Electro-Harmonix Small Stone Mods

This project has been “in the works” for a while. I’ve had the pedal working for sometime but finally got around making the modifications to make it a modern pedal.

EH Small Stone with working LED indicator

Let’s start with a bit of backstory: Last summer, my wife and I were helping to clean out my late father-in-laws tool shed. He had a lot of stuff and a lot of that stuff was entirely random. One such item was a late 70’s Electo-Harmonix Small Stone phase shifter. It was in decent shape, but upon opening it, the 9v battery corroded and ruined the battery snap. So it was unusable as-is. There’s not a definitive way to date it, but the pot is labeled 1377825, which means it was manufactured the week of June 19th (25th week) of 1978 by CTS (manufacturer’s code 137). So the pedal was likely build and sold in late 1978 or 1979.

EH Issue J board: the red (9v for LED), gray (ground), green (signal in) and yellow (signal out) wires were ones added as part of this mod

The Small Stone is the other phaser sound from the late 70’s, where as the MXR Phase 90 is the one that Eddie Van Halen made famous (I have some theories on why that might have been, too.). That being said, it’s a great sounding phaser. I’m not a fan of the color switch on, personally1. But with the switch off, the effect has got a rich, space-y sound. This particular pedal just needed a bit of love.

The first thing was to put in a new battery snap to power the pedal. This pedal had a 1/8″ audio jack-style power jack. There are adapters for using this with a modern, Boss-style (2.1 mm barrel) DC power plug. However, it was a pretty simple operation to just drill out the case a bit larger and install a modern power jack. That got the pedal working again and how it stayed for about a year. And it sounded great.

Well, except for one issue and it’s why I think this pedal was never nearly as popular as the MXR or, for that matter, many of EH’s other pedals such as the Big Muff π. That is there is a serious volume drop when the effect is on. Imagine Eddie Van Halen turning the effect on for the drop-C# chug in “Unchained” and then back off for the chord progression. The riff would be ruined! 2. So I really wanted to fix that. Fortunately, 40+ years of history with this design and folks have figured out ways to address the issue. There are two resistor values that can be changed that dramatically improve the volume drop. I swapped out R11 and R42 and a quick test (outside of the case) saw the issue improve dramatically.

Mods completed: 1) Boss-style AC jack, 2) LED indicator, 3) resistors swapped for volume drop (blue resistors), and 4) true-bypass switch wiring

The bypassing mechanism on this pedal was fairly transparent. I personally can’t tell much of a difference when it’s in my signal chain or not. However, I did decide to make it a true bypass pedal along with the other mod, mainly just to add an indicator LED. Though I’m not a serious guitar player and never actually play live (or record), I do like having indicator lights on effects. If nothing else, it just reminds me to turn them all off when I’m done playing for a bit as a break during work hours! The updated switch, even just a cheaper “Taiwan blue” is still a lot less of a “ka-chunk!” than the old switch, too.

The last step was to drill out the hole for the LED bezel. Drilling steel is a bit harder than aluminum. I used a step bit as usual, but cutting fluid is a must in this case. Unfortunately, a couple of steel shavings scratched rings around the opening as I was drilling. I can probably buff them out, but a simple piece of painters tape would have protected the surface when drilling (and I usually think of that when it’s a powder-coated enclosure!). I boxed up the effect, plugged it in, and SQUEAL-EEE-OOO-EEAAA! Turns out, the output jack can rotate just a bit and short out on the color switch connectors. A small piece of black electrical tape fixed that, though.

Black electrical tape over the color switch connectors to prevent it from shorting on the output jack

Reverb has these vintage v7 Small Stone pedals going from between about $150 to $200, depending on their condition (they retailed for around $80 back in the 70’s). Even non-functioning, this one could have sold for $75-$100 (which would have easily covered the cost of a modern “Nano” re-issue model). So did I reduce its value? Maybe. Maybe not. There are some modded Small Stones also sold on Reverb going for even more. Many of those have additional controls added or the ability to attach expression pedals or other more significant modifications.

