fact that I was using +/-15v rather than +/-12 and could be solved by some small resistor tweaking.  I took video of my oscilloscope to demonstrate the problem.

it happens at about 10 seconds in, then it happens a bunch more times.

I was unable to solve the problem then, so I decided to shelve the project for a later date.

After 8 or so months, I figured I'd learned enough to attempt to correct this problem.  I assembled the circuit on a breadboard and ran into the same problems.  No self-oscillation and whatever you call what is happening in this video.

I toiled over it for a whole day, trying to set a limit to incoming CV but it never truly felt like I was attacking the problem at the source.  Finally, right as I was about to give up for the day, I decided to change R27 and R28 to 100k and the problem in the above video went away.  I'm not sure how this change affected the topography of the filter but I did notice that the bandpass output got quieter which I can't really explain why.

At this time, I decided to try and implement the darlington transistor pair inside the LM13700 that Ray mentions trying to integrate on the "oldies but goodies" page.  I guess I wanted to simplify the circuit even more and I was in a general electronics exploration mood.  He presents a circuit in the MAKE: Analog Synthesizers book that unitizes the transistors in this way, so I had a nice guide to work from.

I was able to to do it, but not without some trouble.  I now had the opposite problem, when the incoming CV and Cutoff voltage was so low that it turned of the Darlington transistors, causing the outcoming voltage to swing all the way to -15v. I solved this with the 2m2 resistors connected to ground, they are intended to keep the transistors on.  I'm sure this affects the 1v/oct tracking but again, I can't even get the filter to self oscillate.

In the end, I'm not even really sure what I have here.  I ended up with a similar circuit to the one in the MAKE: Analog Synthesizers book but with a Hi-Pass Filter and slightly more precise CV input.

I'm not happy enough with the circuit to build a module, and I'm so burned out on it, I can't tell if it even sounds good anymore.  I guess I will shelve it again for a while and let the ideas stew.  I did benefit from toying with the filter in my attempts to tame/simplify the design.  Comment with any suggestions.  I guess I'm moving on the the YuSynth Steiner filter next, or perhaps this MS20 design I found.

Attack Decay LOG LIN Gate controlled Portamento --Ziggy Stardust Rise and Fall module

This circuit is primarily based on a Harry Bissell design.  I changed some values in order to make the input impedance 100k and I added a gate controlled switch, which I borrowed from the YuSynth portamento.  The comparator circuit to control the LEDs which indicate the state of the portamento was my own design. This circuit allows you to adjust Attack slide separate from decay slide.  It also allows you to adjust the portamento between linear slope and a slope resembling logarithmic.
above is the schematic.  I know you are probably thinking, when is this guy gonna get a fucking scanner? I'm sorry, I'm broke right now. 

I'm not gonna spend a lot of time how how to assemble this one.  For me, I got lost somewhere along the assembly. It was just too complex and I had to rewire a bunch of connections I made. In the end, I can't remember what I got right and what I got wrong on my PCB labels. With 12 panel mounted knobs, 12 jacks, and 12 leds, it made for a lot of hook up wires.  Below is the PCB without labels for hook up wires, to be amended at a later date. 

Friday, August 30, 2013

Super Simple Linear Asymmetric Portamento -- Glissando -- Slew Limiter -- Glide

FYI, this is not the schematic for the Attack Decay Gate controlled portamento I just built, I will be posting that build/schematic very soon.  Thanks! (that schematic incorporates aspects of this schematic, so if you're at all into understanding analog circuitry, this post will help you understand the upcoming post)

I just finished designing a far more comprehensive portamento module but I'm waiting on a few parts in the mail to complete it.  While that's brewing, I thought I'd take the time to show an extremely simple and awesome linear portamento circuit. It's similar to a portamento modules I worked out in an earlier blog post, this one has the proper resistors to give it a 100k input impedance and a 1k output impedance which I find ideal for modular synthesizers.

For those who don't know:  Portamento, glissando, glide, and slew limiter are all different names for the same musical concept. It's basically sliding between notes. Since Modular synthesizers are analog, their "musical note information" is represented by a voltage between 0 and 5v instead of a digital number.

An overly simplified example: a C note might be represented by 1v and a D note might be represented by 1.5v. If we wanted to slide between these notes, we would alter the rate at which it the circuit could move from 1v to 1.5v. We do that with an RC Circuit.  The R and C are resistor and capacitor.

The two main types of portamento circuits for modular synthesizers are exponential(logarithmic) and linear. For linear portamento, the slide time is dependent on the difference between the voltage(note) values. There is a longer slide time to get from C to G than from C to D.

In exponential portamento the slide time is not dependent on the difference between voltages(notes). The slide rate is based on internal resistance, so it is consistent no matter the distance between voltages(notes).

