Converting 117 volt MXR pedals to 18 volt.

  • Thread starter Thread starter psychodave
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psychodave
psychodave
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Was tinkering today and converted two more pedals to modern wall wart power (typically 18volt) vs the 117v A/C. One big advantage doing this is no need to have large power strip and the other is to eliminate the dreaded A/C hum. I figured I’d post this to help anyone who wants to tinker as there isn’t much info out there and I’m sure techs will want to charge $50 to do it.

I’m including pics for each unit. There are a few way to do this, I chose to keep a diode in for polarity protection (only one I didn’t do this with is the limiter). I do lift the one end of the other diode as it is not needed. I heat shrunken it so it can be put back to stock. None of the circuit boards were cut or modified in any way. I even left in the transformers.

I still need to work out the 10 band EQ so I’ll update this thread later.

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First up is the stereo chorus. You can see that I lifted the two diodes and have the input voltage going into the diode that feeds the regulator. The negative goes to the center tap of the transformer. One big thing to note is the voltage regulator on the chorus drops it down to 12 volts.

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Next up is the Flanger. This one is done the same as the chorus. The voltage regulator drops the 18 volts down to 15 volts. Note that the diode where the input of the voltage comes in drops it down around 1/2 a volt (same as with the chorus).

1719806484318.jpeg


Next up is the limiter. I did this first, so I just looked at the design and tapped into the transformer leads to the voltage regulator. The regulator drops the voltage down to 15 volts. This was super easy as I only soldered two wires in. There is no polarity protection. I am too lazy to change it. 🤣

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Neat, thanks for posting this! I'll have to keep this in mind if I ever come across some of these.

Some nitpicks on the stereo chorus: you probably already saw them, but just in case, there are screenshots below of two spots with damaged wires.

Bottom right corner, looks like the insulation is cut and allowing wire strands to escape:
1719811000009.png


Bottom center, by the sticker, it looks like one or both of the wires got a bit melted and twisted, but I can't tell if any conductors are showing through:
1719811098746.png
 
7704A said:
Neat, thanks for posting this! I'll have to keep this in mind if I ever come across some of these.

Some nitpicks on the stereo chorus: you probably already saw them, but just in case, there are screenshots below of two spots with damaged wires.

Bottom right corner, looks like the insulation is cut and allowing wire strands to escape:
View attachment 321831

Bottom center, by the sticker, it looks like one or both of the wires got a bit melted and twisted, but I can't tell if any conductors are showing through:
View attachment 321834
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That is hot glue residue. I forgot to add glue to the jack nut to prevent it from moving over time, so I had to pull up the hot glue to lift the board. I didn’t bother taking it all off since I didn’t want to stress the floating diode during the picking off process. Thanks for the message though. I appreciate it.
 
psychodave said:
That is hot glue residue. I forgot to add glue to the jack nut to prevent it from moving over time, so I had to pull up the hot glue to lift the board. I didn’t bother taking it all off since I didn’t want to stress the floating diode during the picking off process. Thanks for the message though. I appreciate it.
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Ah, my bad. Carry on.
 
Psychodave nice work! Love those vintage MXR pedals. They sound very lush and rich even though there are some compromises with using them like the fixed ac chord and weight. Well you solved one of the issues, well done.
 
psychodave- I just purchased the same version (117.3001.103) mxr flanger and would like to do the same mod but I have two questions as it is not clear in the picture where the red and black wires actually attach to the board. I've made 2 notations on the attached pic that I'm hoping you can respond to . Thanks in advance. Best regards - Analogmind
Screen Shot 2024-09-01 at 8.19.31 PM.png
 
Do you have any ballpark estimate on the current draw or are these all so low that pretty much any 18vdc walwart will be enough?
 
SpiderWars said:
Do you have any ballpark estimate on the current draw or are these all so low that pretty much any 18vdc walwart will be enough?
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The current draw on the reissue flanger is listed as 39mA so it think any 100ma supply will be more than enough juice. The real task is finding a low noise supply. Many switch mode supplies are very noisy.
 
Analogmind said:
psychodave- I just purchased the same version (117.3001.103) mxr flanger and would like to do the same mod but I have two questions as it is not clear in the picture where the red and black wires actually attach to the board. I've made 2 notations on the attached pic that I'm hoping you can respond to . Thanks in advance. Best regards - Analogmind
View attachment 337470
Click to expand...
It’s easy. The red it as shown, lift the diode leg carefully and solder the hot wire to it (use a heat sink because diodes don’t like heat). The black goes to the center tap of the internal transformer (it’s literally the center of the three taps on the transformer). Next you need to lift the remaining diodes furthest leg and simply use heat shrink tubing to isolate it. You could also remove it, but if you ever want to put it back to stock, it will be a pain to source the parts.

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acceptance said:
+1 was going to ask!
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You could always just wire directly to the internal transformer, but you would need a 15v power supply. I’m not a fan of this because there is no diode protection like I have with the flanger and chorus. Plus if you use an 18v power supply you could fry something.

I still need to look at what they have going on inside. It might be as simple as wiring in a 15volt regulator and attaching a diode to add polarity protection. It sounds hard, but would be pretty simple to do. Again, I need to look at it and figure it out. 🤣
 
Analogmind said:
The current draw on the reissue flanger is listed as 39mA so it think any 100ma supply will be more than enough juice. The real task is finding a low noise supply. Many switch mode supplies are very noisy.
Click to expand...
All of the plug in MXR pedals should be the same. I was going to make a faux plug and use my meter to measure the draw, but laziness set in. 🤣
 
psychodave said:
It’s easy. The red it as shown, lift the diode leg carefully and solder the hot wire to it (use a heat sink because diodes don’t like heat). The black goes to the center tap of the internal transformer (it’s literally the center of the three taps on the transformer). Next you need to lift the remaining diodes furthest leg and simply use heat shrink tubing to isolate it. You could also remove it, but if you ever want to put it back to stock, it will be a pain to source the parts.

View attachment 337569
Click to expand...
Many thanks!
 
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