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-   -   USB powered AMP? (http://www.diyaudio.com/forums/chip-amps/224905-usb-powered-amp.html)

Leejin 3rd December 2012 08:18 PM

USB powered AMP?
 
So I want to build a small Desktop Speaker Dock and I ran into this little guy.


Seems pretty awesome. I want to supply it with the 5V coming out of a laptop/desktop's USB port. Maybe then go to a single Dayton Audio ND65-8.

Based on the 2 items, could anyone suggest better components? The purpose is a decent sounding, louder than built in speaker, affordable, nice looking dock.

Thanks!

Arty 3rd December 2012 10:03 PM

1.8W output at 5vdc supply voltage and 1% THD+N.
into 8 ohms.
and the driver You choosen has 78.3 dBL sensitivity.

If You ask me, if You do not want it to be loud, it might do.
but personaly i would try to aim for a 4 ohm fullrange driver.
then You can have up to 2.5 watt / channel.

Leejin 4th December 2012 03:00 PM

Quote:

Originally Posted by Arty (Post 3269119)
1.8W output at 5vdc supply voltage and 1% THD+N.
into 8 ohms.
and the driver You choosen has 78.3 dBL sensitivity.

If You ask me, if You do not want it to be loud, it might do.
but personaly i would try to aim for a 4 ohm fullrange driver.
then You can have up to 2.5 watt / channel.

Duh.. man.. This audio stuff is over my head sometimes. They have the driver I listed in 4-Ohm as well. Thanks for the reminder.

Leejin 4th December 2012 03:06 PM

Photo of my concept. Modeled in Solidworks.

http://imgur.com/CRBUm.jpg

KatieandDad 4th December 2012 03:08 PM

Isn't a single USB port limited to ~600mA.

Ouroboros 4th December 2012 03:32 PM

A class-D amp with enough reservoir capacitance can work surprisingly well from a 0.5A limited USB supply, provided that the audio isn't too compressed. Modern 'loudness wars' material with a 1db dynamic range are pushing it a bit though.

AndrewT 4th December 2012 03:58 PM

I'm not much into gadgets, but I did buy a USB thinguie that makes pretty reasonable job of driving my headphones.
They are ~95dB/mW. Very far from 95dB/W @ 1m speakers and even further away from seventy odd dB/W @ 1m speakers.

Leejin 5th December 2012 07:55 PM

Quote:

Originally Posted by AndrewT (Post 3270252)
I'm not much into gadgets, but I did buy a USB thinguie that makes pretty reasonable job of driving my headphones.
They are ~95dB/mW. Very far from 95dB/W @ 1m speakers and even further away from seventy odd dB/W @ 1m speakers.

Aren't the Headphone amplifiers measured in mW though? Like around 800mW? This thing would at least give me 6W (6000mW) if I bridged it to the single driver.. right?

sreten 5th December 2012 08:54 PM

http://www.diyaudio.com/forums/full-...usd-15gbp.html

Hi,

Assuming the USB power is from a computer you'd be a lot better off with
the above, which won't load your USB ports. I've also seen simple very
simple I-pod "docks" in local "poundshops" that connect to USB, no idea
what they do. (They might just charge from USB and do file transfer.)

I'd say its best to integrate the laptop and I-pod speakers. The above
you plug into the laptop headphone out. With a lead you can plug
the phone headphone out into the front of the speakers.

rgds, sreten.

FWIW that very short TL line will have no bass whatsoever.

AndrewT 6th December 2012 08:51 AM

Quote:

Originally Posted by Leejin (Post 3271946)
Aren't the Headphone amplifiers measured in mW though? Like around 800mW? This thing would at least give me 6W (6000mW) if I bridged it to the single driver.. right?

Except not 800mW the sensitivity is based on mW that is 1mW !!!!
That's the point my post is making.
The sensitivity of the headphones suits a USB powered amplifier.
The sensitivity of big speakers does not suit a USB powered amplifier.
The even lower sensitivity of small or very small speakers is even worse than big speakers.


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