active bax stack w/ faux pentode.

[DummyLoad]

fun with sim b/c don't feel like building.

here's an active tone stack - a spin on the bax of sorts. i don't have access to a tapped 1ML pot IRL much less in the simulator's database, even if i had the smarts to create the element, the database in this free sim is locked. i suppose i could use LT spice, but i don't feel like dealing with the learning curve.

so, you see solid state (Q1 & Q2), well i see a faux pentode. yeah, mods just imagine it's a pentode...     

it's ok, certainly not a perfect example of a bax, but fairly flat and midpoint on the controls and it loses about 1dB overall. again, not perfect but it seems to work.
R11,12,13,14, and 15a+b (R15 is a stereo pot) are replacing a 50cent tapped 1M pot as called out for in peter baxendall's paper: link below.

http://www.thermionic.info/baxandall/Baxandall_NegativeFeedbackTone.pdf

attached is the schematic as are the bode plots: the file names denote the control positions.

if you have a better method for replacing the tapped treble pot, please share. 

--pete

[DummyLoad]

remaining 2 bode plots.


--pete

[HotBluePlates]

What does the sim show when R13 & R14 are ~1kΩ?

[DummyLoad]

not so nice.


bass full down and treble full up in attached bode plot. 


--pete

[DummyLoad]

moe better...


--pete

[DummyLoad]

...continued

the last three...

--pete

[HotBluePlates]

not so nice.

bass full down and treble full up in attached bode plot. 

Are you sure you manipulated the Treble pot properly in the sim for that shot? The other plots behave as-expected.

What I noticed in your first sim scenario was that the treble never boosted/cut as much as the bass. Since the 22kΩ resistors didn't act completely like a grounded mid-tap on the pot, I wondered if making them 1kΩ or even 0Ω would cause the Treble pot to have the same range as the Bass pot. For your later set of plots, each shows the Treble boosting/cutting nearly as much as the Bass, which looks like improvement.

[DummyLoad]

Are you sure you manipulated the Treble pot properly in the sim for that shot?

absolutely.

For your later set of plots, each shows the Treble boosting/cutting nearly as much as the Bass, which looks like improvement.

yes, had to balance the network with larger R values. the real tapped pot, there is a point that has a value of "0" call it the crossover as the wiper in a true tapped pot would work. without that tap, there has to be some resistance and why the gap in the f slope of the treble response from cut to boost.

the best i can do, i think, is in the second scenario posted. at least i fiddled with it to the point where i think it's a viable solution. however, please feel free to spin it up on your own simulation SW and contrib. 

respectfully,

--pete