Tuesday, 6 May 2014

Madbean Boneyard

A project from Madbean which he no longer supplies PCBs for, which is based on the Carl Martin Plexitone.  The switch allows you to put either the Crunch or Hi-Gain pot in circuit and so effectively makes this a dual channel effect allowing you to select between two preset gain levels.  So only a SPDT stomp is required for the channel selection, but I have suggested a DPDT in the notes giving you a second pole for LED indication.  A good opportunity to use those bi-colour LEDs.

One note, this is a high gain distortion and a few people have noted a problem with oscillation in their build, so keep cable lengths short and consider using shielded cables for input and output wires.  I have added other suggestions to calm the oscillation people encountered with this pedal, so hopefully it won't be a problem, particularly when boxed.

Info about the original project:

The Boneyard is a highly modified Plexitone™, which is a high-gain distortion modeled after the classic 60's Marshall amps identified by their Plexiglass panels. The stock unit is powered by an onboard transformer running at +/- 12v and features volume, tone, two gain controls, a boost, and three footswitches for a wide variety of tonal options. To simplify the design, the Boneyard eliminates the transformer and instead uses a voltage inverter to power the effect at +/-9v. The Boneyard also eliminates the Boost function and converts the entire circuit to true-bypass.







And a version with the additional boost pot and switch



15 comments:

  1. Is there a difference on the ICL7660S chips. some are listed a scpa or some such. Can they interchanged?

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    1. The S is the important bit, any further suffix usually related to temperature rating, packing types and similar and so not so important to us. But the S means it includes the boost function so the oscillator runs at around 35-40khz which is important for us because without the boost it runs at a lower frequency in the audible range which can cause whining. The MAX1044 or TC1044 can also be used, but I personally tend to stay away from the MAX because they're expensive and only rated at 10V which is a bit too close to 9V for my liking.

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  2. Wow, quick reply. Great site. Many thanks for your amazing site.

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  3. Just a hint: I used the LM347 wit Sabro's layout and it did sound like crap: noisy, not defined, pure shit. After trying several quad opamps, the TLC274 sounds really incredible in this circuit, give it a try, you'll love it!

    J.

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    1. Cool, I've got loads of them and no LM347's! :o)
      Thanks for the tip buddy

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  4. Hi Mark,

    I built the original. Should anyone have problems with oscillation, the accepted solution on the MB forum is to put a buffer in series in front of the main board. I used your Pete Cornish layout (thanks for that!) and it sounds superb.

    I had no problems with the LM374 btw, I'll will give javiCAP's suggestion a whirl, however.

    Mark

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    1. I hope you'll like it :) By the way, in my build, the TLC reduced drastically the oscillation too but as you say, I adopted too tbe use of a buffer (or buffered pedal) when dealing with these high gain Marshall emulators, the result is amazing.

      If I'm not wrong, Brian admited that his design was poor and some components were placed together, when they should go in the most opposite sides of the board in order to avoid oscillation.

      J.

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    2. Yes I read that Javi, it was the 1K input resistor and the 2K to Sw2. I've done a layout for V2 as well, but to be honest with you I prefer this version with two gain pots. If I needed a buffer I'd just add a small one on a separate daughterboard and tuck it away somewhere in the box rather that have 5 extra rows on the main board.

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  5. Nice. Would you mind adding a layout without the voltage inverter - for those who already have inverter boards. It looks like the top 3 rows, and maybe 4 with a little tinkering, could be removed.

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    1. The problem is that other components are on the rows which I will need to accommodate elsewhere, so you may save a couple of rows, but I would have to add columns. Plus the pins on IC2 that require the supply are isolated with cuts so you'd still need at least one row higher up for you to make the +ve and -ve connections.

      I've got inverter boards made up, but I'd still much rather keep this integrated rather than relying on a separate board and patching it together. The ICs are about 20p each.

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  6. I built rev.2 of this pedal and as well as oscillation there was also popping problems , when the boost and crunch/high gain switches were engaged many of the ''fixes'' on the forum were a joke.using 3 led s for asymmetrical clipping was much better than 4,lower value pots also help with the oscillation and having a low pass filter cap. helped tame the highs .in the end I etched rev.1 pcb now I only have a slight pop when the high gain/crunh switch is engaged .I tried several Tl074/LM374s and found one was really bad for popping ???

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  7. Non boost version is golden....verified!....no problems with oscillation and its actually quite low noise....I used tlc274 and it sounds great

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    1. Excellent, thanks for verifying Mike

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  8. I just built this one, and the layout is fine. However, there are a few modifications I would suggest to make it sound better:

    (1) The 47K resistor to the right of the IC should really be 4.7K. Most schematics have it at 4.7K and it makes sense given that it precedes the inverting op amp stage for the tone. I originally used the 47K, but it was just too big and really affected the output level and tone control adversely.

    (2) Later versions of the original Plexitone had 3 LEDs as clippers rather than 4. I tried both and think it sounds better with 3. The layout makes it easy to switch to 3. Also, you may want to increase the minimum gain by upping the 2K resistor to something like 10K or more, as it seems too clean when the gain is roll back all the way.

    (3) I didn't include the high gain switch, opting for just a 100K pot to control the distortion. That seems like plenty to me, but you can increase it to 500K or 1M to taste. I also didn't use the boost switch.

    (4) I didn't encounter any squealing with my build. The effect actually seems rather quiet. I used a TL074 quad op amp chip rather than an LF347 - don't know if that helped with the noise or not.

    (5) This would be a nice overdrive/distortion if it weren't for the tone control. It's just too basic and it doesn't have a very pleasing range. I think it could be redesigned with perhaps a BMP tone circuit as there is plenty of signal, thanks to the +/-9V split power supply.

    Overall, this is good, not great, overdrive/distortion. If you want something with better tone control and a similar gain range, try the Marshall Shredmaster. However, what makes this interesting is the split supply and I think with a redesigned tone control it could rival the Shredmaster.

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  9. is there any info on how to add a 3 band eq (bass, miss, treble) like the old Vertex modded units?

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