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.

Thursday, April 2, 2015

MXR Script Phase 90

The Script version of the Phase 90 is probably the holy grail of phase shifters and was the first effect released by MXR in 1973. It's probably most famous for helping create Eddie Van Halen's brown sound on the first 2 Van Halen albums. It was designed before dual op amps were really affordable, so it used 6 op amps, in addition to 4 JFETs and a PNP silicon transistor. I've wanted to do a layout for the Phase 90 for a while, but all those op amps intimidated me, so I held off till a request for it came in. I used the original MXR board as a starting point. I ended up with 2 jumpers, but original units had a 150k resistor spanning over half the board (going from the base of Q5 to pin 6 of IC5).


One of the weird things about this layout is how the JFETs are oriented. The drain and source pads are further apart than the source and gate pads because the ground fill has to go between those gaps, and this quirk is evident on the original board from MXR. I would imagine 2N5457s would work if you can't get ahold of the original 2N5952s, and a 2N3906 can be swapped for the 2N4125 if necessary. Also, if you're not a fan 741 chips, a TL061 or 071 should work fine.

40 comments:

  1. Hi, how is the LED wired up? Anode to PCB and Cathode to 3PDT?

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  2. Is speed 3 meant to be connected to the pad in the ground circuit above the 150k resistor at the top ofvthe pcb?

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    1. No, Speed 3 is left unconnected, or you can jumper it to Speed 2. The Speed pot just acts as a variable resistor.

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  3. Just to avoid mistakes... which kind of condenser shall I use for these projects ? Electrolytics are clearly indicated, my doubt is for the green and yellow ones.
    Cheers
    Alessandro

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    1. You mean capacitors? Green ones represent film and yellow ones represent ceramics. Use whatever you prefer.

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    2. Thanks, yes sorry, bad translation from Italian.. I mean capacitors!

      So, for the green ones, i can use these ?
      http://i.ebayimg.com/00/s/MTYwMFgxNjAw/z/vnoAAOxyXzxTIG~6/$_35.JPG

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  4. I didnt do it right i just get clean signal going to amp no swoosh.

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    1. Try to adjust the trimpot while playing.

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  5. That transistors I can replace the 2n5952 ?

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  6. Is the schematic available I'm trying to trace the audio path for it I know it's exactly the same more or less with the one using quad and dual op amps but I'd like to accurately plot it out I'm currently audio probing my non working build thank-you Billy

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    1. I believe I used this schematic when I laid it out.

      http://www.generalguitargadgets.com/pdf/ggg_p90_sc.pdf

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  7. hello i have made this layout and i found a mistake
    the source of the transistors is not connectec to the 5v1 zener supply as shown in the schematic
    the phaser was weak before that and now with a little jumper it became the real thing
    tnx for the layout but pls correct the mistake
    cheers from greece

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    1. Yep, I've been looking at the schematic. You're absolutely correct.

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    2. so which is the wrong part, did it and there is a volume drop, so how do i wired the diode?

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  8. Is this verified..? I also see the difference betwen layout & schematics. Zener 5v1 is not in schematics position..?

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  10. Do you know some layout for phase 90 with tl074?

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  11. Hi, in my city the capacitor of 15 uf is not commercial there are only 10 uf and 22 uf,
    which one should it fit better?

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    1. Try both. Or put 2, 33uF caps in series.

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    2. I did it with the 10uf capacitor and there is massive volume drop
      I also heard that there was a problem with the layout and that the 5.1v diode is not in the schematic or is incorrectly accommodated is it true?

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    3. The 5.1v diode issue was corrected. If you've got a volume drop, increase that cap value.

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    1. Hi, I see above that this design is not verified, someone has built it and can verify its function ????
      Greetings and thanks in advance

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  13. Hi, sorry for the previous post, I see above that this design is not verified, someone has built it and can verify its function ????
    Greetings and thanks in advance

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  15. There has got to be something wrong with my board. o-scope shows that i am phasing on the top two opamps and then 3 and 4 are dead. I will dig into it and report back.

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    1. Hooked up the function generator and o-scope, seems the top two opamps are phasing and the bottom two are not, so i guess i have more debugging ahead of me. Will report back.

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  16. I found a tiny fleck of solder between a trace and the flood ground (I really need to invest in an inspection microscope) and a possibly smoked 741.

    The v2 layout is verified.

    AT the moment i'm using an opa604 in a couple positions but no way should that matter. i have tl061 chips on the way.

    Might have to work up a layout for tl064 / lm348 + tl072 for a smaller build. It's neat to be faithful to the original, but I feel like a 125b is bigger than this effect really needs to be.

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    1. Glad you got it sorted out. If you shave down the sides a bit it shouldn't be hard to fit in a 1590B.

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    2. Maybe, but I already drilled holes in an orange 125b. *shrug*

      Anyway, this is incredibly frustrating, but I'm back to where I was earlier this week.

      After a successful test, I decided to see which of the two 741 chips was bad, since opa60x parts are pricy and gilded for this job.

      Both of the ones I'd replaced with opa604 were fine in the input buffer position.

      And then I discovered that the 3rd stage has heavily attenuated output again. And installed opa606 in all of those positions, and still have good signal output from 1 and 2 but not 3 or 4.

      But when I started, I had good, phased output. *shrug*

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  17. Would LM741CN be ok for this build?

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    1. And are 50VDC capacitors and 0,4W resistors enough? Could BF256B replace 2N5952 and 2N3906 replace 2N4125? I'm really sorry, but I'm green in electronics. I have some manual abilities, but no real knowledge. Always made stuff acording to the instructions without even knowing what is supposed to do what. I'd really appreciate if you could tell me if these could be used in these builds:
      Xotic EP Boost
      Could I use a BC338-25-DIO instead of a 2N5088 and BF256B instead of 2N5457?
      Little Angel V4
      Any common replacements for 7805?
      Hollis Ultra Flanger
      What TL072 should I use? Is BZX85C3V9-TAP ok instead of 1N4730?
      Wampler Faux Spring Reverb
      Are J105 and J106 ok instead of J201? Any common replacements for 7805? What TL071 and TL072 should I use?
      I would be the happiest man alive if you've answered

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    2. The LM741CN should be fine, and 50v caps and 1/4watt resistors are fine. For most of your other questions, you'll need to do some googling and compare datasheets. If the specs aren't too far from the originals I'd guess you're probably fine.
      The 7805 can also be a 78L05. It's a 5 volt regulator, so there's not going to be a ton of alternatives.
      Use whatever TL071/72 you can source.

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  18. I just did an TL072 based one, with geda. I not verified it yet, but if anyone is interested, just send me a note.

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  20. there is an mistake on the PCB... at the fourth UA741, fourth pin must connected with ground with this change is verified.

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