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Audio Amplifier

The last 6 weeks of my course have been spent on an individual design project. The aim of this project was to build a small amplifier for use with a phone / iPod. Everything was designed and built from scratch and I’ve really enjoyed seeing my initial design turn out as an actual product.

After learning the technical aspects of the required circuit components the first step was to calculate the filter cut-off frequencies and the gain of the circuit. We then simulated this using the industry standard ISIS (Labcenter Electronics).

ISIS Design

Then we built the circuit on a breadboard and tested it using a digital oscilloscope to verify the design.


ARES is the sister program to ISIS and is used to design the PCB. It gives you a list of components from the original design and you place them and edit the track connections appropriately.

ARES Design

After a quick lesson in soldering (in which we soldered 10 LEDs and resistors to a board) we received our printed designs and set about soldering the components on.

All worked perfectly on my first go!

All worked perfectly on my first go!

Connecting all the controls.

Connecting all the controls.

A home-made version of the board holder.

A home-made version of the board holder!

It was a few days before the deadline and the realization came that by focusing on getting a working circuit I’d completely neglected building the case. The university model shop which was equipped with a laser cutter had a queue days long, so I decided to do it by hand. A trip to B&Q was in order, the nearest one being around 5 miles from campus. After consulting the map I decided it being such a simple route that I’d walk it. It was a beautiful day and I got to see some not so beautiful parts of Birmingham, walking for hours alongside the A47 (carrying 1m^2 of mdf on the way back).

View Larger Map

For some absurd reason at that particular B&Q you need to be over 21 to buy drill bits. A handsaw and drill were fine but drill bits somehow crossed a line. Luckily I managed to borrow some from a friend. I turned my kitchen and room into a temporary workshop and my bathroom into a painting / varnishing room for a couple of days, and got some parts of the design drilled by a very helpful lab assistant down in a workshop.

Kitchen Workshop

And so after a quick trip to a Screwfix to purchase more appropriate screws and to Maplin to buy a smaller knob, it was finally complete a few hours before the deadline.

Amp Front

Amp Back

Considering how touch and go the last week was I’m really pleased with how it turned out. The acrylic paint and varnish I found in a main building room bring out a really nice look. The gain is less than the theoretical value which I suspect can be blamed on a certain resistor but it does the job and I’m not going to tear it apart now. Next project I’m going to be a bit more organised!

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