I made some ugly face PCBs back in 2009 and had a couple left over. I built this up when I first got the mill.
The Ugly Face is a DIY classic invented byTim Escobedo way back in the early mid 2000s if I recall. It’s a unique circuit with a surprising sound if you haven’t built this you should give it a try.
Check my OSH Park projects I have a great board for this project the builds easily and works well.
This is another Big Muff clone. It’s a green Russian built with a Madbean PCB. I milled the enclosure.
Another Fuzz Factory clone. I used silicon transistors for this build I didn’t have any germanium transistors with the right gains. I think lower gain silicon works best here. I used a couple 2N5401 with gains of 115 and 120. These were about the lowest gain I could find in my parts bin.
I ordered three boards from OSH Park for $7.75. These worked well.
I used the soft switching with the Madbean Softie. Which worked well. I’ve built four of these so far and they have all worked well.
Want to build your own effects pedals? A good place to start is understanding how transistors work. Transistors are those three legged devices seen populating many stompbox circuits.
Transistors are are a core building block in electronics. Integrated circuits, like op-amps, are made up of many transistors! Transistors are used in all of the circuits you’ve probably played or heard on recordings: Rangemaster, Fuzz Face, Tonebender, Big Muff, Tube Screamer, and too many more to list here.
The goal of this series of blog posts will be to present concepts you can use to understand how guitar effects pedals work, apply these ideas to debug, and make your own pedals.
Why I am I doing this? I have been building Stompboxes as a hobby for years now and want to build a deeper understanding of the electronic concepts underneath it all. I have been building pedals for years but it has always been sort of paint by numbers. I had some friends get into the hobby recently and they had lots of questions. Here are the answers I could come up with.
This class will be broken into three parts: a discussion in this blog post, a lab where your goal is to build the Dallas Rangemaster, and a reading assignment and study guide.
Discussion: Dallas Rangemaster
The Dallas Rangemaster is classic guitar pedal. Created by Dallas Muscial Ltd. in the 1960s. With a name like “Dallas” you’d think they were from Texas but in fact the company was located in London England!
The Rangemaster is a booster. Basically it’s a single transistor amplifier that filters the lower frequencies. It takes your guitar signal and shapes it and amplifies it.
The Rangemaster was used by so almost every guitar player you can think of from the 60s. Here’s a short list of notables:
- Eric Clapton
- Tony Iommi
- Marc Bolan
- Rory Gallagher
- … too many more to list
Many more used other pedals similar to or derivatives of the Rangemaster. Many companies sell boosters that are direct copies of the Rangemaster or are built from a single transistor like the Rangemaster for the same purpose. It’s definitely a pedal worth study.
- Zvex Super Hard On
- Electro Harmonix LB1
- Hornby Skewes Treble Booster
- Brian May Treble Booster
- … and the list goes on
The Rangemaster circuit represents a basic building block that can be used in many guitar pedals. Understanding this circuit is a gateway to explaining how lots of classic effects work. It’s also a building block you can apply to effects of your own invention.
Electronic circuits are expressed with schematics that have their own symbols. This is similar to the way music is expressed in notation or way a roadmap may be drawn.
Usually we give each part a number and a value. The lines represent an electrical connection between parts. Here is a list of the part numbers and values for the Rangemaster.
The parts here are four types: Resistors, Capacitors, Potentiometers, and transistors. lets look at each of these.
Resistors are all listed with the prefix R in the parts list. There are three resistors R1, R2, and R3. Resistors impede the flow of electrons. We can use resistors to limit how much current is at any point in the circuit.
POT1 is a potentiometer, which is an adjustable resistor. Use a “pot” when you need a variable amount of voltage or current at a point in your circuit. For example a pot is often used as a volume control.
Capacitors are like little electrical reservoirs. They act as a gap that DC can’t pass but they allow and AC signal to pass! Capacitors used in the Rangemaster are C1, C2, and C3.
