Adding bands to Parametric EQ

[iheartleaven]

Hello! I would like to build this Japanese parametric EQ circuit, but add one or two additional bands. Here's my question: Is it more sensible to add additional bands as complete EQ blocks in series, or to stack additional filters in parallel before the mixing op-amp as in R.G.'s Basic Parametric EQ?

It seems the stacking approach would involve using only 3/4 of a TL074 for each new band, and sending the output of all filter sections to pin 5 of the original TL074. Is that nuts? Is there any reason, other than parts count, that it would be better? I've included edited schematics showing how I imagine each approach would be hooked up. I included a coupling cap between stages in the "series" configuration. If you see any glaring problems, please let me know.

Thanks!

Original Circuit:


R.G.'s Parametric EQ:


"Stacked"


Versus "Series"

[PRR]

> sending the output of all filter sections to pin 5

I don't think that will work for *this* design.

Your "series" should work. You do not need the added coupling caps.

[iheartleaven]

Awesome, I'll get breadboarding. Thanks for responding!

[Thecomedian]

Im thinking the "coupling" cap is meant to disconnect the DC of the first circuit from the second, basically like plugging the previous one as a complete pedal into a "parametric EQ pedal". Only the AC would be going to the next pedal, or in this case the next stage.

Is that what you were thinking, op?

[PRR]

> Im thinking the "coupling" cap is meant to disconnect the DC of the first circuit from the second

Look at how IC1 couples to IC2.

*All* the stages are DC biased at V/2, and have unity gain at DC. Therefore they can be direct connected.

[Thecomedian]

Thats true. I've been over that before. The idea of isolated "stacks" as a modular system, but if it all runs off the same battery anyway, decouplers wouldn't really do anything.