Author Topic: Upcycling an old MXR Analog Delay enclosure with a MadBeanPedals Setback board  (Read 602 times)


Completed my first build since college days 20 years ago!

Prompted by a retail experience. Bought a late 70s MXR Analog Delay from a local shop. A couple of days later I noticed a minor switching issue, which I probably could have fixed myself, but I thought “I just bought it, and their tech is surely more skilled than me.”


Phone call from them: “I think we’ve destroyed the pedal.” It seems their tech was probing around and shorted the 120V AC (it’s a plug-in pedal that includes a transformer to 12V DC) to the signal ground, in the process frying every IC on the board. Including the unobtainable Retcon R5101 delay chip. A “Charge Coupled Device” - subtly different from a BBD, in terms of implementation. Bummer!

I am fortunate enough to own a couple of other pedals that use the Retcon R5101, and by swapping them around, confirmed that it was indeed fried.

The shop were super cool about it. Gave me my money back, and the fried pedal for free.

So now I had this sweet vintage 70s enclosure, and no hope of obtaining another Retcon R5101, without cannibalizing another pedal. I saw some posts about retrofitting these pedals using PT2399-based circuits (like here

But that approach felt so… 2010’s. We have CoolAudio, Belling, and Xvive BBDs now! And the MadBeanPedals Setback promised about 300 ms and self-oscillation, so similar specs to the MXR that used to live in that enclosure.

So I ripped out the dead guts, set them aside in case someone makes a drop-in replacement for the R5101 (my money is on “not in my lifetime”), and built a Setback into this case. It rips!

Build notes:

  • It’s true bypass now which is cool

  • Found a panel-mount DC jack that perfectly covers the hole that held the AC cable strain relief. Don’t know why this makes me so happy
  • Didn’t have an easy way to mount this tight little board into this giant enclosure, so I found some vintage MXR-style crappy foam to wrap it in. It definitely gives the tone that extra push off the cliff. As they say, “the toan is in the foam”
  • During testing I found only the dry signal coming through. I thought I’d screwed up somewhere; the clock circuit looked good on my scope, but the audio input and output around the BBD didn’t sound right on the audio probe. It turned out both my compander and my MN3005 were sketchy because I got them from eBay. Noob mistake. Got replacements from Cabintech and now I’m stylin’. Very glad I socketed all ICs

Minor issue:

Noticing a slight volume drop with Mix at full dry

In any case, this was an awesome fun build.