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.