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03-30-2010

Low-distortion Audio-range Oscillator

Generates very low-distortion sine waves up to 1V RMS. No thermistors required - No settling time

Circuit diagram:

Low-distortion Audio-range Oscillator

Parts:

P1

10K Log. Potentiometer (Dual-ganged)

P2

2K2 Linear Potentiometer

   

R1, R2, R4, R5

3K3 1/4W Resistors

R3, R6

820R 1/4W Resistors

R7

10K 1/2W Trimmer Cermet

R8

22K 1/4W Resistor

R9

Photo resistor (any type)

R10

8K2 1/4W Resistor

R11, R12, R14, R15

3K3 1/4W Resistors

R13

2K7 1/4W Resistor

R16--R20

3K3 1/4W Resistors

R21

56K 1/4W Resistor

R22

68K 1/4W Resistor

R23

1K 1/4W Resistor

   

C1, C6

220pF 63V Polystyrene Capacitors

C2, C7

8n2 63V Polyester Capacitors

C3, C8

82nF 63V Polyester Capacitors

C4, C9

150nF 63V Polyester Capacitors

C5, C10

680nF 63V Polyester Capacitors

   

D1--D4

1N4148 75V 150mA Diodes

D5

LED 5mm. Red

   

IC1, IC2

NE5532 Low noise Dual Op-amps

IC3

TL084 Quad BIFET Op-Amp

   

SW1

2 poles 3 ways rotary switch

Comments:

Producing low-distortion sine waves, this oscillator operates over the range 16 to 22000 Hz.

The circuit is based on two articles that have appeared earlier in Wireless World - Roger Rosens' "Phase -Shifting Oscillator", February 1982 pp. 38-41, and J. L. Linsley Hood's "Wien-Bridge Oscillator with low harmonic distortion" from May 1981 pp. 51-53.

This design features the simplicity of the Rosens' circuit but avoids the use of a thermistor. Instead, oscillator stability is controlled by means of a common photo-resistor driven by a LED, as suggested in the Linsley Hood article.

There is no settling time when the oscillator's frequency is changed and no bouncing of the output waveform. Use of an expensive and sometimes difficult to obtain thermistor is avoided.

Technical data:

Output voltage: Sine wave, 1V RMS max.

Total harmonic distortion @ 1V RMS output:

Frequency

Reading

100Hz

0.0035%

300Hz

0.0028%

1kHz

0.002%

3kHz

0.002%

10kHz

0.001%

Notes:

  • Any common photo-resistor and 5mm red LED can be used, provided they are in close contact and enclosed in a light-proof small box. I used the metal screen of a small IF transformer for AM transistor radios sealed with black insulating tape.
  • The 10K trimmer must be set to obtain a 1V RMS output.
  • The circuit must be supplied by a + and - 15V dual regulated supply. Common 7815 and 7915 regulator ICs should be used for this purpose.

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  • How this circuit works? Who can help me? Write for me in my email: donciakas1@gmail.com

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