Edited:see ‘update’ below for bonus features!
Recently I got a present for Sinterklaas, a USB audio set. I asked for this as I like watching movies from my laptop, but hate the hassle of cables that surround my previous set. Also, my 3,5 year old son popped the tweeters of the old setup by pushing the nice shiny conus….
So I got the….
Trust Mila 2.0 speakers
This system is really easy in use: just use USB for power and the audio jack for the sound. Although I was glad to have a working audio setup again I had a few nuisances with this product:
- No audio-> lots of noise. The volume control controls input volume, but all the noise on the speaker is apparently coming from the output stage, as it’s VERY noisy.
- Overall sound quality is flaky. It sounds very thin. I got the impression that better performance might be possible
- VERY bright blue LED
Other power amp
I opened up the speaker containing the amplifier, and found the PCB shown in the image.
I couldn’t find the datasheet of the amplifier, and thought little improvement could be made to this circuit. I went looking for a replacement amp. The criteria were:
- 4.5 to 5.5 V supply voltage
- More than 1.5W audio power
- Minimal external parts count
- Able to drive 4 Ohm
- Easy to obtain
On the site of maxim I found the MAX9759. It matched my requirements, and I could sample it. Hooray!
The MAX9759 is a 16-lead TQFN, which means it has no legs like a DIL or TQFP IC. I took a deep breath, and soldered it ‘deadbug style’:
This took about 2 hours a piece, I used a normal soldering station, and yes, you can debate if it would have been faster to etch my own PCB. I used the circuit as described on page 9 of the datasheet with maximum gain (G1 and G2 both grounded). The result is a major improvement:
- The speakers sound LOTS better, with less noise. I included a video (shot with a normal still camera) in this post which gives a hint of the difference in sound quality.
- The amplifier IC’s do not get noticeably warm
- Removing the original PCB also removes the irritating blue LED
Finally, when everything was working I added a BIG blob of epoxy glue to fix all wires. When mounting all components I shortened the wires to match the size of my laptop.
I thought about using a USB soundcard I purchased for $2 at DealExtreme some time ago. That way, I’d only have a USB connection to my speakers. I decided not to do that, as that would mean switching soundcards every time I’d plug in speakers. Also, I can use them to play other sources now.
How, ON EARTH can it be cheaper / better for Trust to use this crappy amplifier board with lots of components whereas the budgetary price of the Maxim IC is USD 0.75 at 1000 pieces? I know Trust is known for making decisions based on cost, but this is quite baffling for me. Is can’t be that much cheaper to place and purchase so many through hole components. This does not make sense to me….
After using the modified speakers for some weeks I still found the wires too messy. Also, the sound output from my laptop gives a bit of a buzz when my harddisk is busy. Bad design Acer! I had a $2,80 usb soundcard lying around and decided to build that into the speaker housing. Now I’ve got true USB speakers, with power AND sound over USB. They’ve been in use for some weeks, and I’m very happy with the result.