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, March 8, 2017

Carl Martin Plexi-Tone

This is probably the biggest Marshall-in-a-box pedal out there (footprint-wise anyway). Originals use a +/- 12v supply with a transformer internally. I modified the power section with a +/-18v charge pump and will run off a normal +9v power supply. This saves room so you can use a smaller enclosure and gives more headroom to the effect. It is a buffered effect, so the In/Out pads go directly to the jacks. All switches marked in the layout are the footswitches. It should fit fine in a 1590BB with top mounted jacks.




Edit March 9:
Had some question about how to wire the footswitches. Here's how I'd wire them:


The LED for the channel switch doesn't have to be bi-color, but in my mind it seems like a good thing utilize instead of have a normal LED being on for one channel and off for the other.

Edit Nov. 28, 2018:
Had 2 pads for the Drive footswitch mislabeled. Fixed now and good to go. Schematic for reference (note the pot lug numbering in the schematic does not follow the normal numbering convention used on this site).

50 comments:

  1. Can the LF347 be subbed with a TL series quad op-amp (TL064,TL074,TL084)?

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    1. I would think so, but I haven't compared the datasheets.

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    2. A TL074 has less power supply current requirement.... other than that they appear directly compatible.

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  2. Isn't the ac tone just a few component swaps? I'm sure I've seen a layout somewhere online that does both.

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  3. How should we wire up the LEDs and the DPDT footswitches? I suppose the positive lead from the LED itself should go to FSw5. But should the LED+ from the board go to FSw4 or FSw6? Thanks! I want to verify this in the next couple days.

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    1. the connection of the dpdt is here...
      http://www.taydakits.com/instructions/plexitone/pages/enclosure-and-wiring--6

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    2. You can do it that way, though this layout was designed to use the buffered bypass like the original (In/Out pads going to the In/Out jacks). I'll post an diagram of how I'd wire the switches.

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    3. It could help me with the wiring I did it exactly as indicated but it does not give me clean signal it only works when activating the drive the Chanel switch does not change the channel

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    4. hi
      i have the same problem … did you resolve It ??? i have 2 or 3 hours to find the problem but all is ok i dont understand

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    5. Did you solve the problem? I think i have the same

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  4. What a great project!
    Is much to ask some advice of what I have to avoid if I would like to feed directly with 18v or 9v?
    I have some not verified clue reading the schematic I found around the web..

    Thanks David!

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    1. The effect is designed to run with a bi-polar supply, so you have to use either a transformer like in the original, or the charge pump like I used in this layout. To run it without the charge pump would require some redesign of the circuit and a whole new layout.

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  5. Wow i just found this site googling around for some schematics. Awesome job!
    Is the schematic used for this Plexitone exactly the same as the original except the charge pump? Cos i'm looking for something as close as possible to the original one, and on other sites they applied some mods, like 4 clipping leds instead of 3 and other modifications.

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    1. Yes, this follows the original Plexitone aside from the power section. Early versions of the Plexitone seem to have had a few differences as shown in this schematic:

      http://4.bp.blogspot.com/-ier5Qk_vR-U/Tx1MsJ0sKoI/AAAAAAAAAro/1KKJZX2vyy4/s1600/Plexitone_rev3.gif

      So, not really mods as much as what Carl Martin originally used.

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  6. Hey guys! I already finished and it works very good! VERIFIED!
    Take notes:
    *I just jumpered the Drive Footswitch 1-2, and the 3 I leave empty (no connect)
    *I made True Bypass, as showed on the Tayda page.
    *I used TL074 for the Quad Op amp, it works fine. I must try with LF347.
    * For every diode in the Power Supply stage I used 1N4007.

    Greetings for Corrientes, Argentina!

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    1. Héctor.. gracias por tus consejos.
      Ivan de Mza :-)
      Conseguiste LT1054? tengo el LF374N, pero no consigo el otro.

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    2. Así es, lo compré en Axis. Aunque tampoco te hagas tanto drama, podes armar un doblador de voltaje con un LM555

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    3. Genial...lo voy a buscar ahí.
      Si, lo estuve pensando, mucho más accesible aparte.

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    4. I'm ever using TL074 too but LF347 for this fx is the best for me

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    5. Hey Héctor, if you are doing this True Bypass, you gotta remember it's an original buffered effect. So, i'd suggest you to increase the output resistor (the 22k one on the lug 2 of Level) to something like 220k. If you don't, your 12:00 volume will be WAY louder than the dry signal. Raising it to 220k, your 12:00 knob position is almost the same volume as the dry signal! (;

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    6. specify which resistor needs to be increased

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  7. Wait, can i use 16v Capacitors or should i use 25/50v cause of the 18v pump charge?

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    1. Definitely higher rated ones. I would recommend 50v caps as I've seen 25v ones blow on 18v supply.

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  8. Thanks for your answer! I was in doubt about the power supply. You said original uses 12V, but then a transformer to turn 12V to 18V, right?

