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Audio Sine Wave Generator
Description:
This single IC circuit which is based on the Wien Bridge Oscillator, produces low distortion sine waves in the range of 15 Hz up to 22KHz in two ranges.  The two output voltage ranges are from about 0-250mV and 0-2.5Vrms.  The image to the right shows an actual 1KHz output signal from the generator.

The schematic below shows a TL082 dual operational amplifier being used as an oscillator and buffer amp.  Signals at the output are adequate enough to drive eight ohm phones.  Standby current drain is about 6mA from each battery.  Two output jacks are provided for convenience

1KHz output signal
TL082 dual operational amplifier schematic
How it works:

The gain of this circuit is controlled by lamp L1 and resistors R1,R2.  As the values of these resistors is raised, there is less negative feedback and thus, the circuit oscillates better up to a point where it becomes distorted.  Lowering the values of R1 and R2 too much will cause the circuit to stop oscillating.  The general rule is that you want the cold ohmic value of the lamp to be about 1/3 the value of the resistor combination R1,R2.  This lamp measures 105 ohms cold and it was found that resistance values of 216 ohms just allowed the circuit to oscillate, while 416 ohms and up caused signal clipping.  Thus a total value of 363 ohms was settled upon (330 ohms + 33 ohms).  During oscillation, the lamp heats up a bit and its value raises to stabilize the circuit’s gain.  Meanwhile, frequency is determined by pot R5 and the associated capacitors.  It is the feedback to the positive input through these RC networks that causes oscillation at a particular frequency.  The formula f=1 over 6.28 x R x C may be used to determine oscillating frequency, should you wish other ranges.  R3 and R4 simply limit the high end of each frequency range.   For high output LEDs, use a 4.7K resistor for R6.  For standard LEDs, use a 1K resistor.

Construction:
The LED serves as an on/off indicator only.  Regarding lamp L1, it does not have to be this particular one, however if you use another you will have to adjust the values of R1 and R2.   Many lamps were tried in prototyping,  with the #1764 giving the best all around performance.

Begin by cutting out the printed circuit board material to 5 1/2 in. wide by 3 3/4 in. deep.  I personally, simply use the pattern on the right to mark all of the drill points with a punch and then draw the lines with a Sharpie pen and then etch.  Mount components and solder.

circuit board pattern
Cut two pieces of wood ( I prefer Oak) to ¾ in. thick by 3 ¾ in long x 2 ½ in. high for the sides.  Cut a piece of .062 aluminum to 5 ½ in wide x 5 in. high for the front panel.  Finally cut a piece of white mat cardboard to 4  9/16 in. wide x 2 ½ in high for the dial plate.   Bend two pieces of aluminum to form battery holders and attach them to the wood sides before any further construction.  Now assemble the entire unit and solder.

Parts List for the “Audio Sine Wave Generator”
R1, R3, R4

R2

R5

R6

R7

R8

= 330 ohms

= 33   ohms

= Dual 50K  Potentiometer (linear)

= 4.7K

= 47K

= 5K Potentiometer (linear)

C1, C3

C2, C4

C5, C6

= .022uF Capacitors

= .22uF Capacitors

= 47uF Electrolytic Capacitors (50v)

SW1, SW2

SW3

IC1

D1

L1

J1

J2

= DPDT Toggle Switches

= SPST Toggle Switch

= TL082 Dual Op Amp IC + socket

= LED  (see text)

= #1764   28V/40mA Lamp (wire leads)

= BNC Jack

= RCA Jack

B1, B2  = 9V Alkaline batteries
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