JFET MKIIC+ with Fender Clean channel

TucsonSean

Active member
Hi Everyone,

So, this has been a long time in the making, like 15 plus years... and I'm still tweaking on it but I finally feel comfortable enough to share.

Some quick background info: I owned a Mesa MKIIC+ from 1994 through 2010 that I bought from a blues player for $350. Like a fool, I traded it for a Martin acoustic/electric that I still have. Since that time, I have always wanted to get another MKIIC+ but with the used prices going through the roof, I decided I would make my own instead. That version is still in the works with another variation happening sooner rather than later. Somewhere along the line, I decided I wanted a JFET version with a Fender clean channel (this is a separate board altogether with integrated switching). This is the culmination of all my tinkering over the last decade plus.

I play every week using an amp-less rig based around the HX Stomp XL for my effects and cab sims (see some of my previous posts for pics). I have been using AIAB pedals to get my amp sounds and they have been working quite well but I never was able to get that MKIIC+ articulation and drive from any other pedals, even the model in the HX Stomp. So I did what any crazy person with electrical engineer/machinist/guitarist skills would do. I made my own. I have been tweaking (still am) on this circuit to get the voicing just right but other than that, it definately gives that MKIIC+ articulation that all others have not achived. So without further ado, here are some pics. I will follow up with some sound clips in the next few days.

And yes, there is a stacked inductor based GEQ on board. Sliders are on a separate board with the rest of the circuitry shown in the pic. Currently it is wired as always on. I can change that if I need to later but so far, it has not been an issue.


-Sean
 

Attachments

  • Fen + Boogie MKIIC+ JFET Pedal Gutshot.jpg
    Fen + Boogie MKIIC+ JFET Pedal Gutshot.jpg
    363.4 KB · Views: 67
  • Fen + Boogie MKIIC+ JFET Pedal Top1.jpg
    Fen + Boogie MKIIC+ JFET Pedal Top1.jpg
    207 KB · Views: 66
  • Fen + Boogie MKIIC+ JFET Pedal Top2.jpg
    Fen + Boogie MKIIC+ JFET Pedal Top2.jpg
    280.2 KB · Views: 65
Last edited:
May I ask what JFETs you are using?
I have used the following jFETS: 2N5457, 2N5458, 2SK208-Y, 2SK208-O, and 2SK208-R.

What I noticed is that there was a difference with the "gain" of the circuit as well as the voicing. I say "gain" because what is actually changing is the R-drain value used for biasing the jFET and conversely, that changes the amplitude of the signal along with changing the frequency response due to its interaction with the circuitry that follows the jFET gain stage. I have settled on the following jFETs with reference to my schematic for the MKIIC+ section:
Q1, Q2, Q3, Q6: 2SK208-Y
Q4, Q5: 2N5457
Q19 (just a follower so any jFET would work): J202

The Fender clean section uses the following:
Q1: 2N5458
Q2: 2SK208-O
Q19: J210


These combinations gave me the best gain ranges for both sections and a voicing that is closer to that of the MKIIC+. I continue to tweak the different jFETS and the caps used for filtering throughout the circuit to fine-tune the voicing but so far, I settled on this comination for the time being.

-Sean
 
Last edited:
That's crazy. Good for you, that looks pretty slick!! I like the stamped lettering.
Thank you for the compliment. The lettering is actually milled into the front plate. I then filled in the letters with sharpie to get a contrast that you can see. It did end up looking like it was stamped though, which is cool.

-Sean
 
Impressive! What's your 24V solution?
I initially used a TC1044/LT1054 switched cap circuit to get the 24V supply. I changed to a Traco TEC 2-0915 to get enough current capability to power everything and the footprint was smaller than the switched cap circuit with all of the diodes and caps necessary.

-Sean
 
Back
Top