Interesting little EQ i came up with...Equalite

[dschwartz]

Hello all!
After years and years of just being around, i wanted to collaborate with the forum again.

Bridged T filters are widely used as notch filters and frequency boosters (when used in the feedback path). i wanted a circuit that could do both by mixing the T network in and out of the feedback. At max position, the filter is fully inside the feedback, at mid position it is half at the output and half on the feedback so the notch cancels, and at min, it is after the output, producing a notch.
I don't know if someone has done this before, but i find it very practical as you only need 1 opamp and 4 components to make each boost/cut filter.

it is very extreme..you can get as much boost and cut for each frequency just by tweaking the values (lower resistor to gnd gives more Q, but alters the frequency)

i finally settled on +-20dB and defined 90/600/4K Hz as the three main bands. You could easily add more filter stages but 3 bands are ok for me at least..
this is the schem:
NOTE: The POTS ARE 100K LINEAR


if anyone wnats to make a layout for it and/or test it, please do!

[KarenColumbo]

Looks mighty interesting! Say, which pot value would you suggest?

[dschwartz]

Oh i forgot to label them!!
they are 100kB (edited the post)

[Mark Hammer]

Interesting!  And "welcome back". 

Should I assume that replacing the 1000pf+470pf pair with 1500pf won't change anything in a terrible way?

[KarenColumbo]

Thx! This will be breadboarded a.s.a.p.

[dschwartz]

Interesting!  And "welcome back". 

Should I assume that replacing the 1000pf+470pf pair with 1500pf won't change anything in a terrible way?

yes, it will destroy the nyquist stability coefficient and blow up naaa kiddin´

of course, if you have 1.5n caps..

wait a minute i have a new version coming up!!!!
i´ll post it soon!

[dschwartz]

there we go:
it uses 1 more cap per filter, BUT you can add dual pots to make each band parametric!!

[Kipper4]

Nice one Daniel. Great too see you back too.

I'll have to breadboard at least one stage at some point.
Is there a need for a buffer up front?
Can't wait to see the next incarnation. I love your stuff.
Rich

[dschwartz]

Nice one Daniel. Great too see you back too.

I'll have to breadboard at least one stage at some point.
Is there a need for a buffer up front?
Can't wait to see the next incarnation. I love your stuff.
Rich

Thanks Kipper!

Try one stage with the dual pot for parametric adjustment  
it does not need a buffer in front for 1 stage, omit the gain pot and the last gain stage. but it will need a buffer at the output..

[blackieNYC]

Any risk of oscillation at max? Not suggesting there will be.

[dschwartz]

Any risk of oscillation at max? Not suggesting there will be.

Judging by the Q's , not really..changing the values may get lower Qs to avoid it if it happens.  It is probably less noisy than gyrators

[PRR]

> I don't know if someone has done this before

I can not recall seeing quite this circuit.

> only need 1 opamp and 4 components to make each boost/cut filter.

Indeed interesting, and thrifty.

[Kipper4]

I havent breadboarded it yet but I imagine it has great potential as a tone shaper Pre a distortion.
Also for those projects where you end up with a spare op amp. BANG add some Eq..

[maiko]

nice and interesting.   will be monitoring this and potentially build this.  maybe somebody can
draw up a pcb hehehehe

[Chugs]

Nice. 20db is super powerful! Anyway to reduce the amount of cut and boost?

[Kipper4]

Is it drawn right cuz I threw it together on the bb. Pot one way lots of gain.  Pot tother way no gain. No signal.
Could be my breadboard ingredients skills or lack of.
Only had a few minutes before work.
Should the other end of pot go to output too?
Sorry bout this.

[deadastronaut]

Cool, nice one daniel...

[dschwartz]

Is it drawn right cuz I threw it together on the bb. Pot one way lots of gain.  Pot tother way no gain. No signal.
Could be my breadboard ingredients skills or lack of.
Only had a few minutes before work.
Should the other end of pot go to output too?
Sorry bout this.

If you mean that the gain pot at zero makes no output, then it is right.. the gain is a simple pre volume control. With 20db of  boost you need to lower the gain with hot signals or it will cliip

[Kipper4]

I admit I had no gain pot. It was the clipping that foxed me ill re breadboard tonight . Thank

[Kipper4]

Yay
I breadboarded the mid eq from post #1.
Inc input gain and output make up.
It works a treat. Great amplitude range. Really effective.
C100k pots (it's what I had in my breadboard stash is all.)
TL074.
Thanks Daniel.
I'll try swapping out some caps and maybe even try a 10k pot to Ground from the cap junction.
See what it does.