Tag Archives: zvex sho

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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Building a Z.Vex SHO clone from scratch

In my previous post I had some great success building a very simple boost circuit, the Electroharmonix LPB-1. While learning all about that particular circuit I kept coming across discussion surrounding the Z.Vex SHO; mostly questions of tonal comparison. So I decided to build one of those too, and was greatly excited to find this thread, which spelled it all out for me in simple terms. Here’s the circuit in a simple schematic form (I made it in ExpressSCH (on a Linux box)), then a diagram with some options. And finally one with external components that you’d find on a typical pedal schematic:

My own SHO schematic, with bill-of-materials

My own SHO schematic, with bill-of-materials

ZVex SHO circuit

ZVex SHO “diagram”

Z.Vex SHO schematic

Z.Vex SHO schematic

As you can see, it’s very simple. So much so that a fair few forum members decried it as “too simple” and in fact “retarded”. But I admit to wanting to know how Z.Vex can sell one of these circuits in a pedal for more than $150.

ZVex SHO Updated - from Zach schematic-762360Layout

As with the LPB-1 I wanted to attempt a layout myself, and do it on veroboard. This genuinely was quick easy as this really is a simple circuit. My approach as to keep the relative positions of the components on the schematic. It practically wrote itself. It turns out my own layout was wrong, and non-obvious, so I’ve replaced it (on the left) with a decent layout from Mark at Guitar FX Layouts.

Soldering was simple, and went without drama. I was able to test the circuit within the hour. It worked! When I built it I didn’t have all the hardware, so as you can see from the picture, I used a trim-pot rather than a full-size potentiometer.

SHO clone on veroboard

SHO clone on veroboard


Then the fun part, the enclosure! I’d been wanting to do a decent custom enclosure for quite some time, but never got around to it. This time I decided to make the effort and do something special. First step was to take some good measurements of the enclosure. I had ordered the enclosure from Small Bear, and started by spraying it a lovely fire-engine-red, using Rustoleum paint. That stuff goes on really well and I had no issues with drips or runs.


Then it came to the decal. I’m not a great designer, or at least not one dripping with amazing ideas for these things, so I looked around at other pedal manufacturers for inspiration. In the end I went for a cheesy tribute to Nigel Tufnel in the spirit of his ‘one louder’ philosophy. With my measurements in hand I used Inkscape to create a set of guides so I would know where all the hardware was going to go on the face of the enclosure. Then I made a simple panel-oriented design that would hopefully go well with the red enclosure. I had deliberately chosen the decal paper that had a white backing to it, so I knew that the upper panel would appear white. I also knew that the gap between them would contain the on/off LED, so that was intentional.

Decal shown in Inkscape

Decal shown in Inkscape


Then it was a case of printing out the design on the water-slide inkjet paper (also purchased from Small Bear). Prior to printing it on the (expensive at $2 per sheet) paper, I did some trial runs on plain paper, just to check for size. You can see in the picture below how the ink looks nice and bold on the real paper compared to the plain paper.

Once printed, I then sprayed a reasonable coat of Rustoleum clear onto the inkjet waterside paper, to seal the ink without letting it run. I was surprised that even after drying for 12 hours the paper was still flexible. Next, I cut out each panel with small, sharp scissors, and made sure it all fit nicely. Finally I soaked each panel in water for about 30 seconds so that the decal was ready to slide off the backing paper. It was simple to apply the decal to the enclosure and get it lined up with the edge. It was most pleasing that my measurements were good, and also that the printer was accurate enough to obey my measurements. After smoothing out the decal with a bit of tissue I left it to dry overnight.

Decal ready to be applied

Decal ready to be applied


The next day I got things setup to shoot some clearcoats onto the enclosure. I planned on applying 5-6 coats, or until I got bored. This proved easy as long as I kept within the one hour time limit. If I waited longer than that I’d have to wait a further 23 hours to apply another coat.


Well, it’s all assembled, and it is fully functional, but I’m not magically happy with the finish. It looks great, but it’s really really soft. It dents easily, even with cloth and finger prints. Maybe this means it will hold up really well to abuse because it won’t chip? Time will tell.

