I'm trying to come up with a circuit that will sense when a line level input drops below a certain threshold (say 100mV or so) and control a jfet switch (or something similar).
I'm using a TDA7240 20W amplifier chip, and it has a "standby" pin that when shunted to ground, puts the chip into a low-current mode. I'd like to be able to have that happen automatically when the input signal goes low for a few minutes.
There apparently used to be ICs that did this for use with cassette tape players (BA336, BA338, etc.), but they're NLA.
I've been playing with the circuit found here:
http://sound.westhost.com/project38.htm
The problem is that the output is the opposite of what I want (i.e, the MOSFET source pin is switched to ground with the input signal is high). I've tried implementing an inverting comparator at U1B, but it's not working.
I'm trying to keep this really simple for a small battery powered device running at +18VDC. There's gotta be an easier way to do this with a comparator or a 555 timer or something. Anybody have any suggestions?
I'm using a TDA7240 20W amplifier chip, and it has a "standby" pin that when shunted to ground, puts the chip into a low-current mode. I'd like to be able to have that happen automatically when the input signal goes low for a few minutes.
There apparently used to be ICs that did this for use with cassette tape players (BA336, BA338, etc.), but they're NLA.
I've been playing with the circuit found here:
http://sound.westhost.com/project38.htm
The problem is that the output is the opposite of what I want (i.e, the MOSFET source pin is switched to ground with the input signal is high). I've tried implementing an inverting comparator at U1B, but it's not working.
I'm trying to keep this really simple for a small battery powered device running at +18VDC. There's gotta be an easier way to do this with a comparator or a 555 timer or something. Anybody have any suggestions?