The freeze spray can not change the lowpass frequency, use very short bursts and focus them only on a single semiconductor/component at any one time. Do not forget to spray diode(s).
No sorry, I meant could a problematic bridge rectifier cause the low pass problem? I am basically getting a full spectrum signal through with the low pass working in parallel by the sound of it. It doesn't even sound like a sub at the moment, just a bassy normal speaker.
Am I looking for excess heat, or expecting something in the signal to change?
Am I looking for excess heat, or expecting something in the signal to change?
I found this thread after looking for ages because I have the exact same symptoms with my presonus subwoofer.
Did you end up finding a solution for this?
Did you end up finding a solution for this?
A circuit diagram would really help.
Since you do not have one it would be useful to list the part numbers on all the IC including the 3 IC I seen in the pictures and any others on the second board.
The long IC with many leads looks like a linear integrated amplifier like a LM3886. Likely it drives the sub driver.
It will not likely have much in the way of audio filtering for the subwoofer, the audio filter functions are most likely on a second connected board.
The other two IC in TO-220 style cases, I expect are linear regulators that provide the power rails for the low level circuits that seem to be on a second board.
The second board likely does the filtering and xover functions for the sub and so could also be the source of the noise you hear.
Based on the noise I would think.
1) Transistor/diode noise (based on the design likely using integrated circuits and not separate transistor amplifiers this likely would mean one of the IC is bad). Freeze spray each IC one at a time and listen for a change in the noise. This may or may not allow you to find the noise.
2) A bad solder joint. Inspect and tap the back of both PCB to see if the noise changes. This is less likely a cause if the noise is constant and unchanging in sound and volume level.
3) One or more of the rail bypass capacitors has gone bad where the capatiance value has dropped and the ESR has risen to the point where a amplifier or regulator circuit somewhere (could be on either board) is now oscillating at a high frequency. This can make a amplifier sound very noisy.
Best way to track this is if you have a scope is to check the output pin of each IC for high frequency oscillations are look to the rail bypass capacitors for that IC.
Second best way to test for this is to tack new capacitors over the current ones and see if the issue goes away. It may not.
Third best way is to simply replace all the power rail capacitors and see if it fixes the issue. It may not.
4) A noisy resistor. Possible but less likely on designs like this with most of the amplifying circuitry inside integrated circuits.
Again spray each resistor one at a time on both boards. May or may not find it this way
5) Could be a loose connector pin however if the noise is constant and unchanging this is not likely the issue.
Since you do not have one it would be useful to list the part numbers on all the IC including the 3 IC I seen in the pictures and any others on the second board.
The long IC with many leads looks like a linear integrated amplifier like a LM3886. Likely it drives the sub driver.
It will not likely have much in the way of audio filtering for the subwoofer, the audio filter functions are most likely on a second connected board.
The other two IC in TO-220 style cases, I expect are linear regulators that provide the power rails for the low level circuits that seem to be on a second board.
The second board likely does the filtering and xover functions for the sub and so could also be the source of the noise you hear.
Based on the noise I would think.
1) Transistor/diode noise (based on the design likely using integrated circuits and not separate transistor amplifiers this likely would mean one of the IC is bad). Freeze spray each IC one at a time and listen for a change in the noise. This may or may not allow you to find the noise.
2) A bad solder joint. Inspect and tap the back of both PCB to see if the noise changes. This is less likely a cause if the noise is constant and unchanging in sound and volume level.
3) One or more of the rail bypass capacitors has gone bad where the capatiance value has dropped and the ESR has risen to the point where a amplifier or regulator circuit somewhere (could be on either board) is now oscillating at a high frequency. This can make a amplifier sound very noisy.
Best way to track this is if you have a scope is to check the output pin of each IC for high frequency oscillations are look to the rail bypass capacitors for that IC.
Second best way to test for this is to tack new capacitors over the current ones and see if the issue goes away. It may not.
Third best way is to simply replace all the power rail capacitors and see if it fixes the issue. It may not.
4) A noisy resistor. Possible but less likely on designs like this with most of the amplifying circuitry inside integrated circuits.
Again spray each resistor one at a time on both boards. May or may not find it this way
5) Could be a loose connector pin however if the noise is constant and unchanging this is not likely the issue.