Aion Electronics Refractor/Klon-Centaur

[Ekimneets]

A. Made with: 
   01.   Xicon resistors 1/4 watt, 1% tolerance Metal Film resistors.

   02.    Wima Film capacitors 5% Tolerance (10%where 5% was not
              available). Where no Wima capacitor was available for a
              particular value,  either TDK/EPCOS film capacitors or Kemet Film
              capacitors were used.

   03.   Nichicon fine gold/Muse electrolytic capacitors. USW series LP
              7mm.

   04.   Kemet Multilayer Ceramic Capacitors 5% tolerance. Rated Class
                     1 (C0G).

   05.    Diodes: The exact Germanium clipping diode that was used in the
              original Centaur is unknown. Some sonic testing was done and
              Russian D9E diodes were thought to be an exact sonic match. What
              we know for sure is that the diodes in question had a forward
              voltage of 0.35v. To that end, 200 Russian D9E diodes were sourced
              from Bulgaria. Each was hand tested. All 200 of them clustered
              right around (+/- 0.04v) 0.25v. I made the decision to try and get
              closer to the value that we were sure of, the 0.35v. Kevin from
              Aion Electronics has mentioned having luck with 1n270 germanium
              diodes from Tayda electronics. 100 were sourced and tested. The
              forward voltage varied a great deal. ~16 were very close or an
              exact match to the 0.35v value. ~20 were, "Hot Loads" with a value
              greater than 0.40v. For this production run of 12 pedals the
              values were in-between 0.342v and 0.372v. D9B, D9K, 1n914 and
      1n60 were also tested in significant quantities.

   06.   Alpha 16mm potentiometers were used.

   07.    Pot covers from Small Bear were used to, prevent shorts in-
              between the back of the pots and the PCB.

   08.    Gold-plated IC sockets from Mouser were used.

   09.   IC's: TL072 are made by Texas Instruments. TC1044scpa are
      sourced from Microchip.

   10.    Red LED footswitches are sourced from Amplified parts.com.

   11.    Guitar jacks are from switchcraft.

   12.   DC power jacks are from Kobiconn.







Modifications:

   1. c14 is changed to 6n8 to boost the treble. Many said the original,
               pedal was somewhat dark. This addresses that.

   2. As for the germanium diodes, see above.

   3.  The original centaur used a linear potentiometer as its output
         control. Most people seem to favor a logarithmic taper for that
                 particular stage. Being as that the human ear hears or rather
                 appreciates sound on the logarithmic scale, that seems to make
                 sense. Therefore I am changing this as well, to a 10kA.


QC:
   1. Resistors and capacitors: Each component subjected to physical
       inspection to ensure Good condition and to ensure value needed/picked
       were a match.  This was verified using a HHMM (Handheld multi-Meter,
       a Fluke 17B+).
             
   2.  Solder joints: Each solder joint was individually inspected
        underneath a digital microscope and re-flowed if necessary.      

[gordo]

Nicely done!  I wouldn't have the patience to go to this level of detail but I applaud you for being thorough.  I like the finished inside of the enclosure and the cool detail of magnets for screws.  When mine look like that it means I've snapped the head off the screws 

[Ekimneets]

Thanks. I really like those  anodized aluminum enclosures except they're over 20 bucks a pop. I don't like that. There are also a lot more difficult to drill through as they are much harder than standard enclosures.  As for detail, I worked in neurosurgery for many years and that's just part and parcel of the game.

-Mike

[alanp]

Wow. I'm impressed by the thought behind this. My approach is generally, "close enough for rock and roll!"

[Ekimneets]

You could describe me in lots of ways. Belt and suspenders or thorough would be nice. To say I'm an*l would be closer to the truth. Still it works for some things.

-Mike

[JackSkellington]

I like to work with all these details, always.

I'm planning to build the Klon Centaur, too.
I compared some schematics, with so many options and possible mods, even if I probably settle with the closest original schematic.

[sonnyboy27]

Very cool! Any particular reason you didn't add the resistors on the switch board?

[Ekimneets]

Sonnyboy,

Just unreasoning fear. This was the first time I had ever used the Refractor bypass board and also the first time I've used one of those new LED footswitches. I just was unsure how tt would all interact. Thinking ahead for troubleshooting, I thought it would be easier to put them in, rather than take them out.

Everything works, so now I have to decide if I should put them in.

This is why I say I'm a cook and not a chef. I don't yet fully understand why everything is done the way it's done and so I introduce a little VooDoo into the system.

