Tag Archives: transistor

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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OD2 – final assembly

The Clay Jones circuit, plus layout

The Clay Jones circuit, plus layout. Click to see the big version.

In my previous post I was discussing a new project. Another distortion pedal based on a clone of a Landgraff Dynamic Overdrive. The circuit was drawn out (possibly from looking at the Landgraff device) a few years ago by someone called Clay Jones. See the picture on the right here. This circuit was made available to me, as a beautiful pre-built PCB, by the guys over at DIY Effects. They have a great OD circuit (currently at revision 2, I believe) that I had used previously, but this one is using their “revision one” board.

The clipping switch

The clipping switch. 3 diodes on the left, 2 LEDs on the right.


The major difference between the revisions has to do with the clipping section of the circuit. Rev 2 has ample space for all kinds of options whereas Rev 1 is limited in terms of on board space. In this context that didn’t matter. I knew I wanted to mess around with clipping options and that meant it was easier to do that with a switch off the main board. I chose to try 3 diodes in one position and 2 LEDs in the other. The middle ‘off’ position is just the raw clipping of the circuit alone.

OD1 and OD2

OD1 refuses to make eye contact with the conspicuously naked OD2

Initial tests

I was able to wire up the board with power, pots and jacks very quickly, due to the great instructions, and had it plugged into my amp in no time at all. The goal here was to compare the clipping options and just make sure I wasn’t going down the wrong path. And I was not disappointed at all. The 3 diodes position has tons of gain, but in the lower positions sounds much like a cranked Marshall, but with a slightly softer attack. It doesn’t have the harsh bite of the typical Angus Young tone, which isn’t a bad thing. Then I switched it to the middle ‘off’ position, and it immediately got much louder, presumably because there aren’t any diodes clipping anything. Also for the same ‘drive’ position, the middle position had way less drive. Position 3, the 2 LED’s wasn’t a huge change from the middle position, but it softened the attack a little. Either way, I completely love this pedal!. So now to get it into a usable enclosure.

The enclosure

Measuring and drilling the enclosure holes

Measuring and drilling the enclosure holes

Based on a recommendation from DIY Effects I bought a box from Pedal Enclosures, specifically the YY type, in red hammer finish. All that remained was to drill some holes and start the assembly. This meant I had to think about how I wanted to lay things out inside the box as well as outside. But the basic dimensions of the box decided a lot of this for me. Here’s the basics:

  • The circuit requires Drive, Tone and Level pots.
  • I wanted to eventually add a switchable boost, so I need 2 foot switches. This will be like the “more” switch on Joe Satriani’s Vox distortion pedal.
  • I need a hole for my clipping switch.
  • LEDs for both the switches so I know where I am.
  • The usual 1/4′ jacks and power.
Making sure the parts fit as I go

Making sure the parts fit as I go

I covered the box with masking tape and found my old vernier calipers and a pen. With the box of components at hand, for dimensions, I was able to mark out the locations for the holes and punch them quite quickly. Then it was time for the drill press. After starting with an 1/8th ” bit for pilot holes, I layed into it with my El Cheapo “unibit” that I got from Harbor Freight Tools.


Belly up, with new parts

Belly up, with new parts

Now for the fun part! As I had done most of the assembly work with parts I had laying around, I did have to replace the pots with smaller ones (16mm rather than 24mm), and also I had to wire up the full bypass switch (and the LED). But all of that was just busy work. This time, I purchased extra components from Small Bear Electronics.

I was lucky enough to have wired it correctly first time (as with the original OD pedal) so within the hour I had it plugged into my amp and was jamming away.

I am very, very satisfied with this pedal. I can get a wide variety of usable tones from it very quickly. I do need to replace the drive pot with something else as the range of “no drive” to “loads of drive” all happens in the first few degrees. Not sure if this is simply the difference between linear and logarithmic taper. Anyway, here’s another photo.

(Almost) finished in it's shiny red box

(Almost) finished in it's shiny red box. The toggle switch is for the clipping options. Forward is the 3 diodes, backwards is the 2 LEDs.

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Building a TS Overdrive – from DIY Effects

Adhoc workstation

Here's the board with the instructions on the left. All the components were in neatly labelled baggies.

After my initial trepidation about which transistor to use (and with some patient guidance from Shawn at DIY Effects) I was ready to build the TS Overdrive guitar effects pedal. I’d read the build document many times as I learned from building my AX84 P1 eXtreme that you can never go over this stuff too much.


So step one was to start installing components and get soldering.  I had my less powerful 15W iron this time as it has a smaller tip and will be less likely to cook any components. I also brought out my very handy clip stand device, which helped me hold components as I assembled them. It also has a magnifying glass attached…very handy. I began with resistors, then moved onto capacitors (electrolytic first). Then it was the IC socket and transistors.

Standard TS 808 clipping diodes

Standard TS 808 clipping diodes. There are many options available here.

Clipping options and transistors

There are several options included with the board design that allow for different clipping methods. You can use the stock diodes, or MOSFETs or even LEDs. I went for the original method (which is regular diodes in position D1 and D3. D2 gets jumpered) because I wanted to hear what the original TS 808 circuit sounds like. These things are legend and I’d never had one in my arsenal before. As mentioned in the previous post, I had an issue getting hold of the prescribed MPSA18 transistors and in the end found an assortment of general purpose ones at Radio Shack. So this build used a pair of 2N3904 transistors.

Heat shrink on the pot terminals

Heat shrink on the pot terminals

The remainder of the build went very well. It really was a case of following the build notes, and carefully marking off each component (or indeed wire) as I assembled it. I knew that the board had to mount on top of the pots so I was careful to heat-shrink the wires coming off the pots themselves; I didn’t want any random wires to short out parts of the circuit.

