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Porkstone View Drop Down
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    Posted: 05 July 2015 at 7:11pm
We've just had our local carnival and I was asked last minute to provide a mobile sound system that could be pushed by a willing volunteer. I quickly cobbled together a trolley + amp + speaker. It worked okay but the sound didn't really carry far enough. I want something with a bit more oomph for next year.

The procession only lasts 45 mins so battery life shouldn't be a problem, currently I'm powering via a 22Ah lead acid car booster battery. The trolley worked well and there is no budget for a different speaker (Behringer B1220 pro). I'm looking for a preamp + amp + voltage booster solution that will work well with the Berry and my 12v battery any ideas that won't break the bank?

Pictures may take a while to appear my dropbox seems upload is backed up atm




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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2015 at 8:48pm
2 options - full DIY or good car amp. Price actually quite similar so depends on your desire for kudos and how much you like soldering ;)

Full DIY - Sure Electronics single rail amp board + 500 watt boost regulator, plus if needed a simple line preamp board off eBay, for which you'll need to sort out some kind of rail splitter or virtual ground circuit. The amp can do up to 36dB gain which means it gets to full power from 0.775v input, which even the shittest iPod is capable of. Plus connectors, volume pot, power switch, case. 
This year Sure released some super-powerful 800 watt mono (@4 ohm) boards (also 2x400/ 4x200) which if they work as well as the previous 2x300 watt model, will be very pokey indeed, run totally cool, and don't waste any watts. Now if they had a 1000 watt boost converter as well that would be ace, but my experience shows that you can run a slightly more powerful (on paper) board from the 500-watter with normal music signal and not many problems, so hopefully it wouldn't prove too much of a bottleneck.

Car amp - Vibe Liteboxx series, or Alpine class D. Bit more money, but obviously a totally plug-and-play solution, and these days score very well in the power vs weight vs efficiency scheme. Would not have been a real option up until a couple of years ago, but a lot of progress has been made......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2015 at 9:08pm
ALSO the music your playing will make a difference... if you high pass the whole system at say 60hz you can crank it up louder (with a hotter signal) and not worry about the driver trying to produse super low bass!
If it sounds like a gorilla is trying to escape, turn it down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Porkstone Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2015 at 10:35pm
Thanks for the advice, I didn't realise that a car amp would be an option. I'm not the worlds best solderer but I can get the job done so I'm leaning towards the DIY option. I'm also going to try and pimp out the trolley a bit. This year the music was calypso but who knows what they'll want next year. The Berry doesn't enjoy too much bass so a 60hz filter would make sense. I want to build it into a box just in case it can be put to use for something other than carnival. I have an aluminum toolbox going spare that might be big enough. 

 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 05 July 2015 at 11:13pm
Why not have a crack at a kick cab build and then a small midtop to sit on top?

Pimp out? How about a few under tolly bright LED's and a string of 'fairy lights' wrapped around the system once built and straped down???

If it sounds like a gorilla is trying to escape, turn it down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 06 July 2015 at 3:10pm
My tip for mobile system bass where efficiency and light weight are key, is tapped horns. EG the MTH30 or THAM12. You could go even smaller with a 10" design. In my system, I use a 12dB/octave 3-way active crossover board, with the frequencies set at 50 and 100Hz. I then use the mid and high outputs to drive my bass bin and mid-hi's respectively. This way the bin doesn't try to play super-lows and waste power. I haven't been able to find a board with a separate subsonic filter on the front end yet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2015 at 11:11am
Pointing the sound at peoples feet won't help
Get the speaker up higher!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Porkstone Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2015 at 6:50pm
Me again, I ordered one of these I don't have the first clue of how to wire it up. I assume it goes between the battery and the amp but I'm not even 100% sure of that. If any of you kind folk are able to point me in the right direction I would be very grateful.

There is a photo of the unit with some annotations here please add any info you feel might help me connect it up. 

which has not arrived yet.

The booster does have a large heatsink on the base, does it need good ventilation if housed in case to prevent it from overheating?

Thanks to everyone for all the help so far!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2015 at 8:28pm
Excellent stuff. It's simple to wire that up.
First, you'll need to set the boost converter to the right voltage. So, get out your multimeter. 
Hook up your battery +/- to the Vin +/- terminals on the converter, and it should power up (light its power LED'S). Now, measure the voltage at the Vout terminals, and adjust the trimpot on the board until it reads 48 volts. There may be a current regulator trimpot as well, but just set that to maximum, as we want all the current we can get.
Then, simply attach Vout on the converter board to Vin on the amp board, and it too should power up. Obviously you're also going to want a switch between the battery and the converter board. It seems to have a built-in fuse, but another inline fuse close to the battery to protect the wiring is always a good idea.

edit: Yes the converter is likely to get warm in operation, so give it good ventilation. If you mount it with the heatsink fins exposed to air and oriented vertically, you'll get maximum convective cooling. If you find it still gets hot during your normal use, you might have to add a fan. The amp board itself already has a fan, and it runs pretty cool anyway.


Edited by studio45 - 09 July 2015 at 8:32pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Porkstone Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2015 at 9:38pm
Awesome thanks so much for the advice :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Porkstone Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2015 at 10:53pm
The amp board arrived today so this evening I got a chance to test it. I haven't connected the preamp so for this test I just connected an iphone directly to the amp input. It was too late to crank it up loud. It gave a nice sound and at low volume everything was very cool. The fan on the amp board was only switching on for a small amount of time. I powered this from a 4s lipo pack that measured 14.8v and as suggested tuned the voltage booster to output 48v. This weekend I'm hoping to have time to connect it up to a big battery and crank up the volume.
Thanks again to everyone for all the helpful tips and advice.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 16 July 2015 at 2:45pm
Fantastic! Yes they do sound good those boards - optimised for reproduction of high-definition 96kHz audio streams, according to TI, so a flat response to 48kHz...!
You may want to use some heavier wiring in the final project. 600 watts at 14.8v is 40 amps, and on the 48v side is 12.5 amps. Now obviously that is a peak value, but it's surprising how thick and short cables need to be to prevent the apparent battery voltage dropping at full power. For example, even three feet of 10mm2 copper wire will drop 0.12 volts at 40 amps. 
As a side note, when buying cables, beware of what is known as "CCA" or copper-coated aluminium. A lot of it gets sold unknowingly as pure OFC (oxygen-free copper) but it is *not* as conductive. The way to tell is to cut the cable and check the strands are red copper all the way through - if the cut end is silver-coloured, its is CCA. 
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