Black Keys's Big Muff: dealing with mids frequencies

Another Big Muff clone! This time, I was inspired by the Black Keys (if you do not know this band, go check it out, it is awesome!). Dan Auerbach, the guitarist/singer, uses a lot of fuzz effects, and especially a green russian Big Muff, and a Earthquaker Devices Hoof (a Big Muff variant with some interesting modifications as we will see later).

So I decided to basically mix these two variants in one Big Muff! Here it is, a 4-knobbed Big Muff:

LPB1 mini PCB !

The LPB1 (Line Power Boost 1) is a boost pedal that was commercialized in 1968 by Electro Harmonix. It is the first boost pedal using a silicon transistor. Indeed, previous boosts like the Dallas Rangemaster Treble Booster were using germanium transistors. Another novelty with this pedal was that it was boosting all frequencies and not only trebles, making it the first clean boost available!

 

The circuit is really the most simple one you can imagine for a boost:

First, there is a 0.1uF coupling capacitor that prevents parasitic DC current from the guitar to go in the circuit. With the R2 resistance, it forms a high pass filter : by changing its value, you can modulate the amount of bass going through the circuit. If you increase C1 value, more bass will go through, and vice versa.

Then, there are two resistors forming a voltage divider (R2 and R1), to provide a certain voltage to the base of the transistor. Here it is : R2/(R2+R1)x9V = 43/(43+430)x9=0,81V at the transistor's base.

The silicon transistor is a 2n5088 (originally a 2n5133 - same transistors that were used in the Big Muff later), wired as a common emitter. R4 and R3 will define the amount of amplification. If you increase R4, amplification will be larger. If you increase R3, there will be less gain.
A second 0.1uF coupling capacitor that prevents DC current from the battery to go out of the circuit. Finally, a 100k potentiometer wired as a variable resistor defines the final volume.

If you look carefuly, you can see that the last stage of the Big Muff circuit is exactly the same! A LPB1 circuit is used to increase the final volume.

Indeed, this circuit can be used in a lot of different effects to boost the entry or final level. A fun thing to do is to add a LPB1 boost before a saturation effect to increase the gain. It is very fun on a Big Muff (like in the Musket Fuzz or Supercolider fuzz), or on a Tube screamer (like in the Fulltone Fulldrive)!

In order to be able to add this little circuit when I want, or to test it on several pedals, I decided to make a small PCB that allows you to add a "boost" knob on every pedal you want. There is a "in" and a "out" pad that allows you to place it anywhere in a circuit:

I will test it on a Big Muff or a Jan Ray! I could also try to see if it can fit a Hammond LB enclosure (super small squared enclosures like the one I used for my Strymon Favorite switch) Note that there is no voltage stabilization or polarity protection system on this board (too small, not enough space for it!), so do not hesitate to wire a 100uF capacitor between the two lugs of your power supply input.

I should receive all the parts to test it soon...

Klon Centaur Clone and mods (Aion Refractor)

The Klon Centaur is one of the DIYer's favorite pedal. Indeed, the original version of this mythical overdrive actually costs more than 1500 euros! This pedal is more like a legendary unicorn than a real pedal that you can test one day... Even the reissue, the KTR, which is not hand assembled costs more than 300 dollars... The amount of clones (aka "klones") of this pedal has grown insanely over the years: JHS, Rockett, ARC Effects, Electro Harmonix with the Soul Food, almost every pedal manufacturer has issued their clone, always closer to the original pedal.

Summary

• Klon centaur circuit analysis
• Klon centaur mods and tweaks
• Klon centaur history and versions

For those who do not know the Klon Centaur yet, it is an overdrive created in the 90s by Bill Finnegan and MIT engineers (yes!), that is probably the "hypest" pedals of all. It was used by many guitarists, including Jeff Beck for instance. It is a three potentiometers overdrive: gain, volume and trebles, famous for the light crunchy tones it provides to your sound. It has also an excellent reputation as a buffer or clean boost. In fact, I have already made Klon buffer PCBs to use it in a patch box.

Recently, different PCB makers made Klon Centaur PCBs available, so you can make your Klon Centaur yourself. I used a PCB from Aion Electronics, the Refractor overdrive. This PCB is amazing, a fantastic work has been done by Aion Electronics to make the circuit fit a 1590B enclosure ! If you want something a bit bigger (for instance if you want to make a Klon-like look), you can use the Madbean Sunking PCB. I also wanted to see if there were audible differences between my EHX Soul Food and a replica of an original Klon Centaur (without the goop ^^).

Here is the result!

I used a prepainted enclosure from Banzai Music, in a classic gold color to make it look like the first golden Klon centaur pedals. I used a stamp to "print" a centaur on the enclosure with China ink. Then, I varnish the enclosure. I used a french website, called tamporelle, to make a custom inkstamp. It was very quick, and the stamp is of really good quality. Plus, it is quite cheap. I really like the result, it is not really easy first, but after a few tries it looked good!


I also used my laser engraved plate on the front side of it.

