Easy Mid-scoop Control

[Bill Mountain]

I wired this up last night because I wanted a variable mid-scoop in a fuzz I was working on.



This will go from a flat response to a 26 dB cut at about 400 Hz.

Moving the R's up will lower the scoop frequency (e.g. 22k ohm equals about 220 Hz)

Moving the R's down will raise the scoop frequency (e.g. 4.7k ohm equals about 1k Hz)

This is nothing revolutionary.  I've even seen Bridged-T notch filters like this discussed on DIYSB's before but I thought I would post one that worked well for me.

Good luck!

EDIT:  I think I'm going to try a 10k pot when I get home this evening.  With the 10k at max it may not have super flat mids but I think it will have a better ratio of turn to Db reduction (if that makes any sense!).

[Bill Mountain]

I plan on getting a dual gang pot to experiment with making the notch frequency variable but I usually get in trouble when I have that much tonal control.

[deadastronaut]

cool: i'll try this later...nice one bill..

[alparent]

Did you draw those resistors during an heartquake? 

[Bill Mountain]

MS paint with a mouse that sticks.  That was my third try.

[Ice-9]

Did you draw those resistors during an heartquake? 

No, I recognize those resistors, there a special log to current vairable resistance.

I will give this one a try , thanks

[digi2t]

Did you draw those resistors during an heartquake? 

No, I recognize those resistors, there a special log to current vairable resistance.

Also known as "Chicago" resistors.

Nice Bill. I'm kind of a fan of the mid-scoop. I think it harks back to the first time I heard a Boston tune  .

[ayayay!]

Pretty cool, thanks!  Reminds me of the Mid-Notch that STM posted a little while back.  Very similar low count type of thing. 

[deadastronaut]

@bill, just tried it...nice!...i swapped the 50k for a 10k...seems a better range over the pot sweep...nice!..

i bent my resistors to look like the diagram too...

[Bill Mountain]

@bill, just tried it...nice!...i swapped the 50k for a 10k...seems a better range over the pot sweep...nice!..

i bent my resistors to look like the diagram too...

I was just thinking a 10k would work better.  Did you see my edit or did you try it on your own?

[deadastronaut]

no i just tried it just now!....i used 10k resistors too....didn't have 12k's...

looking forward to the notch freq shifting version...

[Bill Mountain]

Well I'm glad it worked for you.

I went home on my lunch break and tried it after a few of my dirt pedals and I thought it hollowed the sound out nicely.

Now we just need to find some 20k dual gang pots.

[deadastronaut]

yeah just tried it after a distortion too, scooped it out nicely..very punchy.....

i'm not a fan of dual pots...limited knobs n all that....have you a scheme of the dual thingy then?...with wonky resistors too...

[earthtonesaudio]

Another variation is the bridged differentiator:



Pot sweeps the frequency (although the bandwidth and attenuation will change as well).

[DavenPaget]

My Beta Aivin HM-200 surprisingly has a mid-scoop control ( They call it a mid-cut control )
from 200Hz to 5KHz ... 
Although i could open it up and draw up a schem , i can't , 1 of the screw's chipped 

[PereatMundus]

Well I'm glad it worked for you.

I went home on my lunch break and tried it after a few of my dirt pedals and I thought it hollowed the sound out nicely.

Now we just need to find some 20k dual gang pots.

Hey, Nice stuff. I need to try this

btw dual gang pots, 20k.  you meen a simple stereo pot?

If so here is one:
http://www.banzaimusic.com/Alpha-16mm-stereo-20k-lin.html  

edit: ah ok, no you whant notch freq variable. then check the below mouser numbers.

I plan on getting a dual gang pot to experiment with making the notch frequency variable but I usually get in trouble when I have that much tonal control.

and here is some dual gang 20k pots on mouser:

Mouser Part No:         652-PTD902-10BAPB203
                                652-PDB182-K420K203B
                                652-PTD902-2215KB203

[ayayay!]

Another variation is the bridged differentiator:



Pot sweeps the frequency (although the bandwidth and attenuation will change as well).

Something about that looks so fun.  I've got to try that. 

[Bill Mountain]

Well I'm glad it worked for you.

I went home on my lunch break and tried it after a few of my dirt pedals and I thought it hollowed the sound out nicely.

Now we just need to find some 20k dual gang pots.

Hey, Nice stuff. I need to try this

btw dual gang pots, 20k.  you meen a simple stereo pot?

If so here is one:
http://www.banzaimusic.com/Alpha-16mm-stereo-20k-lin.html  

edit: ah ok, no you whant notch freq variable. then check the below mouser numbers.

I plan on getting a dual gang pot to experiment with making the notch frequency variable but I usually get in trouble when I have that much tonal control.

and here is some dual gang 20k pots on mouser:

Mouser Part No:         652-PTD902-10BAPB203
                                652-PDB182-K420K203B
                                652-PTD902-2215KB203

Seems like any of those would work.  I just need to include some in my next parts order (which sadly won't be until after Christmas).

[Bill Mountain]

Another variation is the bridged differentiator:



Pot sweeps the frequency (although the bandwidth and attenuation will change as well).

This seems cool and unpredictable in a crazy/fun/awesome way.

[PereatMundus]

Well I'm glad it worked for you.

I went home on my lunch break and tried it after a few of my dirt pedals and I thought it hollowed the sound out nicely.

Now we just need to find some 20k dual gang pots.

Hey, Nice stuff. I need to try this

btw dual gang pots, 20k.  you meen a simple stereo pot?

If so here is one:
http://www.banzaimusic.com/Alpha-16mm-stereo-20k-lin.html  

edit: ah ok, no you whant notch freq variable. then check the below mouser numbers.

I plan on getting a dual gang pot to experiment with making the notch frequency variable but I usually get in trouble when I have that much tonal control.

and here is some dual gang 20k pots on mouser:

Mouser Part No:         652-PTD902-10BAPB203
                                652-PDB182-K420K203B
                                652-PTD902-2215KB203

Seems like any of those would work.  I just need to include some in my next parts order (which sadly won't be until after Christmas).

yea, same issue here I seriously just added a mouser order yesterday..
(and an expensive one, parts for a SloClone and about 5 Fx boxes...  

So will have to wait to try this until Xmas or later for the next order.

However, as far as knobs to go with the dual gang pot I've always liked these below:
[Edit: that is of-course if you whant the dual/stereo pot with seperated control so you can use concentric knobs,   , guessing NOT cause you wish to vary the both resistor values  at the same time, no? ]

and here is a great hint. to make it nice.
the notch in both lower and upper control of the knob, take a drill and make a 1-2mm hole there instead, and glue a Led in that spot.

Mouser Part No:    755-SLC-22MG3F
                                755-SLC-22VR3F
                                755-SLC-22DU3F
these are GREAT for that due to their shape, able to press the flat top led through the hole and fasten it safely.

I've used this in the past when I REALLY whant to see the knob setting.
Its seriously cool looking and useful. particularly in stacked knobs.

http://www.guitarfetish.com/Concentric-Chrome-Knobset_p_174.html |  http://www.guitarfetish.com/Concentric-Knobset-Black_p_177.html