RSX Sub makes poping sounds
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Joined: Aug 2004
Posts: 2,536
Likes: 2
From: Davis, CA
I ended up putting a Alpine M200 off ebay for $60 in place of the RSX amp and this little enclosure really hits now. Don't bother banging your head on the wall trying to get it to not pop, the enclosure and speaker will perform better with a better amp.
Joined: Jul 2005
Posts: 2,558
Likes: 84
From: Huntsville, Al
Ok, now I am going though this as well. I am an electronics audio-nut but auto-audio isn't' my forte.
From what I can tell (I have hooked an oscilloscope up and am testing) - I have power to the subwoofer anytime the ignition is on. As was mentioned early in the post mine pops (the amp actually turns off) any time you change source, adjust the EQ, change track etc. VERY Annoying.
It appears the HU's internal mute (mine is a Sony) between these functions is taking the audio output to ground. This is sensed by the sub's amp as no signal and it switches itself off.
Anecdotally, I suspect that hooking the amp to a differently power source may prevent (or delay) the sensing of this "input equals ground" condition and therefore remains on, for this momentary input transition to ground.
Other people may not be having this issue because they a) used a different power source and switched though a relay (not just the HUs lead powered through a relay, but a different voltage source) or b) have a different HU which doesn't use a common DC ground for the power and Audio outputs.
In any case, I am headed to the garage now to test my theory.
From what I can tell (I have hooked an oscilloscope up and am testing) - I have power to the subwoofer anytime the ignition is on. As was mentioned early in the post mine pops (the amp actually turns off) any time you change source, adjust the EQ, change track etc. VERY Annoying.
It appears the HU's internal mute (mine is a Sony) between these functions is taking the audio output to ground. This is sensed by the sub's amp as no signal and it switches itself off.
Anecdotally, I suspect that hooking the amp to a differently power source may prevent (or delay) the sensing of this "input equals ground" condition and therefore remains on, for this momentary input transition to ground.
Other people may not be having this issue because they a) used a different power source and switched though a relay (not just the HUs lead powered through a relay, but a different voltage source) or b) have a different HU which doesn't use a common DC ground for the power and Audio outputs.
In any case, I am headed to the garage now to test my theory.
Joined: Jul 2005
Posts: 2,558
Likes: 84
From: Huntsville, Al
OK, I spent quite a bit of time on this and have tried isolating the ground (to something with a different potential from the HU), hooking amps the power direct to the battery, isolating the HU audio signal to the amp through a cap (so only AC passes) and strapping a cap between the audio signal and ground hoping the average power would charge the cap and then the discharge would support the signal long enough to do things like change tracks without a turn-off.
Joined: Jul 2005
Posts: 2,558
Likes: 84
From: Huntsville, Al
There is likely a more elegant way to fix this (re-work the circuit board solution). However, this simple solution works so well it makes it hard to look for any another approach.
The problem is that many (most?) head units ground the output while switching sources etc. The amp sees the ground and is either turning off because it thinks it should in the absence of a signal or because of a protection circuit. On some units, separating the audio signal from the shield may eliminate this, but it all depends on the way the head unit is grounded
In testing, I hooked the amp up on a bench with an oscilloscope, signal generator etc. However, even when turning off the signal generator I am unable to reproduce the problem on the bench (the amp stays on). This leads me to think it
The problem is that many (most?) head units ground the output while switching sources etc. The amp sees the ground and is either turning off because it thinks it should in the absence of a signal or because of a protection circuit. On some units, separating the audio signal from the shield may eliminate this, but it all depends on the way the head unit is grounded
In testing, I hooked the amp up on a bench with an oscilloscope, signal generator etc. However, even when turning off the signal generator I am unable to reproduce the problem on the bench (the amp stays on). This leads me to think it
And only 1.5 years after buying it.
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Joined: Oct 2001
Posts: 147
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From: Orlando
jeallen,
I tried the 22uF cap over 2 years ago with the same results, but found that in practice the sub was not as loud by using a dB meter in the trunk. It could have been an anamoly for me and I did not test it with a signal generator. Also, the cap on the ground line is not necessary, only the signal. Back then I found that going to 100uF cap actually brought the popping back sometimes and bigger than that had it back all the time. I guess the time constant at those capacitances doesnt allow for fast enough discharge to fake being an audio signal. I'm using a circuit but lost the writeup since I installed it and havent had time to redo it.
Mike
I tried the 22uF cap over 2 years ago with the same results, but found that in practice the sub was not as loud by using a dB meter in the trunk. It could have been an anamoly for me and I did not test it with a signal generator. Also, the cap on the ground line is not necessary, only the signal. Back then I found that going to 100uF cap actually brought the popping back sometimes and bigger than that had it back all the time. I guess the time constant at those capacitances doesnt allow for fast enough discharge to fake being an audio signal. I'm using a circuit but lost the writeup since I installed it and havent had time to redo it.
Mike
Joined: Jul 2005
Posts: 2,558
Likes: 84
From: Huntsville, Al
Would love to see your circuit. The fewer components in the signal path the better. I suspect someone at Bose could give us a trace to cut and a lead to tie high and we would have the best of all worlds. 
Just to be sure everyone follows, the caps are only on the audio leads. The reason it works is because capacitors only pass and AC (audio) signal and the grounding of these leads by the head unit isn't passed through to the amp. You might be able to only connect to the positive audio lead only, but these leads don't have a ground reference on the sub-amp side and I don't see any reason to introduce one as it could be problematic depending on the HU.
In theory the cap is seen as zero impedance to an audio signal until a certain resonate frequency is reached. When the frequency is approached, the capacitor develops a "reactive impedance" and the signal is attenuated. Crossover circuits in speakers do this to remove bass from tweeters. This site offers an expatiation's: http://www.phys.unsw.edu.au/~jw/RCfilters.html.
The size of the cap (C ) across the impedance (the
Just to be sure everyone follows, the caps are only on the audio leads. The reason it works is because capacitors only pass and AC (audio) signal and the grounding of these leads by the head unit isn't passed through to the amp. You might be able to only connect to the positive audio lead only, but these leads don't have a ground reference on the sub-amp side and I don't see any reason to introduce one as it could be problematic depending on the HU.
In theory the cap is seen as zero impedance to an audio signal until a certain resonate frequency is reached. When the frequency is approached, the capacitor develops a "reactive impedance" and the signal is attenuated. Crossover circuits in speakers do this to remove bass from tweeters. This site offers an expatiation's: http://www.phys.unsw.edu.au/~jw/RCfilters.html.
The size of the cap (C ) across the impedance (the