These circuits are designed to present a 16 ohm nominal load to the amp; if you want
     a different impedance, you will have to scale the resistive and reactive elements
     accordingly. The impedance scaling factor will be Z = Znew / Zold, and the new
     element values will be as follows:

          R' = Z x R 
          L' = Z x L 
          C' = C / Z

     The primed elements indicate the values after scaling. Be sure to take into account the
     higher currents at the lower impedance levels and adjust the inductor current values
     and resistor power levels accordingly. 

     If you want to add a line out feature for recording, tap off the input of the circuit; that
     is, at the junction of the amplifier output and R1. Use a resistive divider to lower the
     signal level (make sure the divider resistance is much larger than the output or load
     impedance). Note that this circuit provides a load impedance that approximates a
     speaker, but it does not provide a frequency response that approximates a speaker.
     If you want to use such a device as a silent load for recording, you will have to add
     further lowpass and highpass filtering, along with amplitude equalizers which
     approximate a speaker frequency response.  Otherwise, the frequency response will
     be far too bright and buzzy sounding. 

     In addition, you can adjust the resonant circuit values (L2/C1) to change the location
     of the resonant peak to closer match the speaker/cabinet of your choice. The formula
     for the frequency of the resonant impedance peak is as follows: 

          f = 1/(2*PI*SQRT(L2*C1))

     R2 limits the amplitude of the resonant peak and can be adjusted as well if desired.
     The peak impedance limit is equal to R1+R2+R4. 

     The high frequency impedance limit is primarily set by R3 and is equal to
     R1+R3+R4. 

     Note that the large value bipolar caps can be converted to smaller film (or other type)
     caps if you use a capacitance transformer (if you don't know what this is, you
     shouldn't be messing around with this circuit!). In fact, you might be able to replace
     the parallel inductor with the primary inductance of the transformer, or at least
     transform the entire RLC network.