Final assembly

This was tricky for a few reasons:

  • I used solid-core 20AWG wire. This mean that while the wires stayed where I put them, it also meant it was harder to orient the board. See next point.
  • Rats nest of wires

    Rats nest of wires, but it's physically sound and ready to go!

    The holes in the pre-drilled enclosure from Pedals Parts were such that I had to choose between having the tone pot right near the top of the pedal (which looked crap) or the tone pot near the stomp switch. I opted for the latter, but that meant the board had to be oriented the other way round, which then meant the wires I had already soldered in were about an inch too short. Coupled with them being sold core and the result was physically sound, but looked really messy.

Fire it up!

Almost done

Almost done. The view through the looking glass!

So all that remained was to solder in the LED, and put the knobs on. I’d failed to order a bezel for the LED, so right now it’s just kind of floating there. The knobs went on easily, and look good. After using a mix of Alpha and CTS pots on my amp build, I must say I like the action on these Alphas. The CTS pots I used on the amp were nylon shaft whereas these are solid aluminium which feels so much better.

Next step was to plug in a battery, screw on the back, and fire it up. And I must say it sounds excellent! I dialed my amp to be as clean as it gets…i.e. no pre-amp distortion/saturation, and dialed the TS OD to be a clean boost (no Distortion, Level just a bit louder). Harder to  dial in was the Tone. The documents are correct when they say that most of the range is at the end of the knob’s travel, so there’s a kind of sweet spot where you get some good “bite, but it’s not harsh. With the tone on maximum it can be a bit “fizzy”.


From here on I jammed for quite some time, punctuated by twiddling with the knobs on the pedal. It was hard to make it sound bad, to be honest. It’s definitely not a high gain machine, but I wasn’t expecting one (and that’s why I got the Boss DS-1). It’s a fantastic blues overdrive that works well with single-coils as well as humbuckers or P90s. If my SM57 wasn’t broken (might be the cable) I’d record some samples.

I plan to do a number of things from here:

  • Try different clipping options.
  • Try different transistors.
  • Re-finish the enclosure. This Hammerite stuff isn’t pretty. It’s been a week and it hasn’t dried properly, so I think I sprayed it on too thick. I’d probably go for green enamel as a nod to the original Ibanez TS 808 that started all this.
  • Record some samples.
  • Minor adjustments such as mount the pots lower so the knobs don’t stick up so much. Also, buy and install the bezel for the LED (which I might change to blue, just cuz).


An older version of the DIY Effects board, but with a different/better design.


A new enclosure, different clipping method, and a sound sample.

Final assembly of the TS OD

Final assembly of the TS OD from DIY Effects

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Tubescreamer transistor substitution

As part of the Tubscreamer clone project, I ordered parts from Mouser based on the list provided by the DIY Effects build documents.  They listed the MPSA18 as the transistor of choice, but at the time of my order Mouser had none, and I substituted a PN2222ATF. But, I realised much later that I didn’t have even the slightest clue as to whether this was a good thing.

From the Geofex site, there are some recommendations on choosing components:

6. Transistors: When in doubt, use a 2N5088. Or a 2N3904 – or a 2N4401 – or a BC549 – or… find cheap, available NPN and PNP devices that you can get easily and use them.

From a Tonepad customer on a forum:

Tonepad site indicates using a 2N3904. This is certainly acceptable, but you may have a little more oomph on the output with a 2N5089 or an MPSA18. 2N3904 are fine units for a lot of purposes, but in this case not so much. You’ll likely be more satisfied with MPSA18 or 2N5088/5089. Stock TS9s come with 2SC1815 transistors which tend to be higher hfe than 3904s, though not quite as high as the A18s or 508Xs.

So it’s all quite ambiguous as these all come across as “opinions” rather than an objective assessment. Time to learn something about transistors, as right now all I know is:

  • They’re all black plastic things on 3 legs
  • See previous point.

Now of course I know that tubes aren’t readily substitutable without knowing more about the application. You can’t blindly replace a 12AX7 with a 12AT7, even though they’re both 9-pin glass bottles, without knowing that the AX has a gain of 100 but the AT is more like 20. Searching around for answers led me to a document that has been plagiarised all over the inter-tubes:

Understanding the transistor data will definitely helps you to find the right and correct part number for substitution.

So, comparing the various parameter’s ratings as written in the “official” Fairchild PDF documents linked above, I see that the PN2222A is actually a pretty good fit for the MPSA18 in terms of VCEO, VCBO, IC etc. But when I look at HFE, the DC current gain, I see:

  • MPSA18  (VCE = 5.0 V, IC = 1.0 mA ) = Min 500
  • PN2222A (VCE = 10V, IC = 1.0mA) = Min 50

This seems to be off by an order of magnitude (even if you adjust for the current difference), almost like the 12AX7/12AT7 tube swap I hinted at before. So it seems the PN2222 is NOT a good fit. I’m going to ask a very knowledgeable friend about this to confirm my guesstimate.

Until I find a good answer, RadioShack has 2N3904 and 2N4401 transistors on their website, so I’m going to wander over to their store at lunchtime and buy a few of each.

UPDATE: RadioShack has little packets of 15 “assorted transistors” for about $2.50. Guess what’s in there? 2N4401, 2N2222 and 2N3904. So I bought a pack each of NPN and PNP. On the back of the pack it describes the NPN types as:

  • Typical HFE: 200
  • VCE 30V
  • IC 800mA
  • Power dissipation: 1.8W
  • …designed for high-speed, medium-power switching and general-purpose applications.

UPDATE AGAIN: Here’s the post with all the details of the final build.

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