Fender tonestack impedance

[Chevy]

Am wiring up a Bassman 50 to use a "low impedance" tone stack (ie like a typical Super Reverb using 56K (instead of 100K), 250pF, .1uF, .047uF, 250K treble, 250K bass, 10K mids parts list). I like the sound/response of the 56K instead of the 100K.

I'm not up on the impedance characteristics of tone stacks. Can anyone tell me the input impedance of both tone stacks ? What is the importance and effect of using a cathode follower to drive this tone stack ? The Fender tweed 5F6a Bassman uses a 12AX7 cathode follower to drive the stack with a 56K R in it. Will the cathode follower improve tone or frequency response ? Has anyone tried this with and without cathode follower ?

Any input appreciated. Thanks !

[Chuck H]

The tone stack itself isn't low impedance, it's precisely the CF drive circuit that is. The impedance difference for the whole circuit doesn't change significantly with the slope resistor value. Further, the drive impedance, the slope resistor and the pot values can all affect the knee frequencies of the capacitors. A very helpful tool for you would be Duncan TSC here:

TSC

It's free and it's great. It will allow you to see the effects of different values and drive impedances for many types of tone stacks.

[Chevy]

Thanks for the feedback... Am familiar with the TSC, but visually looking at the results are a long ways off from what some experienced ears will know... although... I can see on the TSC that you can change the source impedance, which allows you to show the curves with / without the cathode follower circuit in place... cool ! Didn't know that you could do that part of it.