To compact the Klon circuit in a 1590B enclosure, a fantastic work has been done by Aion Electronics. The PCB is very compact, yet quite easy to populate because it uses classic components, and you do not have to place resistors vertically. The PCB is of excellente quality, double sided of course. The guide made by Aion Electronics to help you to build it is really detailed and well done. If you want to make a small Klon clone, I really advise you to use this PCB.

However, it is not an easy build. The compaction of components is quite high, and you have to be quite precise when drilling the enclosure. Fortunately, the build document is really complete, and you have a drilling template included. Mine worked directly on the first attempt (This is a rare thing when building pedals...) !

I decided to build a replica of the original Klon Centaur circuit. I used tantalum, electrolytic and film capacitors like it was on the first Klon Centaur pedals. For that, I used the document realized by Martin Chittum from freestompboxes.org in 2009. Indeed, the original pedal is gooped. Goop is a kind of black resin that embed the circuit and components, and prevent you to trace the circuit. The freestompbox community decided to buy a Klon Centaur, and sent it to Martin Chittum who managed to "ungoop" the circuit and trace the schematic of the Klon Centaur, and report precisely the components used.

The only point that remained elusive after this work was the kind of diodes used. They were germanium diodes of unknown nature. Some tests determine that the diodes had a 0,35V voltage drop, which matches russian D9E diodes, that I used for my Soul Food mod. I used these diodes in this build:

However, Bill Finnegan himself recently anounced that he used 1N34A germanium diodes in the original Klon Centaur:

"The diode I have always used is a germanium diode with the part number 1N34A, but you should understand that this particular part has since the 1950s or so been manufactured by literally hundreds of different companies, and having listened to as many different ones as I have, I can say with confidence that they all sound somewhat different in my circuit, and often they sound VERY different." -Bill Finnegan, The Gear Page forum post-

These are really basic germanium diodes, quite surprising for these mythical diodes! The D9E are old soviet diodes, so it is true that managing to grab some of them in 1991 (when Bill started to develop the circuit), two years only after Berlin wall's fall, must have been difficult! Moreover, the marking is different between the soviet diodes (blue mark on the anode) and the diodes that you can find in the Klon Centaur (black mark on the cathode). For me, it is probable that diodes used were 1N34A, but maybe as he is saying these diodes were from a batch that sounded a bit different from more recent 1N34A... D9E sound good to me and have the right measured voltage drop anyway, so I'll keep using them.

How does it sound?

As you may know if you know me or follow my blog, I am really sceptical about the Klon "mythical" reputation. My Soul Food seemed like a good reproduction of the sounds delivered by the Klon, and I did not really get the buzz around this pedal. It is a nice clean boost, and good for really light saturations, but was a little too trebly for my ears. With more gain, the pedal becomes really "transistor" sounding, and quite boring... Finally it became more my boost pedal than a true overdrive pedal.

So I started to test the pedal without great expectations. I have to admit that I was surprized! If the pedal really sounds like the Soul Food in low gain settings (really nice for light crunchy riffs), the high gain settings sound really nice with the Klone!

It is very dynamic and powerful, yet quite transparent, with some added mediums and trebles that makes you want to play big crunchy solos! I understand better the setting that Jeff Beck uses on his Klon Centaur:

(gain pot is on the left)

I am really surprised... I will do a blind test to be sure that my brain is not playing with me, but it seems like there are differences with high gain settings.

The pedal was compared to a Klon KTR, and sounds are really close, no audible difference between them. Proof that everything is about circuit and components, and not mojo and magic!

 

You understood, it is really close to the KTR. If you want to have an idea of how it sounds, listen to demo video of the KTR. I will try to record samples as soon as I get gear for recording audio samples.

I am currently making a small serie of 5 pedals to buy some gear to record proper video and audio samples... Send me an email if you are interested.

Circuit analysis

The Klon is a rather complex circuit. It is quite weird because there are lots of informations and tests about this pedal online, however there are few informations about how the circuit works precisely. I have to remind you that the circuit was mainly conceived by electronics engineers from the MIT (and not by Bill Finnegan, who tweaked it more than conceive it), and thus, the circuit is quite "non-standard" compared to classic overdrive circuits (Tube Screamer, Rat Distorsion...etc). So brace yourself, winter is co... lets analyze this!

If you are not very familiar with the different components, and the theory around guitar pedals, I suggest that you read a few articles about theory and other circuit analysis before reading this one!

Here is the famous circuit:

You can already see that, contrary to many overpriced "bouteeek" pedals, the circuit is not a tubescreamer, and is entirely original!

So we can already see 4 operational amplifiers (OP amps), the famous germanium diodes between the second and third OP amp. If we try to see where the signal goes, we can see that there are several pathes that the signal follows, we can see that the signal is divided between clean and saturated, and then mixed again. When the pedal is "off", the signal still goes through the top part of the circuit.