Capacitors are used to affect how audio is passed through your circuits. Capacitors are used to create filters and control the frequency of AC.
Some capacitors are polarized! One leg is marked with a + and that leg should go to the more electrically positive side of the circuit with the other leg going to the more electrically negative side of the circuit. Notice C3 has a + on the bottom that connects to the +9V in the schematic.
In the original Rangemaster the transistor was OC44 or OC71. This was a germanium transistor. Transistors come a few varieties. Two of the most common are PNP and NPN. The OC44 is a PNP transistor.
You can build Rangemaster type circuits with almost any transistor. This is great because the OC44 and OC71 are hard to get and expensive these days. Some common transistors that would work as replacements are: 2N3906 or 2N5087. These are silicon transistors rather than germanium.
The symbol for PNP and NPN transistors look like this. These are almost the same. Note the arrow! You can remember which is which with this: NPN = Not Pointing iN, PNP = Pointing iN.
The original Rangemaster was built with a PNP transistor. You could also build a Rangemaster type circuit with a NPN transistor. Some common part numbers for NPN transistors are 2N3904 and 2N5089.
Notice the changes to the circuit. (1) the transistor Q1 is NPN. (2) the +9v and -9v are swapped. This is where your battery would connect. (3) the capacitor C3 has been flipped around so that the + terminal is pointing towards the more positive side of the circuit and it’s other terminal connects to the -9v the more negative side of the circuit.
OHMs law is a basic principle of electronics. OHMs law determines the flow of electrons through a circuit. If you thought of electrons like cars and the circuit diagrams above like a roadmap OHMs law could be used to predict the flow of traffic!
OHMS has three ideas:
- Voltage (abbreviated E) is the electromotive force (measured in Volts, millivolts, and microvolts)
- Current (abbreviated I) is the number of electrons in the flow of “traffic” (measured in amps, milliamps, and microamps)
- Resistance (abbreviated R) is the opposition to the flow of electrons (measured in OHMs)
We can use math to calculate the flow of electrons through our circuit. Use the diagram above to help you remember the formulas.
- E = I * R (find the voltage from the current and resistance)
- I = E / R (find the current from voltage and resistance)
- R = E / I (find the resistance from voltage and current)
The numbers you use need to be in the same realm. If you are working with Volts (E) then Current (I) needs to be amps. If you have voltage in millivolts then current needs to milliamps. If the units are mixed you can multiply or divide by 1000.
|Volts V||Amps A|
|Millivolts mV (V / 1000)||Milliamps mA (A / 1000)|
|Microvolts µV (mV / 1000)||Microamps µA (mA / 1000)|
What does this mean? Take a look at the images below. You can use OHMs law to calculate the current and voltage.
In the first image we have 9 volts going through R8 which has a resistances of 2000 ohms (or 2K ohms). Whats the current? Using OHMs law we can figure it out!
- I = E / R
- I = 9 / 2000
- 0.0045 Amps or 4.5 milliamps or 4500 microamps
What about the second image. Image we don’t know the voltage but we do know we have 2 milliamps going through 1000 ohms resistance.
- E = I * R
- E = 0.002 * 1000 (Notice I converted milliamps to amps)
- 2v = 0.002 * 1000
Traffic moving down a road divides when it reaches an intersection some traffic will go one direction and some traffic will take the other route. The same is true of electrons moving through a circuit. If you were watching the road from a helicopter you’d see more traffic take the larger roads and less traffic take the narrow roadways. Think of the size of roads as resistors. Larger roads have less resistance and narrow winding roads create more resistance that slows traffic.
Look at the first example. There is 9 volts going through R1 and R2. What is the voltage at the intersection ?1. You can solve this if you understand voltage dividers. The formula is:
- ?1 = 9V * ( R2 / (R1 + R2))
- ?1 = 9V * ( 1K / (1K + 1K))
- ?1 = 9V * 1000 / (1000 + 1000)
- ?1 = 9V * 1000 / 2000
- ?1 = 9V * 0.5
- ?1 = 4.5V
Here I walked through the steps to solve the problem. Notice I converted 1K to 1000 ohms. Then finished up from there.
