dedicated cicuit ? (1 Viewer)

Brad Russell · Aug 13, 2003

I'm planning on running a dedicated circuit to my home theater and have some questions. The main reason I'm doing this it to eliminate the hum un my sub. My house was built in 52 and the basement finished some time in the 80's, so the electrical circuits are a mish mash of old and new. I figured the only sure way to get rid of a ground loop would be to run a dedicated circuit. So do I just go get a Hospital Grade plug at the Home Depot and run some 12/2 on a 20 amp. circuit to my Monster HTS 1000? Sould I usr 10 ga.? Right now I'm running a Yamaha a-1, DVD, VCR, Crown D-150A for a Polk passive sub and a PSB Subsonic 3i, and a JVC 32" TV. I'm hoping tp some day move up to a pair of SVS monster subs with an outboard amp and a front projector.

Thanks for any advice!

Brad

Dave Milne · Aug 13, 2003

run some 12/2 on a 20 amp. circuit to my Monster HTS 1000?

I assume a "Monster HTS1000" is some sort of line conditioner? My humble opinion is that these are rarely worth the money. A real dedicated circuit generally solves interference/spike issues (generated elsewhere in your house electrical system) while providing stiff, fluctuation- and sag-free power. Line conditioners on the other hand exacerbate voltage sags because their filters introduce unwanted impedance.

"Dedicated circuit" to me means adding a 20A breaker to the main house panel and running 12/2 from it to a set of outlets that you use exclusively for A/V equipment. 10ga is even better and will allow a 30A breaker, but it doesn't bend easily (difficult to snake through walls) and not all standard outlets will accept it.

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Rick Wilson · Aug 14, 2003

"Dedicated circuit" to me means adding a 20A breaker to the main house panel and running 12/2 from it to a set of outlets that you use exclusively for A/V equipment.

Can this one circuit run:
Sat. receiver (2)
65" RPTV
A/V receiver
Sub
DVD
VCR

If not, what should be separated?

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DavidPAnderson · Aug 14, 2003

Yes one 20 amp circuit should be able to run all of that and more (probably 2 of each of those) unless you have some insane equipment that sucks power like nobodys buisness in which case you'd probably know already because you'd have trouble using it in your house already.

Brad Russell · Aug 14, 2003

Thanks for all the responses. I added up all my components:

A-1 500w
VCR 18 W
DVD 15w
TV 130w
Crown Amp 750W

Can't find the power consumption of the PSB Sub. So far the total is 1411 watts without the sub. So I think I'll go with a 10awg and a 20 amp breaker. I couldn't find a 30amp mini at my Home Depot so I'll go with the 20 and have a little extra protection.

Thanks!

Brad

Wayne A. Pflughaupt · Aug 14, 2003

Brad,

Hospital-grade outlets are not necessary, just an added expense that will offer no benefit for this application.

The 10ga is overkill, but it won’t hurt to use it. However, as Dave mentioned, not all outlet devices will accept 10ga. Your best bet will be to use rear-loading industrial-grade outlets that have screw-down clamps. You will not be able to wrap 10ga wire around the screw of a standard outlet.

Regards,
Wayne A. Pflughaupt

Brad Russell · Aug 14, 2003

Thanks Wayne! Could you be more specific about the industrial grade outlet so when I return the Hospital one th Home Depot I know what to look for?

Thanks!

Brad

Ron-P · Aug 14, 2003

I ran two 20amp breakers with 12/2. One for all my components (Projector, 5 amps, DVD, HTS-2500, Receiver, 15" Tempest SonoSub). The other line is for lighting, A/C and misc. I used 20 amp heavy duty outlets found at Home Depot.

10g and 30 amp breakers is over kill, you'll be fine with 12/2 and 20amp breakers, you'll be hard pressed to pop'em. I have yet running everything at reference +.

Dave Milne · Aug 15, 2003

10g and 30 amp breakers is over kill

Overkill perhaps... but considering the modest price difference between 12ga and 10ga, might as well go for that tiny extra benefit.

Think about this: A 100' run of 12ga has about 0.32 ohms resistance. The same loop of 10ga is about 0.20 ohms. At full 20A load, this equates to a line drop of 6.4V vs. a 4.0V. Now, a 200W amp puts out 40Vrms into 8 ohms - in other words about one-third line voltage. So, that extra 2.4V at the wall corresponds to 0.8V of output voltage. Therefore the amp that makes a full 200W with 10ga will make only 192W with 12ga.

So that modest price premium for 10ga wire yields a very measurable increase of 8 watts per channel. There are a lot of much-higher-priced "tweaks" that offer no measurable benefit!

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Drew Eckhardt · Aug 15, 2003

1. Note that you can't legally have 15/20A outlets on a 30A breaker.

2. I have 6 stereo power amps (7.1 with actively tri-amplified fronts) having a total placarded maximum consumption of 5760 Watts. They work fine on a 15A circuit, probably because the consumption at idle is just 350W total and they're pretty much loafing along.

Andrew Lillie · Aug 15, 2003

Actually I don't think it works that way. Using DC ohms law on AC voltage current and power is not correct. When calculating AC current requirements we should include the power factor (PF) and efficiency (EF) of the circuit.
See here: AC Currrent / Power app note

Also, remember that all of your AV equipment have regulated supplies, in other words they can accept a range of voltages to assure an exact 12V (or whatever - typically DC) output voltage. If the input voltage dips, the regulator will consume more current and maintain the output voltage. This is why high end eqpt has big, complicated power supply regulation units. (It also makes them heavier). Also, your 120V mains is never exactly 120V and it probably fluctuates throughout the day - especially today in the NE) (couldn't resist).

