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Dagarman #118994 04/16/21 02:58 PM
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The 5K potentiometer is part of the audio cassette interface circuits. I don't know if it is required for the emulation.

I didn't think to ask the author that submitted the .wav file to try it on his kim-1 but I will ask him and hope he still has working hardware.

Dagarman #118995 04/16/21 04:26 PM
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The potentiometer is used to tune the free running frequency of the pll between 1900Hz and 6200Hz. It should be set so that it's in the middle between the two frequencies the kim actually uses.

It's a seriously complicated circuit to simulate, and it's part of the code I don't want to look at at this point. But it explains the system being able to pick up data from an otherwise not so nice audio file.

Dagarman #118996 04/16/21 04:37 PM
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FYI, the two peaks seem to be a 2500 and 3600Hz, so the potentiometer is probably set around 2270 ohm, giving a 3050Hz frequency.

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