Still standing, last I checked. :)
? 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.
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- 43 posts total
@mfiddles D753 is a diode in series with the 10 Ohm resistor, R783. The screen for the resistor might be visible once you clean the board. This resistor is in the protection circuit and is not part of the amplifier circuit itself. So the amplifier circuit was undamaged in any way. However, given the state of the resistor its a good bet the protection circuit for that channel is damaged. It may fail to give protection if an event occurs in the future. I would start by replacing the resistor and testing the associated diode for a short. |
The cost of a tech’s repair might be more than the value of the amp, so that must be considered. I have several amps in my collection that would sell below $200., and they all work great. But if 1 of them failed and I could not do the repair myself, it would become a recycled item and imo not worth the investment. I predict that mcfiddles will continue to use the amp, as he sounds like he will. My best to all, MrD. |
I repaired stereos for 4 years in college and I can tell you that blown amps do take out speakers. I'd give you 3.14% odds depending on how good the protection circuitry is, how it fails and how robust your speakers are. It could also cause a real fire, maybe 0.1% odds. Is running it really worth this risk? You could be your own technician, buy some large enough dummy loads, 8ohm resisters, and run your amp full power for about 30 min. You need some idea of what full power is since you don't have an oscope. If it survives, then your odds of failure went down. Also, open it up again and look really closely in the area of the orange glow with a very bright light. You might find something you missed the first time. If it's a resister, compare the value to other channel. |
Thank you, Nagel. Well 3.14 x R^2 = area, so I suppose the 3.14% odds you cited are not too bad. Lol. How do I "buy large dummy loads?" Do they sell them at Target? Walmart? Do you just mean running a high-volume signal into the amp, with nothing on the outputs, for 30 minutes, and hoping there is no fire? |
- 43 posts total