Aion Electronics Refractor Overdrive User manual

1KLON CENTAUR / REFRACTOR OVERDRIVE
Refractor Overdrive
Klon Centaur Professional Overdrive
Controls & Usage
Standard overdrive controls on this one.
• Treble control allows for EQ adjustment of the top end.
• Output is the overall effect volume.
• Gain simultaneously increases the gain and blends from clean signal to dirty using a dual pot.
Modications&Experimentation
No built-in mods for this one, but there are a few part substitutions you can experiment with.
Tonecapacitormod: A very common and well-regarded modication is to change C14 to either 6n8 or 8n2. It
xes a complaint of Centaur clones that the treble is a little thin, and nearly everyone who’s done it says it’s a
huge improvement.
Socket the diodes. The original uses germanium diodes with a forward voltage of around 0.35v, but others
have reported good sounds from BAT41, OA126 or even the plain old 1N914.
Sockettheopampsaswell. The original uses TL072s, but many people have reported good things from
mixing these up, such as an LF353 or JRC4558D for IC1 and a NE5532 for IC2.
Bassguitarmod: Use a 390n lm capacitor for C1 if you’re going to use it as an overdrive for bass.
The Refractor is a part-for-part replica of the legendary Klon
Centaur Professional Overdrive. The Centaur is a really
unique overdrive pedal, an original design not based on a
Tube Screamer or Big Muff like a lot of other “innovations”
in the past 20 years. This project was designed to t into a
1590B, so it’s a great deal smaller even than the KTR (the
“miniaturized” reissue of the Centaur).
The Centaur’s switch wiring is pretty cumbersome. Check out
the Refractor Bypass PCB for an easy solution.
Newversion2: The Refractor has been redesigned for a
more optimized layout. Power and signal ground have been
separated (see new wiring diagram on page 7) which should
theoretically cut down on noise. The diodes have been
given more space, and best of all, there are no more 1/8w or
standing resistors!
The part numbering is identical, and the drilling template is
the same except that the LED moved up about an eighth of
an inch and the Gain and Tone knobs swapped places.
Refractor Project LinkOverview

2KLON CENTAUR / REFRACTOR OVERDRIVE
Parts
Resistors
R1 10k
R2 1M
R3 100k
R4 560R
R5 5k1
R6 10k
R7 1k5
R8 1k5
R9 1k
R10 2k
R11 15k
R12 422k
R13 1k
R15 22k
R16 47k
R17 27k
R18 12k
R19 15k
R20 392k
R21 1k8
R22 100k
R23 4k7
R24 100k
R25 560R
R26 68k 1
R27 68k 1
R28 100k 1
R29 27k
R30 27k
LEDR 4k7
Semiconductors
IC1 TL072
IC2 TL072
IC3 TC1044SCPA 2
D1, D2 Ge 3
D3, D4 1N4002
Z1 1N4742 2
LED 5MM
Potentiometers
Treble 10kB
Output 10kB 4
Gain 100kB dual
Capacitors
C1 100n
C2 4u7 electro
C3 100n
C4 68n
C5 68n
C6 390n
C7 82n
C8 390pF MLCC
C9 1uF lm
C10 1uF lm
C11 2n2
C12 27n
C13 820pF MLCC
C14 3n9
C15 4u7 electro
C16 1uF tantalum
C17 47uF electro
C18 47uF electro
C19 1uF electro
C20 1uF electro
C21 1uF electro
C22 1uF electro
See next page for footnotes and part notes.

