calculate frequencies for active EQ circuit

[maertz13]

trying to figure out the EQ points on the 1212, and I'm coming up short trying to find a calculator for this. it almost works in a baxandall calculator, but they all use an op-amp so the configuration is different. can anyone point me in the direction of a resource for this? or if you've got the time, write out the equation?

thanks a ton

 

[mdc]

Isn't that just a passive James stack?

TSC in the web

 

[maertz13]

it very well could be. I'm only familiar with passive filters, not cut and boost. in this equation, is RL the gain pot that comes next in the signal path?

 

[mdc]

There are active versions of the James stack but what you're seeing above is a passive network. The signal gets attenuated by about 20dB and the "boost" is actually just bringing that part of the frequency spectrum back up toward unity. RL is the load being applied by the next part of the circuit (aka, the next stage's input resistance). In the 1212 it looks like you've got a voltage divider and a J201 up next so probably leaving it as 1M is good enough.

 

[maertz13]

this would certainly explain the kind of cheap and boxy midrange (that's a compliment) and the way the bass control seems to only affect sub lows. the bass knob seemed to do very little in the way I expected, so I wanted to see where it was supposed to be and see if my results were similar, and they are. seems to boost sub lows that will get cut off later and flatten out the low-low mids.