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11-20-2009

Amplifier Timer

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

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

 

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.

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