I traced the path followed by the signal:

We can see that the bypass signal (blue) is splitted in two: clean and saturated signal (green and pink, respectively). The amount of each splitted signal is dosed by a double potentiometer, the gain potentiometer. So basically, drive and clean signal are mixed, which allows really light and low saturation mimicking an amplifier just at the break up. If the Klon is so good with light drives, it is surely thanks to this mechanism that allow to have very slight saturations mixed with your clean signal.

You can also see that when the pedal is off, your signal can still go through an OP amp (it is the blue loop at the top of the schematic)... It is the famous buffer!

If we divide the circuit in different sections like we are used to, it can be this:

Finally, in the bottom right corner, you can see a power supply section using a MAX1044, that allows to have different tensions in the circuit. If you remember, the MAX1044 integrated circuits can be use to double a tension, or to invert it. Here, both of these functions are used!
Lets see this part of the circuit first!

1. Klon Centaur power supply

As you can see, there are no more than 4 different tensions delivered by the Klon Centaur power supply! We have V+ (9V), VB+ (4,5V), V- (-9V) and V2+ (18V)! Simple circuits are for the newbies lel!

V+ (9V) is stabilized using a 47uF capacitor, and a diode (D4) prevents polarity inversion. It is the classical power supply scheme.

V+ is then divided by two using a voltage divider with R29 and R30, to have VB+ (4.5V). If you do not know what a voltage divider is, read my post about resistors and their role in effect pedals. This tension is also stabilized with a 47uF capacitor (C18).

Finally, the MAX1044 is used to have an inverted tension (V-, -9V) and doubled (+V2, +18V). The MAX1044 is an integrated circuit sold by Maxim, that allows to transform tensions. Here, it is used as indicated on the datasheet (as simple as that!). For more infos about the MAX1044, read my article avec voltage doublers.

2. Klon buffer analysis

The blue loop on the top of the circuit that goes towards the output of the circuit is only active when the pedal is "off". It is the famous buffer! A buffer has a high input impedance, and a low output impedance, so that high frequencies are maintained all along your signal chain. Here is the scheme of the klon buffer:

(remembre, I designed a PCB to make it)

The first part, until C2, is simply the circuit input. There is a resistor at the input of the circuit (R1), and a pulldown resistor to avoir "popping" noises when the circuit is turned on. For more infos about pulldown resistor, read my article about resistors in guitar pedals.

The C1 capacitor is a coupling capacitor: it prevents parasitic DC currents from the pickups to go in the circuit. With R2 resistor, it also forms a high pass filter. If the value of the capacitor is bigger, you will allow more bass to go though the circuit. Here, with a value of 0.1uF, most of the bass of the guitar will go through the buffer, so the buffer will be transparent!

Then, the signal enters the OP amp, first one of the TL072CP. The TL072 is a double OP amp, very transparent. It is wired in non inverter (signal enters the OP amp through the + input). Usually, they are some resistors to define the gain of the amplifier, here, there are none. Thus, the gain is around 1, which allows you to have the same volume at the input, and the output. The OP amp has a high impedance input, and a low impedance output: the buffer diminishes the signal impendance, and maintains the volume!

Finally, there is a 4.7uF coupling cap, combined with a 100k resistor connected to the ground. This is a high pass filter (again), that will let almost all bass frequencies go through it (again). A last 560R resistor will adjust the final volume, and the signal gets out of the buffer.

3. Signal splitter

When the circuit is "on", the signal does not goes through the buffer, that is disconnected from the circuit by the footswitch, but through a "splitter". This part of the circuit splits the signal in two: clean and saturated signal.

At the input of the splitter, there is the beginning of the buffer circuit. Instead of going to the top partof the circuit, the signal can now take several pathes: down through the 5.1k resistor and the C4 capacitor, go through the second OP amp, or can go through the R17 resistor... What is this mess?

These different splitters selects some specifics frequencies. Unfortunately, I am not good enough with theory to tell you which ones... It involves rather complicated calculations with Fourier transforms and all... If any talented personn could help me with that, it would be awesome!

Lets focus on the bottom part. The signal goes through different components (R5, C4, R6, C6 and R9), then goes through the GAIN2 potentiometer, that set the maximum . You can see that the signal does not goes through any diode clipping system, so this part of the signal stays clean. In the end of the loop, it is mixed with the saturated signal.

The clean signal can also go through the top part of circuit, with the 1,5 and 15k resistor. It adds a bit of clean signal in the end that is mixed with the GAIN2 clean signal and the saturated signal, in order to always have a bit of clean mixed with the saturated signal, even when GAIN2 is maxed.

Finally, the remaining signal goes to the input of the second OP amp. A GAIN1 potentiometer set the amount of signal going into the amplification loop of the OP amp. GAIN1 and GAIN2 are in fact one double potentiometer: when the value of one increase, the other one increase! Thus, it doses the amount of clean and saturated signal to mix together: the more saturated signal, the less clean signal! It is an unique feature that is not present in any other pedal, and this is one of the novelty brung by the Klon Centaur: a part of the signal is kept as is, and the other part is saturated. Thus, the overdrive is really good for low drive.

