Anti-BUMP Speaker Protector for HiFi Amplifiers and Amplifier Modules

by Giuseppe La Rosa

That loud "TUMP" at power ON/OFF kills tweeters and woofers.

This module is powered directly from 230Vac in parallel with your amplifier. At power ON it waits 5.1 seconds (1.1 x R2 x C2) for the amplifier to stabilize, then closes a DPDT 8A relay to connect the speakers. At power OFF it disconnects instantly in <50ms, before the amplifier's capacitors discharge and cause the return bump.

Result: total silence. Zero pop, zero risk.

Designed to be robust and universal:

- Power: 230Vac direct with HLK-PM12 isolated 12V module, 500mA T fuse + 10D391K varistor

- Control: NE555 in monostable, safe reset network R1/C1 (50ms), delay R2 100k / C2 47uF = 5.1s

- Fast-OFF: LEDs + R5/R6 + R8 discharge the 12V rail instantly for <50ms release

- Relay: RT424012 - 2 x Changeover, AgNi, 8A Peak / 6A Continuous

- Power Tracks: 2.5mm with heavy tin reinforcement to handle 6A RMS / 8A Peak

- Safety: double sided professional PCB, safety slots in 230V area, stitched GND plane for shielding, control circuit in center to avoid interference

- Indicators: POWER (Yellow) + MUSIC / Speakers Connected (Green)

Technical Data (limited by relay RT424012):

- Recommended power: 150W RMS @ 4 Ohm / 200W RMS @ 8 Ohm (6A RMS)

- Max peak handled: 8A Peak -> 256W peak @ 4 Ohm (128W RMS equiv.) / 512W peak @ 8 Ohm (256W RMS equiv.)

- Delay ON: 5.1s, Release OFF: <50ms

Perfect for: HiFi, Studio, PA, and all commercial TPA3116, TPA3255, TDA7498, TDA7294, LM3886, LM3886 modules.

Wiring: X3 = 230Vac IN, X1 = FROM Amplifier Output (L-/L+/R-/R+), X2 = TO Speakers.

Includes Gerber files, ready to fab. Tested board, BOM in 0805 SMD + standard parts.

Reference;Value;Package;Description;Qty

R1;10 kΩ;0805;Resistor;1

R2;100 kΩ;0805;Resistor;1

R3;4.7 kΩ;0805;Resistor;1

R4;10 kΩ;0805;Resistor;1

R5,R6;1.2 kΩ;0805;Resistor;2

R7;10D391K;DISC 10mm;Varistor 390V;1

R8;680 kΩ;0805;Resistor;1

C1;4.7 µF;0805;Capacitor MLCC;1

C2;47 µF 16V;5x5mm SMD;Electrolytic Capacitor;1

C3;10 nF;0805;Capacitor;1

C4;100 nF;0805;Capacitor;1

C5;100 µF 16V;SMD Electrolytic;Electrolytic Capacitor;1

D1;1N4148;SOD-123;Switching Diode;1

D2;M7 (1N4007 SMD);DO-214AC SMA;Rectifier Diode;1

T1;BC807;SOT-23;PNP Transistor;1

IC1;NE555;SO-08;Timer IC;1

LED1;Green 3mm;3mm THT;LED 3mm Green;1

LED2;Yellow 3mm;3mm THT;LED 3mm Yellow;1

K1;RT424012 12V;THT Relay;Relay 12V 8A DPDT;1

AL1;HLK-PM12;PCB Module;Switching Power Supply 230V/12V 3W;1

X1,X2;4-pin Terminal;5.08mm Pitch;Terminal Block 4P;2

X3;2-pin Terminal;5.08mm Pitch;Terminal Block 2P;1

F1;T 500mA 5x20mm;5x20mm;Time-Delay Fuse 500mA;1

FH1;Fuse Holder 5x20mm;THT PCB;Fuse Holder;1