Shadow
A Simple-As-Can-Be Double Tracker
Overview
Just like how a shadow follows you around wherever you go, the Shadow is a simple-as-can-be double tracker. The time ranges from 14 ms up to about 50 ms, providing subtle thickening or some moderate slapback. Based on the ES56033, the onboard opamps are used for the input and output buffers with a MOSFET gain recovery stage at the end.
You may have noticed it has only one knob. That is because I used an MN-taper potentiometer, which is a dual potentiometer where one side is at maximum value until the mid point, at which point it begins to taper off linearly to zero for the remainder of the travel. The other side starts at zero and linearly increases to max at midpoint, at which point it remains at max through the remainder of the travel. This could easily be adapted to two separate controls for time and mix, but I have a bunch of 1590G enclosures doing nothing, so I thought it would be fun to design this to work with those enclosures. Of course, you could fit the same board in a 1590B with two offboard pots and it would be awesome, as well.
How It Works
After doing the TBR, I thought it would be cool to do something similar with the ES56033 as a double tracker. The similarities are the use of the onboard opamps for input/output buffers/mixing stages and a MOSFET gain recover stage.
There are a couple of things to point out here. The first is that the mix control is actually achieved by changing the delayed signal's resistance going into the mixing amplifier. Because I am using an MN pot, I didn't want things to go to zero, as you could just turn the effect off at that point. So resistances were chosen set the minimum and maximum level of the delayed signal.
The other thing to note is the use of a resistor and capacitor from the ES56033 output to the Fadj_2 pin. The goal here is introduce just a tiny bit of wobble or detune on the delayed signal to help thicken things up. Breadboard tests suggested it might do something, but in reality, I'm not sure. It's just two components, so it seemed like it was worth a try.
You will also notice that there is no feedback. As a double tracker, we want just a single repeat of everything that comes in. This also helps simplify the circuit by not requiring any controls for feedback.
Shadow Main Stage
As mentioned above, using the built-in opamps in the ES56033 doesn't give a lot of headroom, so I needed a boost stage after the delay stage. This MOSFET boost (a bog standard stage made famous by the SHO) is set with a bias resistor that gives a unity gain output from the circuit relative to bypassed. This is the same stage that I used for the TBR, as well.
Shadow Boost Stage
The power section is a super simple +9V and +5V power section. We've seen this in a lot of my builds. However, I am starting to implement better reverse polarity protection on new designs where D2 is a Schottky diode in series prior to any other power filtering, regulation, etc. This design was done a while ago and I just never changed it.
Shadow Power Section
That's it! It's as simple as we can possibly get and it works rather well. If you're looking for a simple, utilitarian double tracker, Shadow is your ticket. If you want something with a little more features and capability, I recommend the Stalker. If you want to build a Shadow for yourself, you can get build documents, board layout files, etc. here. Enjoy!