The formula is: V * R2 / (R1 + R2)
The shortcut here is if both resistors are the same value then voltage is divided in half. This would be true for any values for R1 and R2. Try it yourself. Imagine R1 and R2 are 10K. Then try R1 and R2 at 47K and 100K.
What happens when the values are not equal? What’s the voltage at the intersection: ?2.
- ?2 = 9V * 100K / (100K + 20K)
- ?2 = 9V * 20K / 120K
- ?2 = 9V * 20,000 / 120,000
- 1.5V = 9V * 0.166
Solve number 3 on your own!
To solve ?4 we have to know that resistors in series are added together. That means that we have a total resistance of 16.7K. To solve ?4:
- ?4 = 9V * (10K + 4.7K) / (2K + 4.7K + 10K)
- ?4 = 9V * 14.7K / 16.7K
- ?4 = 9V * 0.88
- ?4 = 7.92
Solve ?5 on your own…
With this knowledge you can start examining the Rangemaster circuit. Notice R1 and R2 for a voltage divider!
POT1 is also a voltage divider. Let’s take a moment to look at potentiometers.
These are adjustable resistors. You’ll use potentiometers or “pots” when your circuits need to be able to adjust the resistance at a point in the circuit. A pot has three legs. Imagine the center leg is located between two resistors. The resistances change as you turn the pot!
We draw the pot like the image on the left. Internally it acts like the images on the right.
Imagine we have a 10K pot. With the knob in the center the resistance is divided equally with 5K on the top and 5K on the bottom. This is a voltage divider! In this case you would see have the input voltage at the center leg!
If you rotated the pot clockwise the resistor on the top (R3) might be 0 ohms and the all of the resistance 10K might appear at the bottom.
If we went counter clockwise it would be reversed.
If you rotated the almost to the end you might have 2K resistance at the top and 8K at the bottom. Imagine there was 9V at the top, use the voltage divider to calculate the voltage at the center.
Transistors modeled as a current controlled resistor
With these ideas we can now look at the transistor, which is the heart of the Rangemaster. The Rangemaster is an amplifier. It takes a small audio input and produces a louder audio output. The transistor is used to amplify the signal.
A transistor has three legs. For NPN and PNP transistors the legs are called: Emitter, Base, and Collector. The Emitter is leg with the arrow. The Base is in the middle.
To explain how the transistor works we will model it as a current controlled resistor. For this discussion we will use the NPN version of the Rangemaster schematic and the transistor will be NPN.
Take a look at the diagram above. Imagine the transistor drawn on the left is in your Rangemaster circuit. Imagine that inside the device is a resistor. The value of this resistor is controlled by the amount of current present at the base. Outside the transistor the Rangemaster has a 10K resistor (POT1) at the collector and a 3K9 resistor at the emitter.
With no current applied to the base there is so much resistance you can image that there is no connection at all. We would see about 9V at the collector.
When a small amount of current is applied to the base the resistance between the collector and emitter starts to decrease. Imagine the collector/emitter path is now showing 100K resistance. Now we have a voltage divider! You could use the formula above to calculate the voltage at the collector!
With more current applied to the base the C/E path might go down to 10K resistance. Using the voltage divider formula the voltage present at the collector goes down as more of the electron traffic goes through the 3K9 resistor.
With a lot of current at the base the C/E path might go as low as 100 ohms and the voltage at the collector would go even lower!
Did you notice when the current at the base goes up the voltage at the collector goes down. And conversely, when the current at the base is low the voltage at the collector goes up. A transistor amplifies because it allows out circuit to turn small changes in current to larger swings in voltage.
Notice the diagram above. When the current is high the voltage is low! This is an inverting amplifier. The signal at the output will be a mirror or opposite of the input signal.
