Subwoofer Problems

[Dude_Uncool]

I have an old Pioneer SW-8 powered subwoofer that I decided to directly hookup to my tv. It sounds great and all, but it heats up after just minutes of use on normal volume, to an untouchable level on the back metal panel. It was bought in the US and since I live in India now I bought a 230V to 120V transformer for it. The transformer is rated at 150W max(the sub is rated at 100rms). Is this normal or is there anything I should worry about?

[tikker]

I think it's probably normal, depending on how hot "untouchable" in this case is. The metal panel is probably a heat sink for the components inside. Its function would then be to draw away heat from those, so naturally it will get hot.

[Dude_Uncool]

The back panel contains all the controls and ports. That’s why I am concerned.

 

The circled part is we’re it heats up. 

[circeseye]

it shouldnt get to hot to touch like that especially that quick at normal volumes. im betting its the 230 to 120 transformer. throwing to many amps that the subs transformer cant handle maybe?

 

edit

im thinking on this more and researching. it has to be that 230 to 110 transformer. something about it is to much for the sub components to handle. it will eventually burn out if im guessing right

 

another thing im seeing the u.s ac is 120 60hz. eu is "50hz" . it may not like the hz your area runs also. like my sub it says 120 60hz "only" (actually yours says that also) just no only tacted on it

[OhioYJ]

4 hours ago, Dude_Uncool said:

The transformer is rated at 150W max(the sub is rated at 100rms). 

Just as an FYI those are two different ratings. The 100 watts RMS on the sub isn't the same as the rating on the transformer. Pioneer specs that at a 1 Amp power draw, and 1 Amp x 120 volts would be 120 watts. Most manufacturers seem to recommend at least a 50% oversize. I honestly don't have much experience going down in voltage, but I did notice that in your post.

[H713]

14 hours ago, circeseye said:

it shouldnt get to hot to touch like that especially that quick at normal volumes. im betting its the 230 to 120 transformer. throwing to many amps that the subs transformer cant handle maybe?

 

edit

im thinking on this more and researching. it has to be that 230 to 110 transformer. something about it is to much for the sub components to handle. it will eventually burn out if im guessing right

 

another thing im seeing the u.s ac is 120 60hz. eu is "50hz" . it may not like the hz your area runs also. like my sub it says 120 60hz "only" (actually yours says that also) just no only tacted on it

This post makes absolutely zero sense. 

 

If a 2:1 step-down transformer of sufficient size is used, it will be no different from running it off a regular American mains outlet. As long as that 2:1 transformer is rated for more current than the subwoofer amplifier requires, there's no issues. 

Here are a few possibilities:

1) The subwoofer has a linear power supply, and you are feeding in MORE than 120 V, and you're beginning to saturate the core of the power transformer. You will almost certainly hear mechanical buzzing if this is the case, and the transformer in the subwoofer will get hot. Eventually it will start to develop shorted turns on the primary, which will make the saturation worse, and before long it will release the magic smoke.

 

2) The subwoofer has a SMPS, and you are feeding LESS than its minimum voltage. The feedback loop for this power supply (which is regulated) tries to maintain its rated output voltage, and to do this it must draw more current from the AC line, possibly causing things to overheat.

 

3) The subwoofer has a linear power amplifier which is grossly over-biased for some reason. Likely an issue with the bias spreader. In some poorly designed amplifiers, an open wiper on the bias pot can cause this. It could also be caused by an idiot who thinks that they can "get more power" by screwdrivering the trim pots.

 

4) You are somehow driving the subwoofer amplifier to very high power levels above the maximum frequency the woofer can reproduce. This could very well be above 20 kHz.

 

5) Depending on how hot it actually gets, this could be normal operation. Class AB amplifiers are somewhat inefficient by design and some of them do run quite warm. Just how hot is "untouchable" in this case? Untouchable can mean anything from "It's a little uncomfortable to hold my hand on it for long periods of time" to "it instantly burns the skin off my fingertips". 

[circeseye]

2 hours ago, H713 said:

This post makes absolutely zero sense. 

 

If a 2:1 step-down transformer of sufficient size is used, it will be no different from running it off a regular American mains outlet. As long as that 2:1 transformer is rated for more current than the subwoofer amplifier requires, there's no issues. 

Here are a few possibilities:

1) The subwoofer has a linear power supply, and you are feeding in MORE than 120 V, and you're beginning to saturate the core of the power transformer. You will almost certainly hear mechanical buzzing if this is the case, and the transformer in the subwoofer will get hot. Eventually it will start to develop shorted turns on the primary, which will make the saturation worse, and before long it will release the magic smoke.

 

2) The subwoofer has a SMPS, and you are feeding LESS than its minimum voltage. The feedback loop for this power supply (which is regulated) tries to maintain its rated output voltage, and to do this it must draw more current from the AC line, possibly causing things to overheat.

 

3) The subwoofer has a linear power amplifier which is grossly over-biased for some reason. Likely an issue with the bias spreader. In some poorly designed amplifiers, an open wiper on the bias pot can cause this. It could also be caused by an idiot who thinks that they can "get more power" by screwdrivering the trim pots.

 

4) You are somehow driving the subwoofer amplifier to very high power levels above the maximum frequency the woofer can reproduce. This could very well be above 20 kHz.

 

5) Depending on how hot it actually gets, this could be normal operation. Class AB amplifiers are somewhat inefficient by design and some of them do run quite warm. Just how hot is "untouchable" in this case? Untouchable can mean anything from "It's a little uncomfortable to hold my hand on it for long periods of time" to "it instantly burns the skin off my fingertips". 

yea it is a little confusing......the issue is his converter and owning a u.s product set up for u.s ac

u.s ac is 120 60hz. hes in eu so the converter he actually needs is a 230 to 100 50hz. the 230 to 120 50hz is to much (hence why its getting so hot). there are a lot of electronics from the u.s that dont run good on e.u ac because of this. and vise versa,  even if you use a converter. its also why its usually stamped at the plug or in the instructions on what it can handle

a product that can handle both ac's is usually stamped "100-120V, 50-60Hz" just u.s "120 60hz" just eu "100 50hz" asian countries are like this also i believe

[H713]

It's possible that the transformer in the subwoofer is marginal and will saturate when running on 50 Hz. Most decent transformers shouldn't have an issue, but it could be the case.

 

I'm still betting on the amplifier being the issue, since it uses the back panel as a heatsink, and the thermal coupling between the transformer and the back panel will likely be rather poor.

 

Out of curiosity: How hot does this thing get idling with no audio playing?