Home made analog syntheziser

I began this project when I was in High School, near 1992. I had skills in electronics, computer programming and music, and I liked the idea of build an analog synth.

In that pre-Internet era, at least in Argentina, I had to design everything by my self, of course, in a prove and error way.

The first design was the VCO. There were many versions. At first I build a V/Hz oscillator (or almost that), and then a hi-freq VCO that clocked a counter that produce many simple wave shapes via a R2R network (A kind of sampling). Those designs didn’t like me at all, and had many problems.

Then I build a "discrete computer" with many 74HT series IC's to scan a keyboard and produce a Hi-note priority VC and GATE signals. This circuit, with little mods, is now working in the synth. Of course, a microcontroller can do that in a simple way, but I knew them many years later.

In the middle of the 90's I had access to the Internet and could learn how to design a 1V/Oct VCO and a Moog type VCF.

In 2000, I had many designs and circuits tested, so I decided to put them in a cabinet. I bough a not-working Casiotone in a music store and build a wood cabinet. I put everything inside and hardwired each PCB. I design the front panel too, using MS PowerPoint.

The years till now I introduced many improvements, like a more stable VCOs and a Microcontrolled MIDI Interface, that also replace some instable analog circuits, like Transpose and 0800 DAC´s that has a poor performance cause its relative hi error tolerance.

I can say the project is ended, but there are many things I'd like to improve in a future, such as LFOs and Envelope Generator. I suppose I'll do it sometime.





Features:

3 x Analog VCO:
Sawtooth, Pulse w/modulation, triangle
2 modulation channels for each one
Individual transpose: +/- 2 octaves and free
Hard Sync
1 x White Noise Generator
1 x External imput

1 x VCF (4 pole Lo Pass): Moog clone filter w/ 2 modulation channels, and resonance, cut off and envelope amount controls.
(The mixer overdrive the filter producing a very nice overdrive effect, similar to valvulated amplifiers)

1 x VCA w/ 2 modulation channels,

2 x LFOs

2 x ADSR envelope generators

MIDI IN: Note, Pitch bend, Cut Off and Modulation controlled vía midi messages.


Other projets:

These are other synth projects:

-Analog Guitar Synthesizer: it's a simple overdrive-distortion effect box. I put many type of diodes to get different clipping configurations. It has also a tone control and a hi-pass filter in the input.

-Analog electronic drums machine. I had the schematics but only build some parts. I don't thing that I'll finish this project.

-Polyphonic synth: I'm in the beginning of this project. I just design de DCO's (a super stable analog VCO, hard synced with a microcontrolled pulse) and a VC Wave shaper. I'd like to build a polyphonic synth with 100% analog audio signals voltage controlled by a 16-bit microcontroller to get pitch stability, complex patches and modulation capabilities (LFOs, Envelope Generators, Modulators, etc are generated in the microcontroller so there are infinite possibilities of modulate a real analog sound). Now is only a project and I have some schematics but I’m not intended to build it in a near time.

Analog DCO

I want to share this circuit I design for a Poly Synth. VCO are not so good, in my opinion, for polysynths. this digitally controlled analog oscilator have the characteristic lineal response (not discrete) of VCO and controlled pitch without unwanted detunes among different voces.

The circuit is a constant current source that charge a capacitor. The time constant is controllated by R1 and C1. Q1 discharge the capacitor by uC when it's supposed to. The circuit needs a uC that generate the clock frequency and CV (16 bit prefered) because log response.

the uC has to simmulate portamento, pitch bender, note on/off, etc.

Please, test it before use!!

Demo 6

This video shows some capabilities of the synth.

I played in unison a piano patch on my JV-80 and a typical synth sound on the TML-01 in unison, linked via MIDI cable. The TML-01 is a mono synth with upper note priority so I tried to play the melody with using the upper voice.

The performance was more or less improvised on the fly so you can hear some note and tempo mistakes.

Yazoo - Dont' Go

This audio shows many sounds
I created with my synth



Except drums and singer, all you can
hear comes from the synth.

I haven't sequenced this song
I only modified and remixed the MIDI file,
added voice track, added some other things and
rendered all sounds with the synth
In almost all tracks I added some delay or
reverb effects.
Sorry I don't know who has
sequenced this song,
I just got the file from the Internet.

Music & Lyrics: Vince Clarke

Here YouTube version:

Portamento Mods

In this video I show you the last mod to my synth. The actual portamento circuit has a logarithmic response since I use a simple passive RC network ((it's important to say that the circuit has a logarithmic response but when you applied to a 1 Oct/volt VCO you cancel the log effect, cause the expo response of the VCO, and you obtain a linear response in frequency, buy musical tones are distributed exponentially in the frequency range so this linear in frequency response in not musically natural)).
The result is a fast sweep at then beginning and a slow sweep at the end of the portamento effect. You can hear this effect at the beginning of Erasure’s Chorus. Many synths have this type of portamento but I don't like it. There are other electrical negative effects when the value of R is very high (R is a 1Mb potentiometer which change the portamento time), at this point the output voltage never riches the input voltage, I don't know why. Although, I suppose this is a defect of my design.

So, I decided to replace this circuit with one with linear response (exponential effect in frequency when applied to the VCOs). The circuit is very simple too. It uses an integrator Op Amp network placed in output of other op amp before its feedback network. When you apply a specific voltage to the input the output try to replicate the input but the integrator network produce a controlled linear slew rate.
I want to replace the old circuit with the new one but in a fast and simple way, so I build a little daughter board that I placed in the dip socket of the old circuit buffers Op Amp (TL 082). With this I can back to the old circuit just taking of the daughter board and placed an OP Amp in the socket.



Another possibility of the new circuit is the asymmetrical portamento. A diode placed in parallel with the rate potentiometer produce the portamento effect when you play upping phrases and cancel the effect when you play down way phrases. The new circuit has this facility but I don't use it yet because I have to put a switch in the front panel.

Electronics

The following video shows the inside of the synth. You can see a lot of wires and circuit boards. You can see that I have only used printed circuit boards for microcontroller board because its complexity.