However, none of that is really the point for me. I think it’s really cool that this particular one belonged to someone in Angela’s family (most likely her late uncle, John, who played guitar some). I think of all the effects in my collection, this would be one I’d never really want to part with anyway. It’s got some real history; used by people I knew. And it’s been fun to take it and make it hopefully even better than before. It sounds great and though it may not have been the phaser I would have bought otherwise, it’s even better to me.

With all apologies to EVH, my incredibly rough take on the intro riff to “Unchained”

Some notes on that demo: first of all, it’s just recorded from my iPhone X on a tripod (as if the leg wasn’t the giveaway). The iPhone attempts to level out sound, so trying to show that the volume doesn’t drop when the pedal is engaged in this recording isn’t too useful. Next, even though you can clearly hear the switch clicking, it’s truly just because the amp volume is relatively low. There’s no pop through the amp. Lastly, I’m barely passable at playing this riff and trying to coordinate the pedal on-and-off with it was a particularly challenge for me.

  1. The color switch seems to add second layer of phasing at a slower rate than the first so there’s a weirder change amplitude. I think this was more popular with organ and electric piano players than guitarists. I certainly can’t think of any recordings where I may have heard that color switch effect. []
  2. I’m not saying EVH ever actually even used one of these… In fact, after about 5 min of research, EVH actually used a flanger rather than a phaser for that particular song; but he did and does famously use a phaser for other songs such as Ain’t Talkin’ Bout Love), but for anyone who did they surely would have noticed the volume drop. []

LED Wiring

This is a basic element of many electronics projects: how to wire up an LED with a current limiting resistor. Most effects have a 5 mm LED and many wiring diagrams show a 4k7Ω resistor. There’s a fairly wide range of values you can use, depending on how bright you want the LED (and what the LED’s specs are). You can calculate out the exact value to use if you have the specs for an LED, but using a 4k7Ω works well enough for most situations.

What’s a bit less obvious is how to solder a resistor’s legs to an LED leg and the connecting wires. Here’s my method:

  1. Using a pair of craft tweezers, I roll up the positive leg of the LED.
  2. Then take the resistor leg and bend it through this loop, then twist it around once. This forms a chain-like connection.
  3. Solder this connection and then trim the resistor leg back.
  4. Curl up the outstanding leg of the resistor in a similar fashion.
  5. Bend the tinned tip of your hookup wire at a 90° and hook around this loop to solder just like you would a jack connection.
  6. Curl up the negative leg and solder a 90° bend from another hookup wire to this end.
  7. Apply heat-shrink tubing over both connections. I picked up using the barrel of soldering iron from Collin of CS Guitars.

You could do NASA-spec solder joints if you want, but this is typically more than strong enough for connections. As for the resistor, it doesn’t really matter which leg you attach it (that is, before or after the LED in the circuit) as it will have the same effect. However, by definition, current will only flow through a diode in one direct, so it does matter that you have the LED leads clearly identified. That’s why I try to be consistent with using red as the positive (and typically black for the negative, but I was out of black hook-up wire during this particular project).

Amp Channel Footswitch

Most amps have the ability to use an external footswitch to change between a clean and distortion channel. Of course, some have more sophisticated options than this, but the channel switch is a pretty common feature. My older brother recently got an awesome-looking, orange Fender Duo-Sonic and a small Fender practice amp to play it through. This little Mustang amp has a lot of presets and he can use a footswitch to select between a pair of them. Of course, it being an affordable practice amp, the footswitch is sold separately.

But a footswitch is a pretty easy thing to make yourself. In my case, I had the double pole single throw (DPST) footswitch taken out of my Dunlop Wah pedal when I modded it (post to come someday!) and an old stereo audio jack. That, a bit of wire, and something to put it in is all you need! In fact, the fact that it was a double pole switch and a stereo jack made them both overkill for this small project! But why not recycle the parts for a good cause?

I purchased a powder-coated 1590LB enclosure from Mammoth Electronics. At 2″ by 2″ by 1″ tall, this is about as small an enclosure as you can get, but plenty big for a small switch and a jack. I got the orange to match his guitar (well, as close as I can get with stock powder coat colors, anyway). I laid out the switch and jack to ensure I could arrange them how I wanted; though I could have also just had the jack on the “side” of the enclosure. The circuit soldering here is super-simple: just solder the “tip” lug of the jack to the center lug of one of the poles (three of the lugs in a line make a pole). Then solder the “sleeve” lug of the jack to either the left or right lug on the same poll of the switch. That’s it! Did you mess up and wire the sleeve to the center lug on the switch? It’s still fine! All this does is connect the tip to the sleeve when the switch is “on” and then breaks the circuit between the two when it’s off.