Biasing the Transistor
There is a little more needed to make this work. Imagine the incoming signal might swing between +1v and -1v. When the input is above 0V the transistor starts working. When it’s 0V or less the CE path is closed off.
Look at the diagram above. The signal going in is a sine wave but the signal coming out is getting chopped. This would cause some distortion! In this case it probably wouldn’t sound too good. It also explains why your transistor circuits sometimes don’t sound right!
To make the amplifier work we need to bias the transistor so with no input the output settles at a point somewhere between the extremes.
Take a look at the diagram above. Here I’ve added R1 and R2 from the original schematic. These provide an amount of current to the base so that it sits around 7V. With this arrangement positive input pushes more current to the base opening the CE path and lowering the output. When the input signal is negative this pulls current from the base which increases the resistance of the CE path and the voltage at the output goes up.
Biasing is the term that describes applying a DC current to the base of a transistor such that it is it near the middle of it’s range. It needs bias so the output can go up and down from the bias point.
All 4 of the resistors play a part of the amplifier. R1 (470K) and R2 (68K) provide the current to bias the transistor. POT1 (10K) and R3 (3K9) also determine where the bias should be since the lowest voltage output is determined by the voltage divider created by these two resistances. Imagine the CE path had 0 ohms resistance.
- ? = 9V * 3.9 / (10 + 3.9)
- ? = 9V * 3.9 / 13.9
- 2.5 = 9V * 0.28
This concludes the discussion of the Rangemaster. From here the goal is to build your own! Along the way think of this discussion.
Building the Rangemaster
For this part of the lesson it’s up to you to figure out which build method and which circuit you want to build.
There are several approaches you can take to building the Rangemaster:
- Terminal strip
- Solderless Breadboard
Buying a kit will cost more but you’ll get everything you need in one package!
A PCB makes for an easier neat clean build but you’ll have to source parts yourself.
This is perforated boards with strips of copper. Use it for prototyping.
Like vero board but has one pad per hole.
The original Rangemaster was assembled on a terminal strip. This is for the artists and historians.
Solderless bread board
Use a solder less bread to experiment with the design.
Here is some reading material to follow up the discussion above.
This guide to Breadboarding the Rangemaster at Small Bear Electronics is a great guide to circuit.
Stompboxology was a news letter put out in the early days of DIY when the internet was young. It never caught on and it and it’s creator mysteriously vanished. That said I found this issue to contain one of the best discussions of transistors for stompbox usage I have read. It also contains a discussion of core concepts for electrical engineering that you will need to know to build effects pedals.
This article provides an in-depth analysis of the Rangemaster. Most of it is over my head but it’s still good reading.
Forbidden Planet is a movie from 1956. It featured a sound track and sound effects entirely created by electronic circuits. I say circuits because this was 8 years before Robert Moog would produce the first synthesizer. The sound track was produced by Bebe & Louis Barron using circuitas invented for the purpose and test equipment.
Watch the movie here: https://archive.org/details/ForbiddenPlanet1956_201707
I thought I should try my hand at recreating the music of the Krell with circuits I had made!
A good starting recipe is an oscillator, delay, and reverb. The Ugly Face (right) is an oscillator drive by a guitar input. When the threshold is turned up it will self oscillate. The out put is as square wave.
The Barron’s used ring modulation copiously in the Forbidden Planet sound track. I thought I’d get out yhe Zvex Ringtone. The Ringtone is sequencer and ring modulator. The Barron’s didn’t have access to a sequencer since it hadn’t been invented yet.
A ring modulator produces a signal that is the sum and difference of an input frequency and another frequency which is usually produced internally. The sequencer allows us to program the internal frequency in 8 steps. The input frequency comes from your instrument, in this case it’s the Ugly Face.
This time I used the Fuzz Factory as an oscillator. This pedal will oscillate on some settings usually when turn down the Stability and turn up the Drive, Comp, and Gate.