3KLON CENTAUR / REFRACTOR OVERDRIVE
Build Notes
1 These resistors are wired off-board and are not found on the PCB itself. See wiring diagram further down.
Note that these three resistors are not shown in the schematic.
2 Can use a MAX1044 as well, but I recommend the TC due to the higher maximum voltage. If using a
MAX1044, use a 1N4739 for Z1 to keep the voltage below the MAX1044’s max voltage.
3The original uses germaniums of an unknown type. But germanium diodes have such wild ranges that even
if the part number was known, it wouldn’t necessarily mean that another of the same name would sound the
same. What is known is that the Centaur’s diodes have been measured at around 0.35v forward voltage. I’ve
had pretty good luck getting this value with the 1N270 from Tayda Electronics, but you may want to order 5 or
10 and then measure them to nd the ones that are closest to 0.35v.
Keith Vonderhulls from Build Your Own Clone did some extensive testing of different diodes and found that
Russian D9E diodes were an exact sonic match. (D9B, D9D, D9J, D9K and D9L are equivalents and can
usually be found cheaper.) Many people have tried this diode since then and agreed that it’s very, very good.
It’s unlikely that the real Centaur unit uses this exact diode, but it’s the closest that the DIY scene has gotten.
However, a lot of people have used other types of diodes and found that they preferred them over standard
germaniums. One good one that is often tried is the BAT41. Others have reported really good results with the
OA1160, which are pretty much impossible to nd as of recently, but if you can nd some then grab them!
4 The original uses linear taper (B), but lots of people prefer audio taper (A) for the Output control for ner
control over the volume. The maximum available volume wouldn’t change.
Silver Pony specs
In July 2014, Build Your Own Clone reverse-engineered a silver Centaur, serial S2207, and found a number
of discrepancies. No one’s quite sure what to make of this. It is not representative of standard-production
Centaurs but many people have tried these specs and liked the result. The “Silver Pony” values are as follows:
Part Original Silver Pony Effect
R10 2k 47R More gain
R17 27k 10k Increased volume & treble for the dry signal
R18 12k 4k7 (along with R17 change) Better wet/dry ratio
R21, R23 1k8 / 4k7 4k7 / 1k8 Slight shift in range of Tone knob
C13 820pF 560pF Slight increase in overall brightness
Additional Part Notes
• Capacitors are shown in nanofarads (n or nF) where appropriate. 1000n = 1uF. Many online suppliers do
not use nanofarads, so you’ll often have to look for 0.047uF instead of 47n, 0.0056uF instead of 5n6, etc.
• The PCB layout assumes the use of lm capacitors with 5mm lead spacing for all values 1nF through
470nF. I prefer EPCOS box lm or Panasonic ECQ-B/V-series.
• Potentiometers are Alpha 16mm right-angle PCB mount.
• Switches are Taiway (Small Bear) or Mountain Switch (Mouser) brand with solder lugs. I prefer the short-
toggle variety, but that’s just a matter of aesthetics.
• I recommend using these dust covers / insulators from Small Bear to insulate the back of the pots from
the board and prevent shorts. If you don’t use these, use some electrical tape or cardboard to act as
insulation. The right-angle pots will make direct contact with the solder pads otherwise.

4KLON CENTAUR / REFRACTOR OVERDRIVE
Schematic

5KLON CENTAUR / REFRACTOR OVERDRIVE
General Build Instructions
These are general guidelines and explanations for all Aion Electronics DIY projects, so be aware that not
everything described below may apply to this particular project.
Build Order
When putting together the PCB, it’s recommended that you do not yet solder any of the enclosure-mounted
control components (pots and switches) to the board. Instead, follow this build order:
1. Attach the audio jacks, DC jack and footswitch to the enclosure.
2. Firmly attach the pots and switches to the enclosure, taking care that they are aligned and straight.
3. Push the LED1 into the hole in the enclosure with the leads sticking straight up, ensuring that the at side
is oriented according to the silkscreen on the PCB.
4. Fit the PCB onto all the control components, including the leads of the LED. If it doesn’t t, or if you need
to bend things more than you think you should, double-check the alignment of the pots and switches.
5. Once you feel good about everything, solderthemfromthetop2as the last step before wiring. This way
there is no stress on the solder joints from slight misalignments that do not t the drilled holes. You can
still take it out easily if the build needs to be debugged, but now the PCB is “custom-t” to that particular
enclosure.
6. Wire everything according to the wiring diagram on the last page.
1FortheLED: You can use a bezel if you’d like, but generally it’s easier just to drill the proper size of hole
and push the LED through so it ts snugly. If you solder it directly to the PCB, it’ll stay put even if the hole is
slightly too big. Make absolutely sure the LED is oriented correctly (the at side matches the silk screen) before
soldering, as it’ll be a pain to x later! After it’s soldered, clip off the excess length of the leads.
2Noteonsolderingthetoggleswitch(es): It will require a good amount of solder to ll the pads. Try to be as
quick as possible to avoid melting the lugs, and be prepared to feed a lot of solder as soon as the solder starts
to melt. I recommend waiting 20-30 seconds between soldering each lug to give it time to cool down.
“RPD”and“LEDR”resistors
The resistors marked “RPD” and “LEDR” are generally not original to the circuit and can be adjusted to
preference. “RPD” is the pulldown resistor to help tame true-bypass popping, while “LEDR” controls the
brightness of the LED. I generally use 2.2M for the pulldown resistor and 4.7k for the LED resistor.
Sockets
Since double-sided boards can be very frustrating to desolder, especially components with more than 2 leads,
it is recommended to use sockets for all transistors and ICs. It may save you a lot of headaches later on.

