Need help troubleshooting a active audio amplifier. - Page 1
Forum section: electronics / repair

author: laban93
author_rank: Contributor
timestamp: February 05, 2018, 10:14:01 pm
content: My sub amp is connected to my home cinema system by a rca cable. It's an active woofer with automatic "wake up" (for lack of better words) function.When it receives audio signal, it wakes up. But this one keeps waking up, even with no input signal. A small bang can be heard as the amp comes on. Then it turns off and the cycle repeats every few minutes. I've got a pair of them, and the other one is just fine.Well, i just don't really know what to look for. All the caps are ok, and zeners and resistors measure just fine on the input board. That is about where my knowledge stops. Does anyone have any idea of what to look for and what may cause this?(it is a DSL SUB 3.10 if anyone is curius.)

author: Armadillo
author_rank: Super Contributor
timestamp: February 05, 2018, 10:22:36 pm
content: The proper name is called the auto mute circuit.Check the auto mute transistor which is supposed to pull the signal to ground.

author: mzacharias
author_rank: Frequent Contributor
timestamp: February 05, 2018, 10:32:50 pm
content: A funky connecting cable or intermittent connections at the receiver output or sub input could cause this.

author: Pizzallonut
author_rank: Newbie
timestamp: February 06, 2018, 09:22:58 am
content: I need help too. I'm having the same problem with you. Please help me

author: cvanc
author_rank: Frequent Contributor
timestamp: February 06, 2018, 03:09:10 pm
content: You have two identical subwoofers, right?Try swapping their locations and wiring. See if the problems follows one woofer to the other side of the room, or if the problem "stays on one side of the room" regardless of which woofer is installed there.Good luck with your fix.

author: Shock
author_rank: Super Contributor
timestamp: February 06, 2018, 08:55:18 pm
content: Another test in addition to the above is try individual subs on an isolated or battery operated signal source, some source of audio that won't have coupling issues or preferably not mains derived power. But do perform other tests like having no input or when the home cinema is turned off, etc.It could be is leakage current from the home cinema, to reduce issues make sure all devices are powered locally from the same power outlet board when doing tests etc as this will often uncover weird faults. Eliminate RF noise being a factor by turning off phones WiFi and lighting. Eliminate mains noise by either turning off other devices in the house combined with moving your setup to another circuit or premises to test. Look at how you run your cabling and if running mains cables next to signal cabling.Once you have determined it's a problematic sub swap the power circuits between the two devices, that may be the fastest way to deduce a noise problem. Otherwise it's oscilloscope (or if you have to - multimeter) time and measure supply ripple. You could also scope the inputs with the home cinema connected and see if you can identify a source of noise, compare the two and if reducing the signal (if it exists) remedies the problem. This could help with isolating the problem to the sub input circuit. Remember not to "earth out" mains referenced voltages with your oscilloscope earth/ground.