Rezz-Fuzz 3 in 1: RAT + βr + Octaver

For this guitar pedal project I wanted to mix some of my most iconic distortion effects into a single one:

1. Turbo-RAT is the distortion that was used by one of my favourite 90s bands: Teenage Fanclub
2. βr (Beta or hFE reverse) is a technique used on the Fuzz War pedal by DeathByAudio, designed by Oliver Ackermann, singer and guitarrist of one of my favourite 2000s bands: A Place to Bury Strangers
3. Octave Up was kind of a wink to noisy fuzz pedals like the Shin-Ei Fuzz used by Jesus & Mary Chain, one of my favourite bands of 80s, 90s that adds a doubler to increase high frecuency harmonics.

Gerard Love, TFC bassist, showing a Turbo RAT pedal (picture from Bandwagonesque album vinyl jacket)

Fuzz War pedal by Death by Audio

Shin-Ei Fuzz Wah pedal

William Reid "pedalboard" (Fuzz-Wah on the right)

So the Rezz-Fuzz 3 in 1 pedal basically had to be a:

RAT + βr + Octave Up

Apart from that, I wanted to experiment with different type of diodes for the hard clipping section of the RAT distortion part.

The main issue was that mixing both pedals into one would require too many knobs: 3 for the RAT, 3 for the Fuzz War, plus one for the octave up, plus at least 2 switch buttons: one for clipping diode selection and at least one for effect switching, that is far too many controls for a single pedal to be packed in a 1590BB box.

Some simplification had to be made, the first one was to remove tone control on the RAT and replace it by octave up control. But since only one effect is used at a time, it would be good to reuse the same knobs for both effects. The solution was to use analog SPDT switches for two potentiometers on each of the 3 potentiometer contacts, plus another 2 SPDT switches for effect input and output selection. A 4053 device includes 3 SPDT switches, 3 of them were required.

Schematics

These are the schematics of the Rezz-Fuzz 3 in 1 effect in Eagle CAD:

On the top it's the βr or reverse hfe part of the circuit consisting of 7 transistor stages. At first sight there seems to be a big mistake on this circuit: Those NPN transistors seem to be inverted, but they are actually not, collector and emitter are inverted on purpose, actually base-emitter and base-collector both consist of a PN junction and they could be inverted, except that the gain of the resultant inverted transistor is what is called the βr (or hfe reverse) which usually is much lower than the direct gain. Here is an article from AMZ website that explains the characteristics of  reverse beta amplifiers, apparently the clipping on a reversed transistor is quite different from a regular transistor generating different harmonics. The reason for having 7 transistors is because the gain on reverse beta transistors is much lower.

The problem with this is that actually the reverse hfe on most transistors is not specified, is not part of the manufacturing control process, and hence it may have wide variations. So the only choice here is manual selection after gain measurement with a multimeter able to measure hfe. On the other hand, this add a uniqueness to each pedal, and maybe the need to manually adjust resistors for each manufactured effect. The other issue is that I am not sure that Spice models can actually simulate the real behavior of transistor in reverse configuration. For this reason I will not include LTSpice simulations of the circuit.

I had to manually adjust the resistor values to make this circuit work, the final resistor values were very different from schematics published on internet. The recommended transistor base pull-ups were 430K on the first 5 stages and 910K on the last two stages, I had to change the value to 820K on the first 5 stages to properly bias the circuit and make it work. The recommended transistor emitter pull-downs were 390 ohms, I changed the values to 270 ohms. The recommended transistor collector pull-ups were 100K on the first 6 stages and 180K on the last 2 stages, I had to change the values to 1.2K in all stages in order to make it work.

In the middle of the schematics page, there are three 4053D 3-SPDT analog switch devices, the one on the left only uses two SPDT switches to select the input and the output of the selected effect (RAT or βr), the other two switch devices connect the three potentiomenter terminals to the desired effect. The switch device at the center is used to select the gain (RAT or βr) and the switch device on the right side of the page is used to select distortion/octave up mix for the RAT or tone for the βr effect.