The circuit below is linear portamento. There is a potentiometer labeled 1M in the middle of the circuit.  This is the main R in the RC circuit and determines the amount of portamento.  The more resistance we add with this Potentiometer, the more portamento we get. By adding a switch and diodes, we give can voltage a path through a diode and around the potentiometer. The diodes allow either positive or negative voltage through dependent on it's orientation. This gives us the ability to have slide only on ascending notes or only on descending notes

The left side is the input and the right side is the output.

2 X 100k resistor
2 X 1k resistor
1 X 1m potentiometer

2-3uF non-polar capacitor
2 X diodes 1n914 variety or similar will work
1 X spdt (center off) switch

2 X op amps.  either 2 X 741's or a single TL072 or half of a LM324 or whatever

I've tested this circuit on a breadboard and it works great but I didn't build a module based on it.  It's simple enough that it could be easily done on prototyping board.  ENJOY!

Sunday, August 18, 2013

AttenuVCA mixer -- Auto Panner --Simon Pegg

I recently moved to Portland,OR from Ann Arbor MI.  A little before the move I was working on a newer version of my 10 step sequencer but I ran into a bunch of problems and although it turned out OK, I won't do a post on it until I get it figured out completely.  That being said, my first project after my move was to build a simple 4 Channel VCA to replace my earlier VCA.

There were a few things I wanted to improve on the older, modified MFOS VCA I built.  I figured it would be cool to design in a simple Mixer circuit to allow the module to be used as voltage controlled mixer.  I also thought it would be nice to be able to invert the individual channels CV so I could use the module as an auto panner or subtractive VCA.  To accomplish this, I include attenu-verters on all the inputs.  The VCA I designed is mostly based on the MFOS VCA and the VCA that Ray put in his MAKE book, which came out this year.  I decided to skip the whole LIN/LOG aspect of the VCA and just make it a simple LIN VCA.  This kept the overall circuit much less complex.

There is a mistake in the schematic above.  the NPN transistor was switched out for a PNP.  the LED connects positive side to ground and negative side (shorter) to the emitter of the PNP.  the collector is connected to -15v via a 2k4 resistor.  the base is the same,  connected via a 100k resitor to pin 7.

Thursday, May 30, 2013

Rick Moranis 10 Step Baby Gate Sequencer module based on the CD4017

I Just finished my newest version of the "baby 10 sequencer".  It has control voltage and gate switches.  I found some problems with it, and subsequently this module.  I will be posting some modifications in the next few days. 

In preparation of improving my baby 10 sequencer, I've been coming up with things to do with the CD4017.  A couple weeks ago I built the sub-oscillator out of the CD4017.  That introduced me to the 2 transistor Schmitt Tigger which I borrowed from the Yusynth clock divider.  I also borrowed from that same clock divider, a diode "and" gate which I modified for this project.  I also chose to incorporate a "gate to trigger" circuit similar to Ken Stones Gate to tigger circuit for my reset sync input.  I'm not sure how much of this module you could actually call mine, but I guess this is how you learn at first.  Working out this circuit will be a big help when I move onto my all encompassing 10 step baby sequencer.  possibly my next project.

I did a mock up on a breadboard of my idea to make sure they would work.  here is a video.

Monday, May 20, 2013

Square wave sub oscillator based on the CD4017

Wouldn't it be cool, to be able to mix in different sub-octaves of a frequency, similar to an organ or my old Korg poly800, without using up a bunch of oscillators?  NOW YOU CAN! This module is in the realm of wave folders and saw tooth animators.  an oscillator augmenter.
I got an idea of how to do that with the CD4017 when I was looking up schematics for building a Gate sequencer and a clock divider.
Essentially,  how the module works is, you feed it a very high frequency from an oscillator.  it creates a square wave version of the original signal and the 3 octaves bellow it.  you can access any of the signals directly, or mix them via potentiometers to a mixed output jack.

Below is a schematic I drew up that shows the basic idea.  This schematic only shows one sub-octave, not all three.

Friday, April 26, 2013

Midi2CV module via Midimplant board

UPDATE 8/19/13 -- I'm working on a new version of this module with buffered outputs.  Stay tuned

 This is a module I built based on the Midimplant board.  They are capable of different configurations which you can upload via midi Sysex.  The website has a configuration widget here, which makes things incredibly easy.  One of these options will convert midi to CV and Gate signals for 2 independent midi channels.  My eventual goal is to have a 4 channel midi to CV module, so I hope to be getting another board when they are available.  With that in mind, I designed the module and the PCB to be ready for my future configurations.

Here's the board. I soldered a header on it, to make it easy to play with.

Here's the pinout.  Something to keep in mind, is the gate signal is whatever the Positive voltage input is.  my system is a standard +/-15V.  All my modules seem to work fine with 15v gate, so I didn't really worry about adding a voltage regulator, but it would be easy to implement if that was a requirement.