-Mike

[Ekimneets]

So what do you think SonnyBoy27, Any reason to not put those three resistors in?

-Mike

[sonnyboy27]

There's really no reason not to put them in. I believe it's just part of the switching setup. They shouldn't have a big impact on tone. They aren't in the schematic in the documentation though. From looking elsewhere it looks like they have something to do with the output section (probably impedance or something with preventing switch popping, total guess there). If it's working and you like the tone though then I'd leave it as is.

Edit: I checked Coda's breakdown of the circuit and feel slightly justified. He also says he has no idea what those resistors are for.

[Ekimneets]

I assumed they were part of the buffer system/wiring. I'm going to put them in and see if the tone changes. I'll post later.

-Mike

[Ekimneets]

Well, uh.

Maybe my minds playing tricks on me but the sound is not only noticeably louder, but brighter as well.

Remind me not to think.

-Mike

[stringsthings]

   Gold-plated IC sockets from Mouser

Excellent.



Suggestion for build description:  Make/Model of soldering iron/station ... details of solder used for builds  ( i.e.  63/37,  60/40, diameter, ... )

[Ekimneets]

Hakko-FX888D (Love)
Solder:0.7mm 60/40

[midwayfair]

Nice looking build.

But ...

   05.    Diodes: The exact Germanium clipping diode that was used in the
              original Centaur is unknown. Some sonic testing was done and
              Russian D9E diodes were thought to be an exact sonic match. What
              we know for sure is that the diodes in question had a forward
              voltage of 0.35v. To that end, 200 Russian D9E diodes were sourced
              from Bulgaria. Each was hand tested. All 200 of them clustered
              right around (+/- 0.04v) 0.25v. I made the decision to try and get
              closer to the value that we were sure of, the 0.35v. Kevin from
              Aion Electronics has mentioned having luck with 1n270 germanium
              diodes from Tayda electronics. 100 were sourced and tested. The
              forward voltage varied a great deal. ~16 were very close or an
              exact match to the 0.35v value. ~20 were, "Hot Loads" with a value
              greater than 0.40v. For this production run of 12 pedals the
              values were in-between 0.342v and 0.372v. D9B, D9K, 1n914 and
      1n60 were also tested in significant quantities.

People still think this? Or more to the point: Aion is still claiming this in the build doc?

Bill F said that they were 1N34A. He put it in a post on TGP for everyone to see probably 5-6 years ago now. He said he bought out all of a particular manufacture he could find of them. Notwithstanding that any two different multimeters are going to give you two different forward voltage measurements for the same diode (so you can't usually use anyone else's numbers), 1N34A are also the only Ge diode that typically measures 0.35V.

The only people to ever claim that they were D9E were people who misunderstood what BYOC meant when they wrote that the D9E they used in the kit (which, let's be honest, just happened to be some of the cheapest germanium diodes you could buy at the time) were the closest to their reference model. The original diodes had black stripes, which none of the Soviet diodes had, and D9E had a blue stripe, so there was zero chance of them being D9E. Also, it's exceptionally unlikely that anyone was using Soviet surplus diodes in the early 90s, for any number of reasons.

Also, re the C14 mod, that mod actually lowers the frequency affected by the treble control. Aion's a little unclear when he says the treble is "a little thin" (I'm, not really sure what that's supposed to me ...). In other words, if the pedal were too dark, increasing the size of that capacitor is going to make it darker.

Here's how that control works:

When the pot is clockwise, C14 forms a high-pass filter with R22 (the 100K). Low frequencies are blocked by R22 and high frequencies are allowed to pass.

As the pot travels counterclockwise, the capacitor begins to bypass the feedback loop gain in the last op amp stage. Without the treble control, that stage is unity gain: R22 and R24 are the same value, which in an inverting op amp stage gives you 1x gain. However, R23 and the tone pot have a resistance much lower than 100K, so along with C14 (which is in series with them), they allow frequencies above a certain point to ignore that 100K resistor. The result is that those frequencies now get much less gain, because they divide with R22, the 100K resistor.

There are some ways to brighten up the pedal, but increasing the size of that capacitor doesn't do it. I suspect the build document is meant to communicate that people think the pedal as a whole has too much treble compared with the midrange and lower frequencies, so lowering the frequency of the "treble" control gives the sound more midrange.

The resistors on the switch allow a small amount of the buffered signal to appear in the final sound regardless of where the volume control is set. Looking at a schematic that actually includes them would be helpful: http://madbeanpedals.com/projects/Sunking/Sunking2015.pdf