electro-music.com wiki | Schematics / The SN-Voice Project

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DIY | VCO | 76477 | Thomas Henry | Scott Stites | Square | Noise

The SN-Voice Project by Thomas Henry and Scott Stites visit http://www.birthofasynth.com/Thomas_Henry/Pages/SN-Voice_main.html for many details on this project ,construction and calibration guides and lot more .

Notes from the page :

If you're new to Synth DIY and have never heard of the SN76477 IC, there's a good reason - it's long been out of production. But it still exists out there in the wild - a few supply houses on the internet still list it, and it's been known to inhabit parts bins all over the world waiting for just the right application.

The SN76477 appeared in many a video game of the late '70s and early '80s, supplying players with bleeps, bloops and swept noise as they vanquished pixellated aliens dropping from the skies. It was also featured in other items, more often than not, toys. There were a few kits out there for hobbyists. Some were music related, others were for just making revving engine, steam engine, explosion and gunshot effects. Somewhere between the mid '80s and early '90s (I'm not sure when) Texas Instruments terminated the SN76477. With prejudice.

The SN76477N didn't deserve such an unceremonious fate; if ever there was a feature packed DIY wet dream, it was the SN76477N. In fact, the SN76477 is a fully loaded synthesizer on a chip. Within its silicon boundaries lie the following functions:

A Voltage Controlled Square Wave Oscillator

A Super Low Frequency Oscillator (a fancy term for LFO)

A VCA-like 'modulator'

A Sweepable Digital Noise Generator (shift register based)

A Filter for the Digital Noise Generator

An Envelope Generator (Attack/Decay)

A programmable Mixer

The Sn Voice itself ,as designed by Thomas Henry has the following features :

- V/Oct VCO with Square or PWM (modulated by either LFO or EG) output. This output can be switched between pulse/square output or digital noise output. The amplitude of this output can be controlled by the envelope generator or be locked to a constant output amplitude. Output is 10Vp-p max, with an output volume control.

- VCO Triangle wave output. This output is a constant 10Vp-p and is not controlled by the envelope generator.

- VCO is controlled by a V/Oct control voltage input, an expo modulation input (with associated level control), a linear modulation input which can be either AC or DC coupled and also has a level control, a coarse tune control and a fine tune control.

- Sweepable Digital Noise Generator

- The Digital Noise Generator can be controlled by a keyboard control voltage input and an expo modulation input, which has an associated expo modulation level control.

- Manually adjustable Noise Filter.

- Wide range triangle wave LFO (less than .2 Hz to over 200 Hz over three ranges) and 10Vp-p output. Frequency of the LFO is set manually.

- A gated ASR (attack/sustain/release) envelope generator that is active when the pulse/noise output is set for EG. Output is 0 to 5V. Maximum attack and decay time is approximately 6.5 seconds each. The envelope generator accepts +5V gate signals and will remain high as long as the gate is applied.

visit the Thomas Henry subforum http://electro-music.com/forum/index.php?f=148 for more info and pcb offers

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