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I have a set of Logitech usb speakers which I wish to convert to bluetooh speakers. A usb has the the power, ground, data+, and data- connections. Which i believe cannot be simply replaced with a battery & bluetooth data connections(no drivers etc). So I intend to build a chip myself but the the tutorial is for 3W audio amp chips BUT the newegg specs for my speakers show total power of 1.3W.

Is 1.3watt the correct value I am looking for? or would be that the power prior to an amp chip in the original circuit I currently intend to build this circuit for each amp chip I need (2)

Is there some way i could test for the correct wattadge without breaking the speaker?

Edit:

Thanks for the advise I will try my best to apply it tomorrow. And for the images here it is.. ( will update with part numbers at a later time ) complicated sideSimple side

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  • \$\begingroup\$ Are you trying to just use the speakers from the Logitech speaker set.. ie. rip them out, or are you trying to keep them intact and use them as powered off the wall or additional battery back speakers? \$\endgroup\$ – Nimjox May 27 '14 at 20:16
  • \$\begingroup\$ I have already ripped them out. The back magnet has 1066 & YDDE50-17A stamped on it \$\endgroup\$ – user13186 May 27 '14 at 21:11
  • \$\begingroup\$ I intend for them to be powered off a rechargeable LiPo battery. \$\endgroup\$ – user13186 May 27 '14 at 21:18
  • \$\begingroup\$ And yes, upload a picture of the circuit board. Always always helpful. \$\endgroup\$ – Passerby May 28 '14 at 0:02
  • \$\begingroup\$ @user13186 I updated my answer based on the picture \$\endgroup\$ – Passerby May 28 '14 at 3:36
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Easy enough, you need to look at the circuit board. Typical USB Powered speakers can be broken down into three parts. Part 1 is the USB Sound Card. This is powered by 5V and accepts a USB connection and decodes the audio. Part 2 is the amp stage. As most USB soundcards have internal pre-amps, there will only be one or two identical 5V amplifiers. Most amps can power two speakers in single ended mode, or one speaker in dual/double ended mode. Finally, Part 3 is the speakers themselves.

To know what wattage the speakers are designed for, get the part number of amplifier IC(s) and look for the datasheet. That will tell you the maximum wattage. And then sketch out the circuit. 9 out of 10 times, the circuit on your speakers will match the Typical Application/Recommended Design/Layout Schematic in the Amplifier datasheet. The actual resistor/capacitor values and layout will tell you the actual wattage it is designed for.

Again, 9 out of 10 times, the circuit will match the typical application for both the usb sound card IC and the amplifier ic, be a simple single or double layer board, and be fairly easy to figure out. Shouldn't take more than an hour, even for a beginner.

To add in your bluetooth control, replace the USB sound card IC with your bluetooth audio driver. Leave the amplifier in place unless you need to change it for some pointless reason :D.

Update: The posted circuit board only has one IC, the TP6902 (or clone). It is an old (2005) all-in-one USB Audio Controller, USB HID Buttons (Maybe), and two D-Class amplifiers built in. Each channel can support up to 5v * 346mA or 1.75W. The typical being 200mA or 1W. So those speakers are probably not more than 2.5W each, and the only way to mod the speakers for bluetooth is... completely replace the IC with a custom Bluetooth Audio receiver + D-Class Amplifier board + LiPo Battery + LiPo power regulator. The only thing that you would be using is the case and the speakers themselves.

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The logitech speakers you have linked to both derive power and digital-audio data from the USB. If you are looking to feed them with an analogue signal you'll need to strip them down and do some rework (if you can get in without breaking the plastic box).

Assuming you do that then it's easy to limit the peak power going into the speakers by adding a series resistance - probably about 10 ohms but it depends on the amplifier spec and the internal speaker impedances.

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  • \$\begingroup\$ I am not worried about the box, the speaker/circuit has already been removed. & I assume I cant reuse the circuit they are currently attached to as I assume it requires a driver installed on a PC. I can provide photos of any/all parts but I don't know the amplifier spec or internal impedances at this time. \$\endgroup\$ – user13186 May 27 '14 at 21:17
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The speakers you have listed appear to be made by Jiaxing Zhongyong Electronics Co and they have a max rating of 5W RMS at 4ohms which means you should be able to use them in the instructable without any issues.

It looks like the 1.3W rating is the limit of what the Logitec internal power amp can provide to the speakers but is not the max limit of the speakers themselves. It's quite typical for engineers to design products with this sort of overhead to prevent damage at max power use cases.

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