Amplifier auto-start on sound input
Good day folks. This was originally meant for the "troubleshooting" category, but I decided it should be more of a generic discussion for now since I haven't actually started working on the device and I don't really want to ask for help before actually attempting something on my own.
This is about an active Jamo "SUB 260" subwoofer. The chap brought it in with no power at all after it's been fixed before by someone else (pretty sloppy job, but that's not important). He told me the thing only powers on when there's an input signal present, which I took with a pinch of salt at that time, but then I looked up the manual and indeed it supposedly turns on only when an input signal comes into the RCA terminals on the back. I tried it out for myself and of course I got nothing, no power at all.
The fuse was blown on the mains input despite none of the major components being shorted - I checked. Since I recently switched jobs, I don't have my trusty "safety lightbulb" assembly on hand at my new workplace (left it at my former shop) so I didn't want to plug it straight into the mains after simply replacing the fuse, so while I'm waiting to get my bulb back (sounds funny
) I began pondering how the circuit operates. I'm fearing I may have to do some digging in the control side if the power section appears to be fine and I still get no power.
I'll post some pics soon, but there aren't any microcontrollers in there - just some op-amps as far as I could tell.
The way I imagine it with my modest electronics knowledge is an op-amp in an amplifier configuration boosting the input signal from the RCA inputs, which is then fed to the NI input of another op-amp whose inverting input is tied to GND. Therefore any signal higher than "GND" will trigger it to turn on, driving whatever's required to turn on the supply...ok, so there's a lot more to it than this, because the way I "designed" it would probably mean the amp would either stay on all the time due to noise on the line (most likely) or shut off intermittently during quiet parts of a song (less likely)....but I hopefully got the basics down. Like I said, I fear it's THIS part of the circuit that's not operating and we'll have to troubleshoot multi-layer SMD boards....NOT very easy TBH...I'll post back with some pics tomorrow (haven't got them off the phone yet).
This is about an active Jamo "SUB 260" subwoofer. The chap brought it in with no power at all after it's been fixed before by someone else (pretty sloppy job, but that's not important). He told me the thing only powers on when there's an input signal present, which I took with a pinch of salt at that time, but then I looked up the manual and indeed it supposedly turns on only when an input signal comes into the RCA terminals on the back. I tried it out for myself and of course I got nothing, no power at all.
The fuse was blown on the mains input despite none of the major components being shorted - I checked. Since I recently switched jobs, I don't have my trusty "safety lightbulb" assembly on hand at my new workplace (left it at my former shop) so I didn't want to plug it straight into the mains after simply replacing the fuse, so while I'm waiting to get my bulb back (sounds funny
) I began pondering how the circuit operates. I'm fearing I may have to do some digging in the control side if the power section appears to be fine and I still get no power.I'll post some pics soon, but there aren't any microcontrollers in there - just some op-amps as far as I could tell.
The way I imagine it with my modest electronics knowledge is an op-amp in an amplifier configuration boosting the input signal from the RCA inputs, which is then fed to the NI input of another op-amp whose inverting input is tied to GND. Therefore any signal higher than "GND" will trigger it to turn on, driving whatever's required to turn on the supply...ok, so there's a lot more to it than this, because the way I "designed" it would probably mean the amp would either stay on all the time due to noise on the line (most likely) or shut off intermittently during quiet parts of a song (less likely)....but I hopefully got the basics down. Like I said, I fear it's THIS part of the circuit that's not operating and we'll have to troubleshoot multi-layer SMD boards....NOT very easy TBH...I'll post back with some pics tomorrow (haven't got them off the phone yet).
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