6KLON CENTAUR / REFRACTOR OVERDRIVE
Drilling&Placement
Print this page and have an adult cut out the drilling template below for you. Tape it to the enclosure to secure
it while drilling. Note that the holes are shown slightly smaller than they need to be, so drill out the holes as
shown and then step up until they are the correct size for the components.
Parts Used
• Switchcraft #111 enclosed jacks
• Kobiconn-style DC jack with internal nut
Hammond1590B
(bottom/inside view)

7KLON CENTAUR / REFRACTOR OVERDRIVE
AdditionalNotes&WiringDiagram
The wiring for this project is very non-standard since the circuit uses buffered bypass rather than true bypass.
Though it is most likely possible to make this circuit true bypass, that version is not supported or covered in this
build document. The original circuit was designed around the buffer, so I’d recommend trying that rst and only
attempt a true bypass version if you absolutely need to.
The wiring diagram makes use of star grounding principles where all of the grounds connect to a single
ground point (in this case the sleeve of the input jack). This is best practice to avoid added noise caused by
improper grounding. The sleeve of the output jack is unconnected.
If using a painted or powdercoated enclosure, makesurebothjackshavesolidcontactwithbare
aluminum for grounding purposes. You may need to sand off some of the paint or powdercoat on the inside in
order to make this happen.
I’ve tried to make the diagram big enough that it’s easy to read, but if you’re having trouble then try zooming
the PDF document. The diagram is in vector format so it will scale with the zoom.
Note the positions of R26 and R27, the 68k
resistors. These will get pretty tight, especially
the middle lug which has four leads crammed
into one eyelet. I’ve found that it helps to
make a loop with one of the resistor leads
in the center lug and use it for the wire. I
recommendusingtheRefractor Bypass
PCB instead of doing it as shown, but if you
you don’t, denitely use 1/8W resistors here
instead of 1/4W—they’re much easier to t!
R28 is a 100k resistor from output to ground.
You do not need to put it here, and in fact it
may be easier to run it from the output jack’s
lug to the star ground on the input jack. As
long as it’s connected to ground you’ll be ne.
A 3PDT footswitch is shown below with only
the outer two poles being used. You can use
a DPDT here as well—depending on the type
of switch, it may even allow a little more room
for the resistors. My only advice is to avoid the
Alpha “X-wing” style switches, as those are
reported to have reliability issues.
IN GND 1.1
+9V
1.3 2.1 2.3
PGND
SLEEVE
TIP
TIP
R26
R27
R28

8KLON CENTAUR / REFRACTOR OVERDRIVE
License / Usage
NodirectsupportisofferedforthesePCBsbeyondtheprovideddocumentation.It is assumed that you
have at least some experience building pedals before starting one of these. Replacements and refunds will not
be offered unless it can be shown that the circuit or documentation are in error. I have in good faith tested all of
these circuits. However, I have not necessarily tested every listed modication or variation. These are offered
only as suggestions based on the experience and opinions of others.
No bulk pricing or discounting is offered. No attribution is necessary, though a link back is always greatly
appreciated. The only usage restrictions are that (1)youcannotresellthePCBaspartofakit, and (2)you
cannot“goop”thecircuit,scratchoffthescreenprint,orotherwiseobfuscatethecircuittodisguiseits
source. (In other words: you don’t have to go out of your way to advertise that you use these PCBs, but please
don’t go out of your way to hide it. The guitar effects pedal industry needs more transparency, not less!)