Paradigm Sub - 60Hz hummmmmm

[jbravo103]

I realize this may not be an electronic troubleshooting forum, but maybe someone can help me out.

I recently inherited a Paradigm sub from my brother who had it in storage for a number of years. It has been shipped around from place to place as he moved from job to job.

As soon as I took it off his hands I hooked it up to my home theater receiver using the LFE output on the receiver and low-level inputs on the sub. The first thing I noticed was that as soon as I plugged the sub into the wall outlet it produced a 60Hz hum. I could adjust the amplitude of the hum with the amp gain control. The sub didn't play any music, but just sat and hummed away.

So I turn everything off and unplugged the inputs, then turned the sub back on. This time I got no sound from the sub (which is good). So I turned it back off, grabbed a different set of RCA cables and connected to the low level right channel input and left the other end in free air. I turned the sub back on and got the hum right away. Then I swapped the right channel input to the left channel input. No change, still had the hum.

At that point I noticed something strange. When I had the RCA cable plugged into the either the left channel, right channel, or both channels, and I put my hand on the back on the amplifier, the amplitude of the hum increased.

Finally I decided to try the high level inputs on the sub, and those seemed to work fine. No hum and music was playing fine.

Well anyway, your thoughts are appreciated.

John

[noddin0ff]

I'm no electricity genious, but 60Hz is the frequency of your AC outlet. Could be ground loop hum. If I understand, this is caused by having both components on the same power circuit, sharing the same ground. Plug your sub into a different outlet, perhaps one that is on a different circuit breaker and see if it persists. Easy enough thing to try until someone with a bone fide EE degree answers your post.

[jbravo103]

That's a good point, but why didn't I get the hum when I switched to the high-level inputs? From what I have observed so far, I could put the sub in my car, drive to 200 miles south, plug the sub into an isolated power supply on a remote island, and get the same problem. It is when I plug and RCA cable into the low-level input. The other end of the RCA doesn't have to be plugged into anything.

I'm thinking it has to be something wrong with the amp itself. Bad component, short or open on the circuit board, or something else. It's weird that the high-level inputs work while the low-levels don't. From what I can tell, the high-level signals just go through some fancy op-amp network to bring them down to a low-level signal, but otherwise they are practically on the same bus.

John

[Woochifer]

I would also guess that it's a ground loop. Try plugging the subwoofer onto a different circuit and see if it still does the same thing. Then try unplugging some of the other electrical devices to see if the humming goes away (and also try unplugging the cable TV connection).

60 Hz is the frequency of AC current, so you just need to locate the source. My subwoofer started doing the same thing whenever I had my printer plugged into the wall and connected to my computer. That apparently created a ground loop.

[poneal]

Had Time Warner Cable installed and as soon thereafter I noticed a 60hz humm. I mean no bass whatsoever, just a nice loud 60hz humm. I tried different outlets, blah blah, none of it worked. Even tried the balun's and transformers with some luck but not much. In the end I solved the problem by going to Home Depot and buysome some 4ga IIRC bare copper wire about 3 foot long. Cost a couple of dollars. Went to the back of the house and took off the ground Time Warner had put (flimsy 14ga piece) and replaced it with new ground wire. I also scrapped the pipe to bare metal where they had connected the cable to earth. I also replaced the copper ring that goes over your grounding rod and used to tighten all grounds to the rod. Tightened everything up and to my glee it solved the problem. Of course don't do this in stormy weather :).

Legal Disclaimer:
All of the information provided herein is for personal Do It Yourself (DIY) use. I am not responsible for injuries sustained while doing any of the above. This requires skill at basic electricity design which can be difficult and dangerous for a beginner. There are no warranties express or implied on any information I have provided herein so do it at your own risk.

[Florian]

Other solution is a "cheater plug" for 39cents at Home Depot :-)

-Flo

[kexodusc]

Yup, Flo is right, a 3-prong to 2-prong adapter will solve this problem 99% of the time.

[jbravo103]

I don't think a cheater plug would help me because the power cord coming out of the sub is only 2-prong.

This weekend I went a bit extreme and unplugged every piece of electronics in my house except the refridgerator. I also disconnected every cable tv connection. Then I took my sub upstairs and placed it in the living room. Next I took a mono subwoofer RCA-type cable made by Monster cable and plugged into the right low-level input on the sub. The other end of the Monster cable was left lying on the carpet. Then I plugged the sub into the outlet. As soon as I plugged the sub in the hum was there. I tried the left channel input and got hum too.

I then took my sub out to garage and plugged the it into a 500W inverter connected to an Optima gel-cell battery. Got hum.

I just want to reiterate to everyone following this thread, when I use the high-level (speaker level) inputs on the sub instead of the low-level, the sub works perfectly fine - no hum. Whenever I try to use the low-level inputs, the sub just hums and won't play any music. So it seems to me like the RCA input connector on the sub gets shorted to ground as soon as you plug a cable into it because no signal makes it to the preamp.

I took the amplifier out of the sub cabinet and looked things over. Everything appeared fine for the most part. I didn't notice any breaks or shorts in the land and no components looked burnt or brown.

I'm not sure what to try next except send the amp back to Paradigm.

[kexodusc]

Is there anything else plugged in that is connected to a 3-prong plug? Receiver, power bar, etc? Generally the amps ground themselves through the LFE sub cable, that 60 Hz is the standard PSU frequency. Could be something else, but 90% of the time it's ground loop.

Weird.

[jbravo103]

Just got off the phone with a local Paradigm dealer he said they had to send a floor model back to the factory for the same exact problem I have. He said there is something on the amp that goes out, but he didn't know what.

He also said many other Paradigm customers have had the same problem with their subs and had to send them back for repairs/replacements.

[kexodusc]

Just got off the phone with a local Paradigm dealer he said they had to send a floor model back to the factory for the same exact problem I have. He said there is something on the amp that goes out, but he didn't know what.

He also said many other Paradigm customers have had the same problem with their subs and had to send them back for repairs/replacements.
Wow, this is news. Considering the many Paradigm sub owners that frequent this board alone, I'm surprised I've not heard of this previously. But then again, 1% of Pardigm owners is a pretty big number. I lucked out with the three I owned. Hope the guys I sold them to did as well.

Plate amps are known for going in a lot of subwoofers though, it's not surprising. The more gizmos on them the higher the chance of failure too. With all the advancements in subs the last few years, I'm not surprised - more power, and lower prices must force a compromise somewhere.

[pelly3s]

try an iso transformer. components dont always ground through power they also ground through signal cables. so that can cause your ground loop. to be effective you need to put the iso transformers in the right places.