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-   -   Small 12v Amps (50w RMS x2 @ 8ohms) (http://www.diyaudio.com/forums/class-d/227696-small-12v-amps-50w-rms-x2-8ohms.html)

dacomputernerd 13th January 2013 03:27 PM

Small 12v Amps (50w RMS x2 @ 8ohms)
 
Hey guys,

I'm looking for suggestions for a small 12v amp for a project. It needs to push ~50w RMS per channel @ 8ohms. Two channels is enough for my use.
I'll take 30w-50w RMS if it's the right price. Working on a student budget.


If they make a bridgeable 15w-25w RMS @ 4ohms amp, that would also do the trick. I'd be willing to run two amps if necessary.


Weight and size is also a concern, hence why I just don't buy something bigger/more powerful. As is cost, as I'm on a student budget.

Thanks!

P.S.
I was considering this amp.
http://www.parts-express.com/pe/show...number=320-303

Any idea of the
power output at 14v? The quoted values are at 32v.
It should be the same no? The amp will just draw more current at a lower voltage.

theAnonymous1 13th January 2013 03:48 PM

You can't get that kind of power into an 8R load with a 12-14V supply. You would have to use a switching supply to get a higher voltage first.

The datasheet for the TDA7498 shows roughly 18W @ 10% THD into a 8R load with a 14V supply.

Quote:

Originally Posted by dacomputernerd (Post 3323864)
It should be the same no? The amp will just draw more current at a lower voltage.

No, it doesn't quite work that way.

Saturnus 13th January 2013 03:48 PM

Quote:

Originally Posted by dacomputernerd (Post 3323864)
The amp will just draw more current at a lower voltage.[/B]

As a student you should be familiar with Ohm's Law, so no. Power output depends on voltage and impedance.

Wrms = Voltage ^ 2 / (Impedance * 2)

Wrms is in this case maximum output but it's at something like 10-20% THD. Around 80% of that value is the maximum you can expect with reasonable quality.

dacomputernerd 13th January 2013 04:18 PM

Quote:

Originally Posted by theAnonymous1 (Post 3323888)
The datasheet for the TDA7498 shows roughly 18W @ 10% THD into a 8R load with a 14V supply.

I didn't think there would be a datasheet for this amp! Perfect! :)




Quote:

Originally Posted by Saturnus (Post 3323889)
As a student you should be familiar with Ohm's Law, so no. Power output depends on voltage and impedance.

Wrms = Voltage ^ 2 / (Impedance * 2)

Wrms is in this case maximum output but it's at something like 10-20% THD. Around 80% of that value is the maximum you can expect with reasonable quality.

Yeah, I was hoping by some feat of design that wasn't the case here.

How efficient are switching power supplies?

------

Maybe I should elaborate on my whole project. :)

I'm building a third prototype for a wearable audio system. I am trying to get loud, good quality sound. Without breaking my back, or the bank.

Power is a large concern. I was planning on using three 12v 7AH mobility scooter (sealed lead acid) batteries (5lbs each). I'm aiming for 6-8 hours of battery life.

I could use a fourth battery and run the bank at 24v for 14AH. Although this will probably not get me the runtime I want, and also add an extra 5lbs to an already heavy setup.

DUG 13th January 2013 04:46 PM

http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf

You can get free samples from TI.

You need to have a pcb for these but it may give you an idea of what you need to do.

dacomputernerd 13th January 2013 05:08 PM

Well unfortunately I don't have the money for Lithium based batteries. If I want it LOUD and want it to last all day long, there's no other alternative that I see right now. I'm willing to put up with the extra weight.

My plan is to carry speaker/amp components in a backpack setup, and the batteries on a toolbelt.

By the way, here's pictures of the first two prototypes. ;)

v1.0 puts out ~20w RMS per speaker.
v2.0 puts out 10w RMS per speaker.

V1.0 - Talk about heavy! Backpack weighed 17lbs, and shoulder-carried battery+inverter setup (not pictured) weighs 32lbs.
http://i50.tinypic.com/6ixp1t.jpg

V2.0 - 5.5lbs, with internal battery included. Audio quality leaves a lot to be desired, but it can be worn all day long.
http://i47.tinypic.com/2ltrho5.jpg

KMossman 14th January 2013 12:14 AM

try using 10 8ohm speahers in //

lol

Redshift187 14th January 2013 04:52 AM

Get more efficient speakers and aim for 10-20W. It'll make your goal WAY easier. Not only will 12V do, it'll last much longer.

dacomputernerd 14th January 2013 03:06 PM

Quote:

Originally Posted by Redshift187 (Post 3324860)
Get more efficient speakers and aim for 10-20W. It'll make your goal WAY easier. Not only will 12V do, it'll last much longer.

There's no replacement for wattage, when you're aiming for volume though.

I'm refoaming a set of JBL500 bookshelf speakers, they take 50w peak. They briefly sounded great before the foam surrounds split during testing!

So if no other alternatives present themselves, i'll try out the TDA7498 and see how they sound at 14v and 28v, and go from there. I could also make a switchable setup, run 28v when I need the volume, and 14v when I don't.

Saturnus 14th January 2013 04:29 PM

Quote:

Originally Posted by dacomputernerd (Post 3325422)
There's no replacement for wattage, when you're aiming for volume though.

Watts means nothing, or very little, in this context. Sensitivity is king.

The difference between 15W and 50W max output is about 4dB. It's enough that you will notice it being louder but that's about it. It's nowhere near being experienced as much louder.


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