What's a good design/topology that uses a single-channel op-amp?

[Buran1997]

I've built a couple of BJT-based pedals so far (a Bazz Fuss and an Electra), and I want to try doing something with op-amps. I've got some single-channel op-amps on hand (LM741, TL071, LF351, CA3140), and I want to try out different designs that make use of these chips. Some designs I've come across so far:

• MXR Distortion +/DOD 250 (I breadboarded it and it sounds... kinda bad, TBH, which is why I'm looking for other designs.)
• ProCo RAT
• Dan Armstrong Blue Clipper
• Jack Orman's Shaka Braddah 5
• BJF Honey Bee Overdrive
• Crowther Hotcake
• MXR Micro Amp

I'm interested in finding more designs, or more generally, circuit topologies, which make use of a single-channel op-amp.

[willienillie]

Not a dirt box, but the Orange Squeezer compressor is quite simple and can be built with a single opamp (most used half of a 4558, some early ones used a 741).  You will need a couple JFETs though.  I built one recently and it was nice.  So nice that some dude bought it from me, but I intend to build another.

[antonis]

I'm interested in finding more designs, or more generally, circuit topologies, which make use of a single-channel op-amp.

Any design with essential offset nulling (usually DC applications) or frequency compensation (Bandwidth/Slew rate)

More generally, any design worthing extra pins/space/items..

[patrick398]

Active Baxandall tone control:

https://learnabout-electronics.org/Amplifiers/images/baxandale+amp.gif

[iainpunk]

welcome to the forum

there are lots of things you can do with a single op amp, i love using op amps as an add on to transistor circuits. i think transistor based drive pedals generally sound better, but op amp eq's are second to none after a transistor based drive. i have a design with a jfet based distortion/fuzz, which is crunchy to begin with, but there is an op amp boosts the 1kHz region with up to 30 dB to ad a lot of "grind" if that's your thing, but the filter can be changed to boost different frequencies, i'll search my schematic folder for the design.

[iainpunk]

found the schematic:



the values in the feedback loop of the opamp can be changed to boost different frequency bands, i use this calculator to come up with values. http://sim.okawa-denshi.jp/en/TwinTCRkeisan.htm
(this design tool is for a twin T filter, instead of a bridged T as per the design, if you put in "0.1p" for R1 and C1 you effectively eliminate them from the design)
i like the R2 100k and R3 2.2k as standard value potentiometer and resistor and i change around the capacitors for different frequencies, this gives you up to 28dB of boost for any chosen frequency if the capacitors are the same value

[garcho]

Since you're only just beginning your op amp journey, I suggest the Blue Clipper. It's basically the original op amp distortion circuit. So many pedals are riffs on that, and it's simple enough to really help give you an idea of how op amps work. Also, check out these videos: