Amplifier Timer Circuit Schematic

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Turns-off your amplifier when idle for 15 minutes, Fed by amplifier tape-output

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.

Amplifier Timer Circuit

Amplifier Timer Circuit Diagram

Parts:

R1,R8___________1K 1/4W Resistors
R2,R3___________4K7 1/4W Resistors
R4______________22K 1/4W Resistor
R5______________4M7 1/4W Resistor
R6,R9___________10K 1/4W Resistors
R7______________1M5 1/4W Resistor
R10_____________100K 1/4W Resistor
R11_____________15K 1/4W Resistor
R12_____________10M 1/4W Resistor
R13_____________1M 1/4W Resistor
R14_____________8K2 1/4W Resistor
R15_____________1K8 1/4W Resistor
C1______________470µF 25V Electrolytic Capacitor
C2,C3,C6________100nF 63V Polyester Capacitors
C4,C5___________10µF 25V Electrolytic Capacitors
D1______________Diode bridge 100V 1A
D2,D7___________1N4002 100V 1A Diodes
D3______________Red LED 5mm.
D4______________Yellow LED 5mm.
D5,D6___________1N4148 75V 150mA Diodes
IC1______________78L12 12V 100mA Voltage regulator IC
IC2______________LM358 Low Power Dual Op-amp
IC3______________4060 14 stage ripple counter and oscillator IC
Q1______________BC557 45V 100mA PNP Transistor
Q2______________BC337 45V 800mA NPN Transistor
J1______________RCA audio input socket
P1______________SPST Mains suited Pushbutton
P2______________SPST Pushbutton
T1______________220V Primary, 12V Secondary 3VA Mains transformer
RL1_____________10.5V 270 Ohm Relay with SPST 5A 220V switch
PL1_____________Male Mains plug
SK1_____________Female Mains socket

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.