At the bottom of the page it's the RAT effect with input and output buffer, soft clipping amplifier (that uses unbalanced diode clipping, R42 resistor is not installed) on top and octave-up on the bottom. Octave-up amplifier uses the feedback voltages between the feedback diodes and resistors to build a fully rectified version of the distorted signal.

The mix of soft-clipped signal and octave-up goes through a hard-clipping section where three options can be chosen: hard clipping with germanium diodes, no clipping or hard clipping with LED diodes.

On the bottom left side of the page it's the +9V DC input jack connector, battery terminals, an EMI filter, resistor divider to generate mid point voltage of +4.5V, decoupling capacitors and inversion protection diode.

On the top right side there is a 6-pin 0.1'' header footprint to solder a flat cable between the effect PCB and the 3PDT push-button foot switch PCB. A small PCB was designed in order to directly connect the foot switch and the PCB with a 0.1'' pitch flat cable.

PCB layout

The PCB was made on two layers with dimensions of 85 mm x 75 mm with chamfered corners to leave place for box screw holes. Three footswitch PCBs were also added.

PCB top layer

PCB bottom layer

The finished pedal with a Turbo RAT look:

Rezz Fuzz 3 in 1: RAT + βr + Octaver

Source files

If you want to build your own RezzFuzz 3-in-1 pedal find Eagle 6.3.0 files (schematics, PCB, gerbers, BoM) on this github repository.

Shin-Ei Fuzz-Wah - Univox/Unicord Super Fuzz - Sound check (4/4)

The reference signal is just a sequence of chords recorded into the computer with the pedal in bypass mode. This is the bypassed clean signal: This is the same sequence of chords with Fuzz at maximum gain, tone cut off and Wah off: It's a rough tone with lots of high harmonics due to the octaver fuzz without tone filtering. Now the chord sequence with Fuzz maximum gain but this time the tone cut filter is on. Wah is off. High harmonics are somewhat reduced while mid tones are reinforced by the tone cut filter. Chord sequence with Fuzz at maximum gain, tone cut is off, Wah is on: This time a guitar riff is used instead of a sequence of chords, Fuzz is set at maximum gain, Wah is of, tone cut filter is set consecutively off and on: Guitar riff with fuzz at maximum gain, Wah is on, tone cut filter is set alternatively on and then off: This is the playlist with all the different sounds used in the sound check for comparison: I thought that the best way to check the sound of the Super Fuzz-Wah pedal was on a real song, so this is the cover of Jesus & Mary Chain's song Just Like Honey, from their album Psychocandy. The Fuzz-Wah pedal was connected as input to the TubeSim amp and Rezzonics 1x12 cabinet speaker:

Source files

If you want to build you own SuperFuzzWah pedal find Eagle 6.3.0 files (Schematics, PCB, gerbers, BoM) on this github repository

Shin-Ei Fuzz-Wah - Univox/Unicord Super Fuzz (not a clone!) - Schematics, PCB layout, simulations (1/4)

(Update 23/08/2015: Source files on Github)
I am a big fan of shoegaze / noise rock bands and one of my favourites bands is Jesus & Mary Chain and their album Psychocandy. That album is well known for its unique and characteristic dense wall of sound with that white noise (switch-on vacuum cleaner, washing machine and all appliances and let them couple to the guitar amp) that served as inspiration for a coming shoegaze generation of bands: Ride, My Bloody Valentine, Cocteau Twins, Lush, Spacemen 3, Loop... and even today shoegaze bands like A Place To Bury Strangers, Skywave, Ceremony, Screen Vinyl Image or 93MillionMilesFromTheSun, The KVB, The Lost Rivers, The Soft Moon...
It seems that one of the keys of that sound is the use of a Shin Ei Fuzz-Wah (8 transistors) pedal. This is a two/three effects into one pedal, a 6 transistor fuzz with octaver (high octave) plus a 2 transistor Wah effect at the end. JAMC did not make lots of use of the Wah pedal as it is normally used, but they used it to reinforce the gain of a band in the mid tones to couple the sound, so they set the pedal at one position and didn't move it.
These are the schematics of the original Shin Ei Fuzz-Wah pedal:

