This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Wednesday, September 2, 2015

Shin Ei OB-28 Octave Box

Here's a weird one for you–the Shin Ei Octave Box. It's apparently an all analog clean octave down effect. I'm not going to pretend to understand how it works, but there are a lot of transistors. Originals used 2SC644 and 2SC666 transistors, which I think were in the massive TO-3 package. I've drawn the layout for more modern replacements, BC547s and a BC557. Other transistors like the 2N3904/06 or 2N5088/87 would probably work as well. Socket and experiment with what you have on hand.



16 comments:

  1. Can you make a layout of the switches' wiring? It will be very useful

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    1. Check out this link: http://www.learningaboutelectronics.com/images/DPDT-toggle-switch-diagram.png

      There will be two different DPDT switches on this layout. SwA is one, SwB is the other.

      Follow the numbering as stated in that link. :)

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  2. Thanks you very much my friend, i have a question, the diode 1, 2 & 3 is a germanium, silicon,?

    Thanks :)

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    1. Hey Carlos! The schematic I found for a similar circuit is here - http://topopiccione.atspace.com/pjimages/ShinEiOctave.sch.jpg

      It calls for SH-1 diodes.

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    2. Also read this, it has some interesting info about matching Q9 and Q10:

      http://topopiccione.atspace.com/PJ15ShinEiOctave.html

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    3. SH-1 will probably be pretty hard to source. They were just silicon rectifier diodes though, so 1N4001s or similar will probably work fine.

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  3. Hi, I found bc547 and 557 with letters A, B and C (bc547A, bc557B and so on...). That defines different hfe. So does it matter to choose BCs with hfe close to original 2SCs or with same letters?

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    1. Those letters refer to the Hfe ranges. A is lower gain than B, B lower than C. You'll have to compare datasheets to find which is the best replacement. But I would guess B or C will work fine.

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  4. Hi again, is it right wiring? https://drive.google.com/file/d/0B-yOZ9M95dxrV1ZkTnRYRXRsZTA/view?usp=sharing

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    1. It just doesn't work wiring like that, and i have no idea, what is wrong

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    2. It looks like you've got it right. Here's the original schematic I laid this out from.

      http://www.tremolo.pl/Efekty/Octaver/Octave%20Box.gif

      Have you tried using an audio probe on it?

      http://www.diystompboxes.com/pedals/debug.html

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  5. Ok, i found one my idiot mistake - I soldered the 100n capacitor intead of 2,2k resistor.
    After replacement bypass mode started to work, but when i turn on the switch A, istead of notes i hear only indistinct clicks, swB just increses hum a little and alone makes even no clicks, how with swA; turning swB off to bypass (when only B turned on) makes a not quiet click.
    Checking the cucuit with audio probe (main effect part), the blue point and all the signal way before produces any kind of fuzz, but then, after 100k resistor (red point and line), isntead of notes are heard clicks like when swA is on.
    Also capasitors marked yellou are 6,8uf, but your layout has them 6,8nf - is it a mistake?
    https://drive.google.com/file/d/0B-yOZ9M95dxrSzB1eFMydmlkNWM/view?usp=sharing

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    1. That would probably be a mistake on my part. Try replacing those caps and see if it fires up.

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    2. I found another schematic that has all those 6.8 caps as uF, not nF. So go ahead and try replacing 3 6.8nF caps in the layout with 6.8uF caps.

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  6. Replaced 6.8 caps with sockets, tried different combinations - even no clicks became heard, only q1's and q6's collectors give a voice. Most schematics, including factory, have 6,8s all in nF. I have even no idea, what's wrong...

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