The saturation comes mainly from the OP amp saturation. Another thing that is not usual with classic overdrives circuits! It has quit a high gain. We can calculate it. It is wired in non-inverter, so the gain will be 1 + loop resistor / resistor to ground = 1 + 422 / (15 + 2  + value of the 100k potentiometer  = 1 + 422 / (117) = 4,6 with the lowest gain, and 1 + 422 /  (17) = 25,8 when gain is maxed.

Then, there is a coupling capacitor (C9), and signal arrives towards the famous germanium diodes D2/D3. Most of the times, with moderate gain, these diodes are useless! I could test that with my soul food mod. They only are important when the gain is set up pretty high.

Finally, at the end of the splitter, all the signals are mixed again together.

4. Output signal mixer

Here we are, this is the last part of the circuit, the "signal mixer"!

The two signals that were mixed at the end of the splitter are going to be amplified and filtered a bit.
A first OP amp wired in inverter amplifies the signal. This OP amp has quite a high gain, that insures a high volume gain, useful if you want to use the Klon as a boost. This is where the incredible amount of volume of the Centaur comes from.

A second OP amp with a gain of 2 (look at the values of R22 and R24) will allow to set the final amount of trebles in the output signal. It is a classical high pass filter: you let the signal go through until a certain frequency, defined by the C14 capacitor. Decreasing the value of this capacitor will let more treble go through. A common mod is to increase the value of this cap to have less treble (we will see it later). The amount of trebles that can go through this cap is set by the treble potentiometer.

Finally, a 4.7uF coupling capacitor prevents parasit DC current from going into the last section. A 560R resistor the volume potentiometer will define the final volume of the output! There are also two resistors, R27 and R28, but I have to admit that I have no clue about their role... if anyone knows?

There are still things that I do not really get with this circuit... I guess it is a little bit overcomplicated. I would love to understand the splitter in details, but I am still lacking some precious filters knowledge...

I hope it still gave you an idea about how the circuit works. If you have any question, do not hesitate to post a comment. Lets have fun now that we know the circuit: what can we mod?

Klon centaur mods and tweaks

The Klon centaur circuit can be modded easily to modulate the gain, bass response or diode clipping. Lets see a few Klon Centaur mods together:

• Increase C14 value: it is a very common mod to set the tone response a bit better. It allows a bit more bass to go through and make the Klon less "thin sounding". I usually use a 6.8nF capacitor, treble pot is thus more useable.
• Separate the dual gain potentiometer in two pots: instead of using a double potentiometer, you can split each parameter with two 100k potentiometers. You can choose how much clean signal you will blend with the overdrive sound, or use only the overdrive part of the circuit. It is also useful for bass, if you want to let more bass goes through the circuit. I guess that the blend potentiometer on the bass soul food comes from this mod.
• Diode clipping switch: you can choose between two sets of diodes with a simple DPDT switch. This is what I did with my Soul Food mod. There are not much changes between germanium and silicon diodes, however LED gave some nice results. There is much more headroom, it feels a bit like a distorsion!
• Bass switch (madbean "fat" switch): this switch will affect the amount of bass that goes through the second OP amp. To do that, we can add a switch to choose between the 82nF stock capacitor and a 150nF one for C7.
  
  
• Bass contour mod: instead of using a switch, you can use a 50k potentiometer to blend the higher value capacitor in. You can also use a bigger value like 220 nF or even 1uF! However, you can see that this mod is only acting on the saturated part of the circuit, and not on the clean signal that is blend later. Thus, it is more hearable with high gain values... To have a proper bass knob, you can try to use a double potentiometer, and blend a higher value capacitor in parallel of C4 (68nF) too! I have never try that, maybe I will give it a shot at one point.
  
  
• Using different OP amps: instead of the TL072CP, you can use different less noisy OP amps, or more "classic" overdrive OP amps. The simplest solution is to use sockets for OP amps, and try any double OP amp IC that you would like. To test: LM1458, OPA2132, LF353, JRC4558D... Any double OP amp can give you interesting results!
• Increase gain: to have more gain on your unit, you can modify R10 resistor. It has a 2K resistor originally, and you can use a lower value to have more gain, or even a jumper!
• Using the Klon Centaur with a bass: if you cant to use the Klon Centaur with a bass, you can change a few values to let more bass going through  (from Madbean pedals): C1, C3, C4 : 220 nF, C5 : 100 nF, C6 : 1 uF, C8, C13 : 1 nF, C7 : 330 nF, C11 : 6,8 nF, C12 : 56 nF, C14 : 15 nF. I also strongly suggest to separate the gain and blend knob (second mod), so that you can dose how much bass will go through the circuit. The Bass Soul Food actually uses this mod. Here is the traced scheme for our bassist fellows:

• 1994's specs switch: in 1995, Bill Finnegan slightly modified the circuit (see below). Most of the changes were not affecting the sound, except the addition of R11 (15k resistor), that was supposed to boost a bit the bottom mids. If you want to hear what that does to your tone, you can put a switch there to choose between the 15K resistor or a jumper.

