The following pages contains some useful articles and projects in basic electronics.
LOW DISTORTION
AUDIO OSCILLATOR
It
is a low frequency Wiew bridge sinusoidal oscillator for the audio range with
very low distortion, useful to test a variety of audio equipments. The circuit
has been fully tested and a PCB circuit board is available to easily mount all
components.
The
circuit uses only one integrated circuit, some passive components and is able to
provide more than 15 V peak-to-peak or 5V RMS with a distortion less than 0.1%.
In addition it uses a FET transistor to control the output amplitude and
maintain it flat across the frequency range.
The
oscillator uses a simple circuit to generate the following fixed frequencies in
the audio range:
20 Hz
200 Hz
1 KHz
4 KHz
8 KHz
16 KHz
The
simplified circuit diagram is showed in the following figure.
The
output frequency is defined by the R and C values and can be calculated using
the following formula:
1
Frequency
(Hz) = ------------------
(1)
6.28 x R x C
The circuit
The
circuit has been designed to be simple, small and effective. A single PCB
(printed circuit board) is used to hold all electronics parts.
The
circuit has been designed to use a single uA747 chip that includes two op-amps
inside. The first op-amp (U1A) is configured as a Wiew bridge oscillator with
very low distortion. The rotary switch SW1A, B provides the connection to six
different resistances and capacitor couples to cover six different audio
frequencies. The operating frequency can be easily changed using the formula in
1.
Q1
operates as an AGC (Automatic Gain Control) and controls the OP-amp gain in
order to maintain fixed the output signal level.
The
second op-amp U1B is used as an inverting output amplifier to decouple de
circuit from the load and increase the output signal up to 15 Volt peak-to-peak.
The
output potentiometer P1 provides a way to control the output voltage from 0 to
15 Volt pk-pk.
Since
the circuit requires only a current of 5 mA, it can be powered using two
standard 9V batteries.
KIT & PCB
For those that would like to build the Wiev bridge oscillator, a professional made PCB and a complete kit with all parts is available. The PCB is small and able to accommodate all components.
|
PCB, containing the printed circuit board and mounting instructions |
17 US$ (including shipment) |
| Complete KIT, containing the PCB, all electronics parts, connectors, and mounting instructions | 45 US$ (including shipping) |
mailto:generoso.cozza@infinito.it