Benchtop DIY Audio Oscillator-Tester

By Paul Marossy
Last updated 05/22/03



Here is an 1kHz audio tester that I recently built. It is based on R.G. Keen's " Quick and Dirty Audio Test Oscillator ".
It is a basic twin-tee oscillator circuit. It provides a sine wave with a frequency of about 1kHz. I built it per the schematic, and added a selector switch to select the output range, and a volume control. For the enclosure, I recycled an old A/B Switch box which I found in a thrift store. The rest of it is constructed entirely from parts I had lying around. Below is some details of the project.

Here is the front view. From left to right: BNC output, screwdriver volume control, 1/4" jack output, voltage range selector switch, and an on/off switch with a power-on LED indicator.
This is the back. I covered up the cable connector openings with pieces of plastic cut from an old 3.5" floppy disk. Why a floppy disk? Simply because it was a reasonably close color match to the enclosure color. An 1/8" power jack allows for a 9VDC 200mA wall wart to power it up.
Here is what the inside looks like. The upper left perfboard is the oscillator circuit, and the upper right perfboard is the power filtering section, a hum-busting circuit using a 2200uF cap and 100 ohm resistor to eliminate 60 cycle hum. For the output range switch, I used a homeless guitar pickup selector switch. To make the slot for the range selector in the face of the enclosure, I simply used my Dremel tool with a cutting wheel to make the opening and finished it with various small files.
Here is a detail of the mounting of the volume control pot. The mounting bracket is constructed from a 3/4"x4" strip of sheet metal folded as required and then drilled to accept the pot and two mounting screws. The shaft of the pot uses one of two existing holes. I utilized the other existing hole for the 1/4" output jack. I drilled the other six holes needed in the enclosure with a hand drill.

Aside from spending next to nothing to build this project, the cool thing about this project is that I didn't even have to paint the enclosure. I just removed the existing graphics on the front by lightly rubbing them off with a little green 3M pad. They came off with minimal effort and left the paint underneath completely intact. For the labels, I used a label making machine.

This will now serve as my super duper benchtop audio tone generator for use with my guitar effects prototyping. It turned out pretty well for a spur-of-the-moment idea. It took two evenings to construct, troubleshoot, and perfect.


My Guitar Effects Prototyping Board