I will try to do some videos of some of these mods.

Klon centaur versions

Aestheticaly, the enclosure design changed a bit around the production time. Lets do a bit of "klonology" (chronology, get it ?! OK, I'm out...)

Gold and silver klons were produced at the same time, however the silver Klon was introduced in the early 2000s, and the graphics changed a bit with time. Three graphics can be considered: no centaur, big centaur with "open tail", and small centaur with closed tail. There were 5 different colors: 4 different gold colors (that you can see on the picture above), and the bare polished aluminium color (aka "silver" centaur). Around 8000 Klon centaurs were made between 1994 and 2009 according to Bill Finnegan (1.5 Klon centaur a day!). All those Klon worth today more than 12.000.000 euros!

First, there are no differences between gold and silver centaurs. The circuit and component values are exactly the same. Hearable differences should be really low and due to component's tolerances (Bill Finnegan used carbon film resistors with a 5% tolerance,  capacitors with 20% tolerance, so you can expect some slight variations from units to units)

Concerning the electronics, contrary to many other guitar pedal lines (Big Muff...), no big changes happened over time. The first version produced in 1994 lacked the resistor at the beginning of the circuit (R1), had no ground plane, and missed the R11 resistor. All these changes were processed in 1995. The 15k R11 resistor was added to have a bit more low-mids response. However, if you try to remove, the changes are incredibely subtle...

“The fact is, under the hood they’re all basically the same. In 1995 I made three small changes: I added a resistor to give the circuit some protection against a static charge delivered to its input—a change that has no sonic effect. I also had the circuit board redesigned with a ground plane for better grounding—again, no sonic effect except the potential for a little less hum. And I added a resistor to give the circuit a very small amount of additional low-mid response—I wanted it to have a little more roundness when used with, say, a Strat into a Super Reverb. I made no other changes.”   - Bill Finnegan, Premier Guitar interview -

Another change noticed by Manticore FX is that another resistor was added at some point at the end of the circuit. It is R28, a 100k resistor that is present just before the switch. I do not really know its role, if you have any ideas...

The KTR version was issued in 2012. It basically has the exact same circuit as the Klon centaur, and the same diodes for clipping, but it was intented for mass production. It uses surface mounted devices (SMD), so the production could be automatized (the KTR is not handmade, but made by robots), so Bill Finnegan could focus on control quality. The price tag is still high though, especially for a mass produced device. The four years during which the Klon was discontinued has been the Klones golden age, and a lot of klon clones were issued during these years. Even today, as the KTR is quite expensive and big, there is still a lot of room for klones, and some builders find their way there (Rockett for instance), making Bill Finnegan a bit angry. Indeed, it is a bit smaller than previous versions, but uses 1590BB enclosure. Bill spent a lot of time testing different SMD components to make it sound exactly like the original Centaurs units. He also avoided to use electrolytic capacitors, and kept the tolerances of the components low, in order to have similar sounding units.

Bill Finnegan was aked whether he would try to make another pedal, but obviously he has some issue with kloners all around (especially with Rockett):

"If any new product I come out with will be ripped off immediately after its release, and if unscrupulous people will again be making money off of my work, and if on top of that Klon’s reputation and my own personal reputation will be at risk every time someone decides to put out his own version of one of my designs, then where is my incentive to release anything new at all? Over the past few years, I’ve talked with a number of other pedal designers about this stuff—good people who design their own circuits, and whose circuits have also been ripped off—and we all agree there is now an enormous disincentive for any of us to create and release new products." - Bill Finnegan, Premier Guitar interview -

Maybe next Klon product will be a numerical SMD pedal (not klonable!). Obviously, the Klon case introduced the ethical problem about cloning pedal in the DIY and guitar pedal afficionados community. As there is almost no legal protection to clone circuits, the only barrier is ethics. I think it is an interesting debate to have. I am currently writing an article about that, including some pedal patents and reflexions about cloning.

Fun facts about the Klon

• The name "Klon" is a shortener for "Klondike", a region of the USA famous for its gold rush during the 19th century (among other facts).
• To order a Klon Centaur when it was produced, you had to call Mr Finnegan to discuss the pedal and it could fits your needs, and give him a professional adress (it could not be shipped to your home!)
• Hitler is not satisfied with his Klon Centaur (Bill Finnegan actually found it hilarious)
• There is a 20-pages thread on the Gear Page to discuss whether the KTR design was real or not when it was released
• Some people are ready to spend more than 2000 dollars for the original version of the Klon Centaur!

There it is, this is the end of this post! I know it is dense, so take your time, and do not hesitate to ask questions by posting a comment! I this point, I am not totally sure about how each part of the circuit works, so do not hesitate to correct mistakes I could have made in the circuit analysis.

Did you like this article ? Thank me by liking the Coda Effects facebook page!

