Here is the
schematic of the Klon Centaur:
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.
~~~~~~~~~~~~~~~~~~~~~~~~~
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.
~~~~~~~~~~~~~~~~~~~~~~~~~
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 abouttheory 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 rolein 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 GAIN 2 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 GAIN 2 clean signal and the saturated signal, in order to always have a bit of clean mixed with the saturated signal, even when GAIN 2 is maxed.
Finally, the remaining signal goes to the input of the second OP amp. A GAIN 1 potentiometer set the amount of signal going into the amplification loop of the OP amp. GAIN 1 and GAIN 2 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 lowmids 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 threadon 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!
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