ROG's "Mr. EQ" question

[powerplayj]

For those of you who have built this, you know it's a nice little addition to any pedal line-up and can give you all kind of voicings with the flip of a switch.  I think ROG did a great job with tweaking the frequencies of the humps/dips as they seem to accent just the right frequencies for guitar. 

For my purposes I rarely use the treble and was curious what values would be needed to change my treble boost into a "presence" boost.

Thanks,

Jason


http://www.runoffgroove.com/mreq.html

[stm]

You may try halving the 100p and 680p caps to 47p and 330p, respectively.

[primalphunk]

Old post I know but I'm seriously considering giving it a go. For this mod suggested by stm I know I'd change out the 680p for a 330p but would I need to put a 47p cap in both C4 & C3(Referring to Gringo's Mr. EQ layouts http://www.runoffgroove.com/MrEQ-layouts.pdf ) or just C4?  Yes, I am that easily confused.

Thanx for any help you can provide,
James   

[B Tremblay]

Both 100p are replaced by 47p.

[Elijah-Baley]

Hello.
It's a very old thread. There are some about this little eq, so I didn't want to open a new one.
I want to play around this eq but it's very hard to change the frequency of the peak whit this schematic, when I change a single part of one of the stage the response results very unbalanced, sometime.

For example, I like the idea to extend the treble frequency, and I tried this mod in my software.

You may try halving the 100p and 680p caps to 47p and 330p, respectively.

It kind of works, the frequency peak is around 5kHz, not of 7-8db like the other stock controls, but it's 12db. And the high end (over the treble peak) is boosted, too, over 6db. The low end is not changed.

This is a kind of issue I got when a I tried to change some value: small peak, or exaggerated peak, or asymmetric responses, boost all the signal.
It's like if the original values are in a perfect equilibrium about boost, frequency and balance, and we can't change without mess up a linear response.

I really like to know a way to choice the frequency and getting the right values this schematic need.

(I admit I'm working on Tina TI, and I'm using single stage of TL071 inverter input, with the non-inverting input in the voltage reference, because I can't insert in the software the CD4049UBE, but following the original schematic everything works like ROG said).

[Vivek]

Some filters are very difficult to design with exact Formulae. They might have empirical formulae

or they need to be simulated

Mr EQ seems to have a bunch of Bridged T filters

AMZ had a trick on easy way to simulate Bridged T

See his trick here of using Big Muff tone control for Bridged T filter simulations: http://www.muzique.com/lab/notch.htm

Then go here : http://www.guitarscience.net/tsc/bigmuff.htm#RIN=1k&R1=270K&R2=100M&RM=270K&RL=1M&C1=100p&C2=680p&RM_pot=Linear


I filled up the values from filter near U1B
I made R2 very big
Then placed Pot wiper at 10

I found that created a notch at 2200 Hz

A notch becomes a hump when used in a feedback loop.

Hope that helps.

[Vivek]

See this calculator :

http://sim.okawa-denshi.jp/en/TwinTCRtool.php

R1 = R2 = 270K
R3 = 100M  (effectively not used, so that Twin T calculator becomes a Bridged T calculator)
C1 = 680p
C2 = C3 = 200p (double the 100p since there are 2 caps in series)

There will be many other such calculators on the net.

[Vivek]

https://www.diystompboxes.com/smfforum/index.php?topic=113138.0

Formulas for Bridged T filter including Q and Bandwidth
January 28, 2016
by garybdmd

[PRR]

You may try halving the 100p and 680p caps to 47p and 330p, respectively.

It kind of works, the frequency peak is around 5kHz, not of 7-8db like the other stock controls, but it's 12db.

There are two 100p caps. Change both to 50p(47p).

In other words: change ALL the caps in the filter the same percent.

(I *think* you can just change the second stage, there seems to be little interaction between stages.)

[Rob Strand]

Keep in mind the calculations will match the opamp version of the simulation but the actual response will be off because the CMOS inverters have limited gain.   Typically gains will be lower and EQ peaks will be lower on the real circuit.

*For simulation purposes* You can use a circuit like that in the dotted lines for each inverter.  It uses two opamps for each inverter.   The simulation will be closer to the actual response.

[Elijah-Baley]

There are two 100p caps. Change both to 50p(47p).

In other words: change ALL the caps in the filter the same percent.

(I *think* you can just change the second stage, there seems to be little interaction between stages.)

Thank you, PRR. That's the key.
I changed in the software the cap in front of the feedback loop and the other two caps in the feedback loop to move the frequency.

If I really wanted to enhance this schematic I could use all the six stages of the CD4049UBE to add, for example, an higher frequency (5kHz) and a low mid frequency (500kHz).
Even with the same method of the mid control with boost and cut.
It will made just of five three-way switches for Boost-flat-cut eq (and the Volume control), but it could be fun.

Right now (not a very original idea) I'm drawing a veroboard layout for a Red Llama + the Mr. Eq using all the stage that the chip has.