I am however pleased with the LED lenses, which I got from Mouser. Fulltone use a fresnel-type lens on their pedals, which I liked immediately. And to be honest I’m tired of the standard ‘chrome plated cone’ type that I’ve been using up until now. These ones are made by VCC and available from Mouser…try part 593-3210C (tall, like on this booster) or 593-2800C (flatter)

The finished article

The finished article

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Building an Electro-harmonix LPB-1 from scratch

Thus far my effects building experience has all been limited to assembling pre-made boards and soldering the components. Along the way I’ve tried to study the schematics of the original effect, such as the Tubescreamer, but none of it was really sinking in. To remedy this I have decided to go back to basics and learn more about the principles of audio electronics from the bottom up. I have defined ‘the bottom’ as a guitar tone control.


My starting point then is some kind of boost circuit. Many great tones from the 60’s were achieved by driving the front end of a tube amp quite hard using something like the Rangemaster. Certainly Clapton was rumoured to have used one to brighten up his Les Paul in the Beano sessions.

So I looked for boost circuit schematics. One of the first ones I found was a really good single page explanation on how a boost works:

Beavis Audio – How It Workz

This was perfect as it explained it in dumb-musicians terms. For more detail (and for later consumption) I am reading this:

The Transistor Amplifier

Things of note:

  • Notice how similar a basic common-emitter transistor amp is to a common-cathode tube amplifier?
  • All boost circuits are basically the same. They might bias the transistor differently, or they might have extra components (for protection or good behaviour) but fundamentally a clean boost is a common-emitter amp.
  • I can probably build one of these quite quickly.

Which one to build first?

The LPB-1 schematic I started with

The LPB-1 schematic I started with

My choices were between the ZVEX Super hard-on (the SHO) or the Electro-harmonix LPB-1 as they have plenty of reputation in the industry and they’re incredibly simple devices. I decided on the LPB-1 for no apparent reason other than it featured in an article on Beavis Audio’s site which helped me greatly in knowing how to approach this. Here’s that article, go and read it if you’re interested in doing this.


As encouraged by the beavis article I downloaded DIY Layout Creator, and literally created my own veroboard layout using the LPB- 1 schematic. This was loads of fun and surprisingly simple. It forced me to know the schematic in great detail. I tried to keep in mind the how-it-workz article so I had a feel for why each component was there. Here’s the resulting layout:

Simon Allaway's First LPB-1 veroboard layout

Simon Allaway's First LPB-1 veroboard layout

As you can see, it is pretty simple and even though I haven’t done this in years I was able to assemble all the on-board components in about half an hour. I bet I can do it in half that time now as I kept screwing up.

I made a part substitution as I failed to order some 2N5088 transistors. I was under the impression I already had some, but didn’t. Instead I used a 2N4401.


So, once I’d wired up power, switching and signal jacks I plugged it into my amp to try it out, but all I got was hiss and distortion. So I unplugged and checked all the solder joints, reflowed a few and tried again. No different. I began to suspect the transistor as that was the only deviation from the schematic. I tried a 2N3904 this time, with much better results. I do get a boost (not as much as expected) and also lots more bass, which isn’t necessarily a good thing. At this point I was discouraged.

Time to re-evaluate. After some thought, I recalled the Beavis document, and some other discussions surrounding the SHO boost; check your transistor pin-outs. I had stupidly placed the transistors pins into the overboard without honestly checking that the collector, emitter, base pins were actually in the right place. I couldn’t tell what brand I was using, so I used a technique I found online here to derive the pins using the diode test function of my multimeter. And sure enough, I had it wired incorrectly.  Literally 180 degrees wrong.

Alright, so put the transistor in the right way around and it now works. There’s definitely lots of gain in this device, and lots of bottom end boost too. And its more than happy driving the hell out of a tube-amp.

The following pictures is before I trimmed the board down to its final size. You can also see I went for an on-board trimmer (as I didn’t have a 100k pot to hand). I may well leave it like this for when it gets integrated into my OD2.

My LPB-1 clone

My LPB-1 clone

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