Turns-off your amplifier when idle for 15 minutes
Fed by amplifier tape-output
Circuit diagram:
Parts:
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R1,R8 1K 1/4W Resistors |
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R2,R3 4K7 1/4W Resistors |
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R4 22K 1/4W Resistor |
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R5 4M7 1/4W Resistor |
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R6,R9 10K 1/4W Resistors |
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R7 1M5 1/4W Resistor |
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R10 100K 1/4W Resistor |
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R11 15K 1/4W Resistor |
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R12 10M 1/4W Resistor |
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R13 1M 1/4W Resistor |
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R14 8K2 1/4W Resistor |
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R15 1K8 1/4W Resistor |
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C1 470µF 25V Electrolytic Capacitor |
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C2,C3,C6 100nF 63V Polyester Capacitors |
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C4,C5 10µF 25V Electrolytic Capacitors |
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D1 Diode bridge 100V 1A |
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D2,D7 1N4002 100V 1A Diodes |
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D3 Red LED 5mm. |
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D4 Yellow LED 5mm. |
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D5,D6 1N4148 75V 150mA Diodes |
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IC1 78L12 12V 100mA Voltage regulator IC |
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IC2 LM358 Low Power Dual Op-amp |
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IC3 4060 14 stage ripple counter and oscillator IC |
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Q1 BC557 45V 100mA PNP Transistor |
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Q2 BC337 45V 800mA NPN Transistor |
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J1 RCA audio input socket |
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P1 SPST Mains suited Pushbutton |
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P2 SPST Pushbutton |
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T1 220V Primary, 12V Secondary 3VA Mains transformer |
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RL1 10.5V 270 Ohm Relay with SPST 5A 220V switch |
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PL1 Male Mains plug |
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SK1 Female Mains socket |
Circuit operation:
This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least.
Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting. Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.
Notes:
- Simply connect left or right channel tape output of your amplifier to J1.
- You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.
- The delay time can be varied changing R13 and/or C6 values.
- Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.
