Simple active EQ

I did. I've also worked with enough real life audio equipment to know the proportions of google results and real life are very different.

NT

IIRC, the squarewave response (at the middle setting) is kind of warped or wiggly looking, but approximately correct. Which implies the two poles are in about the same place, which is the right idea.

Tim

Great. It's only audio, so it doesn't have to be perfect.

People used to make center-tapped pots, which would be handy here. And there is a trick.

Blasphemy! Monster will get you.

Do you mean four terminal?

No, here's the trick, which I just invented.

If R1 is lower than R2, you get a virtual center-tap, for flat response at mid-rotation, and a sort of audio taper towards the HF and LF boost points, nice and sloppy like audio people enjoy. It needs tubes, of course, preferably something awful like 6SN7s.

I have even worse ideas.

Ha, i like it. (I'd want a little more R somewhere in the LF, HF path when the pot gets to one end or 'tother.)

George H.

Build that up and report your results >:-} ...Jim Thompson

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I picture the output going into an inverting opamp... summing circuit. But I've got zero playtime at the moment... If I clean out some free time I do have a couple of fun diode laser things to do... those have the potential of generating more sales. (Which is permissible fun :^)

George H.

You have to be careful to match the phases of the HP and LP parts, if you do not want a bump or notch at the cross-over frequency.

Google for 'crossover filter'.

Yep. There was an old National booklet, IIRC called "Floobydust", that addressed how to fix that. ...Jim Thompson

The R1 path dominates at the center position, so the phases of the HF and LF parts don't matter much.

It was in the National Audio Handbook, 1973.

Cheers

Phil Hobbs

Actually an old (1976) National audio applications book with a chapter "Floobydust"...

Note paragraph 5.2.2 regarding constant voltage and constant power... that's the secret to no "bumps". ...Jim Thompson

Yep, I found it. Mine is dated 1976. Cover and Floobydust first page link in a prior post.

...Jim Thompson

Hmm OK thanks. I'm not at all an audio guy. I have done tricks, breaking up an error signal in a feed back loop to HF an LF parts and sending those to two different actuators. There I just used a single RC and sent the voltage difference across the C to the HF section and across the R to the LF. More poles would be more complicated.

George H.

The problems arise from combining two or more signals that have traveled the separate paths. As long as the separated signals do not meet after filters, everything is OK.

More poles _isn't_ more complicated unless, of course, you insist on using S-K configurations >:-}

State variable configurations make it easy.

For no "bump" requires at least third-order cross-over networks. I've found fourth-order easier to implement, particularly if you want to vary the cross-over frequency with a pot. ...Jim Thompson