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Topic: 70s DOD Electronic Phasor |
Liam Sullins
From:
Dayton, Ohio
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Posted 5 Feb 2021 12:56 pm |
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Hey all you electronic guys out there I have a few questions! I have m grandfathers old Big Box DOD Phasor from the 70s. He bought it new. There is almost no information on it online at all. Anyways, it's been to three techs and all of em cannot figure it out! Where can I go to get it fixed properly? My grandpa has been a guitar player since 57 and it was his most favorite pedal he had. I've worked on this thing a little, and I cannot even figure it out. I'll drop some pictures and a schematic the founder of DOD sent me, not sure if it's 100% accurate.
 
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66 Sho~Bud Fingertip |
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John Poston
From:
Albuquerque, NM, USA
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Posted 5 Feb 2021 1:02 pm
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| When I used to live in Chicago, I had pretty good luck taking old weird things to Deltronics. |
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Liam Sullins
From:
Dayton, Ohio
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Posted 5 Feb 2021 2:39 pm
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Those guys seem pretty expensive!
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66 Sho~Bud Fingertip |
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Jim Kennedy
From:
Brentwood California, USA
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Posted 7 Feb 2021 10:33 am
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It looks like the op amps have been replaced before. Not easiest thing to do. You really need to be good with a soldering iron to not damage the chips. I would suggest checking your voltages first. If good, change the chips. If that doesn't work you will probably need someone who is familiar with these, or someone competent enough to trace the signal.
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ShoBud Pro 1, 75 Tele, 85 Yamaha SA 2000, Fender Cybertwin, |
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Pete McAvity
From:
St. Louis, Missouri USA
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Posted 8 Feb 2021 6:53 am Pete's Pedals
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There's a guy here in St. Louis that revives old pedals, does mods, etc. I've seen a TON of things he's done on Facebook & have a Boss DD5 w/ his "analog mod" that I use for steel. If he hasn't had this very model in his hand at some point (probably has), I'm sure he'd be familiar w/ any old DOD idiosyncrasies. Really nice guy. Get in touch & ask him. Bet he'll set you right.
Petespedals.net
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Excel Superb D10, Sarno Black Box or Freeloader, Goodrich L120, Boss DD5, Baby Bloomer, 1965 Super Reverb chopped to a head, feeding a mystery PA cab w/ a K130.
They say "thats how it goes". I say "that ain't the way it stays!" |
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Scott Swartz
From:
St. Louis, MO
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Posted 9 Feb 2021 8:08 am
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Liam,
Ther could be lots of things causing the issue but there is one specific thing to look for on these.
This unit is a so called FET phaser, where the FETs conduct or not conduct to provide the phasing effect in response to the signal from the LFO. All 6 FETs must be reasonably matched and the correct type for the circuit for the phasing to work.
https://www.diystompboxes.com/smfforum/index.php?topic=50746.0
If some has changed these or the opamps it could be tricky to unwind.
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Scott Swartz
Steeltronics - Steel Guitar Pickups
www.steeltronics.com |
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George Biner
From:
Los Angeles, CA
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Posted 9 Feb 2021 3:45 pm
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It looks like the FETs are part of a all-pass RC filter circuits, of which there are 7 in cascade -- the filters will introduce phase shift. https://en.wikipedia.org/wiki/All-pass_filter
A couple things you can do:
1. check the Zener diode D3 to see what voltage it's setting up -- it's a 5.1V diode.
2. check the U2C circuit to make sure it is oscillating (creating the low frequency wave)
3. check to make sure that each op amp stage's inputs (+ & -) are roughly equal DC voltage to each other
4. make sure the op amps all have power and ground present
if it passes all that, then it's time to dig further and check more voltages and maybe look at signals on a scope
I usually work on amps (retired, part time), but if you can't find anybody to work on it, I can offer to help just out of historical interest. Or I could take a look at it myself. I am in Los Angeles.
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Guacamole Mafia - acoustic harmony duo
Electrical engineer / amp tech in West Los Angeles -- I fix Peaveys
"Now there is a snappy sounding instrument. That f****r really sings." - Jerry Garcia |
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ajm
From:
Los Angeles
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Posted 9 Feb 2021 7:00 pm
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Since no one has asked...............
What is it doing?
Or not doing?
And..........
Do you get the bypassed signal through it?
Switched in, do you get any guitar signal?
Do you get any effect "swooshing" noise?
Etc etc etc..........
What do you know about it's history?
Has anyone done anything to it? (You said that some techs have had a look at it.) |
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Liam Sullins
From:
Dayton, Ohio
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Posted 9 Feb 2021 7:50 pm
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| ajm wrote: |
Since no one has asked...............
What is it doing?
Or not doing?
And..........
Do you get the bypassed signal through it?
Switched in, do you get any guitar signal?
Do you get any effect "swooshing" noise?
Etc etc etc..........
What do you know about it's history?
Has anyone done anything to it? (You said that some techs have had a look at it.) |
It's not phasing at all, it acts as a small boost, almost nothing but a boost. I do get the bypassed signal, I do get guitar signal in both. No swooshing effect. I know my grandpa bought it new in 1978. Used it in the Bars around Dayton Ohio. He's still here at 78, plays guitar everyday! Yeah the techs really looked at it and tried almost nothing.
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66 Sho~Bud Fingertip |
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ajm
From:
Los Angeles
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Posted 10 Feb 2021 8:54 am
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OK, NOW we have more information.
You didn't say what your electronics skill set is.
Or, if you have an oscilloscope. (We'll assume no on this one.)
It looks like you have a soldering iron.
If you don't have a DMM, and do stuff like this occasionally, you should probably get one.
You don't need a top of the line Fluke.
Mine is a Sears that I got for between $20 and $40 (it's been a long time so I don't recall the exact price).
George Biner came up with a pretty good set of things to try.
One more thing to try: Make sure that the In/Out switch is working. It sounds like it is.
And I'll add one thing to George's list: You could try heating up and reflowing the solder pads on the board. I would stay away from the IC and FET pads/leads at first, since those items may be more easily damaged by heat.
Just off the cuff, totally spur of the moment......
It sounds like it's not oscillating, which will start "moving" the FETs to produce the phasing.
Either the oscillator is not working, or
maybe the bias to the FETs is messed up, or
one of the later op amp stages is dead and stopping the signal from getting through.
If you find out what it is please let us know. |
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