Battery powered ... amp head?

[neepheid]

I might have to play some bass on a beach in July. No power nearby so I'm scheming about building a 12V system, running off a rechargeable lead-acid battery (like ones for mobility scooters or leisure use that can deal with deep discharging). I know very little about stuff like this, but I was thinking of mounting it all in an old computer case for now.

I presume that I'll need some kind of 12V preamp (like a Velleman kit preamp or something) before feeding that to an automotive power amp of some kind (full frequency range, not just for driving subs). Would I control the volume at the preamp, or should I have a separate preamp gain and master volume control in between the output from the power amp and the output?

I'm going to feed the output into my trusty RedSub 1x10, so it can handle up to 250W at 8 ohms, but there's no reason why it couldn't feed other cabs, as long as the power amp can handle the impedance and the cab can handle the power output, yes?

If the amp gubbins take a 5A draw and if I got a 20Ah battery then in theory that would run for 4 hours on a single charge, yes?

I presume any tone shaping will need to be done at the preamp stage.

Still scheming stuff out, but I think this would be a cool thing to build, as long as I can scrounge together the parts relatively inexpensively.

Does this sound feasible, or am I barking up the wrong tree?

[icastle]

Why not just buy an inverter and a car battery?

[neepheid]

[quote name='icastle' timestamp='1336779546' post='1651138']
Why not just buy an inverter and a car battery?
[/quote]

Full sine wave inverters are expensive, car batteries don't like deep discharging and I'm not subjecting my gear to the abuse that is modified square wave power. I think a neat, self contained unit would be a cool thing to put together.

[mushers]

hire a generator ? or better get the event organisers to do so

[neepheid]

[quote name='mushers' timestamp='1336821715' post='1651511']
hire a generator ? or better get the event organisers to do so
[/quote]

Generators make noise. We are the organisers.

[neepheid]

Thanks for the comments so far but I'd prefer some advice on my idea rather than ways of avoiding it. I'm going to build it because it amuses me to do so. It may not even be a good idea, it may not even work. But this is how progress is made. The 40 in WD-40 and all that

[mushers]

[quote name='neepheid' timestamp='1336825061' post='1651585']
Thanks for the comments so far but I'd prefer some advice on my idea rather than ways of avoiding it. I'm going to build it because it amuses me to do so. It may not even be a good idea, it may not even work. But this is how progress is made. The 40 in WD-40 and all that
[/quote]

your idea does seem sound however with batteries the issue always is once they lose their top end charge which could happen within an hour, will it be pushing enough amps out to keep running the amp after say the first hour ? i have a feeling it should but you wont know till you try it

are the whole band going to be using the same amp ?

Edited May 12, 2012 by mushers

[Batfastard]

You'll need to sort out a regulator/rectifier circuit to stop peaks and troughs in power delivery. Also You may want to put a acouple of vents and fans in the case to deal with cooling.
Most importantly though go for a bigger battery spec than you think you need because what ever you build will not be 100% efficient.

[neepheid]

[quote name='mushers' timestamp='1336829415' post='1651653']
your idea does seem sound however with batteries the issue always is once they lose their top end charge which could happen within an hour, will it be pushing enough amps out to keep running the amp after say the first hour ? i have a feeling it should but you wont know till you try it

are the whole band going to be using the same amp ?
[/quote]

Well, I'm hoping that using an automotive power amp will mean that it is happy to work within a fairly wide band of tolerances as it is designed to be powered from a lead acid battery.

I only intend this to be a bass amp for me at this time, but I suppose it could be used for keyboard or vocals.

[neepheid]

[quote name='Batfastard' timestamp='1336832197' post='1651694']
You'll need to sort out a regulator/rectifier circuit to stop peaks and troughs in power delivery. Also You may want to put a acouple of vents and fans in the case to deal with cooling.
Most importantly though go for a bigger battery spec than you think you need because what ever you build will not be 100% efficient.
[/quote]

Forgive my high school electronics knowledge, but isn't a rectifier for converting AC to DC? This system will be purely DC. Using an old computer case means that there will be places to mount fans should airflow be an issue.

