MXR Distortion +

I decided that I wanted to have some FX processors for my synth so I started looking at simple modules to build and I come across the distortion+.  The distortion+ is a soft clipper, however as you can see it turns the pretty sine into a hard square so the circuit may need some tweaking. The clipping comes from a diode network at the output of the circuit, different diode materials and placement will determine how much the signal is clipped, this is how you get the ‘fuzz’, ‘hard’ or ‘soft’ clipping sound. I have posted a video to show it working with my Roland synth.

 

Heres a link to the video!

 

Square!

The final output stage is the square wave. The output of the sine leads to an amplifier with a huge gain which heavily distorts the sine wave into a square shape. The pulse width of the square can be adjusted through a positive and negative input voltage through a buffer which leads to the negative input of the amplifier. The output result is an adjustable pulse wave. An additional input can modulate the pulse width changing the timbre of the sound giving it a vibrato effect.

Back to The VCO!

Next in the line of outputs comes the sine wave, you will notice the crossover distortion at half wavelength. The sine is shaped through a differential transistor pair which distorts the triangle wave to sine. A nice explanation of the differential transistor network can be found in electronotes. The input voltage can be controlled through a couple of variable resistors which control the points of the positive and negative amplitude, so you can shape or tweak to how you want.

Below is the sine output shown on the oscilloscope. (Note that I have a signal generator on top of the scope which is connected but switched off!)

Tunes!

As a keen lover of electronic music and all things dark and dirty, I thought it was a good idea to write some of my own stuff a couple of years ago. I started out on reason and fruity loops, then progressed to a mac using logic and a great number of processor plugins.

I have uploaded a couple of tracks on soundcloud here.

I designed my ‘Gnasher’ logo in photo shop following a pretty cool tutorial and making some minor changes. Im sorry, if I could post the link I would, however I have lost all my previous references on my other laptop which died from beer overdose… over the keyboard.

VCO triangle output

OK, now the basic waveforms of analogue synthesizers come in the shapes of sine, square sawtooth and triangle, they can be generated through many different types of circuit and can also be distorted or shaped from one wave to another.

I decided to use a simple voltage controlled oscillator design from Thomas Henry which has a Triangle, Sine and Pulse output. The whole thing is shown on breadboard just below. (Please take a note of the complete scrappiness of the circuit layout. It was my second try at putting the thing together and it worked so no need to change it, it works, and can be rearranged on strip board, however a tidier circuit is a happy/stable circuit).

The triangle wave is generated through an integrating op amp circuit, this part of the circuitry is the main wave form generator, and I will explain the use of other parts of circuitry which connect to it in my next blog.

The output of the triangle generator leads to a Schmitt trigger in the feedback network. The use of the Schmitt trigger is to give a more stable output and increase the switching time, this gives more stabilisation in the higher frequency ranges which gives a better tuning of output frequency. The output frequency is determined by an exponential voltage to current relationship where Vin stays linear and current increases exponentially. The reason for this is because the current is what is driving the oscillations and the human ears frequency detection work in a logarithmic fashion.

DIY synth

So, after pondering for weeks and weeks on what to post in this blog I decided to pick up where I left off with a project I started nearly 2 years ago for my HND.

I decided to bite off more than I could chew and went head first into the world of the DIY synth. My aim was to build a simple analogue synthesizer consisting of a single oscillator, filter and amplifier. As a big fan of the good old synth, digital or analogue, this was not enough, so it had to consist of all the bells and whistles and be able to make me a coffee (because my girlfriend is a lazy so and so). In the end I wanted my final design to include multiple oscillators, LFOs, variable filter responses, multiple ADSRs, effects processors and so many routing capabilities it will put the spaghetti junction to shame.

I would say I’m ¼ of the way there, I have a great collection of schematics to leech off and change to my personal preference and I also have the main body of the synth working and on bread board with a couple of guitar effects to add in to the circuitry. It has been sitting for nearly a year now doing nothing so now is the time to get back on it and share the love.

I’ll start off with going through the basic building blocks and circuitry needed to construct the device and reminisce the anguish of learning how to transfer a schematic diagram on to strip board. I will also talk over certain chips and ICs I used and why they are necessary in the circuits.

Stay tuned and be prepared to be bored to death, unless this is what you’re into..

Cheers n’ gone.