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d1030180 30th October 2012 11:58 PM

Laptop computer sound system
 
1 Attachment(s)
I would like to build a pair of micro-size active speakers to be used with my girlfriend's laptop computer. I have a pair of 2" Peerless PLS-P830970 full range speakers which I would like to utilize. Its data sheet can be viewed here:
http://www.tymphany.com/files/PLS-P830970%20Rev1_0.pdf

TDA 2822M chip amplifier would be very simple to use and it should be possible to power it directly from the USB +5V line.

I reckon a standard USB port can provide about 2 watts of power. Would it be okay for a pair of TDA 2822M chip amps?

I've also considered adding a micro-size (3", 4"?) subwoofer speaker to augment the mid-bass response a bit, but would the power output from a standard USB port be inadequate for that?

sreten 31st October 2012 12:17 AM

Hi,

The reality is you will be totally wasting your (expensive)
time attempting to do this, its simply not worth the effort.

These are great for the minimal cost and USB powered :
Amazon.com: Logitech S150 USB Speakers with Digital Sound: Electronics

rgds, sreten.

d1030180 10th November 2012 09:55 PM

2 Attachment(s)
I have built both the stereo and bridged mono amplifiers on a prototype board and they seem to work fine. I used a 9V battery as a power supply during testing.

I also tried to add a simple op-amp lowpass filter circuit into the bridged mono amp to drive a 4" TB as a tiny bass speaker; however I get only strange 'burping' sounds and see the speaker cone rapidly moving back and forth even when no input signal is applied.

I tried the attached circuit with op-amp chips LM358, TLC2272, LF353 and MC1458P. The component values used were:
Cin = Cout = 10 uF
R1 = R2 = 22k
C1 = 100 nF
C2 = 200 nF

sofaspud 10th November 2012 10:36 PM

Have you considered using a rechargeable battery, and using the USB power just as a charge source?

freax 10th November 2012 11:13 PM

Quote:

I also tried to add a simple op-amp lowpass filter circuit into the bridged mono amp to drive a 4" TB as a tiny bass speaker; however I get only strange 'burping' sounds and see the speaker cone rapidly moving back and forth even when no input signal is applied.
Thats either a ground loop coming through your RCA connectors. (if the line-in cable is still connected to something which is running from mains, try using an iphone/ipod/laptop (not plugged into the wall). or you are picking up interference some other way. Or you've got an oscillation somewhere in the circuit, somewhere a resistor and capacitor are causing an oscillation. A capacitor is being charged by a resistor and the cap is discharging, rinse and repeat. http://en.wikipedia.org/wiki/RC_oscillator

I bought one of these and was quite happy: Stylish Portable USB Powered Laptop/PC Speaker (USB Jack) - Free Shipping - DealExtreme

That usb speaker off dx sounds great by the way, and is fairly loud up to a point, but its nice and clear and loud up until then.

d1030180 21st November 2012 02:07 PM

I have tested the TDA2822M amp chip in both stereo and mono (bridged) operating modes, but I soon became really put off by the amount of static background noise it produces. We find it unbearable even for this kind of miniature laptop sound system. After applying power to the circuit without any input (but cable connected), the sound from the speaker(s) is like somebody just turned on a fan.
Both configurations (stereo/mono) exhibit this behavior and it seems like I have to choose another amplifer IC to be used in this project...

sreten 21st November 2012 04:55 PM

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

Hi,

The above is far better than a simple driver in a box with an amplifier.

rgds, sreten.

JMFahey 10th December 2012 08:28 PM

Quote:

I have tested the TDA2822M amp chip in both stereo and mono (bridged) operating modes, but I soon became really put off by the amount of static background noise it produces. We find it unbearable even for this kind of miniature laptop sound system. After applying power to the circuit without any input (but cable connected), the sound from the speaker(s) is like somebody just turned on a fan.
Both configurations (stereo/mono) exhibit this behavior and it seems like I have to choose another amplifer IC to be used in this project...
Rather than simple white noise (which would barely be heard with the speakers close to your ear), I'm quite certain your amps are oscillating at very high frequencies, probably because of poor grounding/shielding/decoupling/all_of_the_above .
Sorry.

jorge morales 11th December 2012 05:09 AM

1 Attachment(s)
:) schematic diagram audio amplifier tba820

JMFahey 11th December 2012 06:12 PM

Hi Jorge, thanks for posting.
The project looks good , I'd only suggest in this particular case it's safer to avoid the DIP socket and solder the TBA820 straight into the PCB.
Better contact plus better heat dissipation through its legs.


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