Totally with you on the battery point - will try and get the biggest one I can that fits into the case.

[LawrenceH]

Can you get class D car amps that are any good yet? That will surely help a lot with the battery life.

[Beer of the Bass]

You could buy or borrow a plywood double bass, spend the six weeks between now and July cramming frantically and go unplugged. Of course, that's only a good idea if you fancied doing it anyway and you're not playing with anything louder than a drummer with brushes or rods, but there a few DB buskers on here (including myself from time to time), so I thought I'd put it out there...

[Batfastard]

[quote name='neepheid' timestamp='1336837432' post='1651780']
Forgive my high school electronics knowledge, but isn't a rectifier for converting AC to DC?[/quote]

True, I meant just a regulator circuit. Another thing to consider is shielding of the signal wires.

[orangepeelneil]

Hello,

You are correct about cheap inverters having rough (pseudo sine) AC output.

I've always used Antares equipment ([url="http://www.antares.co.uk/"]http://www.antares.co.uk/[/url]) to provide true sine AC output on the battery powered vehicles I have worked on- though it's not cheap, but essential for expensive computing equipment and pretty efficient too.


1. I would get yourself something like a diesel car/ marine battery >60Ah, the bigger the better, you can get a battery pretty cheap- or even look out for a discarded one which may be fine with a bit of proper conditioning.

Battery science can be quite complex and dividing the Ah of the battery by the your load is only ball park figure,there is inefficiency so using a large battery with lots of Ah will be a good start.

I've used simple lead acid batteries for traction batteries in deep discharge mode successfully- which would be like your application, but having more Ah is better as batteries can unpredictably "fall over/die" without warning on a heavy discharge cycle towards their lower limit.


2. Car power amps don't seem to have controls on them-just input/ output and power supply remote.
So the output is proportional to the input they receive from a source, like a car stereo- I guess this will be in the range of 0-2V(max)

You will need a simple 12V DC pre-amp module to take the bass output to the power amp input.

Bass -> 12V DC preamp (with tone and master volume ctrl) -> 12V DC power amp (car amp) -> Speaker

Something like this might be fine,with master volume, treble and bass-although the input impedance sensitivity may not be great for a bass, they do a "guitar preamp" kit too, they are so cheap too and simple to modify/ play with.

[url="http://www.quasarelectronics.com/cpm005-mono-pre-amplifier-module-with-tone-controls.htm"]http://www.quasarele...ne-controls.htm[/url]

[url="http://www.quasarelectronics.com/smart-kit/1091-guitar-preamp-with-tone-controls-tl082.htm"]http://www.quasarele...trols-tl082.htm[/url]


Otherwise they are loads of simple designs on the net with a proper gain and master volume control for bass.


3. There are loads of Class D power amp module/kits on bay from China, some of which may be fine if you don't already have a car power amp.
If your a putting it all in the same enclosure, consider a proper grounding strategy and heat sinking/cooling if you are using a simple Class D power amp module.


Hope that helps

Edited May 13, 2012 by orangepeelneil

[BILL POSTERS]

[quote name='Batfastard' timestamp='1336852891' post='1652048']
True, I meant just a regulator circuit. Another thing to consider is shielding of the signal wires.
[/quote]

+1 for a requlated supply, How about using two 12V batteries in series, regulated at say 15 or 18V. that way your battery volts can drop off a fair bit before you notice any ill effects. Or two batteries as above with a 24V to 12V converter like what truck drivers use. Have a mooch on ebay etc, loads of class D output boards and kits around last time I looked, simple pre amp from Velleman or copy something commercial using a couple of 741s or 4558s.

Cant see screening being much of a problem, no mains on a beach / no AC = no hum problems, inverters, or DC-DC converters might radiate though.

