Download The auto standby circuit is built around the LM324 quad operational

The auto standby circuit is built around the LM324 quad operational amplifier.
It has six wires to connect, +9v Red, -8v White, ground Black, standby control in Grey and out Yellow
(the existing pcb track linking these two points, needs cutting) and an audio pickup Black screened.
The audio signal is picked up from the output of the opamp feeding the sub channel amplifiers. I used
this signal as all the seven audio inputs bass signals are summed together and are sent to the bass along
with the dedicated bass signal. This way if any of the eight channels have an audio signal the circuit will
keep the unit switched on.
The audio input is buffered by the first opamp so as not to load the audio signal in anyway. The second
opamp has a gain of about 200 and boosts the signal to a usable level. The third opamp is an active
rectifier with a peak hold, this gives a DC voltage out when audio is present, and this holds TR1 on
which keeps capacitor C5 discharged.
With no audio signal, TR1 switches off and C5 starts to charge up via R11. With the values given the
CR time is 484 second or 8mins (CR time is to 0.7 of supply voltage), this voltage is connected to one
input of the fourth opamp. This opamp is set up as a comparator and it’s other input is set at about 0.7 of
supply voltage by R7 and R8, about 6.2v.
If at any time an audio signal is picked up, TR1 will be turned on and rapidly discharge C5 via R13
(100R) and the timing period will restart. If C5 reaches 6.2v the fourth opamps output will switch high
and pull the control line to 5v via R4 and D1, this will switch the sub to standby in an orderly way. At
any time an audio signal will ‘wake up’ the sub by switching this line back to 0v.
If the sub is switched to standby using the control pod the I/O control ics output will switch to +5v and
this will, via R3 and D2, switch on TR1 discharging C5 and the timer will be held at zero. This will
ensure an instant switch on the next time the standby button is used to switch the sub on.