Matt's big class A

amplifier topless This is from my archived web pages. "Matt's Big Class A" was published in the September 2003 issue of AudioXpress magazine.

Schematic, parts placement, more pictures, and a descriptive article long enough for bedtime reading.
The article describes the amplifier and its design. All the Figures and Photos mentioned in the article are listed at the bottom of this page. The Photos can be enlarged by clicking on them.

The amplifier was my senior project at San Diego State University (SDSU) for the fall 1999 semester. The design uses a differential input stage, gain stage, and single ended class A output (plus two buffer stages). I wanted to build an amplifier that was low in distortion and used a class A output stage. I think the biggest difference in sound from an amplifier comes from the amplifier topology. Many more pictures are below.

Remember, the below figures and pictures are referenced to the article that contains all the details of the amplifier.
Many of the files are in the Adobe PDF format. Just about all data sheets are in this format so if you don't already have the free Adobe Reader, get it at the Adobe web site

The basic schematic
Figure 1

(Figure 2) The amplifier schematic (PDF file) (not including the power supply)
(Figure 3) The current source (.GIF) that was used several times in the design
(Figure 4) Board layout (PDF file)
(Figure 5) The power supply schematic (.GIF)
(Figure 6) The graph of the distortion (.GIF) at 20W
(Figure 7) Parts placement (PDF file)
(Figure 8) Parts list (.txt)
(Figure 9) Transistor pin-outs (.GIF)

amplifier cover on
Photo 1

PCB in amplifier
Photo 2

amplifier topless
Photo 3

Photo 4

I had several design goals that I was shooting for. A list of the objective and measured values are listed in the table below.

Objective Measured
Power 20W 20.0W
Distortion <.1% .02% average
Slew rate >20V/uS 40V/uS
Gain 25V/V 26.4V/V
Bandwidth 20Hz-20KHz 1.7Hz-201KHz
Output Z <.1 Ohms .025 Ohms
Input Z 15K Ohms 14.4 K ohms


Contact info

Last updated 2/25/08 (archived comments)
Matt Tucker Escondido CA.