Re: Infinity PS-12 Powered Subwoofer Fired Amplifier
I think you may be confused on the marking LO= ON marking at the output of U4B, ON means the speaker relay is ON. HIGH = MUTE speaker relay OFF. May be you want it to say - or + instead.
Circuit function: U4B which is setup as a comparator, the DC voltage at pin 6 (- input) will be at 0V when there is no audio is present to charge up the cap C37.
The pin 5 (+) input is bias with + Voltage from the voltage divider R63 10K (FED BY +15V) and R64 2.7K, so the + input is being fed by +3.19V, so the output pin 7 will be positive which will make RED LED D1B to come on - Cathode of RED LED is connected to ground.
When the audio signal is present, C37 will be charged by U4A,when the cap voltage reach 3.2v, the the output of the U4B will swing negative, the Green LED the anode of green LED is connected to Ground so green LED D1A will come on.
Q1 PNP will also be ON when U4B output is LO (-) which turns on the speaker relay.
The delayed time before it goes in to MUTE mode is the RC discharge time of R121-C37 time constant.
BTW, fault triggering by the PROT signal can also cause the relay to turn off, this is done by Q7.
I think you may be confused on the marking LO= ON marking at the output of U4B, ON means the speaker relay is ON. HIGH = MUTE speaker relay OFF. May be you want it to say - or + instead.
Circuit function: U4B which is setup as a comparator, the DC voltage at pin 6 (- input) will be at 0V when there is no audio is present to charge up the cap C37.
The pin 5 (+) input is bias with + Voltage from the voltage divider R63 10K (FED BY +15V) and R64 2.7K, so the + input is being fed by +3.19V, so the output pin 7 will be positive which will make RED LED D1B to come on - Cathode of RED LED is connected to ground.
When the audio signal is present, C37 will be charged by U4A,when the cap voltage reach 3.2v, the the output of the U4B will swing negative, the Green LED the anode of green LED is connected to Ground so green LED D1A will come on.
Q1 PNP will also be ON when U4B output is LO (-) which turns on the speaker relay.
The delayed time before it goes in to MUTE mode is the RC discharge time of R121-C37 time constant.
BTW, fault triggering by the PROT signal can also cause the relay to turn off, this is done by Q7.
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