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Old 9th May 2008, 07:16 AM   #1
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Default battery powered pa rig question(s)

First time poster here, hello, hope I'm posting this in the right forum.

I am looking to acquire/build a portable (backpackable?) battery powered pa rig that I can use for public performance. Acoustic guitar, effects and vocals. As much low end as possible. I'm posting this here because I have yet to find anything that really fits the bill for what I want to do. Currently though, the closest thing to what I'm looking for is the Crate Limo (2 inputs, 10" driver, onboard eq), runs on 4 3.3 ah 12 v batteries:

http://www.musiciansfriend.com/produ...Amp?sku=487761

However, the build quality of Crate products leaves something to be desired (piezo tweeter, poor cabinet design), and reviews have characterized it's sound as being 'tinny'.

Really, what I'd like to use is a powered 10" JBL Eon speaker like this one:

http://www.musiciansfriend.com/produ...net?sku=600202

Unfortunately this speaker is AC, not DC and has no onboard battery. So, my first question is, could I run this 150 watt speaker for a reasonable amount of time (4-6 hrs) on a battery pack like this one:

http://www.amazon.com/gp/product/B00...pf_rd_i=507846

The AH rating of the battery pack is 28; it's a 600 watt power supply.

A few more questions: The Crate box has a class D amp and runs on DC power. That MUST be more efficient than running an ac speaker (the EON) on a dc battery? (with inverter heat loss and other factors cutting down on battery run time...)?

Another option I came across is the Samson Expedition:

http://www.audiolines.com/Samson-Exp...m-p-17533.html

which is a 12" celestion driver and compression horn system that runs on a battery pack as well. 250 watt class D power amp; I believe its a 12v 14 ah battery pack. Supposed to get 2-3 hrs of time out of it. Is a 12" speaker going to give me THAT much more lows? Is it worth the tradeoff in run time? I'm aware that the advantage of a bigger speaker is more sound at the same wattage as a smaller speaker, but does power CONSUMPTION (a critical factor when dealing with a battery) go up?

Also, when dealing with an ac power amp (like the EON 10's 150 watt onboard power), does it consume it's full rated power when turned on? Or only when producing sound?

(BTW, IMHO JBL is a better speaker than samson, and for the weight I'd rather get the JBL EON and a battery pack than an inferior all-in one like the crate or (to a lesser degree) the samson)

Hope this wasn't too hard to follow. Thanks,

R-A-R
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Old 9th May 2008, 08:30 AM   #2
Pano is online now Pano  United States
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Hi - and welcome to the forum.

I can see that you've been seriously looking into this idea! A number of other folks on the forum have, too - for various reasons.

I'll take a stab at it, to get the thread rolling.

1) Larger drivers are generally more efficient than smaller drivers. That's good for battery power. A larger driver will not use more power for the same level, it will use less (unlike cars).

2) You are correct to worry about the DC to AC conversion. There will be losses. And there will be losses in the AC power supply of the amp. You want to avoid that if you can.

3) The 10" Eon is no bass monster, but it's pretty good on vocals and guitar. Much better than the 15" Eon.

4) The amp power supply (Eon or other) will NOT pull its full capacity when the sound is low. It will use some power at idle. To know how much you will have to measure. Check out the Kill-A-Watt. Very handy, it will tell you exactly how much power an AC device uses. Even in Kilowatt hours, which would be very handy for you. You may be able to get a music store to let you plug an Eon into the Kill-a-Watt. Check it at idle and at rocking out volume.

5) You might want to look into car amplifiers. They are already made to run off 12V and have plenty of power. I would imagine that efficiency varies a lot, so you'd want to ask about that.

6) I've seen plenty of guys playing guitar amps outside. Usually run off a small car battery. So it can be done. Doing it well is the challenge.

Hope that gets you a bit further along.
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Old 19th May 2008, 11:12 PM   #3
dangus is offline dangus  Canada
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A conventional power amp will only draw a fraction of its rated power in real watts, even when the music is pumping. Typically the average power will be less than one tenth of the peak output. So, an EON with a nominal power of 150 watts probably wouldn't be using much more than 10 to 20 watts continuously. Still, a DC-AC inverter will have some loss of efficiency, as will the power supply of the amp.

An efficient speaker like a typical 15" monitor can be pretty loud with a modest amount of power. With a 99 dB efficient speaker, 15 watts should give peaks over 110 dB at 1 m. There's a portable/battery hi-fi amplifier that delivers that amount of power: the Sonic Impact portable T-Amp. Search for Sonic T-Amp; prices seem to run from about $55 to over $100 depending on where you buy. Duct tape a battery-operated mixer on top, and there you go.
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Old 20th May 2008, 11:55 AM   #4
col is offline col  Australia
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Iv'e been doing a fair bit with battery powered PAs and I have found that Switch mode power supplies(SMPS) powering Class D amplifiers last WAY-WAY much longer than conventional A/B amps and linear mode power supplies.

