Earthquake Sound FF12 Amplifier Schematic Diagram and Technical Overview

Document Overview

This document provides the schematic diagrams for the Earthquake Sound FF12 audio amplifier. It details the electronic circuitry across two main printed circuit boards (PCBs), including input stages, crossover network, phase control, volume control, power supply, and the main amplifier output stage.

Printed Circuit Board 1 (PCB1) - Input, Crossover, and Control Stages

PCB1 handles the audio signal input, processing, and control functions.

Input Stage

Stereo audio inputs are provided via RCA connectors (RCA1, RCA2 for L/R Line Input; RCA3, RCA4 for L/R Hi-Input) and WP4-4 connectors (J3, J4 for L+/L-, R+/R-). The L input signal from RCA1 is buffered and processed by operational amplifier U1-A (MC4558) via resistor R8 (5.6K) and capacitor C4 (4.7uF/25V). Similarly, the R input signal from RCA2 is processed by U1-B via R18 (5.6K) and C4 (4.7uF/25V). The Hi-L and Hi-R inputs are connected via J3 and J4 respectively, feeding into U1-A and U1-B through resistors R9/R13 (47K) and capacitors C5/C11 (100/C). The output of U1-A and U1-B are connected to the crossover network.

Crossover and Phase Control

A crossover network, adjustable between 40Hz and 120Hz, is implemented using components including resistors R22, R24, R26, R27, R29, R30, R31, R34 and capacitors C8, C9, C11, C12, C13, C20, C21. This section is controlled by potentiometer VR1-A (C20K). The phase control, adjustable from 0 to 180 degrees, is managed by potentiometer VR2 (A10K) and associated components, feeding into the signal path. The processed audio signal is then routed to the volume control.

Volume Control

The main volume is controlled by potentiometer VR1-B (C20K), affecting the signal level before it is output from PCB1.

Output Stage (PCB1)

Outputs from PCB1 include L OUT and R OUT, which are fed to subsequent stages. The circuit utilizes multiple MC4558 operational amplifiers (U1, U2, U3, U4) for buffering, amplification, and signal processing.

Component Details (PCB1)

Operational Amplifiers: MC4558 (U1, U2, U3, U4)
Potentiometers: VR1-A/B (C20K) for Crossover/Volume, VR2 (A10K) for Phase
Capacitors: Various values including 4.7uF/25V, 100uF/50V, 104/C, 683/M, 223/M, 224/C.
Resistors: Various values including 5.6K, 47K, 10K, 33K, 1K, 200K, 1M, 47 Ohm.
Connectors: RCA1-4, J3 (WP4-4), J4 (WP4-4).
Indicators: LED1 (RED, GRN) for status indication.
Switch: SW1 for mode selection.

Printed Circuit Board 2 (PCB2) - Power Supply and Amplifier Output Stage

PCB2 contains the main power amplifier and its associated power supply regulation and protection circuitry.

Power Supply Regulation

The power supply section includes voltage regulators U5 (7815 for +15V) and U6 (7915 for -15V), fed by large filter capacitors C62, C63 (4700uF/50V) and C88, C87 (220uF/25V). These regulators provide stable [+15V] and [-15V] DC to the operational amplifiers and other circuitry.

Main Amplifier Stage

The core of the amplifier output stage is the TDA7295 integrated circuit (U9). This IC receives the processed audio signal and drives the woofer. It is supported by various passive components like resistors R76, R77, R78, R79, R81, R82 and capacitors C76, C77, C78, C79, C80, C81, C82, C83, C84. The TDA7295 operates with high voltage supply rails [+VCC], [-VCC].

Output Driver and Protection

Transistors Q1, Q2 (C1815) and diodes D1, D2, D3, D4, D5, D6 (1N4148) along with resistors R36, R39, R40, R41, R42, R43, R44, R45, R48, R50, R51, R52 and capacitors C10, C14, C15, C16, C18, C20, C25, C26, C85, C86, C87, C88 form part of the output driver and protection circuitry for the main amplifier IC.

Power Input and Control

The unit accepts AC mains input via CN1-A and CN1-B. A Voltage Select Switch allows operation at 115V or 230V AC. A primary fuse [FUSE] (FUSE1, T1A/250V) protects the unit. A POWER SWITCH [SW] (SW2) controls the main power. Warning symbols [WARNING] are placed near the AC input and power switch, indicating high voltage hazards.

Woofer Output

The amplified signal is output to the woofer via connector CN2-B.

Component Details (PCB2)

Power Amplifier IC: TDA7295 (U9)
Voltage Regulators: 7815 (U5), 7915 (U6)
Transistors: C1815 (Q1, Q2)
Diodes: 1N4148 (D1-D6), 1N4004 (D4)
Capacitors: Large filter caps (4700uF/50V, 220uF/25V), smaller caps (104/C, 47uF/25V, 10uF/50V, 681/C, 2.2uF/50V).
Resistors: Various values.
Transformer: T1 (230V AC input).
Connectors: CN1-A/B (AC Input), CN2-B (Woofer Output).
Switches: Voltage Select Switch, POWER SWITCH [SW] (SW2).
Fuse: [FUSE] (FUSE1, T1A/250V).

General Notes and Symbols

The schematics use standard electronic component designators. Key symbols and their interpretations:

[+15V], [-15V], [+VCC], [-VCC]: DC Power Supply Rails.
[GND]: Ground connection.
[IN], [OUT]: Signal Input/Output points.
[WARNING]: Indicates a potential hazard, typically high voltage.
[FUSE]: Overcurrent protection device.
[LED]: Light Emitting Diode for status indication.
[SW]: Switch for control functions.
[VR]: Potentiometer for variable control (e.g., Volume, Crossover, Phase).
[IC]: Integrated Circuit (e.g., MC4558, TDA7295, 7815, 7915).
[Q]: Transistor.
[D]: Diode.
[C]: Capacitor.
[R]: Resistor.
[T]: Transformer.
[BD]: Bridge Rectifier.

Component values are indicated next to their designators (e.g., 10K for 10,000 Ohms, 4.7uF for 4.7 microFarads).

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Earthquake Sound FF12 - Schematic Diagram