To go further

2009 document produced in 2009 by Martin Chittum from freestompboxes.org

Aion electronics building guide, well helpful and with a lot of informations about the Klon Centaur.
Refractor project page by Aion Electronics.
"Klown" Centaur page of the Revolution Deux website.
"Sunking" project from madbean pedals, another Klon clone with a bigger PCB for 1590BB enclosures.
Modded "Klown" centaur of the Revolution Deux website.
Website with pictures of Klon centaur, classified by serials
Manticore fx : lots of informations about the Klon
History of the Klon Centaur on Premier Guitar, with a Bill Finnegan interview.
Klone science on madbean pedal: frequency response plots of different klon clones

Another Jan Ray clone !

Here is a pedal I made, a Vemuram Jan Ray clone!

This time, contrary to my previous Jan Ray clone, I decided to make it in a smaller 125B enclosure. It is not particulary a big deal with this pedal, you just have to be precise, and use a guide. I generally use a plastic card or a piece of cardboard with 4 holes disposed as the holes for the potentiometers on the enclosure, and put the potentiometers inside. Then, I cut and solder an excessive length of wire to the veroboard. I use a wire that you can bend so it can maintain the veroboard. Then, I place the veroboard above the potentiometers, and start to cut the wires at the minimal length, and solder it to the pots.

I used a prepainted enclosure from Banzai music (Vintage Orange sparkle), and classic small MXR style 17mm knobs. I also added a switch similar to the one on the Timmy that allows you to choose between a compressed (2 diodes) and an uncompressed (4 diodes) setting.

 As usual, I use the laser engraved logo:

I had many problem with the enclosure this time, Banzai music apparently have trouble with suppliers, and after 2 months I did not have the enclosure... I finally contact them and change the color of the enclosure. They were really helpful.

If you want more informations about the Jan Ray circuit, read my article here.

JHS Superbolt clone / ROG Supreaux

This is a JHS Superbolt clone! JHS is not one of the most honest builders on the planet, and he is known for his ability to steal circuit designs from other builders. The Superbolt is no exception, and is in fact a really slightly modded Run Off Groove Supreaux. Runoffgroove is a community creating circuits for DIY people, and making it public through Creative Common license. There are many nice circuits there, take a look! JHS did not bother with the license and just copy it and started to sell it.

The circuit is inspired by an old class A amplifier, the Supro 16T. It is a small 5W amplifier from the late 60s. It became quite famous, because like many other class A amplifier, if you push the volume really loud, the amp begins to distort in a really nice way. It was used in studio by many guitarists, especially by Jimmy Page who recorded several Led Zeppelin songs with it.

I decided to make a clone, mainly because some videos on the web of the Superbolt were really good sounding. I used a prepainted grey enclosure from Banzai Music, and the "Supro logo" was laser cut by HPM Laser. 

The pedal has 3 knobs: gain, which acts like the volume of a class A amp: the higher it is, the higher the volume and the saturation. The volume knob acts as a master volume; the tone knob add or remove bass and treble (slightly). There is a two positions switch that allow you to switch between a gainy bassy position, and a slightly less gainy with more treble position.

I also used the laser printed logo I used before:

The build is quite simple. However, I went through many problems doing it. At first the pedal was not working at all, then only a huge buzz came out of this box... I checked everything several times and was quite despaired about it. So I let it aside on my bench for a few weeks... And finally decided to make it work! The audio probe was really a life-saver on this build.

It is a bit messy inside, but not that much for a veroboard with 3 pots layout. At first I was planning to have space for a battery, but the input jacks were too big for that... So 9V power supply only! Adjusting the 3 trimpots was quite easy. I started with 9V on the emitter of each transistor, but this was too gainy in my opinion, so I diminished it (except for the last transistor). The pedal is thus less gainy.

Circuit analysis

Here is the schematic of the ROG Supreaux:

And here is the JHS Superbolt schematic:

You can see that it is basically the same circuit, with an added voltage doubler (top part of the circuit), and a switch adding a 120k resistor connected to the ground before Q3.

Lets divide it in several sections as usual:

You can see that it looks a lot like an amplifier! It is really inspired by an amplifier schematic, except that tubes are replaced with JFET transistors. Which is really appropriate because JFET transistors (Junction Field Effect Transistors) use a technology that is really close to tubes, and they sound quite "tube-like" when saturating: warm, creamy overdrive compared to the aggressive gritty saturation of silicon transistors.
All the saturation of this circuit is based on the saturation of these transistors: you can see that there are no diodes in the circuit. It is different from what we are used to with the Big Muff or the Jan Ray (Timmy).

To sum up, it works like this: the first preamp section amplifies the signal, and will drive the second transistor. The saturated signal will be slightly modified in tone by the tone stack section, and a third transistor will set up the final volume. Like I said, it really works like an amplifier!

Let's see every part of the circuit in detail.

