20Hz to 20kHz Audio Oscillator

Back in 1983, a Wien Bridge Audio Oscillator was published in the French magazine Electronique Pratique. It is designed to generate a Sine or Square waves in the frequency range from 20Hz to 20kHz. The original article is attached.

When I first built the oscillator, it was powered by two 9V batteries.

It seemed like it was due for an upgrade. This new version, besides its redesigned case, incorporates an uninterruptible power supply which can be powered by a single 3.7V Li-ion battery or from a 5V source via its USB-C port. It will also charge the battery when running on external power. The 3.7V or 5V source is boosted to 12V and a -12V generator converts the +12V to a -12V supply to provide +/- 12V to the oscillator.

3D printing

The STL files for the case are attached. All printing is done using a 0.2mm layer height. You may need to orientate the parts on the build plate before slicing.

When printing "Audio Oscillator V2 - Text.stl", switch to a filament of a contrasting color at the start of layer 4.

Print "Audio Oscillator V2 - Front.stl" with supports. After printing, remove the supports and add the switch and potentiometers to their respective holes. Do not use washers as the nuts need sit below or flush with the front.

Place double-sided tape on the back of "Audio Oscillator V2 - Text.stl" and stick it to the front of "Audio Oscillator V2 - Front.stl".

Finally add the toggle switch, SMA socket and 3mm LED.

Add 4mm diameter by 3mm high M3 brass inserts into the holes on the tabs for the bottom and top clam-shells.

Add 4mm diameter by 3mm high M3 brass inserts into the holes for the PCB on the bottom clam-shell.

Add 3.5mm diameter by 3mm high M2.5 brass inserts into the holes for the UPS on "Audio Oscillator V2 - Back.stl".

Assembly - UPS

The UPS and -12V converter module are all mounted on the back panel. Wire up the UPS as shown below:

The 12V output also needs to go to the -12V converter module. This module is attached to the end of the battery holder using double-sided tape or hot glue.

You will end up with 3 wires that go to the Oscillator Board. These will be -12V, GND and +12V.

Assembly - Oscillator

I have included the Eagle files in case you want to get the board commercially made or do as I did and make it yourself. I used the Toner method.

Add the links if your board is single-sided.

Add the diodes and resistors.

Add the IC sockets or you can just solder on the ICs.

Add the capacitors, trimpot and transistors.

Add the pin-header and KF2510 connectors.

Screw the PCB to the bottom of the case using 4 x M3 4mm screws.

Wire up the potentiometers, switches and SMA socket on the front panel.

Place a 1k resistor in series with the 3mm LED and wire it to the +12V and GND connections.

Screw on top clam-shell using 4 x M3 6mm black hex screws.

Conclusion

The UPS module (and -12V converter if needed) turns out to be a great way to power any of my future projects. The oscillator itself isn't particularly special. It works but the sine wave has some distortion and is subject to attenuation at higher frequencies. It probably has little practical use now other than the enjoyment of building it (audio has mainly gone digital these days).

Discrete electronics without microprocessors is still fun. It's a pity in some-ways that it is a dying art but if you are interested in looking at old electronic magazines, the best source that I have found is https://worldradiohistory.com/