Saturday, 26 May 2018

Bixonic Expandora

An old circuit that was missing from the main page.
There was a layout by Harald Sabro in the forum section but this one should be easier to build.
I've taken the "Bite" control from Codtone's Expandra.
You can remove it by adding a link between Bite 3 and 2.
I've also added two more layouts, one with "Forbidden" mod and "Edge" pot as suggested by Dino and one for the Expandora II.






32 comments:

  1. You are a true hero. Thank you!!!

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  2. Can anyone recommend a good place to source the H11F3? I’ve got a bunch of early 70’s NS LM308H I’ll build it with!

    Also have anyone had any experience using the Harris CA3130’s or LM709H’s in this circuit before have they?

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    1. This comment has been removed by the author.

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    2. I think Small Bear has H11F3's

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    3. I think H11F1 should work too.

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    4. I built johnk's version of this and used a H11F1 and it sounded really good, so yes it does wwork.

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  3. Ok perfect thanks very much guys🙂

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  4. Would an h11g1 or an h11L1 work?

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  5. great circuit!!! I was searching this pedal for moth I have an stripborad from the fourm, this is more compact, I will build as soon as I can, the is the link http://guitar-fx-layouts.42897.x6.nabble.com/Bixonic-Expandora-td9152.html#a9188
    is not necesary 9.1 zenner?

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    1. That's just a protection diode.
      You could always add it (if you want) in parallel to the 100uF cap, next to the CLR resistor.
      The layout in the forum section was just a copy of this (no comment):
      http://www.sabrotone.com/?p=1215

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    2. thank alex, in a this days I will try to build, I was waiting the arreving of H11F1, you came with this compact layout your the one!

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  6. can you confirm before making holes, I count 43 not 42

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  7. Ok, so I was crazed by this circuit for a while last year.

    This vero is for the second, most popular version of the pedal.

    Check out this thread by Mr H and Mr P which pretty much says it all:

    https://www.diystompboxes.com/smfforum/index.php?PHPSESSID=8619ace8d25bcb58c4e921155885fe6c&topic=117018.20

    I tried to make the vero version from the ‘contributions’ page here last year, but it would not work, and sadly, I got dressed down for my soldering technique.

    I then tried a pcb from JMK. Even though the website said it would take a while, I was still biting my nails. The pcb was supposed to come with DIP switches but did not. I could not get it to go.

    I then tried Fuzz Dog in the UK which shipped me the stuff as fast domestic products. Also, the ‘Dogs photos and documenation are very pro looking and confidence inspiriing. I nailed the build.

    Then, my spouse gifted me a pristine version 2 of the original pedal.

    I am happy to say the Fuzz Dog pcb sounds identical however the pots were not in the same location.

    Here are my sugestions for this build:

    1) It’s treble forward, so, use humbuckers, and or curly cables. Strats and teles beware!

    2) Socket the Opto and make sure it’s not surface mount before you buy it…

    3) Use NTE 2370 for the transistor

    4) Use a footswich to switch into the “Forbidden’ gated mode.



    Cheers all!

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    1. Hi Highsmith, NTE 2370? I know 2379 and 2327 and both are mosfet, we got here is a PNP, I saw differents schematics with, 2N3703, 2N2206, 2N5087, 2N3906 (the most common).thanks

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    2. Hi there, NTE2370 is a PNP with built–In 4.7k bias resistors...watch the pin-out!

      Also, you can use H11F1 or H11F3...

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    3. Thanks for the info. Is version #3 the one with bass boost switch then? The 22n on the middle left seems the best place to mod.

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    4. yes, it appears version 3 has the bass option, as for the mods, hopefully someone smarter will chime in!

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    5. check Codtone's Expandora pdf, increasing 22nf to 470nf to give more bass. The file explain easy mods

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  8. Using a pair of OP07's. Should any mods be done to the 33p compensation caps? Same question for other op amps, or is those more of a "LM308 or nothing" thing?

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  9. A bit of history; There are four versions of the Expandora. V1 carried no gain switches. The circuit itself may fundamentally be very different too, but I haven't seen one up close yet to determine that. V2 was equipped with gain switches, but they were internal. V3 moved the gain switches to the exterior. These versions were all made by Bixonix in Japan. V4 was a reissue, built under licence buy Godlyke. The circuit was significantly altered where gain control is concerned, as well as switching to a more readily available opto. Gain was converted to a pot, doing away with the switches. Unfortunately, it also did away with the "Forbidden Mode", but no big deal in my book, I considered it a novelty setting. All in all, IMHO, the tone is just as attractive as the V2 and V3 units, although slightly different. The big plus that V4 has over the others is that it is much quieter. V2 and V3 are real hiss-meisters, which really put me off of them. V4 is great though. OK... the flashing VU LED's are a bit gimmicky, but you could always edit those out if so desired. The don't affect the circuit at all. The V4 schematic is here, if you wish to vero that one. I cleaned it up, and the values are all traced to my unit.
    https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=53103&g2_serialNumber=1

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    1. Thanks Dino!
      I would get rid of those flashing LEDs.
      Is the LTV-827 a good substitute for the Sharp optocoupler?