Power supply section

First, there is a protection against polarity inversion with a 1N4001 diode, and voltage is stabilized with two capacitors. More information about voltage stabilization and polarity protection here.
A MAX1044 IC is then used to double the voltage, in order to have an 18 volts bus that will be provided to the JFET transistors. Having 18 volts instead of 9 gives a bit more headroom and clarity to the circuit, and this had been used in the Supreaux Deux version of the circuit. It uses the example circuit that you can find in the datasheet:

It is a very classical layout that you will find in most pedals using a voltage doubler (Klon centaur for instance).


Preamp section 1: gain

First, there are two 1M pulldown resistors. Pulldown resistors prevent loud popping noises when you turn the effect on. There is a 22nF coupling cap that prevents any parasitic DC current from your guitar to go through the circuit.

The signal is amplified by the first transistor (Q1). You can see that the overall gain of the transistor can be adjusted with a 100k trimpot that will adjust the DC current on the drain of the transistor. That way, you can set what the maximum gain of the pedal will be. The maximum possible gain is set also by the resistor R3 (1k5).

Then, the signal is filtered a bit by different means: a 470 pF capacitor connected to ground let high frequencies going to ground, thus eliminating a bit of high frequencies. To eliminate more high frequencies, value of this capacitor can be changed to a bigger value like 560 pF for instance. A 470K resistor connected to ground will set the bass response of the unit, and will eliminate a bit of bass. A potentiometer wired as a variable resistor will then set how much signal will go to ground. Thus, it defines how much the signal is amplified, and how much signal will drive the second transistor: it is the gain potentiometer!


Preamp section 2: tonestack

The amplified signal of the first section will then make the second transistor (Q2) saturate. The amplification of Q2 is also set by a 100k trimpot and R5 (2k7 resistor), and can be modulate to have more or less saturation.

There is a 10 nF coupling cap to eliminate parasitic DC current remaining from the 18V bus, and then the signal is modified by the tone potentiometer. It is wired as a variable resistor connected to ground, and will eliminate more or less bass frequencies. An optional switch also allows you to connect a 120k resistor to ground, which will diminish overall gain (a part of the signal will go to ground), and bass response (more bass will go to ground than high frequencies with a 120k resistor). This allows you to simulate the two High and Low inputs of the Supro amplifiers.

Again, a 470K set the maximum gain of this part of the circuit.


Amplifier: master volume section

This part of the circuit simply amplifies the final signal. The amplification is set by the 220R resistor and a trimpot (again). Residual DC current is then filtered by a 10nF capacitor.
Final volume is set by a potentiometer wired as a variable resistor connected to ground, like we have already seen in many many circuit, like the Fuzz Face for instance. The higher the value of this resistor will be, the less signal will go to ground and the bigger the output signal will be: more volume!

Here it is!
I hope that everything is clear, do not hesitate to ask question if some stuff is still unclear by posting a comment!
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To go further:
Runoffgroove Supreaux webpage
Runoffgroove Supreaux Deux webpage
MAX1044 datasheet.

Rub-a-Dub Reverb (1776 Effects)

Here is my latest build, a Rub A Dub reverb! It is a really simple yet useful "always on" reverb that can go from a minimal amount of reverb to long ambient delay washes, I love it! One knob, simplicity at its finest.

Inspired by Fender amps, I decided to cover an old messed enclosure (bad painting job) with tweed. Oldamp from guitariste.com was nice enough to give me a bit of tweed he had left from the amps he makes.

To apply the tweed, I used a pattern. Corners are especially difficult, because you need to bend the tweed (that is a rather stiff material finally) in a proper way. It was rather a long process because the glue takes quite sometimes to be perfectly dry.

The bottom plate was covered as well. I had to use longer screws in order to be able to close the enclosure! I used a plate that I found on the banzai music website, I thought it was really appropriated for the vintage fender style. There was 3 letters possible: "T", "B" or "V". "V" was the best for me, like "Verb".

It was quite a tight build finally. The enclosure I used was already drilled so I - stupidly - used the same layout. Unfortunately, positioning the power supply at the top of the pedal was not a good idea, I could not directly solder the pot to the PCB. I managed to fit everything. I used gold plated jack input, so gold plated connector could - maybe - finally be useful. I am quite happy with it, because in the end, there is even enough space for a 9V battery!

I got the PCB from 1776 effects, a builder based in the USA (1776 is the year of the independence of the USA). He sells a lot of different PCBs for different projects, from overdrives to delays (the multiplex echo machine for instance). This one is a simple, yet good sounding one knob reverb. There is also a "Deluxe" version of it with more tweakability, but for now I wanted a simple build! 

The PCB is really of good quality, double sided and have a nice layout. Components are spaced enough so it is not too hard to assemble, but it is compact enough to be relatively small and fit a 1590B enclosure.

Populating the board was really fun and easy, I begin to like these circuits with not too many components! For this Rub A Dub reverb, I used a Long Belton brick, Panasonic FC and SMF (except one that is a MKT standard because the value did not exist in SMF... )

How does it sound?

