# Subwoofer locking up AVR



## theJman (Mar 3, 2012)

I just encountered an issue that has me stumped so I wanted to see if anyone else has run across something like it, and if so what you did to rectify the problem.

A subwoofer was recently submitted to me for testing. I plugged it into the surge protector that houses all my HT equipment, attached the RCA cable to the LFE in and then flipped on the power, just like I've done at least a dozen times before. But something new happened; my AVR (a Sherwood R904N) froze. Completely locked up. I shut off the power to the sub and the AVR started working again. This is with the sub in standby - it wasn't even on yet.

Figuring it was a problem with the amp I contacted the manufacturer who promptly sent another amp and torodial transformer. When I got the new parts I swapped them in, hooked everything up again, flipped the switch and the same exact thing happened. That doesn't make a lot of sense, obviously, so I checked to see if the driver was shorted. Disconnected I got a reading of 3.9 ohms across the terminals, so the problem wasn't the driver either. But there's nothing left really. Now here's where it gets weird...

Using both the new and old parts -- in pairs and various combinations -- I tried every conceivable manner in which to connect it. Single LFE in, single low level (first right, then left) both low levels using a Y splitter, etc. Every time I flipped on the power my AVR froze. I checked the electrical outlet the surge protector is connected to, which is three prong, and it's properly grounded, so that's not the issue. Troubleshooting further I plugged the sub into a separate outlet (which is still on the same circuit, but bypasses the surge protector). Flipped on the power, but this time the AVR keeps working. Progress, finally! Flip it into "always on" to wake it from standby, and then the AVR locks up. Back to square one. 

To summarize... if the power cord to the sub is plugged into the surge protector, where all my HT gear is, then as soon as I flip the switch my AVR locks up. That's in standby mode with the RCA cable disconnected. If I plug the sub into a different outlet I can power it up, but when I connect the RCA cable -- to LFE in or low level -- the instant it comes out of standby the AVR freezes.

Counting the units I own personally this AVR/RCA cable combination has been used with 11 different subwoofers, so the possibility something is wrong their is virtually nonexistent. However, it doesn't appear to be the sub either. When the manufacturer got the unit back he tested it on three systems -- Denon, Onkyo and I don't know the third -- and in each instance it worked flawlessly, and that was with the original transformer and amp. I've spoken with this person on the phone several times, so I do believe he's being completely truthful with me.

So, it's not the AVR or cable I use and it's not the sub or amp. What's left? I have to be missing something, but for the life of me I can't see what it is. Any ideas what might be causing this?


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## drdoan (Aug 30, 2006)

if that is the only piece of equipment (the sub) that presents that problem, it must have something to do with the sub's amp. Internal grounding could be a problem, or other problems. Sounds like a great problem. Let us know if you do find a solution. Have fun. Dennis


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## theJman (Mar 3, 2012)

drdoan said:


> if that is the only piece of equipment (the sub) that presents that problem, it must have something to do with the sub's amp. Internal grounding could be a problem, or other problems. Sounds like a great problem. Let us know if you do find a solution. Have fun. Dennis


I was pretty convinced of that last week too, but after finding out the exact same sub I couldn't get to work for me had performed flawlessly on 3 different systems after I sent it back I'm now even more confused.

I actually do reviews of subwoofers and post them on various forums. This exact same setup -- AVR, surge protector, RCA cable -- has been used on about a dozen different subs thus far, and has never presented a problem. Because of that I don't think it's associated to my environment either. Which means the sub works everywhere but in my house, yet every other sub works fine in my house.

The situation contradicts itself at every turn, and defies logic, which is why I threw up my hands and posted this thread. I figured it must be something I'm overlooking, because there's not a whole lot it can be. Hooking up a sub certainly isn't rocket science, but as of now the solution continues to elude me. :dontknow:


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## ansat (Apr 22, 2011)

Out of curiosity have you tried moving the sub to a different circuit. I think your exceeding voltage of the circuit. Electronics don't like dips in voltage beyond 5 percent.


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## RBTO (Jan 27, 2010)

I would suspect that the subwoofer is putting some kind of hash on the 110VAC power line which is getting into your AVR and causing the problem. Have you measured your line voltage? What happens if your surge protector is completely removed from the system? I ask the latter because if the line voltage is high enough, under the right loading circumstances, a surge protector can clip the sinewave and introduce some peculiar spikes. It may, in fact be your surge protector, rather than either your AVR or your sub. Try it without the protector and let us know what happens.


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## chashint (Jan 12, 2011)

You stated regardless of the AC circuit as soon as the RCA to the sub was connected the AVR shut down.
If the sub works on three other AVRs then I would suspect the Sherwood or the RCA cable.
However, if this is a new amplifier design maybe the input impedance on the LFE input is to low and the Sherwood is just more sensitive to it verses the other AVRs.


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## theJman (Mar 3, 2012)

ansat said:


> Out of curiosity have you tried moving the sub to a different circuit. I think your exceeding voltage of the circuit. Electronics don't like dips in voltage beyond 5 percent.


Inadvertently I did; turns out the 2nd outlet is on an entirely different circuit from the 1st, so they're completely isolated. That's slightly different then what I have in the first post.

My house is approximately 60 years old, and I'm the 2nd owner. The original owner had a few independent lines run for room air conditioners. The house has central air now so those window units are long gone. Both outlets I used for testing are on the same wall, so my assumption was they were also on the same circuit. However, last night I went into the basement and traced both of them back to the breaker box. Turns out the 2nd outlet was used for the air conditioner, and is on it's own circuit, while the 1st one -- which is where my surge protector is plugged into -- is an original circuit from when the house was built.

