Wednesday, February 27, 2013

YuSynth ADSR module

So,  A little while back, I built the Ian Fritz dual AD/AR module and it works pretty good but after using it for a few weeks, I decided to upgrade to full ADSR modules.  I have an ADSR envelope generator from but my goal with this project is to teach myself stuff and eventually replace any ready built modules with ones that I've put together.

I can't link directly to the project page because of how their website is set up, but you can find it on YuSynth by navigating through a few menus.  If you are going to build this module, you will find the all the necessary information on that website including PCB's and component layout.  Consider this blog post, like a DIY builders epilogue.

I built the improved ADSR module and in fact, I actually built two of them into one double wide module.  why not do two individual ADSR modules?  well, double wide modules have more space than two single wide modules because they share two edges.  They are also more rigid, and since I'm only using simple panels instead of module blanks, that's also a benefit.  I also have limit power plugs and this way, they can share a power plug too.

I breadboarded this schematic before I built it and it's a good thing I did. because, or at least with the components I used, the LED didn't seem to work.  I tried a few different resistors but it was only after I tried switching the orientation of the Diode and the LED (D5 & LD1) that the led worked.  I'm not sure if this was a mistake in the Schematic or just circumstantial, but anyway, its work just fine now, reversed. 

There was one modification I made to the PCB before I etched it.  In the instructions, there is an optional 150K resistor which changes how the inverted output works.  it essential shifts the inverted output into positive voltage, subtracting from +10v instead of 0V.  I decided to put in another junction allowing for a switch, to switch between these two options.

So,  here's the PCB I ended up etching.  It's a dual and it has the mod for the switch I mentioned above.  You will find all the component placement and stuff like that on yusynth, as well as the original single module PCB.  My modification is in the bottom left corner of each of the two circuits.  the two holes closest to ground in that corner are for the switch.
BE SUPER CAREFUL ETCHING THIS PCB!  because the 3 traces that go under the CMOS 555 chip are extremely close together,  I had to scratch away a little between the traces and put it back in the acid to make sure they weren't connected,  this is where having an LED pen light can come in handy, making sure traces are not connected.  

when transferring  I always double check all the traces to make sure they are nice and solid, I fix whatever looks weak with a sharpie.  They make etch resistant markers, but this seems to work fine.  I also like to fill in big open spots, so there is less to etch. 

Laying my stuff out on the panel to make sure it will all fit nice. 

When my spots are all chosen, I tap them with a nail and a hammer so they don't get erased.  then I circle them with a marker and label them.  Makes drilling the holes to the correct sizes harder to screw up. 

Then I choose the placement of the PCB and put those holes in. 

now for the build.

I know other people use jumpers and connectors and crap, but I just solder my wires directly on,  I ain't got money or time for all those jumpers.  Something I've learned to do though, is prepare all my wires before I start soldering.  By that, I mean, cutting them to the correct length, stripping them, and tinning them if need be. 

by the end of a bigger build like this, my patience gets worn down as well as my soldering iron.  I pretty much went start to finish on this project but it's more likely a two day project.  I find it helpful to change tips often too.  I use a file to make them nice and pointy again, or I just put a new one in.

When I finally finished this project at 11pm last night,  the left ADSR worked great and the right one didn't!  OH NO!!!!  I went back over everything, checking all my pot and switch connections.  It still wasn't working.  Then I went over the PCB with an LED again to make sure nothing was making accidental contact.  I found a hair thin piece of solder connecting to pads,  I scratched it away and it worked great!  BE CAREFUL and dont panic. 

THINGS TO KNOW FOR THIS PROJECT!  definitely use a CMOS555 chip and not a tradition 555.  I used Tantalum capacitors for C7 and C8 like the instructions said but I tested it with Electrolytic caps when I had it breadboarded up and it seemed to work fine. DOUBLE CHECK ALL YOUR TRACES, especially under the 555.

a little demo.

Wednesday, February 20, 2013

Ultra Simple 8038 LFO circuit & PCB

UPDATE!!!! I recently built a triple LFO version of this build and ran into some problems with the new set of 8038 chips I purchased, they don't all work the same,  The amazing range I got were specific to my first batch of chips.  keep your eye out for this set of numbers, because they worked.  

and the following set of numbers did not work with this set up. 

I tried ordering more chips with the correct numbers based on the picture of the chips on ebay and they sent different chips that didn't work.  I'm really annoyed with the 8038 chip situation. So, I'm going to revisit this LFO project with a different circuit,  one that doesn't utilize the 8038. 

