I have a 350W APC power inverter that produces a simulated sinusoidal output. Unfortunately, it currently doesn't play well with audio electronics.
When coupled with a LM3875 chipamp (equipped with a simple non regulated power supply) the amp's output includes a small "buzz". This buzz is much more pronounced when the amp is hooked to other inverters. I suspect the APC unit better approximates the AC signal than some other cheaper inverters.
Since the waveform is approximately stepped out (as opposed to being a basic step function) I believe there is hope in filtering out the last bit of jaggedness. Ideally, I would like to reduce this buzz to make the amp usable in my car.
My plan is to install a choke between the inverter and the chipamp's power supply to reduce the noise. However I am having trouble spec'ing a properly sized choke. Has anyone ever ran into this issue? Any got any suggestions?
btw,
It is kinda interesting to note the power starts off as AC in the car's alternator, then is rectified into DC, then switched into AC inside the inverter, then transformed into another AC voltage, then back to two DC voltages, then ultimately back into AC audio output. Tesla is probably spinning in his grave.
When coupled with a LM3875 chipamp (equipped with a simple non regulated power supply) the amp's output includes a small "buzz". This buzz is much more pronounced when the amp is hooked to other inverters. I suspect the APC unit better approximates the AC signal than some other cheaper inverters.
Since the waveform is approximately stepped out (as opposed to being a basic step function) I believe there is hope in filtering out the last bit of jaggedness. Ideally, I would like to reduce this buzz to make the amp usable in my car.
My plan is to install a choke between the inverter and the chipamp's power supply to reduce the noise. However I am having trouble spec'ing a properly sized choke. Has anyone ever ran into this issue? Any got any suggestions?
btw,
It is kinda interesting to note the power starts off as AC in the car's alternator, then is rectified into DC, then switched into AC inside the inverter, then transformed into another AC voltage, then back to two DC voltages, then ultimately back into AC audio output. Tesla is probably spinning in his grave.
The problem is probably poor noise inmunity in your amplifier. I haven't had any major noise problem in amplifiers connected to modified sine inverters (actually square wave).
Anyway, you may consider getting an high quality true sine inverter. The filter required to get rid of the harmonics is quite big and it would have to be dissipative in order to get rid of ringing.
Anyway, you may consider getting an high quality true sine inverter. The filter required to get rid of the harmonics is quite big and it would have to be dissipative in order to get rid of ringing.
No, modified sine wave is slightly better than square wave (apart from an euphemism) but it still has strong harmonics in it which cause the buzz sound. Transformers are quiet when operated with sinewaves.
An externally hosted image should be here but it was not working when we last tested it.
Eva, you're right, simulated sine = modified sine wave.
The buzz, it turns out, was caused by a ~1v DC offset in the inverter's output. The chipamp's transformer was mechanically vibrating, not the speakers. Two caps tied in series solved the problem entirely.
The below thread explained the fix.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2080&perpage=25&highlight=&pagenumber=1
The buzz, it turns out, was caused by a ~1v DC offset in the inverter's output. The chipamp's transformer was mechanically vibrating, not the speakers. Two caps tied in series solved the problem entirely.
The below thread explained the fix.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2080&perpage=25&highlight=&pagenumber=1
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