This is a very simple Bingham tilt tone control which I found here: https://www.angelfire.com/sd/paulkemble/sound4e.html
I have recalculated components values for lower impedance (= lower noise) and smaller adjustment range (+/-5dB). The original circuit gives up to 40dB variation over the audible frequency range which is a bit excessive to say the least.
Schematic:
Frequency response:
Turnover frequency is 935Hz which is close enough to 1kHz.
Worst case input impedance is ~3kOhm which can be easily driven by any modern audio opamp:
I have recalculated components values for lower impedance (= lower noise) and smaller adjustment range (+/-5dB). The original circuit gives up to 40dB variation over the audible frequency range which is a bit excessive to say the least.
Schematic:
Frequency response:
Turnover frequency is 935Hz which is close enough to 1kHz.
Worst case input impedance is ~3kOhm which can be easily driven by any modern audio opamp:
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