Alesis A6 Service Manual download pdf (Page 6)

Confidential Alesis Service Manual 8-31-0089-C

1.0 Theory of Operation

The A6 is a 16-voice digitally-controlled real analog synthesizer.

The heart of the system is a Motorola Coldfire processor on the Main board. The code for the

Coldfire is in flash memory, and is upgradeable through MIDI. There is also a battery-backed

SRAM for holding user data.

There is a secondary processor on the Front Panel Left, an 87C52 running code from an

EPROM. This processor controls the LCD and does the LED muxing. It does not, however,

read the pot values. This is done by the Coldfire.

The analog sounds are generated from 8 Oscillator ASICs that feed 8 Filter ASICs. Each ASIC

contains two voices.

The diagram below shows the majorA6 PCBs and their functions:

Front Panel Left

Micro, EPROM,

LED muxing

pot muxing

switch matrix

LEDs

switches

pots

Front Panel Center

LEDs, switches, pots

Front Panel Right

LEDs, switches, pots

Control

Main

Coldfire micro

address decoding

flash memory

keyscan ASIC

digital FX

pot/tuning ADC

tuning comparator

ASIC control

MIDI

foot pedals

power regulators

LCD

Analog pot

voltages,

switch

matrix

LCD control

Analog pot

voltages,

switch

matrix

Control

Analog pot

voltages,

switch data

Analog ASIC

4 DACs for analog ASIC control signals

8 Oscillator ASICs

8 Filter ASICs

analog power regulators

Analog Master

analog output circuitry (op amps)

analog distortion

analog noise generator

Databus

Control,

FX return

Tuning

signal, FX

sen

Noise,

external

uts

Voice busses,

tuning,

FX busses

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Alesis A6 Service Manual Page 6

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