Passive mid boost/cut?

[GibsonGM]

Is there such a thing?  We've all seen ACTIVE mid boost/cut, and they work well...but I need a building block that will do this out of just R's and C's.
Anyone know of such a thing?   

[Derringer]

baxandall tone stack, turn down both treble and bass and you're left with a mid hump

or for just a variable cut, take the notch filter on something like the shin-ei or superfuzz
http://experimentalistsanonymous.com/diy/Schematics/Fuzz%20and%20Fuzzy%20Noisemakers/Shin-Ei%20Fuzz%20Box.gif

and put 10K variable resistance between the bottom cap and ground. No resistance = full mid scoop, max resistance = no scoop

[GibsonGM]

Nice, thanks...I've seen those - you can mod a Muff stack to do same....was just looking for a scoop AND hump, but in a simple format.  Those leave you with "scoop or flat".   Might need to get a little more technical to do them both!

Making a booster for leads with adjustable mids, might as well provide for some blues *hump* as well...

[mth5044]

The big muff tone stack can do mid hump, flat and scoop. With no pot, four resistors and two caps is pretty small. You can also do a boost with cap and inductor, possibly some resistors, I forget what all is needed. Bunch check out the brilliant channel on the Super Beatle.

http://music-electronics-forum.com/attachments/2509d1211666621-vox-super-beatle-v1141.pdf

I made a pedal for a guy that isolated the mid range boost, but perhaps tinkering with a sim you could figure out how to scoop as well?

[blackieNYC]

What about a gyrator in a paramedic eq? Op amp or transistor. You could start off with pots, and then settle on a fixed Q and a fixed frequency.
(This thought makes me shudder - I know I would personally have a very hard time replacing pots with fixed Rs, my hole-count gets out of hand quickly.)

[GibsonGM]

Good thinking, Blackie....it's probably going to be that, or I'll have to use *another shudder* a wah inductor as in one of the AMZ tone controls that Jack was playing with.    Mth - some tinkering with the muff stack probably has potential, too. I recall seeing something like that a LONG time ago, but can't find the TSC file I was messing with!

[Gus]

Have you searched for "Craig Anderton mid boost cut"?

[GibsonGM]

Have you searched for "Craig Anderton mid boost cut"?

Uses an opamp, no?  I was hoping to find a passive network; I'm using Mosfets for their "tube like" properties, would rather not toss an opamp in there!    Just an experiment - looking for the best of the mosfet booster with the ability to tailor mids.

[ashcat_lt]

I'm afraid you can't have a passive boost without an inductor.  The closest you'll get is to fade between a bandpass and a notch, but you won't get any gain at any frequency range without involving inductance or active parts.

[GibsonGM]

I was beginning to think so!   I'm trying to cobble this in between Mosfet gain stages, so maybe I can steal something from Anderton, driving it with a gain stage rather than an opamp....

[R.G.]

Let's talk about Q. Q is somewhat mysterious until you've had it on homework a few times. Here's a quick reference: http://en.wikipedia.org/wiki/Q_factor

Q can be thought of as the sharpness of a resonance (or a notch). A Q of 1 is about an octave wide. A Q of 2 is a half-octave wide. Using only Rs and Cs, or only Rs and Ls, you can't get Qs of more than about 0.5. So an R-C only notch is really not very sharp.

As noted earlier, you can't get peaking without additional energy. You have to go to either an active circuit to supply the energy for the resonance from a power supply, or you need at least one L and one C to store the energy for the resonant peak.

So in answer to your original question, you might be able to do it, but it won't be very sharp.

[GibsonGM]

Darn Q.   

So it seems like the best bang for the buck would be to shoot for midscoop but variable to flat rather than a hump....thanks R.G.!   Makes it much simpler, anyway, he he. 

[blackieNYC]

Hold on. Can it be said that the op amp gyrator circuit inRG's Simple Parametric does not pass any audio that you will hear? Having read that article, I (timidly) submit that none of the audio you hear passes thru the op amp. At the resonant frequency, the gyrator is a short to ground, either on the + input (notch) or in a negative feedback loop (boost).  So, your audio signal to the amp is only that which passes thru your mosfets, none of it is tainted by the non-tubelike op amp.
Ok, now let me have it.....


You can make the gyrator with a transistor, so maybe a mosfet as well?

[ashcat_lt]

I guess it's true that the opamp gyrator is not directly in series with the signal path, but I'm pretty sure that any non-linearity there is going to have at least some impact on the sound.  I'm not sure I understand it well enough to say what impact it might have, or under what conditions it might happen.  It just seems to me like if that opamp managed to clip, it would pretty much have to change the way it works.

[GibsonGM]

I'm not sure I understand it well enough to say what impact it might have, or under what conditions it might happen.  It just seems to me like if that opamp managed to clip, it would pretty much have to change the way it works.

^  I'm going with that, ha ha.  

I just really like the way the AMZ Mosfet Boost colors my sound, and was hoping to be able to do some mid adjusting while keeping it 'nearly transparent'...all these ideas have a lot of merit, tho!!  For all I know, til I've tried a few ideas, an opamp coloring the tone may be DESIRABLE (?)  Ya never know.

At times I get a feeling on stage like "This would sound AWESOME if I could just knock down the mid a bit on my leads"...you know how it is.  Then I'll install something, it'll sound good at home, but I'll disappear in the mix      

** EDIT  **   Hey, thanks R.G.!  Went back thru my 1,000's of files, found some EQ stuff from probably 1999 - you had explained an easy EQ using 1 NPN, which you send to a buffer...think I'll try that out.  I can simply do it all with mosfets instead of the opamp!    

[wavley]

There was a great thread discussing this a while back.  I totally meant to try this but never got around to it.  I'm going to try it this weekend.


http://www.diystompboxes.com/smfforum/index.php?topic=84656.0

[GibsonGM]

Holy resonance, batman