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Old 20th June 2012, 07:10 PM   #1
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Default Recommendations for a class-d amp (portable audio device)

Hello forum!

A year ago I built a portable (sort of) ghetto blaster using four lm1875 20 watt chips, two 8" bass and two 5.25" speakers, 50volt 10Ah lithium-ion batteries and a humongous case. The thing turned out well, the sound quality is awesome, nice low-end and a decent playing time, however there is always room for improvement. I'm thinking of upgrading all the electronics, especially the pre-amp and all non-audio circuitry, but then I also thought of swapping the current draining, heating lm1875's for something more efficient. Probably d-class is the way to go, any recommendations?

The only problem with the lm1875's is the heating. So what I'm looking for is something around 30 watts, that is efficient, but still produces good quality audio and especially bass. I'm using an active crossover so I'm going to use 4 chips, so 4x30 watts would be pretty decent. The case has a heat sink installed, so cooling is no problem (actually the heat sink is a bit too small for the lm1875's, it gets super hot when cranked up, that's why I'd like more efficiency). Also I'd prefer making the pcb's myself, so I'm not looking for ready-made ebay modules.

By 50 volt I meant that I have +- 25 volts to use. Also a friend of mine suggested this http://www.datasheetcatalog.com/data.../TDA8920.shtml which on paper looks absolutely perfect for my use, if anyone has used this one I would love to hear some thoughts of it.

I just had to upload a video in case anyone's interested about how the beast looks like. Not much but it's the only video I have. Also the flashy leds look a lot nicer in perfect dark.

http://www.youtube.com/watch?v=pj3cj...&feature=g-upl

Last edited by Setahemuli; 30th July 2012 at 07:57 PM.
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Old 30th July 2012, 06:03 PM   #2
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Join Date: Sep 2011
looking forward to seeing responses to this. btw, what city are you in?
can you check your youtube link? it has an error.

cheers!
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Old 30th July 2012, 08:10 PM   #3
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Join Date: Mar 2011
I fixed the link, don't know how it got messed up. I went ahead and started this project a few weeks ago and now I have everything but the d-class amp ready. That includes a new preamp, blingbling led flasher (hopefully more power with the same leds & more adjustment range), voltage regulation/power supply board and a battery voltage alarm. The overall design and build quality is much improved from my v.1 boards, which look just awful and some connections break every time I open the thing up. Hopefully these problems are fixed when I get the new electronics inside.

I chose to use the tda8920b 2x100w chip for the low-ends (with my voltages and decent THD I should get around 30 watts per channel) and keep the lm1875's for the tweeters. I haven't yet designed the circuit board for the 8920 but I'm aiming to have the whole thing ready by the end of august so no rush yet.

Oh yeah and the front covers that were originally plastic have now been replaced with metal with a fake carbon fibre vinyl on the top. They look like this now:

https://fbcdn-sphotos-a.akamaihd.net...04366046_o.jpg

Also I live in Finland.

Last edited by Setahemuli; 30th July 2012 at 08:34 PM.
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