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Input sound to vintage computer circuit

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neazoi

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hello This circuit is from an old computer which loaded the programs using recorded wav files on a tape.

I have two such computers. The first missing the red resistor and the other has it.

I was wondering, what is the effect of the resistor in such an audio circuit?
 

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Resistors 6.8k and 1k are used for setting bias voltage to the next stage
Bias volt. is 0.64V

TTL integrated circuits LS series used those days, had input low level 0.6...0.7V and high level 2.0V
So biasing near input low , gives more sensitivity for first stage ( amplification and pulse former )

Regards KAK
 
Resistors 6.8k and 1k are used for setting bias voltage to the next stage
Bias volt. is 0.64V

TTL integrated circuits LS series used those days, had input low level 0.6...0.7V and high level 2.0V
So biasing near input low , gives more sensitivity for first stage ( amplification and pulse former )

Regards KAK

Thank you very much!

So it is better to leave the resistor ther?

What about the 54LS series ICs, is it the same?
 

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