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    2. The LTV-827 seems to be a direct replacement for the PC-827. The LTV is made by Lite-On, while the PC is made by Sharp, but the datasheets state identical specs.

      On a slightly different note, I was noodling with an Expandora PCB last year (made by JMK if I recall correctly). I found a way to replace the gain switches with a pot, using a switch in series for the Forbidden mode. This opened up the circuit for a lot more texture, since with a pot all the "in between" settings can be had. Forbidden mode can be activated via footswitch. I don't have my notes in front of me at the moment, but I'll check tonight and post the setup I used.

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  10. Well, I realized tonight that the build actually ended up as a gift to a friend, who now resides in Australia. But... I did take some pictures, and managed to piece together what I did. The original schematic is courtesy of JMK, I merely replaced the DIP switches with a pot, which I named "EDGE". The Forbidden mode switch is shown in series, and can be a footswitch. You can add the CODTONE gain mod as well to adjust the amount of crazy you want in Forbidden mode (not shown on the schematic).

    https://i.imgur.com/zFz8j4h.jpg

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    1. Thanks again Dino.
      I've added a Forbidden/Edge pot version.
      I've removed the Bite pot cause I wasn't sure how it was going to interact.
      Regarding V.4, do you think is the first half of IC2 (from your schematic) that helps with the noise or could it be removed?

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    2. So Edge Pot is equal to Dip switches? is the same as on version 4 Drive pot?

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    3. @Alex: I think you mean IC1 (just before the LED network)? I would keep that, since it also connects to the non-invert input of IC3. There might be some interaction happening there, like a clean blend in, as well as providing signal for the comparator network. D6, Q2, IC4 and all the surrounding resistors, cap, and LED's can be deleted.

      @Claudio: Yes, Edge pot replaces switches. Instead of three fixed settings, you can dial in between settings. Yes, the same as the Drive pot in V4 (don't know why I didn't call it that on my mod?? :-P). The 240R resistor keeps the circuit out of "Forbidden" mode when the pot is as zero. Would be interesting to hear what would happen if we open this connection. ;-)

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    4. Amazing!! I was looking all tis info a year ago, Dino is Expandora's guru!, in JMK (2015) schem. is 330R not 240R.

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    5. I've meant IC2 in the bottom left corner here (Vb one):
      https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=53103&g2_serialNumber=1
      I'm not sure IC1 (just before the LED network)connects to IC3... I may be missing something.

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    6. @Claudio; Woah there Captain Happy!! Guru? No. I'm just a shmuck with a solder addiction. Seriously though, thanks for the kind words. As for the resistors, the DIP switches in the original switched between 560R (mid drive), 1.1K (hi drive), and around 371R (lo drive) when both switches closed (parallel resistance of the 560R and 1.1K). The way I set up the pot, at minimum the 1K and 330R create 248R, + 110R = 358R. This is lower than the original, so my mod can go a bit lower on the drive, without getting into the Forbidden territory. If you look at V4, they use a 240R, so it's all good there. As you dial up to maximum, the 330R gets dialed out as the pot wiper goes to shunt, and pegged you get 1.11K. Close enough to the original. Of course, bridging lugs 2 and 3 on the pot does shift the taper EVER so slightly, but it's not really noticeable.

      @Alex: Ohhh OK, gotcha. That would be IC2a. It's a voltage divider, and supplies IC3b, IC1b, and Q1 with 1/2vref. That's a keeper.

      IC1a connects to IC3b AND IC1b via R8 (100K), but looking at it more closely, this is all part of the vref network. I could see it being used as a buffer driver for the comparator network, but I'm not sure how it would affect the overall sound if it was removed. I would leave it in as well.

      Correction on the Expandora historical account; V3 was also made by Godlyke under licence. V1 and V2 were made by Bixonix. V3 also introduced the Guitar/Bass voicing switch.

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    7. Thanks Dino.
      I've added a layout.
      At the end I didn't keep IC1a.

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  11. Could the guitar/bass switch be the 1uf at the end, which is a 10uf in version "II"? It's the only capacitor in the signal path that looks different, besides the earlier high cut tone section. "II" is supposed to have more low than the previous version, with the third making it switchable guitar/bass.

    The filter cutoff just before the output is about 145Hz in the original. It's the 1uf with 1k1 resistor to ground. Version "II" raises it to 10uf, moving the cutoff down to 14Hz.

    I tried the bass mods on Codtone and Fuzzdog's layouts, but this is the only mod that made a difference to my ears. I had to use an octave pedal, so I'd like to hear a bassist test it out.

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