I also added the Zvex Seek Wah. This is a wah controlled via an 8 step sequencer. Imagine a wah pedal stepping through 8 different positions of the foot pedal.
This demo makes use of the Deadastronaut Tremshifter. The Tremshifter is both a tremolo and phase shifter in one box.
This demo uses the Commonsound.org Triwave Picogenerator as the sound source. This is a legend in the DIY realm. It’s has two oscillators, and three LFOs. You can mix the amount of LFO that influences the pitch of each of the oscillators. The LFOs also have a rate and shape control.
build your own Ugly Face!
Ugly Face is a racus squarewave guitar synth oscillator disguised as a fuzz pedal.
Originally created by Tim Escobedo on his Circuit Snippets web page, it’s become a DIY classic. The ideas here are great and inventive there are a lot of building blocks. Out of all of these the Ugly Face leaps out at your like a rabid warthog.
The board here was design in Eagle PCB. The pots and LED are mounted to the board for easy assembly. Get boards at: https://oshpark.com/shared_projects/BldK2X8b
Notes: Solder parts to boards without the LED or pots. Drill your box with the guide at the end of this document. Fit the pots and LED in the board without soldering. Mount the pots into the enclosure with the nuts and washers. Then fit the LED through the hole. Now solder the legs of the pots and LEDs.
NOTE! I found an issue with the ground connection on the output side. It’s not connected to the group plane! Otherwise everything works.
|VACT||Any LED/LDR pair will work|
I created a PCB you can order at OSH Park.
|RLED||1K-10K (adjust to taste)|
I built this a while ago. I recently built a couple more Fuzz Factory clones. I used sockets for the transistors so this made a good place to audition transistors for the new pedals.
It got me thinking about the transistors I used in this pedal. I used germanium transistors in the new pedals but silicon in this one. The transistors here sound different not better or worse but definitely different. There is a lot of overlap in sound.
The germanium transistors fall in a gain range of 70 to 120 hfe. This is pretty low. It’s hard to find silicon transistors this low. I used 2N3906 types. These are pretty common, I had a bag them on hand. I measured the bag and chose the lowest gains I could find.
I used colored knobs with the idea that the color would remind me what each of the knobs did. Violet: Volume, Green: Gain, Chocolate (brown): Comp, Scarlet: Stability. It wasn’t working too well. The Sharpie worked better, with no ambiguity.
I may change these knobs for some with knurled grip. It’s hard to turn these smooth plastic knobs that are packed together so tightly.
the AionFX aboard was way to assemble. It uses 9mm PCB mounted pots for all 8 of the pots. The LED is also mounted to the PCB. This saves time and cuts down on the amount of off board wiring. This is older version of the Flare, they have a newer version which looks to have a few small updates. Definitely use sockets for Q2 and Q3. This will give a chance to experiment with transistors.
What’s it sound like?
Sounds like the Fuzz Factory. Like I said earlier it sounds different from the Germanium box but similar with it’s own character. There is something about the Comp control with the higher gain transistors where it goes very gated zippers fuzz at the very end of it’s range which the germanium doesn’t go if I recall correctly.
Generous Reddit member sent me this Breakfast Audio PCB. It looks like a clone of an Ibanez version of the Super Fuzz. They threw in stickers to, awesome!
I had not heard of this circuit though I was familiar with the Super Fuzz. I found this discussion over at the DIYStompboxes.com forum.
Physically the board is wider than a 125B so it probably needs to be built into a 1590BB. You might be able to get this into smaller box in portrait orientation.
We’ll call this the BZ-1. What got me started on these Boss rehousings was seeing the Boss Tone Bender TB-2w going for 3k on Reverb.com. These were super cool pedals but not worth more than than the list price of $350. I understand the idea of scarcity and knew there were only 3000 made, but I wasn’t going pay even $350 for a fuzz pedal. So I figured I could make one!