If you have the bux and are looking for something you can buy off-the-shelf powering using a (usually golf wheel chair 12v battery 38-45ah) battery and 600w inverter there is really only one option worth considering. That is the V2 "plastic Mackie" or SRM450 (make sure its the V2). This will out-blast and out-last any other commercial rival. It will make the eon look like a joke.

If you don't have the bux to buy such a thing but are a bit handy with electronics and carpentry pick up a sure electronics 4x100w Class D amp module off ebay (a little bit hissy but awesome power for outside) and a 12v --> 24v DC to DC 5A laptop power supply. That and a couple of P-audio 10" woofers. You could probably build the whole thing for under $500 and have the best system around.
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Old 21st May 2008, 12:42 AM   #5
col is offline col  Australia
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oh yeah, check out the boominator for some inspiration:

The Boominator - another stab at the ultimate party machine
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Old 21st May 2008, 10:51 PM   #6
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If you search eBay for TA2024 you'll find the Sure Electronics boards for about $20, which is a whole lot less than the Sonic Impact. At that sort of price you could go biamped with a pair, or with three, a biamped WTW arrangement.

Or maybe it makes better sense to series up two 12V batteries for 24V and use a more powerful amp, as col suggested.

Or maybe there's already something with "Made In China" on the back that is already cheaper and better than anything you can build yourself.
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Old 2nd June 2008, 02:30 PM   #7
Dan2 is offline Dan2  South Africa
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Default Re: battery powered pa rig question(s)

Quote:
Originally posted by Rent-A-Rocker


[Unfortunately this speaker is AC, not DC and has no onboard battery. So, my first question is, could I run this 150 watt speaker for a reasonable amount of time (4-6 hrs) on a battery pack....

what if you bypass the transformer in the JBL amp and series connect a couple of batteries to get the right voltage - although you would need 5 12v batteries if the rail voltage is +-30V

It wouldn't be the most efficient but it might be a cheaper option.
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Old 2nd June 2008, 08:43 PM   #8
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Ah, this is a difficult one, it really depends on exactly what you want from your PA.

I used to do a lot of busking on the street, I used to use a small Peavey practise amp which had a DC inlet. I used to run a drum machine in the mix, and with a load of pedals, I could produce a surprisingly full sound. I used a piezo tweeter with the basic amp, which was otherwise had a very clicky, thumpy sound with the drum machine. The tweeter didn't cure the clicking, just masked it a bit. This was with a Strat, not acoustic.

You will find all off-the-shelf practise amps run on comparatively LV DC if you hack into them, you can just match the voltage with batteries.

The advantage of a practise amp is that many of them have really quite good valve sound and overdrive and even some effects. I have a Marshall DFX15 now, I went into the shop just to try it, and I just couldn't leave without it. Unlike some practise amps which are open baffle it is fully enclosed, but still manages reasonable bass.

Of course if you're playing acoustic and maybe singing, you may want a cleaner sound. I also have a homebuilt system with a FR elliptical junk-box speaker and a low-power chip amp and tone controls I built (from the datasheet I think). It runs off 18V supplied by some old 4AH NiCd cells I got when a mate was replacing the batteries in a hotel emergency lighting system. It has a much cleaner sound.

Bass is naturally the problem with small systems, but an 8" driver even in an enclosed box should still work down to low E on a regular guitar. You can get 10AH NiMh cells which have a huge current capacity for transients. If you go for an efficient driver (and you should in these circumstances) they will give quite a loud sound for hours. Personally I'd avoid systems with a crossover as they are generally inefficient. You have to accept some compromises in the sound to get portability and some FR speakers are excellent.

If you build your own system then you get to design in as many inputs as you need, otherwise you may need a little mixer. If you want the Marshall sound, then the nearest you'll get is the Marshall practise amp.

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Old 2nd June 2008, 09:27 PM   #9
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I always hang onto old wall-warts and laptop power supplies, as they're useful for charging or even running some of the things I've built with the NiCds.

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Old 3rd June 2008, 06:06 PM   #10
col is offline col  Australia
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Default bang4buck powered pa rig

If you pick up one of these amp modules

http://cgi.ebay.com.au/2-100-watt-4o...742.m153.l1262

and one of these battery bags with a 7.2ah battery

http://www.batterydoctor.com.au/stor...product=BCB127

You can power it with one of these 24v DC->DC inverters

http://www.batterydoctor.com.au/stor...product=MW2173

I use a pair of JBL GTO937 6x9" 2ohm with a cap to cut out the lower frequencies, they are VERY loud 94db efficient and as they are 2ohm utilize the full power from the amp/inverter. They are also cheap and you can usually get a pair of 6x9" enclosures to put them in at any car audio shop.

http://www.jbl.com/car/products/prod...CheckProduct=Y

and don't forget your portable 9v battery powered line mixer.

http://www.rockby.com.au/searchres.c...t=91&subcode=6

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