The "mix" potentiometer is really making a mix between the dry signal and the treated signal. So, the reverb is more or less present. It is really a nice feature, you can vary from a slight reverb in the background or a huge swampy reverb signal. I really like it at high settings. 

My only concern was that I used a Long brick, and as it is not possible to set the decay, the reverb is always very long, even when the mix potentiometer is low. If I remake one, I will use a medium or short brick. Or I will go for the "deluxe" version of the rub a dub reverb that has a potentiometer for decay using the 3rd new version of the belton brick.

I will compare with my Chasm reverb when it will be finished!
 

Circuit analysis

A stompbox reverb is most of the time a digital effect, simply because an analogue reverb requires a spring or plate system that is way too big for a standard 125B enclosure format. Fortunately for us, a manufacturer called Belton provides Digital Reverb modules that can be used for such projects. They are declined in 3 types corresponding to the possible duration of the reverb: short, medium and long.

This brick contains a rather complicated circuit with 3 PT2399 (numeric delay chip) that follow each other with really short delay time to act as a reverb.

Bam! I told you it was kinda complex...

They managed to make it smaller as possible with surface mounted components so we, small DIYers can use it at home to make our reverbs!

It has 6 pins:

• Pin 1 should receive  a regulated +5V voltage
• Pin 2 should be connected to power ground
• Pin 3 is the input of the circuit
• Pin 4 is the signal ground
• Pin 5 is the output 1
• Pin 6 is the output 2 (for stereo applications)

So it is like having another circuit in your circuit (circuitception!)
The Rub a Dub reverb is a circuit surrounding this belton brick in order to get the most of it with a simple layout. Here is the schematic:

 

Let's divide it in three sections:

The input buffer is a simple OP amp boosting the signal before it is split between dry (analogue signal) and wet (numeric conversion and treatment by the Belton brick). First, there is a 1M pulldown resistor that prevents "pop" noises when a charge accumulates at the entry of the circuit. The excess of current is going to the ground when the effect is activated. Then, there is a coupling capacitor (22nF), preventing any parasitic direct current to go in the circuit. The signal then goes through a resistor and the first OP-amp of the TL072. The TL072 is an IC containing 2 OP amps, which is a low noise JFET amplifier.  It is wired as an inverting amplifier. Thus, we can calculate the gain of it, which is simply R3/R2 = 360/180 = 2. The OP amp multiply the signal by 2, so when it is split between the dry and wet section, it is like having 2 signals like the original one going on each side of the circuit.

The treated signal section (wet section) simply is the Belton brick circuit. The signal enters through pin 3 and goes out through pin 5 and 6. It is then mixed with two 4,7k resistors accordingly to Belton mono circuit example. The signal that goes out the brick is the reverb signal ("wet" signal).  The signal then goes back to the amplification loop of the second OP amp. First, the "mix" potentiometer sets how much wet signal is going back in the circuit to be mixed with the dry signal. So you define how much signal there will be in the final sound! A coupling capacitor prevents any parasitic DC current to go in the circuit, and a 20k resistors defines how much signal can go through at the minimum mix level. A fun mod to do is to put a switch before the 22k resistor in order to make the entire signal going through the wet section: all the signal will be treated, and you will not have a dry signal anymore, creating a "wet" reverb.

The mixing section mixes the dry signal with the wet signal using the second OP amp of the TL072. The amplification gain is around 0,5, so that the mixed signal will be of the same amplitude that the original input signal. Thus, the volume will stay constant. By modulating the resistors values, for instance the 12k resistor, volume can be increased or decreased. It is also possible to put a potentiometer there in order to have a volume / boost knob. Then the signal goes through a 1uF coupling capacitor, and there is another pulldown resistor to prevent noises, and it finally gets out!

The power supply section stabilizes the current and offers a 4,5V voltage, and a regulated +5V voltage. This is important to supply the voltage needed by the TL072 and the Belton Brick. The current enters via +9V(T), goes through a 33R resistor. A 1n4001 diode protects the circuit against polarity inversion, and a 100 uF capacitor eliminates all the residual oscillations that may come from the power supply. More details about the stabilization of the power supply in my dedicated article. On the left side of the power supply section, there are 2 resistors that act as a voltage divider. Half of the current goes through the 10k resistor linked to the ground, and half of it goes to VB. We have a 4,5V VB voltage, perfect for the TL072! On the right of the circuit, there is a 7805 REG regulator. Even if it looks like a transistor (with 3 pins), it is an integrated circuit with a simple role: a voltage between 7 and 36V can enter through pin1, and a stable 5V voltage goes through pin3. Pin2 is connected to ground. It is really convenient when you need a stable particular voltage. There are many possible versions for voltage regulators, depending on which voltage you need:

• 78xx: positive voltage
• 79xx: negative voltage
• "xx": voltage value of the regulated voltage output.

There it is! I hope that everything is clear for you!
Any questions? Post a comment!

To go further:

Belton brick BTDR2H official webpage and datasheet.

Rub a Dub reverb bill of material and informations

About 7805 voltage regulator: more infos here.