Easy Music Everywhere. Audio Amplifier – Part 1

While in high school, I bought a really cool rack mount amplifier at a garage sale.  It was branded Queon, and had lots of inputs – it was great.  It was supplemented during my university years with an 8-track player/amp combo, acquired from Value Village.  The Queon met its end when a roommates’ cat knocked over a vessel of water that had been rested on top of the amp.  The 8-track player/amp combo met its end in a post-university move.

I’m not an audiophile, and have been using PC speakers ever since.  They sound OK, but:

  • The volume control always seems to fail
  • The permanently wired connections seem to fail
  • Sometimes, it is nice to listen to the radio
  • The bluetooth connectivity of little portable speakers is pretty handy
  • DLNA / Airplay / Google Casting functionality is also pretty neat

So what I want is an amp for some bookshelf speakers that have been sitting unused.  My ideal amp:

  • has a volume control
  • has a minimum of 4 inputs (PC, radio, Bluetooth, DLNA or alternative)
  • has a remote
  • is smaller rather than bigger

As most people are looking for home theater systems, there’s not much around that meets this criteria.  I have looked at inexpensive amplifiers from Amazon, such as the Lepai LP-2020, but it only has a single input.  I came across a place called Shenzen Audio, which had all sorts of neat audio products, but it’s hard for me to order something >$100 from completely unknown brands.  The Teac AI-301DA is what I want, but more than I’m willing to pay – I can sacrifice on audio quality and power.

So, I’m going to put together my own.  I’m going to pick an off-the-shelf amplifier module, and connect it to an audio switch, add a micro-controller to control the inputs and volume.  I’m even thinking of adding an “auto-input” switch, which tries to auto-switch to the intended input (there must be a reason amps don’t do this – I’ll find out when I try).

I’m sure I just don’t know how to search, but I’m surprised how little I could find about such circuits.  The best article I read was “How-To: Make a solid-state A/V switcher” on Engadget, but I wanted to avoid soldering surface mount components.  There are many switching chips out there, I found it challenging to pick out a basic one.  I also considered just using a mechanical switch, but decided I wanted the option of using a remote.

Finally, I decided to use an older design using a chip called a 4066.  A number of forums indicate that the audio quality of designs using this chip is poor, but I tried it out – it sounded fine to my ears.  It will be hard to tell for sure until it’s done, but there’s always an opportunity to replace it in future revisions.

Update – Weather Station

I finally moved my weather station from a solder-less breadboard to a prototype board.  I’m actually surprised the breadboard survived last winter.

Until I get around to adding an anemometer and rain gauge, this is probably as far as this project is going to go.

Weather Station Circuit Board
Weather Station Circuit Board

Designing A Mobile Phone Mount

In the car, I like to use my phone for playing podcasts and directions.  My work phone was recently upgraded, and I was looking for a practical way to mount it.

As cars are kept for years, and phones change regularly, I didn’t want:

  • anything permanent
  • anything that used adhesives (they never come off!)
  • suction cups
  • anything that blocks vents

The neatest design I’ve seen so far is a steering column mount on Thingiverse, which I had been thinking of modifying for my phone.  As my car has a two-tiered dashboard, I thought I would just create a dock that fit my phone in the lower tier.

I prototyped the dock with pink insulation foam, intending to model  and then 3D print the finalized design.

Foam Prototype of Mobile Phone Mount
Foam Prototype of Mobile Phone Mount

After using the prototype for a week, I realized a 3D printed dock was overkill.  The phone pretty much stood up by itself on the dashboard, without the dock, so long as I wasn’t driving on ramps well over the speed limit.

I just needed something to provide a little friction, to stop the phone from slipping around.  I ended up sacrificing a beloved mouse pad.

Slot cut in Mouse Pad for Mobile Phone
Slot cut in Mouse Pad for Mobile Phone

It works great!

Final Mobile Phone Car Mount
Final Mobile Phone Car Mount