Building a Z.Vex Box of Rock on vero-board


As most guitarists will admit, we’re always looking for a better sound. Some look for new and perhaps innovative sounds. Others, such as myself, want to sound like the players we admire. One classic tone I had never really toyed with is the sound one gets when you crank a JTM45 Marshall. In my opinion it is in my Top 5 sounds. The likes of Clapton, Hendrix, Young (Angus), and many others, started their careers with it. There’s no need for me to recount the origins of the circuit as that’s well documented.

So, you might ask “why not just buy a JTM45?”. Well, one in good condition from the 60’s might set you back 5-10 thousand <local currency units>. A new one, such as those available at Ceriatone go for about $1000….a ‘real’ Marshall? more like $1800.


One solution is to approximate the tone in a pedal. And yes, I’ve built way too many overdrive/distortion pedals already, but not one like this. The approach here is to cascade two or more gain stages to ape the design of the JTM45. This has been done may times in plenty of pedals, but a popular one is the Z.Vex Box of Rock. I first heard of this device when it was mentioned by Davy Knowles, who is an excellent blues guitarist. Searching briefly online and I found that the design of the pedal built upon the Super Hard On booster; one of which I built last year. This struck me as a great way to go as I understood that circuit.


ZVex Box of Rock schematic

ZVex Box of Rock schematic

Even if you can’t read schematics, you can probably see a pattern repeating itself. There are 4 BS170 transistors arranged as gain stages. They’re chained together and setup in such a way to simulate the characteristics of a tube amplifier. There’s a 4th one (at the bottom right of the schematic) which is the boost section. That will have its own footswitch, so it can be turned on when you “need a bit more”.

I went for a slightly different EQ section. As it stands the BoR just has a simple Muff-style filter. As in, a low-pass filter and a high-pass filter ‘mixed’ together by the tone knob. There’s a great variant that adds a ‘mid scoop’ control, as specified beautifully here by AMZ. It was simple enough that I decided to add it myself.


I got the veroboard layout from my usual place: Guitar FX Layouts. This guy always does a great job, and is always around to help or explain things. Fantastic!

ZVex Box of Rock - Complete

ZVex Box of Rock – Complete


The build in-progressThe build started off ok, but proved tricky. I quickly realised that I’d done something very wrong as it just sounded very odd. I remembered experiences from previous builds and went back with a fresh printout of the layout, and ticked off each cut, link and solder spot, and made sure the component values were correct. It turned out I had got some cuts in the wrong place. Literally as simple as that. I was careful to use sockets for the BS170s; this meant I was able to leave them out until the last minute so as to not expose them to static shock risk.


Spray and bake

Spray and bake – the black paint hardening under the lights

I went for some custom graphics again. As is typical I couldn’t really think of anything particularly innovative, and ended up calling it “Bed Rock”. This stands to mean two things: 1) This tone is the bed-rock of modern music 2) You can get that tone at low volumes so you can ‘rock’ in your ‘bedroom’. I know, cheesy.

Most of all I wanted to created something with a splash of colour. So many pedals look so very boring. I did the usual flow of finishing the enclosure with enamel based spray paint. This time it was a cheap can of black from Ace Hardware. I was actually going to try something new and bake the enclosure in a toaster oven, but I realised that I was already doing a kind of slow bake with my work-lights. And as I wasn’t in a hurry, I stuck to my usual routine.

For the decal itself, I used a combo of Photoshop and Illustrator to create an image. It was printed on my trusty HP Office ink-jet printer, onto white-backed decal paper; purchased from Small Bear Electronics.

One pleasant discovery was that you can get high-quality fonts for free at sites like FontSpace. Here’s the one I used for the main wording, All Ages.

Almost there!

Almost there!

The finished 'Bed Rock'

The finished ‘Bed Rock’


I think it came out well. With a Les Paul, it’s ridiculously easy to get that classic AC/DC rhythm tone with everything at 12 o’clock, and with the boost section kicked in you’ve got just that little bit more sustain available for a solo. Even a Strat sounds good. On mild gain settings it really makes single-coils come alive. I ought to do a recording of that too, I suppose. Here’s a demo file of the device.

My setup is the same as usual: Steinberger GM-7SA plugged into an AX84 tube amp, running clean into a 2×12 open-backed cab, with Celestion G12-75T speakers, miced by a Shure SM57 being recorded by an Apple Mac.

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7 thoughts on “Building a Z.Vex Box of Rock on vero-board

  1. Hi! Thanks for this nice post. I’ll Like to see the schematic of the proyect but with the mid control that you have incluied. Thanks again!

    • simonallaway says:

      Oddly enough the link I included in the post, for the article on Beavis Audio’s site, doesn’t work. So sorry about that.
      Try this one from AMZ, it’s the same thing:
      The tone stack on the BoR is a variant of the Big Muff, so the AMZ presence control mod is totally appropriate, and it’s very easy to do.

      Do you plan on modding your own BoR, Emir?

  2. jonathanunderwood says:

    Did you try wiring it to have the boost section before the overdrive section? I’m actually not sure which way round the original Zvex has things, but I thought it was boost, then distortion.

  3. Peter Thramkrongart says:

    Hi! It looks and sounds great

    What exactly did you alter to in circuit for the mid-boost? It’s really hard to decode just from the picture and the AMZ diagram uses different values.

    Any help will do thanks!

    • simonallaway says:

      After re-reading my article I suppose I should change it a little for clarity. The AMZ version 1 modification that I used is not really a mid-cut or boost. The Big Muff EQ has that characteristic all by itself, the AMZ mod puts all that mid-range back in so that if the tone knob is in the middle, the frequency response is flat. You definitely don’t get that with the stock Big Muff EQ. And you are right. The AMZ mod definitely does use different values. It isn’t simply an additional pot.

      I like the BoR specifically because it does not have the mid-range honk of something like my Tubescreamer or an OCD. It has a very big and rich sound with lots of bottom end, for that big Marshal stack sound. I rely on boosters to give me a bit ‘more’ for a solo. Comapred to other OD pedals the BoR sounds positively scooped.

  4. Peter Thramkrongart says:

    And what value is the pot then?

    btw sorry for reopening your post..

    • Walker says:

      For it to br “flat”, you’d want R15*C8 to equal R16*C7. Since you want to make R16 variable (that is what you want, right?) that’s what you solve for.

      47*22 = R16*10
      R16 = 103.4 KΩ
      To make that the center of a 50K pot, subtract 25K to get 78.4. In series with the section of the pot you’re using, use a 78.7K if you have E48 or better resistors. Use 75K if you have E24. Use 68K if you only have E12.

      Then your highpass section of the tone control can vary between 1/(78.7K*10nF) to 1/(133.7K*10nF), so 1270Hz to 74Hz. When the cutoff is above the lowpass value of 1/(47K*22n)=967Hz, there will be mid-cut. Below, mid boost.

      Use a different pot value to get a wider range, and follow the qbove technique to recalculate the standard resistor that goes in series (if you care about noon being flat.) You could choose for noon to be the stock response, instead of a flat response, by using 50K pot and 82-25=57K in series. You’ll have to use 56K. There isn’t much reason to use the available but more uncommon 56.2K or 57.6K or 56.9K when it’s in series with an imprecise pot.

      All of these calculations assume that the actual tone knob is infinite in resistance, and that the mids pot has perfect tolerance, and that the preceding stage has zero output impedance. So yeah, keep in mind that the actal behavior will be much more interesting, “less sterile” if you will, than what I’ve described. I may follow up on my own blog if I get bored today.

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