2. amps-preamps
  3. 186313-184988

? about Smoking Power Amp

I made an error in connecting my amps last night, and one of them started smoking. It now appears to be working fine, as do my other stereo components. But I am trying to assess whether there is likely to be any lasting damage to the amp that should give me pause before using it again, or damage to other components. If someone with more technical knowledge than me could please help me understand what took place to cause the smoke, I would appreciate it.

Let me explain in more detail the setup that caused the problem. I have two power amps being fed by two sets of line-level outputs from a single preamp. One of the amps then powers stereo speakers, while the other powers a passive subwoofer. Last night, I placed a passive low pass filter (100 Hz) into the signal path going from the preamp to the amp that powers the subwoofer. This passive filter is female on one end, which is supposed to receive the input, and male on the other, which is supposed to provide the output. I instead plugged the male (output) end of the filter into the output jack of the preamp, and then I plugged a cable leading to my power amp into the filter's input jack.

With this erroneous setup, I turned on all of my components in the normal fashion. Very soon after (before I played any music) white smoke, smelling of burning plastic, started to come out of the power amp connected to the stereo speakers (which produced a moderately-loud buzzing sound). An orange tinge was visible through the grates of the amp producing the smoke. I turned off and disconnected everything and realized my error in the setup. The smoke stopped right away when I powered down the amp.

As I said above, I tested everything, and all components now appear to work as they should. I tested the smoking amp by connecting it to some budget speakers, just in case it had an issue that could cause damage further downstream. Even this amp appears to be working normally.

So I am not sure, in any precise way, what caused this. To the best of my layman's understanding, the reversed low pass filter blocked the signal coming out of the preamp output, probably causing something such as voltage to get messed up in the signal that was coming out of the other set of preamp outputs. This "messed up" signal was then transmitted to the power amp that started smoking.

I feel certain the speakers are fine. I am wondering if there is any reason to be concerned about latent damage to the preamp, which is a valuable unit. I am less concerned about the amp that was smoking, which is an inexpensive older unit (market value <$150), which I had been using for convenience. But I am still wondering if I can safely use that amp in the future, and if it is possible that something extraneous (such as a plastic coating or paint) was smoking and nothing more than that. I am not too worried if that amp burns out from continued use, but I don't want to: 1) start a housefire; or 2) cause damage to my speakers.

Any guidance you could offer would be appreciated. I already know I need to be more careful when setting up my components, needless to say. Thanks and have a great day.

mfiddles
erik_squires
16,042 posts
 

2) if the amp blows, it seems unlikely that it would damage anything but the amp itself.

 

Good thing speakers are free. :D

atmasphere's avatar
atmasphere
11,785 posts
 

@mfiddles 

First you said:

An orange tinge was visible through the grates of the amp producing the smoke.

Just now you said:

Yes I think I saw a tiny flame inside

Which is it?

If flame, then the amp cannot be trusted. If smoke and the amp is still running as it used to then it is as I described earlier.

Resistors can heat to the point that they can turn red hot and in doing so will burn off their coating, which smells like plastic burning and makes a bit of smoke. But the resistor can survive if detected soon enough and allowed to cool. Its a good idea to have the part tested, since heat can cause some resistors to change value.

czarivey
5,946 posts
 

Yes I think I saw a tiny flame inside, as you said, and this would be logical given that there was smoke. Yes, I did take the cover off the amp. No shards are visible, and none of the components look burned or visually damaged.

It really looks like you've been smokin somethin, not amp and there may be no issue at all, but just an illusion.

audio_guy_uofw
42 posts
 

Nobody has commented on the preamp and what might have caused this. You said the filter was passive, right? No active components? So the input of this filter was plugged into the power amp input, and the output was plugged into the preamp.

The two preamp outputs should be individually driven, but they may just be in parallel. I suspect that the incorrect wiring caused an oscillation which fed into the other power amp pre-out.

Could also be a grounding issue. They are all balanced connections, right? Have you confirmed the xlr connections on the passive filter are correct for your setup (+ve, -ve, ground)

mfiddles OP
10 posts
 

Thank you for all of the helpful feedback! 😊 I appreciate it and will consider all of it. My understanding has been that, when an amp blows, it does not blow components upstream from it (e.g., preamp, DAC, etc.). It could blow the speakers but that is fairly unlikely. I could be wrong though. Of course, if it catches fire or explodes, it could "blow" everything.

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