This is another Big Muff clone. It’s a green Russian built with a Madbean PCB. I milled the enclosure.
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.
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.
I think this is #5 I’m losing count. These are so much fun to play the world needs a couple more! I used matte black sand textured enclosure. Which give this a good industrial vibe.
This is a pretty easy build for what you get. The board is a good size and parts are comfortably spaced. All of the pots are mounted to the board making wiring easy. The switches require some work but the pads are well organized.
The only down side is finding FETs and Ge diodes. Luckily D1 and D2 can be replaced by just about any type of type. D7, D8, and D9 could also be any type but Ge will have a noticeable sound to them. Ge diodes here will have a particular sound, not better or worse. If you’re looking for “that” sound you might stick with Ge for these. Otherwise test out any type of diode and use your ears to decide what sounds good here.
The main distortion circuit is based on the LM308 op-amp which are hard to get and can cost $5 or more, that’s a lot for an op-amp. Luckily the part is not critical. You can a few replacements. I used an OP07 which was $0.50 at Tayda.
The PF5102 FETs are hard to get. I used J112 from Tayda successfully.
And, it sounds amazing! This might be for sale check my for sale page.
This is a clone of the 1981 Inventions DRV rehoused in a Boss DS-1 enclosure. I used the PedalPCB Informant PCB and the MadBean Softie for this project.
Good question! I suppose I saw the ridiculous prices people were paying for the Boss Tone Benders that had come out recently and thought I could just make my own. While I was exploring the idea it seemed it was easiest to three knob Boss enclosures. The cheapest pedals seemed to be the DS-1, SD-1, and the BD-1. So building a three knob was the best option. There are many three knob pedals out there. Big Muff, Tube Screamer etc.
I got a little sidetracked and built a Big Muff in a DS-1 enclosure first, see my post here. The second build was this 1981 DRV. I have a board for a three knob Tone Bender and am planning to work on that next.
The process The process was pretty straight forward.
The Boss enclosure is pretty roomy. Figure you can fit anything that might fit 125B sized box into a Boss enclosure. The donor pedal comes with LED, Jacks, much of the wiring already. No need to drill or install these things.
One thing that needs some work is the power jack. The power jack is mounted to the original DS-1 PCB in my build there was no place to mount this. To solve this I used one of those standard DC jacks with a nut. I needed to ream the enclosure to allow it to fit. I added a couple spare washers so the jack didn’t extend too far out of the enclosure.
Switching is an area that needed some thought. Boss uses an electronic switching system. The system uses a couple JFET transistors to route the signal either through the effect or from the input to the output. Another part of the circuit turns this off or on. There is also buffer.
A side effect of this system is that your signal is always passing through some electronic components unlike true bypass where the signal is essentially traveling through a wire from the input to the output when the effect is bypassed. I’ve never heard any complaints about The Boss bypass. Another potential problem is the signal is lost when power is lost, even when the effect is bypassed.
I used the MadBean Softie which uses a micro controller and an electronic relay. The relay is an electromechanical switch. It’s a DPDT switch that is activated by an electronic signal. This offers a couple advantages. First, it works with the existing switch in the Boss enclosure. Second, when in bypass it acts as true bypass, the signal is essentially traveling through a wire from input to output when in bypass. Third, if power is lost the relay switches to its default state which bypasses the effect. Last, the relay has a failure rate of 100k cycles so it should outlast a mechanical 3PDT switch, which typically has a failure rate of 30k to 50k cycles.
It isn’t all upside. The cost of the Softie PCB was $4 and you’d need an SPDT monetary switch which is another $2.50. That’s $6.50 compared to $2.50 for one of those standard blue 3PDT switches. In this case the Boss enclosure came witch an SPST.
I thought the Softie worked well. Madbean makes three versions of this board for different sized enclosures. I chose the smallest version that was meant to fit 1590B enclosures. I think I could choose a one of the other boards for the Boss enclosure. The reason the board I chose has a small footprint but mounts parts on both sides of the board making it taller than other boards, which makes it a tighter fit than it would appear.
The Informant/DRV needed three A100K pots. The DS-1 has two B100k and a B20K pot. I could have tried the B100K pots. Since I needed to replace on of the pots I replaced them all.
I used some of those 9- degree PCB mounted pots, two 16mm and one 9mm. I cut a piece of strip board and mounted the post to this. Then ran the wiring from the Strip board to the PCB.
I color coded the wires by the PIN number of the pots to make it easy to get them matched up to the correct holes on the PCB. I just did it alphabetical to make it easy to remember: Brown, Gray, Orange. Notice the center pot is backwards,
The cost of this project was higher than a typical pedal but not as bad as i was expecting. The cost of the donor DS-1 was the biggest expense. The DS-1 was $40 and it replaces about $10 of other parts. So this was roughly about $30 more than your typical pedal build.
The total cost was about $60 which was not that bad, or at least than I thought it might be when I started. The pedal is pretty solid and works well.
What’s it sound like?
Hopefully like the 1981 Inventions pedal. I haven’t tried one of the originals but this sounds similar to the demos I’ve seen on YouTube. Its a really driven sound with a tight low end. It has a very 80s sound.
The drive control starts at distorted and goes quickly to high gain. I find it sounds best to turn up the Cut control as you increase the gain to “shave” some of the “hair” off as gain increases.
For myself I like the lower range of the Drive control. Everything past 25% (9 o’clock) sounds very similar. I’d like to play with Drive and gain in the future. This might be replacing the Drive pot with a 50k pot, or possibly changing some of the other components to get a more useful feel for this control.
I was trying to up the quality of my builds and thought about shielding and noise. Did a little research on the interwebs and came up with a few tips.
First a little background. High gain circuits often run series of gain stages in series. If you have an input stage of x10 followed by an adjustable stage of x10 to x100 you have a minimal gain of x100 to a max gain of x1000. That’s a lot of gain. Anything that gets into your circuit at the input will also be boosted by x100 to x1000! Think of cable crackles, switch pops, scratchy volume pots on your guitar, and more.
Then there’s the noise in the air from electromagnetic interference. It’s not uncommon for pedals to pick up radio transmissions, remember that scene from Spinal Tap? Or the hum of electronic devices like fluorescent lights.
In many ways the enclosure acts as an antenna picking up electromagnetic noise. But it can also be used as a Faraday cage which can be used to protect the circuit inside from electromagnetic interference from the outside. To do this the enclosure must be connected to ground.
if you have open frame jacks like the Switchcraft jacks the sleeve will make contact with the enclosure. This grounds the enclosure for free. If you’re using those jacks with the plastic body you’ll need to run a wire to the enclosure somewhere.
Is it enough to ground the box? Yeah but in the case of painted boxes or boxes with a powder coat the bottom cover may not make an electrical connection to the main body of the enclosure. I used a drill bit to remove the paint from one of the counter sunk screw recesses. This allows the screw to make contact with back cover and main body of the enclosure.
Vulcan pcb built up. This is version 2.
Building some ugly faces
This is Joe Davisson’s Vulcan overdrive. Starting with a prototype board made at home with the Othermill, then turned this into a board from OSHPARK. Boxed up and is working well. This is an interesting overdrive with a couple unique circuit features.
Box of Rock bootleg in process. Milling the box on the Bantamtools Othermill.
Jack Deville Dark Echo.