The Burns Buzzaround
If you’re curious about the Burns Buzzaround and how it relates to the Tone Bender check out here articles:
Building the BZ-1
There is always a solution when you can make your own! Since it was hard to get a two knob Boss enclosure, I decided to go with a three knob Tonebender variation. There are a couple to choose from. In the end I decided to go with the Madbean Pasty Face which is a clone of the Burns Buzzaround which is variant of the three transistor Tonebender family. I had read some good reviews of the Buzzaround and hadn’t built one before which made it more attractive.
I started with a used Boss DS-1 from Reverb.com. Used these seem to go for about $40. I ordered a board from Madbean and I had most of the other parts on hand. The DS-1 comes with a lot of parts that can be reused: switch, LED, jacks, and the enclosure itself. I pulled everything out and except the jacks. I left all of the original wiring in place since I can reuse it.
The LED is mounted to a small PCB along with two wires. These wires were too short to reach the far side of the enclosure where the switching board will be so I replaced them with longer wires.
I built the Pasty Face circuit board first. I left the transistors off since these need some special selection. The build is pretty easy there are only a handful of parts and there is plenty of space to work.
Since I’m putting this into a Boss enclosure the pots will be mounted off board. I cut a piece of strip board to mount the pots to. This was tight fit using 16mm pots but just makes it. Then I soldered some strips of ribbon cable to the this board and then to the main PCB. I made the ribbon cable a generous length since to allow me to pull the PCB out without having to also remove the pots.
Boss uses an electronic switching and the enclosure is nice the way it is. I wanted the switching to work as it was without adding a 3PDT switch. To do this I used a MadBean Softie PCB. This is a relay switching system that works with a Microcontroller. The microcontroller is triggered by the original Boss SPST switch. The relay is a DPDT that handles true bypass switching, while the microcontroller handles the LED.
This system works pretty well and offers a couple advantages. The relay has a failure rate of 100k cycles which beats the 30k cycles of those blue 3PDT switches. Also, if power is lost, the relay switches to bypass. Overall I’d say this relay switching works well and is easy to install. The downside would that the cost is higher than the mechanical switch, and the parts are harder to get, I had to order relays from Mouser.com.
The circuit uses three germanium transistors. With these old circuits there was a lot of variation with some Devices sounding better than others. I found this great thread with some suggestions about the gain and leakage for each of the transistors:
All pedal questions seem to lead to answers at DIYStompboxes.com. Great site and community, I highly recommend you check it out.
I have bag of germanium transistors. I got these from eBay and other sources and have been pulling parts from it for a while. What’s left are parts with less desirable values at this point. Luckily the thread above recommends lower gain devices for Q1 and Q2 and I have plenty of these!
In this circuit the first two transistors are setup in a Darlington pair. You can think of the two together as a single transistor with an hfe that is the product of the two. For example if both transistors had an hfe of 10 the pair in this configuration would act like a transistor an hfe of 100. This also multiplies the leakage of the two transistors. Which can increase noise.
Seems like the best choice here is low leakage, and low hfe/gain. Two transistors with an hfe of 50 would be considered low gain but in this configuration as a pair they would have gain of 2500!
Q3 seems like where all of the distortion/fuzz magic happens. From what I read in the thread above a higher gain, hfe 100+, is better here.
I identified three transistors that I thought would be suitable. I soldered some sockets into the board and auditioned the transistors with the back of the box open.
Everything was sounding pretty fuzzy good, so I removed the sockets and soldered the transistors to the board. I left about an inch of leg since I’d need to bend them over to fit everything into the enclosure with the back on. I wrapped the legs and the transistor body (not shown) in heat shrink tubing to make sure nothing shorted when I closed up the box.
What’s it sound like?
Sounds a lot like all those other 60s fuzz pedals but with its own character. The sound is thick and fuzzy. The tone control has a useful range. The sustain control goes from a muffled to tight buzz. Sort of like fuzzy bumblebee to swarm of wasps.