Passive AMP for Smart Phone

I have had a few requests for me to make a passive amp for smart phone. So I decided to take the challenge and give it a go. Now over all the idea is pretty simple the sound channeled to to the speaker chamber and hopefully resonates to make it that little louder. The one thing that it will most definitely and noticeably do is change the tone giving it a deeper and more rich sound. Will it beat the electronic one. Most definitely not but for what it actually is it is pretty cool and did surprise me a little on the difference it did make.

I first cut the stock that I require to a close final size. I cut two pieces of 100mm thick stock on the mitresaw and then put through the thicknesser to tidy them up a little as well as take out the slight cup that had formed on the stock. I then use the table saw and the table saw and cross cut sled to cut the stock to rough dimension. I don't do the final size because I will trim once all glued up.

Once sorted I then stick the template on to one of the 100mm stock and cut the sound channels out on the band saw. Because I forgot to put the pattern on for the phone holder I quickly trace the area on the second 10mm piece of stock and cut out on band saw and I simply use my rotary tool tidy up the cut.

I then measure and mark out where to drill the speaker holes using an adjustable square. And use an awl to mark for the drill. Ensure the pieces are all align and flush and clamping all the pieces together except for the back piece I use a battery drill to drill the pilot hole for the hole saw. Taking it to the drill press I have a 55mm hole saw installed and drill and cut the holes out. I drill about half way and flip over and drill from other side. This helps eliminate any blow up as well as makes it easier to get the stock out of the hole saw once cut. On the final or the back piece on a spur of the moment decision I change size of hole to a smaller forstner bit (about 40mm) This was to give a little bit of a cone shape inside the speaker. Drill it to about just over three quarters of the way. I do not know if this makes any difference probably not.

With hole saws you need to take your time and let the saw do the work with out you wrenching on the drill press handle.

I decided I would to the glue up in two stages this will help line thins up better and stop the movement when actually clamping as the stock slides on the glue. I first glue the 10mm stock pieces together the clamp and then the two thicker pieces and clamp. Ensure the are best aligned and flush as possible. But it is near impossible to achieve and this is why the stock was not cut to final size. Once these are dry I remove the clamps and glue the to blocks together, again ensuring that the sound channels are on the inside and that everything is aligned and flush as best as possible.

I did totally forget that the back piece did not need glue around the smaller hole inset and I should have left that area clear of glue. I did wipe as much out as I could after the clamps were on but it just meant I had a bit of scraping to do after the glue dried.

Once dried I trimmed to final size on the table saw as well as the mitre saw. I the used a round over bit on the router but leaving the base flat and sanded. I scrapped as much as the glue as I could and then use my rotary tool again the a small flap sander to tidy up on the inside of the speakers.

This is where I was originally going to finish. But I then said lets go to the next level of appearances.

So I used acrylic black paint and proceed to paint the inside of the speakers. The using some mahogany accent off cuts I cut a square on the table saw, just a little larger than the speaker holes. I then mark the centre using the diagonals and using the same hole saw I used to cut the speakers I drill and cut a hole in this speaker cover. I take to the bandsaw and slice the the stock in two by resawing it. I use the sanding wheel to round the edges. With one of the off cuts from cutting these covers, I cut a strip of at the same thickness. This will be used to add extra accent to the front and to help channel the sound, as well as to also help hold the phone in the slot.

I use some thin black gauze material cut to just smaller that these covers but larger than the hole. I use plenty of glue thad place the gauze in the glue. While this may have been enough I decide I would brush a little more glue on to be on the safe side. at the time I was unsure if this was going to work But my theory was it is thin enough and the gauze itself is still allowing the glue to bond on both sides.

Placing the still wet glued in gauze and speaker cover over the speakers I clamp doing my best to keep it aligned. I then glue in the final piece in between the two speakers and clamp. Letting this dry over night.

Following morning removing the clamps I give a spray coating of clear lacquer and let dry. Then it is time to test my theory.

As I said above it did make a noticeable difference and it definitely changed the tone for the better.

Regards
Nighthawk