CASE # 55: Gary Liked to Pump Up the Volume

April 10, 2006

Ever turned on your car stereo and BOOM! the woofers unexpectedly jumped out for one filling-loosening bass note? Just great, you've just been diagnosed with turn-on thump - either due to an amp that never had a muting circuit or one that's failed open circuit. Either way, OUCH! To fix this problem, Gary built a circuit that connects externally to any car audio amplifier and keeps his speakers completely disconnected from his amplifier until it's been completely powered up. Plus, it also works with a mis-matched set of amplifiers.

For Gary Reck's complete instructions to build a customizable audio amplifier muting circuit, click here .

Customizable Audio Amplifier Muting Circuit Parts List
Amt Part Description Allied Part #
1 Darlington Driver Array 248-2007
1 Single Supply Quad Comparator 568-4666
1 General Purpose Diode 568-0144
1 Capacitor 47 uF, 25V, 20 percent 852-7078
1 Resistor 10K 895-0355
1 Resistor 38.3K 895-1159
1 Resistor 7.5K 895-0833
1 Resistor 1M 895-1141
1 Resistor 681K 895-1108
1 Relay, SPDT, 12V dc Coil, 15A Contacts 850-0205
1 Relay, DPDT, 12V dc Coil, 15A Contacts 850-0410
1 Fuse 5A, PCB Mount 846-2014
1 Fuse .125A, PCB Mount 846-2002
Additional parts required: For a list of optional parts, go to

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