Baffle protector

Baffle protector . This circuit is used to protect the baffles of a high fidelity acoustic cabinet. It handles peak voltages between 6.5 and 24.5 V with effective power at the speaker between 5 and 75 Watts. Drift dangerous spikes ignoring normal music. The board does not require any external power


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  • 1 Principles of operation
  • 2 Connection
  • 3 Resistance values
  • 4 List of components
    • 1 Resistances
    • 2 Semiconductors
  • 5 Assembly
  • 6 Sources

Operating principles

This circuit uses the property that thyristors have to conduct current between their anode and their cathode when a potential difference is applied between the cathode and its gate.


2 push-pull thyristors are connected , this is done so that each thyristor works for a half cycle. When the voltage over R1 or R3 exceeds the tripping value of the corresponding thyristor, it is switched by placing a 4.7 ohm resistor in parallel with the load, so that the circuit is again in an alert state.

Resistance values

The value of resistors R2 and R3 is determined by the power that the baffle has to handle . The following table shows the value that these resistances should have according to the output power of the equipment to be protected.

Component listing


  • R1 = 27 Kohm (Red-Violet-Orange)
  • R2 = See notes
  • R3 = See notes
  • R4 = 0.47 Ohm 4W (Yellow-Violet-Silver)
  • R5 = 4.7 ohm 4W (Yellow-Violet-Gold)
  • R6 = 4.7 Ohms 4W (Yellow-Violet-Gold)
  • R7 = 27 Kohms (Red-Violet-Orange)


  • T1 = TIC 106A
  • T2 = TIC 106A


The circuit must be mounted between the frequency divider and the baffle , inside the acoustic cabinet. If the circuit is going to be used in an acoustic box that usually works near the limit, that is, it will make the protector act at all times, it is convenient to place a L-type sink for TO-220 on each thyristor. It is also convenient to place silicone grease between the thyristor and its dissipator to improve the thermal contact between them. The circuit does not need any external power supply.


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