Baxandall inspired tone control – response simulation

Here is an example of parametric sweep, showing one possible way of potentiometer and variable resistor simulation in LTSPICE. I will use commonly referenced tone control, originally suggested by James and modified by Baxandall to utilize active tone control scheme.

I scaled values of Baxandall circuit and also used operational amplifier instead of electronic tube used in original schematic. I’m mostly interested in frequency response simulation, so I’m not very concerned with quality of LT1128 model supplied by Linear Technology as “black box”. It should be good enough for our purposes.

Files, used in this example are included in Baxandall Tone Control.zip

 

Modified Baxandall tone control

Modified Baxandall tone control

 

Baxandall tone control frequency response

Baxandall tone control frequency, phase and impedance response

You may have noticed low input impedance with some potentiometer settings even with relatively high resistor values. This circuit requires input buffer for most real life application. You should be careful, deciding what will drive this circuit.

Additional bands could be added to provide control over mid frequency range.

3 Band Tone Control

3 Band Tone Control

 

3 Band Tone Control Impedance, Phase and Frequency Response Plot

3 Band Tone Control Impedance, Phase and Frequency Response

While I’m not big fan of this kind of tone controls, and their usability is very questionable to me, we are not going to discuss it now. Purpose of this post was to show one more example of parametric sweep and the way to simulate potentiometer in LTSPICE.

Comments

3 Responses to Baxandall inspired tone control – response simulation

  1. Thank you for the auspicious writeup. It in fact was a amusement account it. Look advanced to more added agreeable from you! By the way, how could we communicate?

  2. Steven says:

    Baxandall inspired tone control

    looked good until I did the .tran analysis on a sine wave input.

    .tran 15us
    .param RLF1 = 23.5k
    .param RHF1 = 23.5k
    setting V2 = sine 100mv, 640Hz

    the output oscillates at ~ 2.5MHz with a peak-peak amplitude of ~3.5v .

    Curiously, the envelope of these oscillations follows the input signal.

    Eh ??

  3. Jos Franke says:

    Add a 10p capacitor between the output of U1 and it’s inverting input.
    This will stop the oscillation of U1.