1970s DOD Electronic Phasor needs some TLC

Discussion in 'Burnt Fingers DIY Effects' started by lljsullins, Jul 23, 2019.

  1. lljsullins

    lljsullins TDPRI Member

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    My grandfather loved this pedal for many many years, he bought it new in Dayton of 78 I think. He used it in all of the clubs, he always said you can get a Lonnie Mack sound and a "creamy" Waylon sound. So now on to how it broke, he was replacing the battery and put it in backward I guess and it shorted out something, I really want to get this fixed for him, he's 77 and still gigging. It runs on a regular 9 volt, but I would like to use it with a wall adaptor if I could. Does anyone have a schematic or diagram for it or does anyone have one? Is it worth rebuilding? It's very very rare.. .

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
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  2. zippofan

    zippofan Tele-Afflicted

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    Wow! That's an oldie, and here I thought my DOD 201 was old. Unfortunately I don't have a schematic for it, though hopefully someone here or on one of the stomp box forums does.

    I cheated with my ca. 1978 DOD by replacing the guts with a General Guitar Gadgets Phase 45 circuit, which is pretty identical to the 201 except true bypass. Good luck!
     
  3. lljsullins

    lljsullins TDPRI Member

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    Hopefully, someone will help me out! Thanks man!
     
  4. jimdkc

    jimdkc Friend of Leo's

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    Nice pedal... especially with the grandfather story!

    Kinda hard to tell from the photos, but are there any obviously burnt components from the reverse voltage?

    Looks like it's been repaired at least a couple of times... lifted solder pads... wire jumpers... etc...

    Do you want to retain as much originality as possible? Or just return it to functionality?

    If it were mine, I'd be tempted to make a new circuit board for it.

    Should be pretty easy to wire in a power jack that disconnects the battery power when you plug it in.
     
  5. jimdkc

    jimdkc Friend of Leo's

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    Also... did you disconnect the wiring, or did somebody else? Do you know how everything wires back up?
     
  6. lljsullins

    lljsullins TDPRI Member

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    I have seen some pictures online about it and have tried to wire it back to specs with an old buddy of mine, actually an old teacher who used to do this stuff back at NASA. He said we could create a new board. Only thing is this board is kinda falling apart, I had it wired once where I got a signal through the pedal but the knobs would do nothing.
     
  7. lljsullins

    lljsullins TDPRI Member

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    The resistor on the back of the board (10k I believe) was burnt I replaced it to the best of my ability, this was before he got a decent soldering iron.
     
  8. lljsullins

    lljsullins TDPRI Member

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    I could get a breadboard and start doing some things...
     
  9. jimdkc

    jimdkc Friend of Leo's

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    Can you identify the transistors?

    Looks like it's probably a 6-stage op amp phaser circuit. These are pretty common and there are a lot of similar ones out there. The 2 chips are fairly common quad op amps. Six of the 8 op amps make up the 6 phaser stages. One of the other 2 op amps probably is used as an LFO (low frequency oscillator)... and the other is probably a gain stage or an input or output buffer.

    The transistors are probably FETs that are driven by the LFO. These FETs act as voltage controlled resistors which change the frequency response of an RC network connected to each op amp stage. This causes a phase shift of the signal going through the op amp. Run a bunch of op amps in a row like this (6 in this case), and you get the swirly, shifting, ethereal effect we know as "phaser".
     
  10. DeanEVO_Dude

    DeanEVO_Dude TDPRI Member

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    The great thing about the "antique" circuits with discreet components like this is they are generally easier to repair. However, without a schematic or an extendensive knowledge of electronics engineering, there will be great difficulty In executing the repair.
    Old pedals are cool. Good luck, hope there is some info and assistance out there for you.
     
  11. lljsullins

    lljsullins TDPRI Member

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    Those six transistors I cannot read 5 out of the 6, but one says "singa" followed by some code.
     
  12. jimdkc

    jimdkc Friend of Leo's

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    They say "Singapore" on the top... Country of origin... anything readable on the front?
     
  13. jimdkc

    jimdkc Friend of Leo's

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    I would be surprised if the schematic of this circuit wasn't very similar to a MXR Phase 90... with a couple more stages added... Many MXR designs are re-worked DOD designs...

    Here's a very good analysis of the MXR Phase 90:

    https://www.electrosmash.com/mxr-phase90
     
  14. lljsullins

    lljsullins TDPRI Member

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    I'm stupid, forgive me ahaha. The code reads, "TIP5T-5460"
     
  15. jimdkc

    jimdkc Friend of Leo's

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    Don't feel bad, I'm sure I've made similar mistakes!

    Hmm... coming up blank on the JFETs... There is a 2N5460 that's a P-Channel JFET, but P-Channel devices aren't that common (although it is possible!). N-Channel JFETs are more likely. It might help to know the part number to know the pinout to figure out the circuit better, but that can be figured out by other means!
     
  16. radiocaster

    radiocaster Poster Extraordinaire

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    Check that diode if the battery was reversed. I once fried an effect by reversing the polarity of the adapter, unfortunately didn't keep the busted pedal when I moved way back in the day and I wish I did because it's not that cheap or easy to find anymore.
     
  17. ICTRock

    ICTRock Tele-Afflicted

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    if the electro caps are original, replace them
    socket the op amps
    socket the transistors
    wire it all back up
    this puts you in the best position to be able to test and swap parts out should those steps not remedy the issue.
     
  18. jimdkc

    jimdkc Friend of Leo's

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    Yeah. This is what I would do, too!
     
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