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  9. Anyway, i'm out of 100uF's 50v atm, i'll get tomorrow by the morning. But i'm using 2 10uF 25v and 1 63v. I think i'll just buy everything new @ 50v just for security (:

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  10. Mine didnt work. Its squelling and whinning. The sound is good before entering tone pot, and lost there. And i think the crunch and gain pots wired backward also. Any comment guys?

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  11. Hi, can you help me please?
    I have no bypass sound, the bufered bypass does not act or the boost, can it be because I am using a MAX1044CP for the pump?
    The rest if it works well, it has good sound in drive and select and in this mode if the boost works perfectly
    I thank you in advance, greetings

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  12. Very nice sound!I realized this true-bypass mod, but i have a big problem of popping at engaging boost. There anyone can help me solve this? Do you have a dpdt connection diagramm? thank you

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    1. hello, did you solve boost pumping ?

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    2. no, unfortunately .. I don't want to risk damaging that .. at the moment, i'm boosting with an external pedal.

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  13. Hello evrybody,
    nobody have a link to buy the "LT1054"

    Please … cant find it

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  14. Hello evrybody,
    nobody have a link to buy the "LT1054"

    Please … cant find it

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    1. US $3.30 | 5 шт./лот LT1054 DIP-8
      https://s.click.aliexpress.com/e/cjfI8iQI

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  15. Sorry I'm not unkwnow I'M Francky !!

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  16. Hi very body !
    Please what kinds of DPDT are they ? Momentary or locked ?

    Thx
    Franck

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  17. :) ... thanks for your very fast answer..

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  18. How are the IN and OUT jacks connected?

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  19. Works great but for me all pot are reversed and a Strange thing i have no sound in bypass mode ! just work when i engage the drive !! it's not very clear but normaly in/out on pcb are in/out jack ?

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  20. Hello DAvid, what about the big pumping when boost swicht is engaged ?
    Any idea ? cant touch my money for that …. ;)

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    1. Did you try adding pulldown resistors?

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    2. no, because i dont know exactly where i have to put it . :)

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  21. I found this for boost switch popping problem: "The pop when switching in the boost is probably because unless you use a make before break switch there's a brief period when the connection is broken and the opamp has nothing in its feedback loop. I would rewire it so lug 1 of the boost pot connects to pin 8 of the opamp, and put the switch so it shorts out lugs 2 and 3 of the pot. That will switch the boost on and off without breaking the feedback loop."

    I tried it and it works! Popping problem disappeared!;)

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  22. I've just built this, great sound and nice job to put in a 1590BB, the stomp are quite close but still usable. There's a mistake I believe, the crunch, higain, Tone and boost are reversed. I've built twice, and verified this. In the following schematic the lug orientation is more clear (it's without drive fw). https://www.diystompboxes.com/smfforum/index.php?topic=111395.0
    Lug 2-3 should be shorted and connected to the neg input of the op amps (pin 2-6-9 in this layout), otherwise the controls act reverse.
    A solution without modifying the layout is mount the pots reversed, with the potz back against the solder side of pcb (back isolation needed, I use felt pad for chairs), changing the drill layout and jack layout, i did so. The Level pot orientation is correct, if all the other will be reversed is better use a solder lug potz or cut the through hole angled lugs and connect it with cables.

    Also boost popping issue solved, like suggested by Ian Rider, just need to short/bridge lug 2 and 3 of boost switch, with the potz correctly soldered (potz lug 1 to boost fw3 lug). The hard pop disappear and boost works great.
    Last, the boost pot is 500kB, not 50kB, but due to the excessive amount of db is better to try smaller potz, such as 250-100 kB, have enough volume.
    See this topic https://www.freestompboxes.org/viewtopic.php?f=7&t=1113&p=265933&hilit=carl+martin#p265933 for more info.
    About mods, I think i'll build also a simplified version, without boost and true bypass, to fit in a 1590BB vertical with 2 stomps (drive and channel). Thanks again David for all your job, it helps me to learn a lots about effects electronics.

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  23. Awesome pedal, I had one I bought based on the boneyard project I think, but I didn´t like it much, it sounded harsh and has too much low end in the hig gain channel.
    This one sounds just great.
    As Lorenzo said BOOST CRUNCH HI GAIN and TONE pot are reversed. I managed to change the wiring without installing the pot over the soldering. TI left the Tone pot just like that, reversed, I´d call bass and that´s it; does not bother me much.
    For the BOOST pot I used the 50k , havn´t tried a bigger value, I think its totally usable like that.
    I have a minor problem, when bypassed, or with only the boost activated, there´s some of the distortion passing through, at a verylow volume, but it´s there in the background, any ideas what could it be? also a get a bump when activated the drive.

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  24. by the way, are you sure thw gain pots is not wired backward? I think lug 2-3 should be joined together, not lug 1-2, is it?

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