Now, this particular build relies on an instrument cable to connect the footswitch to your amp. But you don’t have to use a shielded cable for this as the guitar signal itself isn’t passing through that cable; just a relatively low voltage (around 4-5v1) is flowing through to tell the amp the gain channel should be on. So you could actually skip the jack and just use any old wire (speaker cable, a lamp cord, etc.) and wire that into a 1/4″ audio cable end. I was just using as many spare parts as I could. In fact, I finished the bottom by cutting up a kitchen jar grip pad and gluing it to the bottom with spray adhesive (it won’t slide on his hardwood floor!).

Given that the Fender single footswitch costs around $15, this probably is not much of a cheaper alternative. But it was a fun gift for my brother and if you’re interested in practicing some soldering, this is a great and practical project to start with!

So, amazingly enough, there’s a video in which YouTube channel MerwinMusic makes the exact same footswitch as mine – down to the orange color! Check it out! He also does a great job of explaining how to test out that this sort of switch works with your amp before you go to the trouble of building one, which is a good idea as some amps may vary (but all good amps just copy Leo’s original!).

I built this exact same project almost!
  1. The voltage is low enough that my Blackstar head’s footswitch doesn’t even have a resistor on the LED. []

Mini MicroAmp Build

With each new pedal build, I try to focus on some aspect that makes it a new challenge or something new to learn. My first pedal build ever (about 18 months ago) was a boost pedal. I decided I’d build another boost: this one using the MXR MicroAmp circuit. I used the General Guitar Gadgets MAMP PCB, which in addition to selling the PCB sells entire kits and has excellent documentation1. Since it’s a relatively simple circuit and, therefore a fairly small PCB, I wanted to try to fit it into a “mini” enclosure (i.e., a 1590A format). This means having to really think ahead about aspects of the build so that everything can squeeze into such a relatively small enclosure.

The completed enclosure, including the mis-aligned hole for the input jack on the right side

The first thing is that this pedal format can’t utilize a battery for power; the pedal will be AC powered only. That’s fine as I don’t use batteries in any pedal anyway and only ever added a battery snap to that first pedal build. Secondly, the height of the components really matters. The taller components (generally, the capacitors) had to be bent over. For the electrolytic capacitors, I had to remove and replace a couple in order to facilitate this (I had planned ahead otherwise – as my sketched notes on the wiring diagram shows below, but I am just so in the habit of soldering the completely vertical I forgot!). In the end, the tallest component off the PCB was the integrated circuit (IC), as it was mounted in a socket. This way I can potentially swap out ICs in the future. Speaking of ICs, I went with a low-noise TL071 op-amp (in place of the original pedal’s TLo61 – which consumes less current but, again, I’m not using a battery so I don’t really care about that). The only other modification I made to the GGG circuit was that I swapped out a 10MΩ in place of the 22MΩ pull-down resistor (R1). Really, any fairly large (<1MΩ) resistor value will do here and 22MΩ are a little harder to find.

The completed wiring. This was a tight fit! Notice all the taller capacitors look like a strong wind came through.

Lastly, the arrangement of the larger off-board components such as the footswitch, jacks, LED bezel, and pot really came down to millimeters. I had to use calipers to measure every last item and meticulous sketch it out on a printout of the enclosure. I still managed to mess up drilling one of the jack holes (I located it 1/2 the diameter off, which s about the worst place to mess it up!). I was able to re-drill the hole thanks to having a drill press and some clamping blocks. It’s a bit ugly and the jack’s nut is a bit crooked, but it worked out fine.

Re-drilling a hole for the output jack. Drill press & clamps absolutely required to fix this sort of bone-headed mistake.

The pedal works great. I mean, it’s about as simple an effect as you can get. It simply takes the guitar signal and makes it a lot louder (probably around the order of 20-25db). I’m pretty pleased with how clean the wiring worked out, as well.