Also, audio power can be deceiving. As I recall you need an order of magnitude (actually its 8x) more amplifier power to double the sound pressure level (loudness). 8w is not even going to be noticeable at 100W (or less). You need twice as much power as your reference to achieve a "Just Noticeable Difference" JND.

I agree with you on the lin conditioners. If anything I would use a UPS instead to try and smooth out the brown outs etc.

To reduce hum on a sub, make sure that the sub, and amplifier/receiver/source are all connected to the same powerstrip. Worst case, you can also try and lift the ground connection to your sub, i.e. don't connect the third prong. You can actually buy plus that do this for you, for this very reason.

I hope this helps
Andrew.

Brad Russell · Aug 15, 2003

QUOTE]To reduce hum on a sub, make sure that the sub, and amplifier/receiver/source are all connected to the same powerstrip. Worst case, you can also try and lift the ground connection to your sub, i.e. don't connect the third prong. You can actually buy plus that do this for you, for this very reason.[/quote]

What about when your sub hums and only has a two prong plug to begin with? Everyting else goes through the HTS 1000 as well but it is the only thing othat hums.

Wayne A. Pflughaupt · Aug 16, 2003

Brad,

Could you be more specific about the industrial grade outlet so when I return the Hospital one the Home Depot I know what to look for?

Standard outlets have two options for termination: Rear spring-loaded connections, and side screw - i.e., the wire wrapped around the screw.

Industrial outlets (at least the ones I was speaking of) connect from the rear only, and the side screws serve to secure the connection via an internal clamp (they aren’t designed to have the wire wrap around the screw). Plus, they have a larger frame and are heavier (in weight) compared to the residential devices.

So-called commercial outlets are also a good choice, if you’re going to use 12ga. wire – heavier-duty than the residential devices. They aren’t as rugged as the industrial, but they are quite a bit cheaper.

However, if you’re set on 10ga. wire, your best (perhaps only) option is the industrial devices.

Regards,
Wayne A. Pflughaupt

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Andrew Lillie · Aug 18, 2003

Brad,
On the sub hum thing, does it still hum when the audio signal is disconnected?

If so, I'd say its the sub, and there's not much you will be able to do other than try moving it to a different location and see if it still hums. Try grounding the metal chassis of the sub amp with a thick copper cable to the metal chassis of your receiver, or the same outlet. (Receiver chassis would be betterm, it may even have a grounding screw on the back for a phono or antenna! Be careful though, don't want to damage your receiver with your sub!

If it does not hum with the audio cable removed, try a different audio cable, audio source (just for a test) and see if it makes any difference.

Andrew

Brad Russell · Aug 19, 2003

Andrew,
I think I remember testing it and it is still there with the interconnects disconnected. I'll check again tonight when I get home.

Thanks!

Brad

Brad Russell · Aug 25, 2003

Ok, I ran the dedicated circuit this weekend and tested it out. The sub still hums! Anybody have any idea what gives? I get 60hz hum no matter what. I've tried it with the interconnects off, with the sub as only thing on the circuit. I've tried it with a cheater plug and reversed the polarity. The sub has only a two prong plug. So I took the amp off and found that the ground wire was just going to the back plate of the amp. So I tried attaching a ground wire to it and wired it directly to a three prong extension cord and plugged that into the dedicated circuit all by itself. Still have that damn hum.

Any suggestions?

Thanks,

Brad

Wayne A. Pflughaupt · Aug 25, 2003

Brad,

If it hums with nothing connected to it, then it’s not a ground loop. The sub has a problem.

But before you chalk it up to that, do you have any light dimmers? If so that could be the problem, if they are on the same circuit or electrical phase as the sub. Try plugging the outlet in to several other outlets around the house

Regards,
Wayne A. Pflughaupt

Brad Russell · Aug 25, 2003

It is on a dedicated circuit. How would you check or change the pahse of the circuit?

Thanks
Brad

MikeWh · Aug 25, 2003

You said you've got a mish-mash of old and new wiring, so you could really have a problem with the basic wiring in the house.

If you have a breaker box and were just working with a "normal" 2-phase system, then the box is usually configured like this:
http://www.x10ideas.com/articles/ima...ASECOUPLER.gif

Disregard the info about a "coupler"... I'm just trying to point out the 2-phase system, and how the positions in the breaker box between phases. Look for sources of interference, such as dimmers, fluorescent lighting, motors, etc. on the same phase as the circuit you are currently working with. Unfortunately, your major appliances are likely using both phases, and they oftentimes have motors that may interfere. If you don't find an obvious source of interference on the phase you're currently working with, look for a circuit that's on the other phase (like Wayne suggested), then take your sub over there and plug it in.

BTW, my sub hums... at least a bit. In a totally silent room, I can tell if the sub is on or not by its hum. I also know that I have very sensitive hearing (despite the loud movies).... I think it's not unusual for powered speakers to make at least a little hum.

Which sub is humming? You mentioned a Polk passive. I'm assuming it's the PSB and not the Polk. Is that right?
If so, have you heard other powered subs?
Can you borrow a friend's sub and test it at your house?

Brad Russell · Aug 26, 2003

The house has a mish mash of old and new but I just added a cedicated circuit for the HT. The sevice was updated to 200 amps before we bought the house. It comes into a 125 amp pannel that has mostly old and some new wiring. There was one open slot where I added the dedicated cicuit for the HT. Yes it is the PSB that hums. The Polk is powered by a Crown D-150 AII and is quiet. I have a KLH sub upstairs (that doesn't hum). I'll have to try swapping them and see if the PSB hums upstairs.

Brad

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