Bridged T Peak Filter - LTSpice Simulation and Audio Tryout

This can create some interesting audio effects for music such as a wah-wah effect, or the scanning/sweeping filtering effect heard in some electronic music where the sound seems to hollow out as the resonant peak scans through the audio band.
Starting from a passive Bridged-T notch/band reject filter, this project uses an op amp to transform the filter into a bridged T peak filter, and using a potentiometer, the resonant peak can be moved within the audio range from below 100Hz to around 14.5 KHz.
This project includes an LTSpice simulation and a breadboard prototype with some audio examples.
LTSpice Files:
github.com/GadgetReboot/misc_...
RC Filter Topics
www.johnhearfield.com/RC/RC4.htm
sengpielaudio.com/calculator-b...
sound-au.com/articles/active-...
tf.nist.gov/general/pdf/2526.pdf
Music used in the demo from the KZbin library:
Andrew Huang - Hyped
Max McFerren - At The Game
Quincas Moreira - Shoelace
Support me on Patreon: / gadgetreboot

[@ristomatti]

Well executed progression from schematics to simulation and finally to an actual demo. Nice touch even giving examples from too almost opposite genres of music. Clearly a lot of time and planning went to do this. This was also inspiring to my planned experiments with op-amps some time in the future. I'd definitely like to see more of this type of videos. Thanks for sharing!

[@GadgetReboot]

For op amp experiments, these are very simple circuits with just a few components that can have a big impact, making it worth experimenting with. The project definitely took some time and some failures before I got it working but it was worth it. I do plan to do lots more like this.

[@leachim66]

These videos are fantastic, I love electronics and playing guitar. However, the analog electronics involved with building effects was always really intimidating. Explaining audio effects from an electronics-first perspective is incredible. Please keep making these videos!

[@drunkenastronomy]

Something I kinda thought I understood before. Now I get it, great demo!

[@pileofstuff]

You're gonna turn into Look Mum No Computer if you aren't careful. Today it's only filters and oscillators, but tomorrow you'llbe touring Europe with a van full of homemade synthesizers!

[@GadgetReboot]

Right? I better go looking for Furbies and gameboys on eBay.

[@electronic7979]

Helpful video 👍

[@Scrogan]

This is exactly the sort of simple but practical video I like to see. I noticed that you ended up with a maximum gain of about 22dB, I’d be interested in seeing how this compares to actual pedals or other analog effects boxes. Makes me wonder how the pedal hinge potentiometers are constructed. Though they’re probably even more expensive than standard stomp-box switches. I’d also like to see making one of these where the frequency of some other waveform determines the peak frequency of the filter, like a sort of mock auto-tune, but that sounds like a really difficult thing to pull off, if only because of he requirement for analog electronically controlled floating potentiometers. Maybe PLLs too, I don’t know. JFETs?

[@GadgetReboot]

Controlling one circuit from another circuits waveform output, music to my ears so to speak. Lots more to come. When I get more into the groove, I plan to characterize some pedals I have and try to make everything make sense but for now, mishmash is king. Get it working, get it grooving, get it going on, then figure it out later. Works either way. Something is good, go with it. Something is bad, move onto the next possible good.

[@SimpleElectronics]

"band reject filter" reminds me of my childhood; not being good at any instruments :(

[@SimpleEnough2k9]

That could be interesting to develop something using the concept. Sine I'm actually working on an Arduino related project, the first thing that came up to my mind is some sort of random generator and potentially preset sequences to control a digital potentiometer values along with the speed at which these variations would occur. Oh well, this might become a project for the future, who knows.

[@GadgetReboot]

Of course the digital pot if it’s used in place of those resistors in the filter network, would have to be the sort that truly acts as a variable resistor and doesn’t require that one side of the pot is essentially connected to ground like some of them require. And even then, the maximum operating voltage of the pot needs to be taken into account depending on the op amp signal voltage. So a 5 V circuit where the op amp has a virtual ground at 2.5 V may work well.

[@DrexProjects]

I have 3 wa-wa pedals. Now I have to take them apart. I wanna see what's in there.

[@GadgetReboot]

I have one crybaby. Maybe I should do a tear down on that.

[@gandsnut]

White / pink noise as the input signal might show the notch/peak moving across the spectrum?

[@GadgetReboot]

That sounds like it just might work! My signal generator has a noise output that I should remember to try while everything is still hooked up.

[@JoaoNuno1995]

Hi! I found your video very interesting! However I came here in search for an answer that you didn't mentioned... My question is: how do I change the "fatness" of the pick? normally called the Q... I think its related to the value of some of those resistors but I dont know which one and which the values are! Thank you!

[@Abihef]

Whats this calculator😮😮 Ik looks amazing😮

[@GadgetReboot]

search for desmos scientific

[@Abihef]

@@GadgetReboot thank you very much you're amazing. I've been getting so sick of splitting everything up into tiny sums multiplying those and dividing the added Answers lately in my basic calculator. Especially now that I'm building synths it was getting crazy. I was thinking how I needed something like this just two days ago.

[@GadgetReboot]

@@Abihef I also like how I can copy and paste formulas entered earlier like a text editor and use them for a current equation I'm entering and then just change a few things before entering it to make it easier, and also, updating numbers back in history will update all the stuff, so if I'm calculating a frequency of a filter with Resistors and Capacitors, I can set up a big series of equations and then go back and change one value and see how it affects the rest below it if they use the previous ANS as part of the next calculation. I'm working on a DDS (direct digital synthesis) synth oscillator project right now, a few videos will be coming out over the next few months.

[@Abihef]

Ooh, thats amazing, sure am gonna use that, can't wait till I need it and experience the bliss Just the other day I was calculating voltage dividers and parralel resistors and caps for drum timing and filtering and with the various bpms and drums and pot settings I was going crazy. Took me hours and then I had to do it all over again because I realized with the caps I chose I couldn't get the bpm as fast as I wanted without having to use insane discharge circuitry or massive massive resistor values. Very annoying circuit I came up with anyway because it has either bpm limits, attack limits or needs tonnes of amplification. Anyway, to make a long story short, that's gonna be amazing.