My generator can produce sine- and squarewaves with frequencies between 1 Hz and 100 kHz and amplitudes ranging from zero to 1.55 Veff in 600 Ohms. Sinewave distortion is 0.1% or less between 20 Hz and 20 kHz, somewhat greater outside this region. The output voltage varies less than 0.1 dB within the audio range (20 Hz to 20 kHz); there is some rolloff (less than 1 dB) at the frequency extremes.
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An audio frequency generator is a very useful addition to the workbench. Common purposes of this instrument are:
1. Signal source, to check if amplifier stages actually work (requires additional signal tracer);
2. Measurements of AC gain at various frequencies, i.e. assessment of frequency curve and -3 dB bandwidth (requires AF millivoltmeter);
3. Examination of the transient response of a circuit: do squarewaves cause ringing or oscillation? (requires an oscilloscope);
4. Assessment of the overload margin of an amplifier, i.e. determining the input voltage required for onset of clipping (visible check on a scope);
5. Distortion measurements (please note: low levels of distortion, i.e. < 0.1%, cannot be determined with the circuit described here)
The instrument consists of four different modules within a single enclosure, and is fed from an external (+ and - 15V) power supply. The modules are:
Sinewave generator with amplitude stabilization circuit [1];
Schmitt trigger (sine-to-squarewave converter) [2];
600 Ohm line driver (with stepped attenuator and volume control) [3];
Output indicator [4].
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