I used a circuit tester on both outlets, and they check out fine; no open or reversed hot, ground or neutral. So it looks like I'm back at square one...


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## theJman (Mar 3, 2012)

RBTO said:


> Have you measured your line voltage?


I didn't do that yet, but it's certainly easy enough. I'll check tonight.




RBTO said:


> What happens if your surge protector is completely removed from the system? I ask the latter because if the line voltage is high enough, under the right loading circumstances, a surge protector can clip the sinewave and introduce some peculiar spikes. It may, in fact be your surge protector, rather than either your AVR or your sub. Try it without the protector and let us know what happens.


To an extent I've done this already; by using the 2nd outlet I bypassed the surge protector for the sub. Is that what you were referring to, or did I misinterpret what you meant?


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## RBTO (Jan 27, 2010)

That's not exactly what I meant. You need to remove the surge protector _completely _and do without it for a short test period. You should be safe as long as you're not in a lightning storm. Disconnect the surge protector from the wall and plug both your AVR and SUB into the wall socket and give it a try.
Sometimes surge protectors can create line noise that might account for what you're describing. It would be prevalent if the line voltage is elevated which is why I asked about that, but in any case, you need to try the combination (AVR/SUB) without the surge protector to rule it (the surge protector) out.
If it's not the surge protector, we can go from there.


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## theJman (Mar 3, 2012)

Round two will begin shortly... I spoke with my contact at the company -- who's been reading these threads too (I've posted this on several forums) -- and he agreed to send me another unit. Now I'll be able to test some of the suggestions and see if I'm able to resolve this.


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## lcaillo (May 2, 2006)

I would have suggested the same as RBTO, noise from the power supply on the sub. Some units use a zero crossing detect circuit or other sensing on the a.c. line that can be sensitive and if the sub has a sloppy power supply or is defective this could be your problem. There could also be some a.c. leakage current. What kind of surge suppressor is this? Does it have any filtering or isolation between banks?

I'd start with an a.c. leakage test on both units.


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## chashint (Jan 12, 2011)

any updates about this ?


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## theJman (Mar 3, 2012)

chashint said:


> any updates about this ?


Not just yet, but hopefully soon. They did send me another unit (brand new), but I was scheduled for a week long business trip two days after I received it so I didn't even have the opportunity to hook it up. Hopefully this weekend I can spend some time on it, once I get caught up on a few other things.


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## RBTO (Jan 27, 2010)

Did you ever try pulling the surge suppressor out of the system?


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## theJman (Mar 3, 2012)

RBTO said:


> Did you ever try pulling the surge suppressor out of the system?


Not yet I haven't. It's a bit difficult for me to get at it -- I need to move the entire TV stand, and all that's associated to it -- so I was waiting until I got the new sub. Now I can do everything all at once.


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## theJman (Mar 3, 2012)

Problem solved!

I was sent a second brand new subwoofer from the manufacturer, plugged it in using the same RCA cable and power cord I have with all the other units I've reviewed, and fired it up. As soon as it came out of standby the TV locked up, just like the original unit. This was getting ridiculous, so I stepped back to evaluate what else to do. Then, almost by accident, I figured it out...

When I get a new sub to test I allow it to break in for at least 12-15 hours before doing any critical listening. The way I accomplish that is by using the weather channel on my cable system. They scroll the 5 day weather repeated while a jazz soundtrack plays in the background. I merely leave the TV on that channel the entire time I'm breaking the sub in, varying the volume from time to time. Simple, easy, effective. Most of the time, anyway. Never having done anything other then that in the past I essentially overlooked the possibility that something associated to that process could be the culprit. Breaking that pattern was the breakthrough I needed.

Although I had tried it previously I decided a new RCA cable was in order, as was using an electrical socket on a different circuit (which is physically located within a few feet). Same problem - TV locks up. I then used an extension cord to plug the sub into a kitchen outlet, 2 rooms away, and finally made some progress; the TV would lock up still, but only if I raised the volume a little beyond normal listening level. If it was low the TV now worked! Granted that makes no sense, but at least I was getting somewhere.

Now here's the "by accident" part... I shut off the cable STB, fired up the DVD player and dropped in a CD. I was attempting to determine how loud I could get the CD before it started breaking up the TV picture too, but much to my surprise the problem was completely gone! No matter how loud I made it the sub -- and TV -- worked flawlessly. So then I dropped in a movie, and had the same result; it worked perfectly. OK, now at least I know it has something to do with cable.

I checked for a proper ground on the coupler outside the house, just to be sure the wire coming in from the street was being grounded at the junction on the house. Ground was fine there. Inside the house there's a splitter (an expensive one, not some cheapy) so I can get separate feeds for the cable modem, TV in the living room and TV in the bedroom. That wasn't grounded, so I attached one to the cold water pipe (not sure if that was actually necessary, but it couldn't hurt). I also went out and bought a line isolator and placed that strictly on the feed off the splitter to the TV.

Eureka, it works beautifully now! With the sub hooked up exactly as I have done with all the others -- using the original RCA cable and the power cord plugged into the surge protector -- I have no more problem. So in short it appears to have been related to a previously undetected ground loop issue with my cable system, combined with a subwoofer amp that seems to be rather sensitive to such things.

Thanks for everyone's help. It was a learning experience for me, and an interesting problem (to say the least), but in the end it has been successfully resolved.


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## ALMFamily (Oct 19, 2011)

Wow - that is a weird one Jim. Glad everything is working now! :T


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