Feeding a power amp (1 Viewer)

[Dave Falasco]

Hey, all. This past weekend I bought a B&K Reference 30 pre and a 7270 power amp. I'm worried about powering that 7270 amp. In my theater room I've got two 15-amp circuits. One handles all the lighting, and the outlets along one wall. The other controls the outlets along the other wall, where all of my components are plugged in (into a big surge protector, of course!).

I downloaded the user manuals for the B&K gear to get a head start on reading up on them (they get delivered next week), and I noticed that the maximum draw of the 7270 is 17.5 amps. The book also recommends a separate circuit for the power amp. That isn't going to be easy, as I would have to have an electrician out to do a load calculation to see if I can add another circuit, and if not, I'll have to upgrade my service from 100 to 200 amps.

My question is for those of you who have this or a similar power amp--how are you feeding those beasts? Is it feasible to expect a single 15 amp circuit to power the TV, pre/pro, amp, sub amp, DVD player, and satellite receiver? Obviously I'd like to have more power, but if I can't get it, am I risking damage to one or more of the components on that circuit?

Your input is appreciated...I have very little experience with this kind of stuff and I'm worried that I'll finally achieve my dream of owning separates, only to bring down the entire power grid trying to run the sucker... :b

 

[Bill Kane]

Dave,

You could push and exceed the safety limits of one 15-amp circuit with this new amp. A 20-amp line is warranted.

Since you have taken the steps to acquire these reference level components, you owe it to yourself -- at some point --to provide the optimal current supply for the gear, for house circuitry and peace of mind.

Ideally, you wud end up with 200A Service and a dedicated 20A circuit for your HT. However, 150A Service works just fine with 20A circuits, as my house was built in the late '80s.

Remember the big B&K only rarely will reach it's peak outputs, actually 1830 watts for the 7270. In real-world many large systems will only draw or peak at 9.5A to 10.5A. On a 15-amp circuit, the safety limit is not to exceed 80 percent of load rating, or 12 amps amd 1440 watts.

I run a 1800-watt peak capacity power amp, but plug it directly into a 20-amp circuit with upgraded duplex. I live with good weather, good local utility, so I am letting my power amp's internal protections be the line of defense for surge suppression. My tv, sub amp and the rest run off this circuit which handles nothing else but two floor lamps.

People who install a dedicated 20-amp HT circuit often will use 15-amp duplex outlets, since 20-amp seem overkill. Nearly all HT electronics are geared to 120V 15A application.

Also note that most consumer surge protectors are 15-amp, 1800-watt rated. Meaning just because one has a 20-amp outlet, and plug in the surge protector power center and the big amp into this unit, the surge protector itself is a limiting element for excessive current draw. That is, its fuse wud tend to blow before a service main breaker. This isnt particularly desirable. There are 20-amp surge protectors, like the 2-outlet Brickwall, in which one wud plug his high-current power amp, and perhaps the power center and its own plug-ins in the other outlet.

hope this helps

bill

 

[Dave Falasco]

Bill, that is fantastic information, thank you. I am going to have an electrician or three come out and give me estimates on upgrading my service to 200amp, but from poking around on the internet it seems that such a service runs about $2000. That's a lot of money right now, considering how much I just dumped on the components themselves. But you are right, it is definitely something I am planning on doing, either now or soon (oh for a Xmas bonus in August...).

If I am forced to wait on the upgrade and I go ahead and try the unit in the 15amp circuit, are there warning signs I should watch for? There are no lights on the circuit so I can't watch for dimming (although I could plug a small lamp in as my "canary" so to speak). Anything else that could tell me that I am driving the circuit too hard, or will my first clue be when the breaker trips?

Thanks also for the tip on the surge protector. I've got a low-end Monster protector that ran me about $80, so I'm sure it's rated for only 15amp. I will see if I can find a 20amp one.

 

[Yogi]

I am not an expert on this topic by a long shot but my take on this is that you would be fine with just the 15 amp circuits you have. Most amps dont draw their rated power ever even in the most demanding situations. In a moderately sized room you would only use a few watts to listen at reference levels and only during those action explosions would your consumption exceed to more than 100W per channel for a few seconds. Even then the large Capacitors in the power supply would get drained and would fill up during the soft passages and be ready for the next explosion. Moreover most amps (for the US market) have an AC line fuse of 15 Amps. So even though they might be rated for a maximum draw of more than 15 amps they will blow their line fuse before even they get to those output levels.

Check the page 11 in the B&K 7270's manual where they list all the replacement fuses. They mention a line fuse of 15 amps (slow blow). So even if you have a 20 Amp dedicated line the fuse inside the B&K will blow at 15 Amps before you even get there. So I would suggest you save the money and rest assured with the 15 amp outlets. You should be just fine. Also you can plug the amp directly into the wall outlet as surge protectors somehow corrupt the AC signal So I have been advised by Madrigal's (makers of Proceed and Mark Levinson) technicians that for optimum performance I plug my BPA2 directly to the wall. Most of these amps have protection circuits and soft start elements that protect them in case of a surge.

My 2 cents.

P.S. Others, please correct me if I am wrong.

 

[Bill Kane]

Dave,

it's good to have one's own place, isn't it, to own and to fix-up. So the mods you're thinking about just go to update your property.

I don't disagree with Yogi's comments above.