[neepheid]

Chewing the fat with Ou7shined today, I got talking about the project. I tried his Smokey amp (you know, the ones in a cigarette box) in my 1x10, and it was surprisingly loud but farty as hell (as it's designed to distort for guitar). So I was wondering about how to get a convenient rechargeable supply and an idea hit me - power tool batteries. I'm going to play about with a 12V cordless drill I got for free ages ago - batteries might not be any good, but it's a start. If I butcher the handle of the drill then I'll be able to use the battery latch to plug in/out as needed.

As for a circuit, I was thinking of kicking things off with the 5W version of this: [url="http://www.quasarelectronics.com/ce0015-mono-audio-power-amplifier-with-preamp-module-range-1.8-5w-rms.htm"]http://www.quasarelectronics.com/ce0015-mono-audio-power-amplifier-with-preamp-module-range-1.8-5w-rms.htm[/url] CE0016 - I know there's no tone shaping on this unit, but I want to keep it simple for now, and there's always the tone controls on the bass...

Anyone able to tell me if it will work before I waste twenty quid? Here's all the skinny on the unit - [url="http://fadisel.com/docs/E-16(English-Esp).pdf"]http://fadisel.com/docs/E-16(English-Esp).pdf[/url]

I just cracked one of the batteries open and it is a 1300mAh unit. The circuit allegedly takes a maximum of 270mA, so that's a theoretical life of 4.8 hours per battery (and I have 2 batteries).

[MoonBassAlpha]

Have a look at this site: [url="http://shop.41hz.com/shop/"]http://shop.41hz.com/shop/[/url]
They do some tiny class d amps some of which run happily off 12 V.
Been thinking about this myself for a while.
Still need a preamp though.
What about the ElectroHarmonix class d jobbies, 22 calibre of 44 magnum?
All quite efficient so should have a good battery life if you can get enough volts going in.

[BILL POSTERS]

1200mA rechargeable AAs are 2 for a quid at Poundland, and you can get holders from Maplins for not a lot.

[muttley]

[quote name='BRANCINI' timestamp='1336952049' post='1653263']
1200mA rechargeable AAs are 2 for a quid at Poundland, and you can get holders from Maplins for not a lot.
[/quote]

No use for the peak currents the OP needs.

Get everyone to wear cordless headphones? IGMC...

The only sensible advice I can offer is to use the most efficient (ie highest sensitivity) speaker you can get your hands on. Remember, each 3dB increase in efficiency halves your power requirement.

[Bottle]

Behringer BDI-21 or equivalent Sansamp BDDI pedal as preamp running off of it's internal 9v battery (fresh one, obviously)?

Wonder if there's a PA amp that'll run off 12v i.e car tannoy type arrangement. IIRC I used to have a 20w mobile PA amplifier that would run into 4, 8 or 16Ohms or 100v line systems, that I got cheap from Tandy's as they were.

HTH,
Ian

[neepheid]

Heh, I actually had someone offer me one of those. Great minds and all that. Nah, I'm going to have a laugh and build something myself. The idea has moved onto using a butchered laptop for both power (3600 or 4000mAh per battery - I have 4 of them) and a housing for a 20W RMS 12V circuit that someone pointed me in the direction of.

[Matt P]

i've got an old car amp lying here if you decide to try that route, it says 100w on it, nothing special and i think designed to run 2x 4ohm speakers.
It's got a 5A fuse so should be fairly low drain.

I guess i'd take a tenner plus postage if you wanted it.

Matt

[neepheid]

[quote name='Matt P' timestamp='1337422727' post='1659636']
i've got an old car amp lying here if you decide to try that route, it says 100w on it, nothing special and i think designed to run 2x 4ohm speakers.
It's got a 5A fuse so should be fairly low drain.

I guess i'd take a tenner plus postage if you wanted it.

Matt
[/quote]

Thanks for the offer but I have ordered a circuit and plans are already afoot based around that.

Cheers though, if this falls through then I may come back to you.