For my modular project, I'm trying to keep it simple, at least in the beginning, so i can learn what I can from each circuit I build.  A simple LFO circuit, is something I've tried to build a few times, with limited success.  It wasn't until I was clicking around on YUSYNTH (my new favorite website. It's loaded with projects and information), that I came across this ultra simple implementation of the ICL8038 chip.

I wired up the circuit almost exactly how it is here and it worked pretty good, But I didn't have the necessary switch for all the cap and resistor combinations--which led me to experiment with different combinations of resistors and caps to cover the range I wanted.  I put in a 1uF Tantalum cap at pin 10 and a 1M pot (replacing R5, R6, & R7) and was able to achieve the ultra low oscillations I was looking for.  The 1M Pot basically working as a Coarse tune, and the 10K pot working as a Fine tune.  I also found that the voltage input was basically useless to me, it seemed to hardly affect the frequency and when i hit it with higher voltages, it would stop oscillating altogether.  I decided to skip that aspect of it, at this time anyway. 
Theres some extra chips on there because I was testing to see if the square wave output would work as a clock for the a 4017 decade counter chip. it does.  

Above is the schematic that I came up with and ultimately built into a module.
Electronics is one of those things, where I don't exactly understand, at what point you can call a circuit "my circuit". I mean, how much do you need to change and does it really matter if you're giving away the plans for free.  Anyway,  I felt like I changed enough to call it my circuit, but it's really just a modified version of the circuit I found on Yusynth.... It's like a remix

I decided to just draw the PCB.
I made a little mock up of the traces

I thought it might be easier, especially with the chip, to drill the holes first, using a perf prototyping board to set the spacing.  I guess that helped, though drawing little traces with a fat tipped permanent marker can be kinda stressful.  

I realized, after I started etching the pcb, that I forgot to put the transistor rate indicator on there,  so I added that.  Strangely,  I found that drawing on the partially acid etched board was easier, and the ink stuck to it better, probably because the acid made the surface less smooth.  It made me consider dipping my boards in acid for a second before I apply transfers to them also.  who knows?

The board came out good and so i put the components in there.

In the end, I opted for a switch between Sine and Triangle waves.  The square wave gets it's own output, so I can use it as a clock.


so,  I spent some time this weekend and made a PCB in photoshop which everyone is welcome to use.  let me know if there are any problems with it, because, I hand drew mine.  It's designed to be transfered, so you should be able to read the writing correctly after it's transfered.   

So,  things to know about this circuit.  Both the .1uF cap and 1uF cap are bipolar.  The Transistor is a 3904 but you can use an equivalent NPN.  You can change the 680Ω resistor that is connected to the transistor according to the LED you choose.  The negative side of the LED should be connected to ground (I panel wired all of that stuff).  I forgot to mark the orientation of the two 22uF caps, but that's something you should be able to figure out.  The left cap is for the positive rail,  it should be oriented with the positive side of the cap connected to the rail and negative side to ground.  The right cap should be opposite,  positive side to ground and negative side to negative rail.  You will probably need an oscilloscope to tune the 3 trim pots.  you may be able to do it by ear.  One of the 100k pots is responsible for offset, adjust it to center the wave over ground.  the second 100k is for shaping.  The 100Ω is also for shaping,  do that one last because it's more of a fine shaping.  The shape of the wave changes depending on what frequency was when you set the trim pots,  as you get farther away from that frequency, the waves begin to distort.  I set the trim pots to be most accurate when the LFO was at lower speeds because that's when you'd be able to hear it most clearly. so, the wave becomes a little mis-shaped at high frequencies.... enjoy.

In the video,  I have the 8038 LFO hooked up to the cut off frequency of my State Variable Filter.  Enjoy. 

Friday, February 15, 2013

MFOS VCA for MOTM +/-15v take 2!

You may want to consult my earlier blog about the MFOS DUAL VCA.  I wasn't totally happy with the results from that build, so I went back and made better, more informed modifications to the circuit.

I don't want to take credit for doing anything except changing some values to get the circuit to perform better with my +/-15v system.  If you're at all interested in building this circuit, I suggest you start by checking out the original VCA on Rays website.  There you can find the earlier version for +/-12v along PCB layouts for etching. 

This is the circuit and the values I ended up using for the VCA.
These changes gave gave both Log CV and Linear CV similar volumes, which was a problem I was having with the original circuit.  It also brought the overall output volume up in the range of my VCA which was nice.  

