Extremely Simple Parametric EQ Please help!

[Zentner]

Hi everyone,

First and Foremost, I'll admit I know next to nothing about electronics, and this is a new venture for me.

I've done some looking through old topics, and read up a bunch on parametric EQ's- specifically through a bunch of the Meta threads, but have yet to find exactly my answer.

I'm wanting to build an onboard single band PASSIVE parametric EQ section for a guitar, and I think I have most of what I want narrowed down, but I'm a bit confused about how to wire up my Bandwidth (Q) potentiometer.



There Two pictures are essentially my Circuit- I'll have a series/parallel switch to go between the two diagrams: cut and boost for my Potentiometer, so I can select whether I'll be cutting or 'boosting'

What I'm unsure of is how to wire a bandwidth pot. From what I read, All I need to do is wire a pot in series with the Inductor to add/remove resistance and create more of less of a cut/boost... but I already have a pot controlling the circuit above. All I really want to do is reshape the curve from more narrow to more broad, so that I can leave the pot controlling the whole circuit for adjusting how much of a cut/boost.

Does any of this make sense? It seems like just adding a pot to the LC circuit will do the exact same thing as the pot I have controlling how much cut/boost.

Keep in mind I really want to do this all passive.

Thanks!

 

[abbey road d enfer]

What I'm unsure of is how to wire a bandwidth pot. From what I read, All I need to do is wire a pot in series with the Inductor to add/remove resistance and create more of less of a cut/boost... but I already have a pot controlling the circuit above. All I really want to do is reshape the curve from more narrow to more broad, so that I can leave the pot controlling the whole circuit for adjusting how much of a cut/boost.

Does any of this make sense? It seems like just adding a pot to the LC circuit will do the exact same thing as the pot I have controlling how much cut/boost.

Keep in mind I really want to do this all passive.

Thanks!

What you've submitted is a passive EQ; it is not parametric because you would need variable L and C for center frequency and Q variation. There is no way you can wire a Q pot with decent range (I mean you could alter the Q by a few points, that would not really be useful). You need active elements to make a real parametric filter, period.

 

[Zentner]

Thanks for the reply.

I should've mentioned that I have a 6-way selector switch to select different inductor/cap values, so I can narrow down which frequencies I'd like to adjust.

The way I understand it... the bandwidth is calculated by the amount of resistance in the inductor. I take it there's no way to adjust this resistance at all?

Is there any other option (while staying completely passive) for adjusting at the frequencies I've chosen? Maybe an adjustable low/high cut filter based at whichever selectable frequency?

Any thoughts? I really appreciate any responses!

 

[abbey road d enfer]

Thanks for the reply.

I should've mentioned that I have a 6-way selector switch to select different inductor/cap values, so I can narrow down which frequencies I'd like to adjust.

Ok, so that makes it a switched frequency EQ.

The way I understand it... the bandwidth is calculated by the amount of resistance in the inductor. I take it there's no way to adjust this resistance at all?

Unfortunately, it's more complicated than that. The only way to change the Q in an LC EQ is to vary the L and C values in complementary directions, i.e. increasing the L and decreasing the C in order to let the frequency unchanged, but changing the ratio of reactive to resistive terms.

  Is there any other option (while staying completely passive) for adjusting at the frequencies I've chosen?

Not that I know of.

Maybe an adjustable low/high cut filter based at whichever selectable frequency?

Unfortunately these don't live well with the passive nature of guitar pickups.

 

[Zentner]

Perfect, thanks so much for all the info. You've been extremely helpful!