I'm trying change the cutoff point of a vintage mixer's HPF from 80 Hz to 60 Hz

I have the service manual in front of me and located the high pass section of the schematic (attached below)

I found this excellent link explaining a vey similar configuration here: https://www.electronics-notes.com/a...ransistor/active-high-pass-filter-circuit.php

However the circuit in the mixer has an additional transistor, and the formula from the electronics notes article resulted in a f0 value fo 112, not 80 as it should be.

Could anyone let me know how I might go about calculating the correct value for the 2 transistor HPF, and ultimately adjusting its value from 80 Hz to 60Hz?

 

What you have there is a Sallen & Key filter where the unity gain buffer is a compound emitter follower.
This online calculator will work out the values for you
http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm
What value of Q do you require? (Alternatively, is it Bessel, Butterworth or Chebyshev?)

 

What you have there is a Sallen & Key filter where the unity gain buffer is a compound emitter follower.
This online calculator will work out the values for you
http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm
What value of Q do you require? (Alternatively, is it Bessel, Butterworth or Chebyshev?)

Except the link is for the low pass filter.

Sallen Key High pass filter

 

Thank you both for your help, this is exactly what I needed! It is butterworth

 

Except the link is for the low pass filter.

Sallen Key High pass filter

Close!

 

Below is the LTspice simulation of the circuit:
I experimentally tweaked the values of R6 and R7 to give a -3dB gain drop at 60Hz from the passband gain.
Those are not necessarily optimum values.