Somewhere along the line, I accidentally used a 220K for R18 instead of 220ohms. I didn't notice until I hooked it up to my Oscilloscope to compare it to my VCA. Basically, The mistake over drove all the incoming signals and turned all my waves into Square waves.  After hunting around, I found my mistake and fixed it.  It goes to show,  that not all mistakes like that, will make the circuit totally un-useable.  Sometimes those simple value mistakes can take a little while to manifest. 

Thursday, February 7, 2013

Variable Inverting to Non Inverting OP AMP amplifier

This is a pretty simple but useful circuit I put together.  It's basically a variable inverting/Non-inverting amplifier.  When the pot is all the way left, the signal is Non-inverted.  All the way right, it's inverter. the center has no output.  I designed the circuit to mimic a property on my State Variable Filter module. From I can tell, it works exactly the same.  I was surprised when I tried searching for an op amp set up that would do this, I couldn't find one.  I probably just don't know what its actually called.  Anyway, here's the design I came up with.
I used a 741 to test it out. 
In this video, I used it on my Filter with a triangle wave.  as you turn the knob, the signal attenuates all the way to 0, which is about center,  then it begins inverting 

Friday, February 1, 2013

MFOS Dual VCA (Quad VCA) module for MOTM

UPDATE!!!!  2/13/13
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. HERE

Basically,  the best resource for getting started in building Modular Synthesizers is Music From Outerspace.  Most of my modules came from this site, as well as a bunch of core ideas I applied to other modules.  The only thing that can get in the way with building modules from this site, is, most of the schematics are for a +/-12v power supply.  My Modular is the MOTM style with +/-15v.  a lot of the projects are scaleable and don't require any modifications but some do.  The next project has a couple small modifications I made to the MFOS dual VCA project which I found, made it better for a +/-15v system.  REMINDER: I am an amateur and I don't guarantee anything.

so,  if you feel inspired to build this circuit,  I encourage you to visit the MFOS page where you will find more information and PCB layouts for the project.

So, like all projects, I breadboarded it up first and tried it out.  It worked well but there was a huge volume difference between Log and Linear CV response.  Also, I own an VCA and it had a noticeably lower volume over all.  using my VCA as a standard  I decided to mess with the resistor values and see if I couldn't get a similar volume.  Well, as you can see above, Ray actually made some modifications to the circuit in red, and I thought, not knowing exactly what I was doing, I would try reverting those values back to their orignal values to see what effect they would have.  At least then , I could understand how they improved the circuit. I Found that going back to the original values for R15 and R16 gave me more overall volume. I liked that.  R18 I left at 220ohms and R14, I ended up using a 27K resistor because it's what I had.

I still had this problem with the volumes between the modes being really different.  so I played with some of the other resistor values trying to make this better.  It occurs to me now,  after looking at the schematic again, I would approach this problem differently. What I ended up doing was changing out R9 from a 120K to a 1K.  That allowed a lot more current through and brought the volume up.  If you've got this schematic breaded up and you feel like trying some stuff,  I would try changing the R3 and R4 to 10K resistors and see how that affected the circuit.  I wouldn't be surprised if I wrote another blog about this circuit in the future with other changes.

Overall, the circuit works quite well, so I went ahead and etched 2 of them into a pcb to make a quad version of this module.
 I built this handy circuit board holder for the project.  Made soldering a whole lot easier.  I pretty much always use those chip sockets because my soldering iron doesn't have a temp control and I've been known to burn up chips in other ways too.

Making sure my parts would all fit on my double wide panel

I decided to add some leds to my amplifier.  flashing lights make everything cooler.  I built this simple 3904 led buffer circuit on a hand drawn PCB.  basically,  the Base of the 3904 is connected via a 100k resistor to the signal output of the VCA circuit. and the correct resistor value for the LED of your choice should go between the collector and +15v, and the LED should go between the emitter and ground.   I always use a heat-sink when soldering transistors

I didn't have enough spdt switches, so I've got one dpdt switch in there. 

I added a jumper area to the left of the original layout.  I found it's nice to have all the wires leave the circuit board from the same area, makes things cleaner but also adds to the work.  That's also where I've got my power hook up (top left)

All finished!!!

This video is on the boring side,  but I didn't really know how to effectively show the VCA in action without becoming convoluted with the operation of other modules.  so basically,  I change the envelope on 3 channels and also switch between Log and Linear VCA.