Simple tone control?

"Tauno Voipio"
** It's not actually.
Seems like a ballsed up version with missing resistors that will be become unstable at full treble.
** And like most stuff on hobby web sites it is bunkum.
The "Baxandall" tone control design was published in Wireless World in 952 - it used valves. The network is different to the one in the link above and produces variable turnover at both the high and low ends of the range.
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... Phil
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Phil Allison
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A general question:
Should pots used in the audio tone filter circuits be audio (log) taper? Or does this apply only to volume pots?
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This circuit, "mechanically" lifted from the tube era into op-amp implementation, has a flaw: If the treble control is set to maximum, then its gain is not limited at +20dB at 10...20kHz, but keeps rising as far as the gain-bandwidth product of the op-amp allows. Input impedance goes down accordingly. It might result in Hf oscillations in the whole audio chain, even to burning the speakers out if say you leave input unconnected and close to the speaker cable.
To fix the (potential) problem: - insert 470R in series with the input 4.7uF capacitor or insert 470R between the wiper of the treble control and the inverting input of the op-amp; - throw a 47pF cap from the op-amp output to the op-amp inverting input.
Reply to
Alex Pogossov

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