Upgraded breaker panel -- $2,000? No Way.
This may have been a rip-it-all-out and put everything in new job for that cost, who knows...Post in DIY & Home Interiors for others' experience. Ask for an elec'l contractor second opinion or bid. Going all the way to 200amp may be overkill if the interior wiring is left at 15A. I am not recommending rewiring the whole house! Running one, possibly two dedicated 20amp circuits is fairly painless -- Wire 12gauge romex 12/2 properly in 20amp breaker made for existing Service Panel; run wire across attic; drill hole in header stud and feed romex down interior (hollow) wall to duplex outlet cut-out. etc.

To use the elec'l outlet you've got in the meanwhile, first go to the breaker panel, locate and flip OFF the breaker for that circuit (put on a radio and listen for sound to quit, or listen to wife). NOW go back and see what ELSE opertates off that HT circuit. Flip lites on/off and try bedrooms too. (My living room circuit also runs master bedroom incandescent lights on the other side of the wall).

If you find the HT circuit only has a handful of lamps off it, you will be fine. But if there are a whole bunch of light bulbs, a portable exhaust fan motor and any other appliances, they'll be dragging down the capacity of the circuit if they are left on while running the big amp.

Just gotta play and operate with what you've got....for now.

I'd not plug the B&K power amp into an $80 Monster type power strip; just into the wall. (I dont know if you get summer lightning storms there; if so, that's the time to unplug that big boy.)

Many amp makers are so confident in their toroidal xfmrs; heat overload circuitry; internal fuses; power anomaly handing capacity that they say, sure, just plug it into the wall. I wud email or dealer-ask B&K their recommendation for this unit -- beyond saying it's best used with it's own line.

So options: I believe your system can operate safely off one 20amp line. But it certainly won't be much more to add a second circuit for the amp only. This is what critical-ear audiophiles do to forestall any current-limiting loss of dynamics. I wudn't worry much over this. Eventually you'll find a surge protector/powr center with "high-current" outlets for your amp and the rest of it.

For surge protection and power center upgrade, there are many threads and post in the past month on the Tweaking Forum. I'd hold off buying a new one until you can see how to best integrate everything from outlet plug to inlet plug and boxes in between.

bill

 

[Frank_S]

There have been many threads discussing this topic. I had an electrician perform a load test since I had doubts about my 15 amp circuit. Please check out this thread, it has all my related info. http://www.hometheaterforum.com/htfo...threadid=36527

 

[Dave Falasco]

Frank, I had no doubt that this subject had come up before, but I never even thought to look in the Construction forum (stupid of me). Thanks for your link, there is indeed a lot of good information in there.

Bill and Yogi, you guys have eased my fears somewhat--it sounds like if nothing else I won't blackout the eastern seaboard by sharing the 15amp circuit. As I mentioned before, this is terra incognito for me, but you guys have both done a great job in explaining yourselves, and I really appreciate you taking the time to share your thoughts with me.

 

[Yogi]

Dont mention it Dave. After everything is said and done you should have a great sounding system. Best of luck.

 

[Bill Kane]

Frank-S, yes, that was a GREAT thread, and over time, I've reread it several times and it's your load test experience that I relate in my posts.

Dave, we tend to offer advice to install a dedicated circuit because one then gets a clean home-run and it removes doubts about capacity. And from a distance, we don't know how one's house is originally wired, so a fresh circuit is optimal, not knowing if one lives in an old New England house with "funny" grounding (metal conduit vs plastic gang boxes) or the dreaded aluminum wiring.

 

[Frank_S]

I downloaded the user manuals for the B&K gear to get a head start on reading up on them (they get delivered next week), and I noticed that the maximum draw of the 7270 is 17.5 amps. The book also recommends a separate circuit for the power amp.

If you have a very large room and inefficient speakers and play your system at extremely high volumes, a dedicated circuit for the amp is definitely required but in reality I doubt you would ever reach anywhere near the maximum draw they spec.(that is unless you want to go completely deaf)

 

[Howard_S]

Stupid question. If you have many power sockets and plug the amp alone in one socket and others separated into other power jacks would you still have a problem?

 

[Bill Kane]

Howard, please define what "problem" you are thinking about.

And are you talking about plugging components into wall outlets scattered around the room, that may operate off different circuits from the main service panel? Usually, it's best to use just one circuit to avoid potential "ground loop" hum creeping into your A/V system.

 

[Howard_S]

Actually I'm just clueless in terms of these electrical stuff and was wondering if spreading my gear through different wall outlets is a good idea.

 

[Bill Kane]

Howard, no, it's not such a good idea.

What you need is an inexpensive surge protector with 6, 7 or 8 outlets to plug all your stereo and home entertainment units into -- then plug the surge protector into ONE wall outlet.

At $60 U.S., the TrippLite ISOBAR 6 DBS is a real good one and ought to be available in Canada online.

 

[Dave Falasco]

Frank, I've got Mirage speakers all around and they are all pretty efficient (over 90). My theater room is about the size of a normal living room (12X30ft maybe), and while I like to turn it up as much as the next guy, it's rare that I watch a movie at volumes that bring the ceiling down.
It sounds like I can probably get away with not installing a separate circuit immediately, but it's definitely something I plan on doing soon, for the reasons Bill mentioned. The house is about 30 years old; we've owned it for a little over a year, and if the electrical wiring is anything like the rest of the haphazard and sloppy work that the rest of the house is rife with, I'll feel better having all of that pricey gear plugged into at least one outlet I can trust.

 

[Yogi]

Dave if you dont mind my asking, where did you buy your B&K gear and how much did you pay for it. I am interested in buying the 7250 sometime in the future to complement my 3802. You can send me an e-mail or PM if you want to keep it off the thread.

Thanks.

 

[Dave Falasco]

YYGAPM
(Yogi, you've got a PM).