The Time Manipulator is a programmable Arduino based Delay/Echo/Reverb guitar pedal. It uses two PT2399 delay integrated circuits to archive up to 600ms delay. Also, with the help of 4 analog switches, the internal configuration of the pedal can change: placing the PT2399 delay chips in series or parallel and adding extra features:

The code for the Arduino chip is programmed in C and it is Open-Source, so users can re-program the functionality or add new effects and share them in the forum. There are 9 effects included by default in the pedal: short delay, delay, echo, reverb, tap echo, chorus, telegraph, accelerator, and psycho. The schematic and bill of materials are public, the circuit was designed using easy-to-find and through-hole components.

The Guv'nor was the first guitar pedal designed by Marshall, released in 1988 and in production during 4 years. This overdrive/distortion Made in England effect replicates the classic tube Marshall Amp sound into compact and solid state box featuring a sustainable gain with a touch of compression. There are later Guv'nor MK2 models in a different enclosure, but most people prefer the sound of the original discontinued model. 

In this article, we are going to study the original design and see what are the bits that make this effect so desired.

The 1966 Dallas Arbitrer Fuzz Face has become the holy grail of Fuzz tones. It enjoys the most enduring reputation probably due to Jimi Hendrix use and abuse of this pedal. But not all the Fuzz Faces sound the same, in the old days, players sorted through dozens of pedals at a time to find the best sounding fuzz of the store. Why is that? 

In this project, we are going to build the perfect Fuzz with all the knowledge and experience that we have nowadays while keeping the tweaks and old character that make this vintage pedal to sound warm, round, and harmonically pleasant.

The FF circuit is rather simple: 4 resistors, 3 caps, and 2 transistors. Seems like pretty simple stuff, and in principle it is, but there is plenty of black magic and mystery associated with a good sounding Fuzz circuit, and it takes a lot of effort to get the things sounding just right.

The gain (Hfe) and leakage current inconsistency of the germanium transistors (the sound signature of this pedal) and the lack of ability/will to use the right components could make a huge impact on the tonal heart. The circuit layout in a pedal with a huge gain like this is critical and the component selection will leave its footprint on the sound.

The PT2399 is a CMOS echo/delay processor developed by Princeton Technology Corp. This digital chip includes an ADC (Analog to Digital converter), 44Kb of RAM to store the samples and a DAC (Digital to Analog converter). Although this chip was created as a simple solution to add delay/reverb/echo to karaokes and set-up entertainment systems, it became very popular in the guitar pedal community due to its ability to emulate BBD-based delay circuits, good price, through-hole package, 5V power supply and tolerance to modifications. 

This integrated circuit has also demonstrated that with a careful design and good tuning, could be a fantastic sounding solution. Many well-known effects like Belton/Accu-Tronics reverb module, Danelectro FAB-Echo, and the Rebote Delay use this chip as the core of the circuit.

With a minimum delay of 30ms and a maximum of 340ms (that could be extended up to 1 second at the expense of sound quality) makes it perfect for delay, echo and reverb effects.

The official Princeton Technology PT2399 datasheet is vague and many of the internal functions of the IC are not explained either, giving the foundations for mods and think-out-of-the-box solutions. In this article, we are trying to give more insights and information about how this chip works.

The M-104 MXR Distortion + aka Distortion Plus aka D+ is a distortion guitar pedal designed by MXR and released between 1978 and 1979. The original stompbox did not have external power jack or indicator LED. Jim Dunlop bought the MXR licensing rights and currently manufactures reissues of this classic MXR distortion effect (with a power jack and an LED). 

The MXR Distortion + uses germanium diodes and its sound could be defined as mild fuzzy distortion, like all of the 70's rock and 80's metal recordings that made this iconic pedal famous. The design of this circuit was reliable and used later on as a starting point for the M-133 MicroAmp which is, in fact, a un-distorted redesign of this (previous) M-104 MXR Distortion+ pedal. 

pedalSHIELD MEGA is a programmable guitar pedal that works with the Arduino MEGA 2560 and MEGA ADK boards. It includes a 1.3 inches OLED screen, a True Bypass footswitch, 2 programmable push-buttons and an analog input/output stage. The project is Open Source & Open Hardware and aimed for hackers, musicians and programmers that want to learn about DSP (digital signal processing), guitar effects, and experiment without deep knowledge on electronics or hardcore programming.

You can program your own effects in C/C++ with the standard Arduino IDE tool and get inspired using the library of effects posted on the pedalSHIELD MEGA online forum.

The Klon Centaur in an overdrive guitar pedal designed by Bill Finnegan with the help of 2 MIT Electronic Engineers between 1990 and 1994. The initial idea was to improve the TubeScreamer transient response and the midrange-bass frequencies in order to create a big open sound with a hint of tube clipping: the so-called transparent overdrive.

The design process took more than 4 years and the result was a mythic $329 hand build pedal that was running in production for 15 years. Nowadays the original models are highly appreciated, you just need to check eBay to see how high it goes.

Pedal-Pi is a lo-fi programmable guitar pedal that works with the Raspberry Pi ZERO Board. The project is totally Open Source & Open Hardware and made for hackers, programmers, and musicians that want to experiment with sounds and learn about digital audio. 

You can code your own effects using standard C and get inspiration from the ready-to-use effects from the forum, like the Clean/Transparent, Booster/Volume, Distortion, Fuzz, Delay, Echo, Octaver, Reverb, Tremolo, Looper, etc.

The project was created with the aim of having fun and learning about guitar pedals. If you want to program digital audio effects in C without deep knowledge of DSP languages or electronics, this pedal is for you. But take also into consideration that it is only 12 bits and does not feel like a finished pedal that you could buy in a shop.