My build cost around $27 for the parts I had to purchase. That’s not including resistors, capacitors, diode, and LED (nor hookup wire and solder), all of which I already had in my parts bins but would run you around $3 in total. I also had to pay around $9 in shipping. The PCB from GGG for was about $3.50 to ship. I bought parts for several builds at once in a large order from Mammoth Electronics (my parts supplier of choice), but smaller orders from there tend to ship for around $5. They have high-quality powder-coated enclosures for really great prices, along with generally good prices on other parts and kits. So, in total, this build is roughy around $39 in cost (and I still haven’t added any artwork, so consider what slide decal or other format might cost).

That being said, unless you really want to build your own, I would not recommend this build to anyone else. You can purchase a TC Electronic Spark for about $35 used on Reverb.com (plus shipping) right now. It has the exact same size as my build, but has their amazing non-latching (relay) footswitch and essentially the same amount of clean boost. If you don’t care about size, you can purchase a used MXR MicroAmp for around $49 on Reverb (plus shipping). Both of those are solid choices if you really just want a boost pedal and are less interested in practicing your soldering skills or learning how to layout a small pedal form factor. And honestly, as much as I think this pedal sounds great so far, those probably sound even better and have less noise at full gain.

But overall, I’m pleased with this build. On the clean channel, it just gets louder without adding anything else noticeable. Best of all: with the knob set to about 3 o’clock, it makes my Blackstar HT-5R head’s gain channel absolutely breathe fire!

  1. I think I could have pretty easily build this circuit on perfboard, but probably not to fit in the this small of an enclosure. So for a bit more cost I opted for the PCB, which has a fairly small footprint. []

Guitar Effect Test Box

I’m in various stages of completion for several guitar effects at the moment and I’ll certainly try to write a post for each of those in turn. However, I first figured I should post about my guitar effect PCB test box I put together. I by no means first came up with the idea. Paul of DIY Guitar Pedals in Australia is who I first saw use & recommend one. In searching around for further ideas, I came across some notes on DIY Stomp Boxes about adding the probe, which can be used in diagnosing PCBs that aren’t working.

A MXR MicroAmp circuit hooked up to the test box

As you can see, I went with a fairly large enclosure for this project. As it’s really just the off-board wiring standard to most any pedal project, with no circuit board, this is somewhat a waste of space. However, I wanted to leave a bit of space for potentially adding some more features at some point in the future1. This is a powder-coated, aluminum enclosure which is not at all necessary for this, as the wiring is outside so the metal box isn’t shielding anything. So the enclosure was a bit of a splurge. But as Mammoth currently sells these 1590BB enclosures powder coated for under $10, it’s not exactly a bank-buster. The entire test box is less than $25, and many of the parts I already had in my parts bin.

I cut up some cheap alligator clips I bought off of Amazon.com to use for the connectors. They have little covers over the clips, so they work quite well even when connecting into closely spaced wiring leads. I did knot these just inside the box to provide some strain relief (though it’s not as though this thing is getting roughed up much). I used a Mammoth Electronics bypass wiring board just to simplify things a bit. I tend to use a standard wiring colors for all my projects: red for 9v, black for ground, green for signal to board, and yellow for signal back from board.

The spacious guts of my test box

The one trick my box has is that I added a toggle switch to use a testing probe. This switch basically hi-jacks the signal return (yellow) and connects the probe (white) directly to the box output jack. So if signal isn’t coming back from the circuit, I can flip this switch and then use the probe (which is nothing more than a 1μf capacitor) to touch along the circuit to trace where the fault is. It’s very simple but incredibly helpful.

So to quote Paul of DY Guitar Effects, if you’re going to even build just more than a couple of guitar effects yourself, you’re going to want to build something like this. It’s so invaluable to be able to test your PCB as soon as you get the components installed but before you try to complete all the off board wiring & stuffing it into an enclosure. It’s also extremely fun to hook up to a breadboard and test that way!

