# HSU ULS15 Recurring Issue - Ideas?



## wingnut4772 (Jun 11, 2012)

Howdy. I have 5 ( yes 5) Hsu ULS 15 subwoofers and I keep having trouble with one in particular. It has had a replacement amp x2 ( The second one is in the shop now). It is suspected to have a blown transistor again. 

Why just this sub?

Info: all subs are gain matched nearfield at 92-93 DB , not from the listening position but approximately 2-3 inches from the woofer. Ostensibly , in my understanding, that means they are all exerting about the same energy. All subs are run at about 76-77 db (measured as one ) in relation to the speakers which are at 75db. Since there are 5 of them, I would not expect anything thrown at them to be terribly taxing and I usually listen at about -10 under reference. 

My electrician tested my outlet on that sub and said everything looks fine. 

I did notice the sub cable prong is slightly bent on that sub and I ordered a replacement. Problem?

Ideas?


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## wingnut4772 (Jun 11, 2012)

64 views and not one thought?


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## Tom V. (Jul 12, 2012)

Its always best to check with the manufacturer but having said that...what are the variables?

1)different AC outlets.
2)different cables.
3)different drivers.

regarding 1,2---is it possible the troublesome unit is getting an AC surge the others won't? 

regarding 3, if there are repeated amp failures as you described perhaps the woofer in the troublesome unit isn't quite at 100% in some manner? BTW, what does the shop say would likely cause the specific transistor to pop? They may offer some good insight to the issue.

Tom V.


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## Wardsweb (Apr 2, 2010)

Have you measured the driver resistance compared to one of the other subs? Have you tried swapping the drivers between two subs to see if the trouble moves with the driver? Bottom line is you have an issue with either the driver or the amp. Is the transistor that goes in the power supply section or the output amp section?


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## hjones4841 (Jan 21, 2009)

Having opened one of my ULS-15s, swapping the driver is no easy task! That thing is heavy! Since I got my original 4 almost 3 years ago I had one amp failure. It was out of warranty, but Hsu replaced it for around $170 or so, don't remember the exact cost. I think they have a fixed fee for amp repairs.

As to the cause, with multiple failures something external just may be happening. How about moving its power cable to another outlet? Are all 4 connected to the same outlet? I have mine split between two circuits - not just two outlets.

Are the cooling fins on the back of the amp getting enough air? Is that amp hotter than the others? With the volume down on your AVR, is that sub's cone moving (some type of subsonic noise or ringing getting into the system?) Are you using wireless and if so do you suppose that some random signal is getting into that amp? Can you try hard wiring the input, if not already done? If not, a different wireless channel?

I suppose that Hsu could have gotten a bad run of amps, but that I think would not be likely.


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## wingnut4772 (Jun 11, 2012)

Thanks guys. 

They are all on different outlets ( except 2 - which are fine). 

I haven't tested the resistance. I'm not sure how to. 

Hsu is stumped as well. 

I did buy some Panamax MD2 surge protectors and a new cable. 

All of the subs have plenty of breathing room and I haven't noticed any extra heat on that one.

All subs are wired. I never liked the wireless.


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## wingnut4772 (Jun 11, 2012)

Wardsweb said:


> Have you measured the driver resistance compared to one of the other subs? Have you tried swapping the drivers between two subs to see if the trouble moves with the driver? Bottom line is you have an issue with either the driver or the amp. Is the transistor that goes in the power supply section or the output amp section?


I did swap out another amp to the damaged sub and the driver is fine. I'm not sure which transistor it is.


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