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.

28 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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    Replies
    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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    Replies
    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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