Interested in modding a Madbean Smoothie to sound more like a DOD Phasor 201

[Johnny Burrito]

Hi guys, for my first non-dirt build, I was thinking of building a simple two-stage phaser. Madbean has a board based on the MXR Phase 45 that I've ordered.

While shopping around, I found the DOD 201, which I think sounds superior to the MXR in basically every way. I found a schematic on Ampage and made myself a parts list, but there are a few differences (Madbean has one more resistor and two more capacitors listed on his build.) As the parts aren't numbered on the schematic I found, and I'm not sure how to number them, I'm a bit confused about how to proceed.)

Does anyone have any advice as to what values I could substitute without basically ruining everything? Should I just suck it up and build the stock phaser (which sounds very good in clips)

Madbean project and parts list:

http://www.madbeanpedals.com/projects/Smoothie/Smoothie_2015.pdf

DOD schematic:

http://www.ampage.org/schematics/dod201.pdf

Thank you so much!

[chuckd666]

There's no harm in just "giving it a go" I guess - try the substitutions and see how it works. They definitely appear (to my dumb head) to have a similar topology or whatever.

[Mark Hammer]

There is a current-limiting resistor on the output of the LFO, that sets the width of the sweep.  On the 201 it is 3M3 and on the Smoothie it is 3M9.  The smaller the value, the wider the sweep.  I'll note that this value was changed over Phase 90 issues and, in conjunction with changes to the amount of feedback used, contributes to why some folks prefer certain issues.

Between differences in sweep width, and the setting of the bias pot (which contributes to where the swept notch/es occur in the spectrum and the "character" of the phasing), people can find they like the one or the other.

But the fact of the matter is that, with the mere change of the resistor value, the two phasers are, and should sound, identical.  As such, I would say, build the Smoothie, but install a toggle that will let you switch between a value of 3M9 and 3M3 for that component.  One way is to install 3M9 and use the toggle to add a parallel resistor to achieve a combined parallel resistance of 3M3.  Alternatively, run a pair of wires from where that resistor would be installed on the board, and use a toggle to select between the values you like.  Again, keeping in mind that smaller/lower values = wider sweep, and narrower sweep is preferred for faster speeds.

Beyond that, you simply adjust the bias trimmer to situate the phasing in the part of the range you like.  One of the roles of the trimmer is to set the bias so that the JFETs actually respond to the LFO, but within a moderate range of its rotation it also sets the flavour of phasing.  It can be more swirly (notches higher up) or more gurgly (notches lower down). 

[reddesert]

The part numbers or lack of on the schematics don't matter. They are just to identify the parts. What you would need to do is match up the schematic topology and figure out which parts are different and if there are any extra connections that you need to make or break.

In this thread on talkbass, someone from Digitech posted a schematic that shows all the MXR vs DOD differences, and they are pretty small, so it should be possible: https://www.talkbass.com/threads/phasors-dod-201-or-mxr-phase-45-or.1116549/

[Johnny Burrito]

Thank you guys so much! The switch is a great idea.

[Mark Hammer]

You won't necessarily notice the difference between 3M3 and 3M9 right off if it's sweeping slowly, but if you set the speed for fast, and switch between the two width settings, you'll easily notice it.

[PRR]

> install 3M9 and use the toggle to add a parallel resistor to achieve a combined parallel resistance of 3M3]

3M9 with 22M parallel is essentially 3M3. Better than 1%, which is far better than we need.

(I had thought it would be an unlikely large value. But 22M also happens to be the highest value normally stocked in common resistors.)

An alternative is to wire 3M3 plus a 600K (620K) to get 3M9, then short the 600K to get the 3M3.