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Mod for Jetter Gain Stage Red, Red Shift & Red Square pedals

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  • Mod for Jetter Gain Stage Red, Red Shift & Red Square pedals

    Most reviews of the Jetter Gain Stage Red, Red Shift and Red Square pedals ignore the similarity to the Zendrive but it is there, as shown in the animated gif in the link below which alternates between the schematic of the Zendrive and the Gain Stage Red (the Red Shift and Red Square are basically the GSR but with extra modes.) The two schematics are posted in-line below the link.

    http://rs76.pbsrc.com/albums/j6/IvIa...h=480&fit=clip





    One fairly unusual feature common to both designs is the use of FETs in series with the assymetrical clipping diodes in the first op amp stage. One obvious difference is that the ZD has a 10k Voice control which the GSR replaces with two different resistors toggled by a Hard/Soft switch (which is omitted in the Red Shift and Red Square pedals which use the Hard setting.) There is also a minor difference in how the Tone control is wired up. With the PCB in my Red Square gooped up with black silicone I did not deal with either of those issues.

    The major issue that my mod addresses is that the Zendrive uses a 100pF ceramic cap in the feedback loop of the first op-amp stage, a cap which can be easily added to the outer terminals of the gain pot (it could also be soldered directly to the back of the PCB.)

    The Premier Guitar review gave the pedal a rating of 4.5 picks out of 5, saying "lacks definition with higher gain settings" under Cons, with several warnings within the text of the review to not set the gain too high. IMO adding the missing cap corrects that problem.

    The Verdict
    Pound for pound, the Red Square delivers one impressive smorgasbord of overdrive tones. It’s simple to use and easy to get clear rhythm and lead sounds, as long as you don’t push the gain to the extreme—but even then it brings some really incredible fuzzy overdrive that will please players who like creamier tones.
    Jetter Red Square Pedal Review

    Steve Ahola

    P.S. I did the mod to my Jetter Red Square pedal based on the attached schematics and I presume that it would work equally well with the Jetter Gain Stage Red and the Jetter Red Shift.

    A quick explanation of the models: the Gain Stage Red came first as part of a series of pedals that included the colors black, purple, blue and gold with different amounts of gain, distortion and tone. After that line of pedals was discontinued Brad Jetter came out with the Red Shift which includes a mini DPDT switch to toggle it between the Red and the Purple modes (the Purple mode emulates a tasty 50 watt Marshall.) The Red Square is a double pedal with a Helium low to medium gain very transparent OD wired up in series after the Red Shift circuit.

    With the PCB gooped up with black silicone I have idea how the Shift switch toggles the pedal into the Marshall mode for more gain and volume. My guess is that it switches out the FETs and assymetrical clipping diodes in the first stage feedback loop replacing them with whatever he used in the Gain Stage Purple pedal. There are 6 flying leads connected to the DPDT mini-toggle Shift switch.

    P.P.S. Although I refer to it as "my" mod the real credit goes to the people who reverse-engineered the GSR and created the animated GIF file documenting the similarities. And although the GSR is pretty much just a clone of the Zendrive I really like how Brad Jetter paired it with his Gain Stage Purple design to create the Red Shift, and then added his Helium circuit to the Red Shift to create the Red Square.

    BTW the added capacitor also smooths out the Marshall-ish "Purple" shift mode very nicely. A big improvement all around!




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    Last edited by Steve A.; 08-12-2016, 05:20 AM.
    The Blue Guitar
    www.blueguitar.org
    Some recordings:
    https://soundcloud.com/sssteeve/sets...e-blue-guitar/
    .

  • #2
    I do have a request from my friend Felix who would like a little more bass response around 150hz from his Zendrive pedal. Would changing the 100nf cap connected to the Voice pot affect the bass response? Or adding a resistor across the 10k Voice pot to lower its resistance? (I'm thinking that it might be like the pre-clip bass control in the Timmy pedal or do I have that wrong?)

    Thanks!

    Steve Ahola
    Last edited by Steve A.; 08-12-2016, 05:15 AM.
    The Blue Guitar
    www.blueguitar.org
    Some recordings:
    https://soundcloud.com/sssteeve/sets...e-blue-guitar/
    .

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