A Bazz Fuzz breadboard circuit on the test box
My enclosure drill pattern
Wiring diagram for my test box


  1. For example, I also saw this post where someone has added in the ability to change the voltage and add a voltage sag (to simulate a dying battery), which is really cool. []

Tremolo Pedal Build

Christmas in 2018 was a lot of fun and my family got me a lot of wonderful things. Among them, my brother, Dave, got me a guitar pedal effects kit. This was a tremolo pedal, which is definitely something I wouldn’t have gotten myself. If you don’t know, a tremolo pedal modulates the amplitude of the signal. That is, it’s as if someone is turning the volume knob up and down regularly. This effect was built into many early electric guitar amplifiers. In the late 50’s an Australian electronics magazine had an article on a relatively simple circuit for this effect. That design has since been modified and incorporated into many popular guitar effects. The kit I got is by Arcadia Electronics and uses the EA Tremolo design.

This kit has all of the components, even jacks and switch, all directly soldered onto the printed circuit board (or PCB). This simplifies building and is, in fact, what most commercial pedals utilize to speed up fabrication (and even allow for automated component soldering). As such, it was a relatively straight-forward build process that probably took me under three hours total. And mind you, I am intentionally slow with this things because I want to really enjoy the process and also to prevent making any easy avoidable mistakes.

Populated PCB for the Acadia Tremolo pedal. You can see that I intentionally bent over a couple of the electrolytic capacitors to keep them well clear of the Depth control potentiometer.

The instructions with the Acadia kits are very sparse. They basically include of a printout of the PCB (which is very nicely screen printed and clearly marked, though) and a component list. That’s it, there’s no other instructions or build steps given. So, if this was a kit for a new builder, I’d suggest downloading the instructions for one of the other Tremolo pedals at Mammoth Electronics. They’re generally similar builds and provide some good information if you’re new to pedal building or electronics. The Acadia kit came with high quality components. I tested some of the resistors and they were closer to nominal values than the ones I purchase. The single diode in the kit had legs that really didn’t fit into the drilled through holes, but I just swapped it out for another 1N4001 in my parts bin. It’s not that the part was cheap; just that the pcb design as-drilled can’t accommodate this particular part. There’s probably several solutions to this, but this would be pretty frustrating for a first-time builder, I think. Otherwise, I really have no issues with this kit. It’s the first pedal build I’ve done that I didn’t have to troubleshoot at least one mistake!

I labeled the pedal once it was all closed up for testing. I’ll paint and decorate the case another day.

I got the hardware all soldered onto the board. I did add some electrical tape to the back of the pots as well as to the inside of the case back. This is probably not necessary, but I wanted to prevent any possibility of the pots or components grounding out.

The pedal sounds great. The volume boost on this was pretty surprising, in fact. Just dialing the Rate and Depth controls to zero makes this a pretty effective clean boost, even. The range of the tremolo is all the way from nothing to complete volume clipping. I recorded a fairly poor sample for this post, but the sound is really great in person.

Tremolo Pedal Demo

My First Stomp Box Project

For my birthday, I decided to work a completely new project: build a guitar effects pedal. I purchased the “Confidence Boost” project kit from BuildYourOwnClone.com (as in clones of popular guitar stomp boxes). It’s a great project for about $15 which comes with detailed instructions and makes a pretty decent little boost effect. The kit itself only comes with the printed circuit board, electronic components, and off-board wiring such as jacks and potentiometer.

PCB components and initial off-board wiring

I soldered up the components and off-board wiring and plugged-it up. And nothing. It didn’t make any sound! I posted a couple of photos to the discussion board and quickly got a response: the input jack was wired backward. In other words, the signal from my guitar was just going to ground and nothing was going on to the effect (or amp). I quickly re-worked the input jack and it worked. The tiny potentiometer (blue screw driver knob in the photo above) was a bit tough to use.

I decided it would be fun to go ahead and wire this up as an actual stomp box, so I ordered a few more components and an enclosure. I spent some time painting and finishing the enclosure. I just used a white pen to draw out the labeling, but it turned out just fine for this project. I read up on how to wire a footswitch for true bypass (when it’s off, it doesn’t affect the signal at all) and with an LED indicator light.

Enclosure design
Fully wired effect in the enclosure
Wired up and turned on

But of course, it only really matters how it sounds. I’m far from a capable guitar player and even worse when trying to film my playing, but here’s a small sample.