The fuzz with octaver is also used on the Univox/Unicord Super Fuzz (6 transistors) pedal. See schematics here:

Find here a demo video of the Shin Ei Fuzz-Wah pedal:

With all that in mind I made a first version of the Super Fuzz with Octaver pedal with scrapped through-hole conventional components on a Vero board using 2N2219A transistors 

 The first version on the Super Fuzz pedal can be seen here on the left of the picture:

The result was quite deceiving, the circuit has lots of gain and it was too noisy, too much, even for playing a PsychoCandy cover, specially when powered at 9V. A higher DC power of 15V reduced a bit the noise but it was still an undesirable result.

Schematics

(Update 23/08/2015: Source files on Github)

I decided to restart the work using surface mount devices (SMD), a professional PCB and include the Wah sections as well as several improvements and modifications to the original circuit.

These are the schematics of the Super Fuzz-Wah design:

I used BC847C high gain (hfe = 520typ) SMD SOT-23 NPN transistors.

The improvements on the circuit are the following:

1. Replacing the two clipping germanium diodes by one dual BAT54S Schottky diode SOT-23 in series with 100 ohms (D1, R22).
2. Replacing the Wah bulky and expensive inductor by a gyrator circuit based on a transistor (Q9) plus capacitor and biasing resistors.
3. Doubling the 9V DC power supply, with a charge pump circuit based on Intersil ICL7660SCBA

Check my post on replacing germanium diodes with Schottky diodes plus series resistor.

The charge pump regulator ICL7660SCBA allows doubling the power supply from 9V to 18V, however this charge pump regulator uses an internal oscillator with a quite low and audible switching frequency of 10 kHz. If it is used in its default oscillation mode this frequency is seen as a ripple frequency on the power supply, since this pedal has lots of gain in its transistor circuits, this ripple noise can be amplified and heard as a very nasty and unpleasant high pitch noise. For that reason, it is absolutely required to short pin 1 (boost frequency pin) with pin 8 (V+) in order to get a higher switching frequency of 35 kHz, out of the audible spectrum.

Wah circuit simulation with LTSpice

(Update 23/08/2015: Source files on Github)
The following schematics shows both Wah circuits: to the right the original wah circuit based on an inductor, and to the left the circuit based on a gyrator circuit, where the inductor has been replaced by a transistor plus capacitor and biasing resistors. Basically the circuit framed by the square on the right side is replaced by the circuit framed by the square on the left.

This is the frequency response of the original circuit when varying the wah potentiometer:

It is a tuned band-pass filter with its peak moving from 240 Hz to 1.28 kHz, increasing the gain from 12.5 to 23.5 dB.
And this is the frequency response of the gyrator circuit when varying the potentiometer:

Again it is a tuned band-pass filter with its peak moving from 260Hz to 1.28 kHz, slightly increasing the gain from 16.5 dB to 19.2dB.
So we obtain a quite similar result with even a more stable gain peak.

PCB Layout

(Update 23/08/2015: Source files on Github)
The PCB was made on two layers with dimensions of 80 mm x 50 mm:

Schematics and PCB layout was designed using Eagle CAD. The PCB layout can be uploaded into Eurocircuits website, and a quote can be obtained immediately, I paid 70 € for 2 boards prototypes in a 7 day turnaround, the quality is really good.

I purchased the components at Mouser website. You can find here the BoM, total cost of components for one prototype was 26 €.

To solder the components I used a low temperature (138°C ) CR11 solder paste Sn42Bi58 and a hot air soldering station, the results are very professional and clean. This is the finished PCB with all components (except external switches, jacks and potentiometers) mounted.

All the cables, jacks, connectors, switches and potentiometers soldered and ready for debug and verification