Thursday, January 31, 2013

Dual Fritz AD/AR Envelope Generator

I was surfing around the web looking for a super simple Envelope Generator that didn't require any CMOS chips.  When I'm looking for projects for my synth, I'm not necessarily looking for the coolest, most wild modules to build.  I'm looking for stuff, simple enough, that I can comprehend what's going on in the schematic and build my knowledge and understanding of circuits.  I came across this build on  and thought I'd give it a go.

As you can see. it's pretty simple.  It utilizes a quad op amp, some resistors and whole bunch of diodes.  If you check out that page I link to above, you'll find 2 pcb layouts ready to go.  One is for a single Fritz AD/AR generator and the other is for a dual.  I opted for the dual

 so,  like all projects.  I breaded it up first to make sure it would work.  the only thing that initially confused me was the polarity of the Capacitor.  if the project doesn't seem to work, try turning your Capacitor around, worked for me.

Then I put the panel together.  The layout is a little strange but it's what worked best for mounting the PCB.  I picked up that Angle aluminum from the hardware store,  I just cut off the length I need with a hacksaw and drill holes in it.  works great.  It also makes the modules more rigid, which is nice.

Etched the PCB and drilled all the tiny holes.  I guess I should do a post on etching PCB's pretty soon.  Totally easy.

In the video, I use the top Envelope to control the VCA and the bottom to control the Filter.  

Asymmetrical Linear Portamento

UPDATE!!!!!! 8/30/13
THIS PORTAMENTO CIRCUIT IS SUCKS!!!!! I created this circuit really early on before I understood input and output impedance.  for a far better circuit.  please refer to my new post 


A while back, I found a simple post on Linear portamento.  it's here.  It was a simple enough circuit but without the resistor and capacitor values, I couldn't get it to work.  I tried a bunch of shit and eventually figured it out.  It works like a charm--except the fact that it will sometimes--unexpectedly--but probably when I'm connecting or disconnecting the module-- it will "burn up" the LM324 quad amplifier chip I've got inside it.  I added a resistor on the output and that may have done the trick, though I have been extra careful with the module.  In reflection,  the addition of the 1k resistor to the output may have adversely affected the module and there is probably a better solution.  anyway, build at your own risk.  I am considering, the next time I build the module, adding an extra buffer on both sides of the circuit. or perhaps using 10ohm resistors/capacitor set up to limit the amount of current allowed into the circuit all together.   Keep in mind that I'm an amateur, here's what I built.

These values made the schematic work, there maybe other options that work as well.  Make sure you use a bi-polar capacitor.  also,  it may be hard to see, but there is a switch that connects from the right side of the 1k resistor and the two diodes facing in different directions.  They should be connected to a SPDT with center off (ON/OFF/ON) switch.  The switch enables the asymmetrical aspect of the portamento, so it sides only when ascending or descending between notes.

What isn't pictured in the schematic is the 1k resistor I added to the end of the output.  It's not in the schematic because like I said before,  I want to try something different next time.

I suggest trying it out on a breadboard first.  I do it with every circuit I make.

I built this module before I'd tried etching a PCB.  Turns out, its really easy to etch a PCB and I probably won't be doing these perf board set ups anymore.

The module is top row, far right.  It's a dual module, dunno, just because.
this pictures was taken later, as you can see,  I have more modules now

Here's a Demonstration of the module with a oscillator.  Sorry that you can't see my fingers turning the knob or flipping the switch, but you get the idea.  ha ha. 

Catching up.... Updated Ring Modulator

I'm way behind.  I've built all all kinds of modules since my last blog post.  With each module I build,  I begin to understand how little I really know about electronics.  I'm learning a lot and I can now recognize reoccurring themes--especially with Op Amps--but I don't guarantee any designs I post on here.  I'm an amateur just trying to figure stuff out.....

So lets start with my updated ring modulator.  The ring modulator itself is a passive circuit but there's a huge volume loss after the signals(input and carrier) pass through the transformers.  The previous design used two LM741's to boost the signal before the transformer Diode ring. The circuit design itself wasn't ideal, at high gain it caused high frequency oscillations and all it really did was overdrive the signal before the transformers.

I rebuilt the module with a single LM741 after the ring modulator circuit as a simple recovery amplifier, to account for the volume loss.
This is a sketch up of the schematic.  Since I bought the Ringmodulator kit from Synthrotek , I really only had to focus on the amplifier aspect of the circuit.  The two potentiometers control the incoming signal volume and arn't really necessary.

It was a simple enough circuit that I went ahead and  sketched the circuit freehand on a piece of copper clad pcb.

The circuit seems to work well, with little or no wave distortion.  I've seen some modules which add a 555 oscillator circuit, but I'm not personally a huge fan of the 555 or using the Ring Modulator with a constant frequency, so I kept mine simple and use external oscillator signals.


in the video I'm using two oscillators with the ring modulator,  I'm controlling the gate with a simple arduino random midi generator sketch I made.  One oscillator is fed pitch voltage from the arduino and the other oscillator is fed pitch voltage from an ADSR.  then my camera ran out of batteries..... ENJOY!