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Thread: Audio Signal Generator Impedance

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    Audio Signal Generator Impedance

    I have picked up an audio signal generator (old one with dial freq adj) with a 600 ohm output and wondering about impedance matching. A long time ago I worked in the Army Signal Corp as a microwave tech and impedance matching (50 & 75 ohms) was very important for RF & microwave frequencies but I'm thinking less so for audio. It may sound silly but I have just used my CD player on tube amps in the past. Now I'd like to start using this sig gen with my scope. Any thoughts?

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    Impedance matching doesn't matter for this application. Connect the 600 ohm sig gen to the amp's input and away you go. 100mV signal should be enough to drive the amp to full output without overdriving the input stage.

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    Apart from the power tube - OT - speaker interface, audio systems generally use 'impedance bridging' between and within equipment, eg load impedance at least 3x source impedance, to reduce signal voltage loss.

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    Thanks! Much appreciated.

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    In RF, mismatching can result in the signal energy being reflected back towards the source and result in little or no signal coupling, so impedance matching is important. At audio frequencies this isn't a problem and at worst a mismatch results in the effective output signal amplitude being reduced. I have a 200 Ohm signal generator that works fine into a 50 Ohm load. Most guitar amps are 1M Ohm input. A simple way of looking at this is to consider the source impedance being in series and the load in parallel. The junction of these two then forms a voltage divider. So with a 600 ohm source and 1M ohm load the signal transfer is 99.94% (1,000,000/1,000,600)

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    Thank you Mick for the very thorough explanation!

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    What is make and model of your new item?

    It is entirely possible you can remove the 600 ohm load in it. But I do agree with all the above that it isn't an issue anyway.

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