How I'm going to attempt to fix my ground hum

ctviggen · « **on:** 12 Jan 2006, 12:58 pm »

I have three subs joined by an NHT X2 active crossover. I have two VMPS Largers and one SVS. I use the VMPS largers in stereo mode and throw in the SVS for movies. Adding the SVS, which is powered by a different circuit, adds hum -- loud hum. So, I purchased one of these:

http://www.jensen-transformers.com/sub1rr.html

I'm going to install this transformer this weekend and report my results. I plan on using my RS meter to gauge the amount of hum before and after the transformer and also I'll try placing the transformer at various locations.

Marbles · « **Reply #1 on:** 12 Jan 2006, 01:00 pm »

You might also try a long extension cord to get the SVS on the same circuit.

Dan Banquer · « **Reply #2 on:** 12 Jan 2006, 01:31 pm »

Sounds like your other circuit is on a different phase than the rest of your system. If you can check for that Bob, that might be the cause of the problem.
There is one problem with hooking all these subs on the same circuit. Current draw of powered subs can be really high due to the inefficency of many of them, and may cause some rather nasty dips in the AC Line.
In any case please report back to us on your results.
Hope this helps;
d.b.

ctviggen · « **Reply #3 on:** 12 Jan 2006, 01:58 pm »

I thought about the long extension cord, but it would have to run basically entirely across the room. It was definitely an option, but I'm trying to hide the wires, and I feel safe hiding low voltage wires but not AC wires. In other words, I have to traipse these through/around metal baseboard heating elements, and I'd hate to have the AC cord short to the metal baseboard. It's still an option, but one I'm not sure I'll do.

As for the different phase -- you could be right. I can check that also this weekend. That would be easy to fix. If that fixes the hum, I'll be hornswaggled! (Especially being out the cost of that expensive transformer.)

warnerwh · « **Reply #4 on:** 13 Jan 2006, 01:12 am »

Did you try a cheater plug? If you know how to move the breaker to the other phase that would be better though. Be careful in there!

Occam · « **Reply #5 on:** 13 Jan 2006, 10:51 pm »

Quote from: warnerwh

Did you try a cheater plug?....

Cheater plugs are a good way of diagnosing as to whether the problem is a ground loop, though its not always definative as to which component is the 'culprit', i.e. with a 2 component system with GL hum, putting a cheater on either might cause the hum to go away.
But we all must realize that cheater plugs are not a solution, only a quick and dirty diagnostic tool. Permanently lifting the ground on a chassis is simply too dangerous.

JoshK · « **Reply #6 on:** 13 Jan 2006, 11:41 pm »

since you can solder, you should try out JM's ground buster circuit. Worked wonder for my ground noise. Its part of JM's PSU circuit on part 4 or 5 of the Building your own Hypex thread. It is pretty obvious what part is the ground buster.

ctviggen · « **Reply #7 on:** 14 Jan 2006, 07:26 pm »

Well, I'll be! It was the other phase that caused the ground loop/hum! Since all of my HT gear is on one dedicated circuit, except for my SVS sub, it had to be the SVS sub that caused the ground loop. The SVS sub only has a two-prong plug, so a cheater plug wouldn't work. I figured out which phase the dedicated circuit was on (easy, as I'm the one who installed the dedicated circuit), then I turned off breakers until the SVS sub went off. It was on another phase! So, I found another circuit/breaker of the same amperage, turned off all the power, and switched the SVS circuit and the other circuit so that the SVS circuit is on the same phase as the HT circuit. I then powered everything up and no there's no hum!

Anyone need a fancy transformer?

Next, I need to update the information on circuit breaker box, but I plan on mapping out every outlet/light/device so that I can see which circuits are heavily loaded. Also, I realized that I only have 100 amp service, but I have some obscene amount of amperage, if one is to simply read off the max amperage on each circuit and add them up. My stove, hot tub (currently drained and turned off), dryer, and well water pump are together over 120 amps, and that doesn't include any circuits for lights. Granted, you'd probably have to have the stove, hot tub, dryer, well water pump, and all lights on all at the same time to actually come near the 100 amp mark, but this is yet one more thing to upgrade. I'll have to check my copy of the NEC to see if there are any guidelines on this.

Dan Banquer · « **Reply #8 on:** 14 Jan 2006, 09:00 pm »

That'll learn ya to go out and buy expensive transformers before you troubleshoot!

Welcome to the club of "experienced professionals" who have done similar things. Can you return them within 30 days for a refund?
d.b.
BTW: Are the well pump,, and hot tub along with the stove wired to 240V? If they are would they bypass the box? and be fused/breakered separately?

ctviggen · « **Reply #9 on:** 16 Jan 2006, 04:48 pm »

Well, I spoke too soon! Changing the phase did lesson the amount of hum on my SVS sub. However, the hum on my two VMPS Larger was still horrible, and I didn't realize this until I replaced the fan on my QSC amp. Once I plugged in the QSC amp and the two subs, the hum was back. I disconnected everything and added things back in, one at a time until the hum came back. The culprit? A cheap interconnect from my preamp to my active crossover! I replaced this interconnect with one from the signal cable company, and the hum -- while still there -- is dramatically reduced. I can no longer hear it where I sit. All this time I thought the 25 or 30 foot line to the SVS sub was causing the problem.

As for the hot tub, etc., they are all on the 100 amp breaker box.

I still have an expensive transformer.

Dan Banquer · « **Reply #10 on:** 17 Jan 2006, 12:14 am »

Well Bob; it looks like you can still put that transformer to good use for the VMPS Subs and kill that ground loop.
d.b.

westend · « **Reply #11 on:** 18 Jan 2006, 06:56 am »

As to the house wiring: as long as the ampacities of the individual branch circuits aren't exceeded you should be OK with 100amps. A draw approaching the maximum of the current draw available would be revealed by lights dimming, motors reducing speed, and other obvious signs. I've seen folks operating a full household and shop with multiple welders, shop equipment, etc. off a single 100 amp breaker box. In my own house, I have a 100 amp. box with well, AC, furnace, small shop, and a lot of electronics. I haven't lost any device. The quality and design of the circuitry and the quality of the source (i.e. what you have beyond the meter) is more important than the total ampacity, IMO. Note:although anecdotal information can be used as a guideline, best practices should always be followed.

ctviggen · « **Reply #12 on:** 18 Jan 2006, 01:36 pm »

Dan, I tried the transformer on the (bad) interconnects, with no luck. I'm not sure if I said this above, but I also tried the transformer near my SVS sub (about 25 feet of wire away from my system), and that actually made the hum from the SVS much, much worse. Putting the transformer near the system helped, a bit. So, currently, replacing the bad interconnect (an audioquest) with the good interconnect (a signal cable) has done as much as I think I need to do. Unfortunately, my QSC amp still has a bad channel, so I'm not using the Larger subs, as only one would work and I have them set up in stereo. Also, one of my other Largers appears to be wired incorrectly, so I have yet one more thing to fix this weekend! Ugh!

Westend -- you're probably right. I thing what's more important for me will be to analyze what lights/outlets/devices are on what circuits and how big (in terms of amps) the circuits are. I think that'll help safety more than how many "apparent" amps there are.

westend · « **Reply #13 on:** 21 Jan 2006, 08:35 am »

A good basic rule of thumb for residential wiring is to design a branch circuit to handle 150% of the anticipated ampacity. So, if you total up the devices and the average current draw they would be 2/3 of the rated ampacity of the circuit. This is overkill but lends to a failure safe installation. In the practical sense, most of the residential wiring I do now is 12 ga. or better with the consequent upgrade in circuit breaker amperage. It is not that more expensive than 14 ga..