Bottom PCB Layout Design | Active Speaker Protector

Top PCB Design | Active Speaker Protector

Speaker Protector Circuit Connection

Active Speaker Protector Part List

• 5-pin 12-volt Relay – 2
• Transistors 2SC945 – 2
• Transistor 2SC9013 – 1
• Diodes 1N4007 – 5
• Elco 220 uF / 50V – 2
• Resistor 10 KOhms – 4
• Resistor 1 KOhms – 1
• Resistor 39 KOhms – 1
• Large 3-pin connectors – 2
• Small 3-pin connector – 1
• Trimpot of 220 KOhms or 500 KOhms – 1

This is 2 way speaker box design for audio system. I’ve used this design for my home audio system, the sound quality is good. Two speakers used for this speaker box that are tweeter / high frequency speaker and woofer / low frequency speaker / subwoofer. Alternatively you may replace the woofer with fullrange loudspeaker.

The ventilation is used for this 2 way speaker box design, you can find speaker box plastic ventilation at electronic part store.

For better audio performance and protect the loudspeakers, you may use passive crossover circuit. Just mount this circuit inside the speaker box.

Below is the example of tweeter loudspeaker, woofer loudspeaker and crossover circuit:

This is the speaker protection circuit, provides stereo speaker protection and prevents switch-on clicks and DC components on the output of the amplifier connected.

Speaker Protection Components List:

R1,R2 : 3K3
R3,R4,R5,R6,R7 : 8K2
R8,R9,R10,R11 : 330K
R12,R13 : 18K
R14,R15,R16,R17 : 47K
R18 : 47
R19,R20 : 680
R21,R22 : 100K
R23,R24,R25,R26 : 1K2

C1,C2,C3,C4,C5,C6 : 1uF
C7,C8,C9,C10 : 100uF
C11 : 220uF
C12,C13 : 470uF

D1,D2,D3,D4,D5,D6,D7,D8,D9,D10 : 1N4148
D11,D12,D13,D14 : 1N4007
ZD1 : 6V8

T1,T2,T3 : BC547B
T4 : BC517

LD1 : Red (ERROR INDICATOR)
LD2 : Yellow (WAIT INDICATOR)

RY1,RY2 : VR15M121C (12VDC – 15A – 1C)
Transfo (1,2VA – 2 x 6V / 2 x 0,1A)
IC1 : LM324

Circuit Notes:

• This circuit uses center tap transformer and the power supply circuit design already provided in the schematic diagram. It powered with 6V dual polarity power supply.
• This circuit available in kits, you may order the kit online. The manual assembly of the kit can be download at the end of this post.

This stereo loudspeaker protection will protect the loudspeakers against the switch-impulsions and the direct current component on the output of the connected amplifier.

Suitable for:

• Amplifiers with symmetrical power supply
• Amplifiers with asymmetrical power supply.

Specifications :

• Switch-delay: ? 6 seconds
• DC protection: +1V/-1V
• Max. input voltage: 200Vpp + DC
• Max. switching current: 10A
• LED indication for: WAIT (switch-on delay) and ERROR (DC on speaker output)
• Supply voltage: 220VAC

Download Speaker Protection Kit Manual Kit

Parts List:

How the circuit works:
The circuit’s operation starts as the stereo sound signal transports surround sound information on the master volume part of the circuit. This will drive the Left channel Lch attached to Model TL072 IC1A and IC1b in which Right channel Rch is attached. The outputs on these operational amplifiers would serve as the input buffer to the following stages of the circuit. IC2C is responsible for summing up the signals from the left and right channels that will power the central loudspeaker output while IC2D is responsible for increasing the phase difference between left and right channels which is encoded in the two channels and will be fed to the rear loudspeakers. It is necessary to ensure that the negative terminals between the rear speaker is not earthed because they will simply function in parallel with the main speakers.

The output of IC2D will power regulated delay unit of audio to the rear loudspeakers. This would lead to the creation of proper sense of spacing in accordance to the size of the room. This will incorporate op-amp sound delay signal IC5 MN3004 which has 512 stages. Since IC4 MN3101 is a clocking signal, it provides timing to IC5 as it functions as an oscillator in the circuit. Variable capacitor C17 regulates the delay time in the circuit. The presence of filters in the circuit is for the purpose of preventing noise that will be produced during the process. These filters can be regulated to cut the frequencies above 8 KHz and under 100 Hz, to be able to drive the rear speaker. The rear loudspeaker is small in size because its input is encoded with a bandwidth of 100 Hz up to 8 KHz. The filters are built around the IC6A/B which is also an output buffer. A potentiometer is placed in every output to aid in the adjustment and regulation of loudspeakers and amplifiers. The supplied power in the circuit is 15 V and every output can drive a single power amplifier.

Surround Sound Decoder circuit
source: http://www.elecpod.com/circuit/av/2010/03011405.html

Circuit Notes:

• This passive surround circuit MUST be connected after power amplifier module.
• Use full range type of loudspeaker. Do not use woofer or tweeter speakers for rear speakers.
• Left Front and Right Front can be speaker box contains woofer and tweeter.
• 5W resistors is a must, 1/4 or 1/2 watt resistor will make it burned.

Loud Speaker Position:
LF : Output > connect to Left Front Speaker
RF : Output > connect to Right Front Speaker
LR : Output > connect to Left Rear Speaker
RR : Output > connect to Right Rear Speaker

Switch operations:
1 : Quadrophonic
2 : Surround
3 : Stereo (passive surround deactivated, Rear Speakers disconnected)

Loudspeaker System Crossover Network Notes:

• Capacitor must be non-polar capacitor types with a voltage rating of 50 volt or more (preferably 100 volt).
• Capacitor may be paralled to achieve specified values.
• Inductors should be air core. Do not mount inductors in top of each other.
• Resistors should be 100 Watts or more.

Passive crossover is made entirely of passive components, arranged most commonly in a Cauer topology to achieve a Butterworth filter. Passive filters use resistors combined with reactive components such as capacitors and inductors. Very high performance passive crossovers are likely to be more expensive than active crossovers since individual components capable of good performance at the high currents and voltages at which speaker systems are driven are hard to make. Polypropylene, metalized polyester foil, paper and electrolytic capacitors are common. Inductors may have air cores, powdered metal cores, ferrite cores, or laminated silicon steel cores, and most are wound with enamelled copper wire. Some passive networks include devices such as fuses, PTC devices, bulbs or circuit breakers to protect the loudspeaker drivers from accidental overpowering. Modern passive crossovers increasingly incorporate equalization networks (e.g., Zobel networks) that compensate for the changes in impedance with frequency inherent in virtually all loudspeakers. The issue is complex, as part of the change in impedance is due to acoustic loading changes across a driver’s passband.