Pedal maestro Brian Wampler of Wampler Pedals shows us how to make two of the most popular overdrive pedals on the planet rule even more.

Basic Modding Supplies
Each of the modifications discussed here require the following:
• Soldering iron
• 60/40 rosin-core solder (don’t buy lead-free)
• Solder sucker (not mandatory, but very helpful)
• Desoldering braid
• Small side cuts/wire cutters
• Felt-tip marker

If you’ve ever owned an Ibanez TS9 Tube Screamer or a Boss SD-1 Super Overdrive, you’ve probably noticed two things: You like the way they sound, but they could also really use a little something more. We’ve come up with some custom modifications that we feel give these pedals that “something more”—and the best part is that you can do the mods on your own! All you need to be able to do is follow instructions and know how to solder and desolder. (If you haven’t soldered before—or if you are a bit rusty and need a refresher—go to YouTube and watch CuriousInventor.com’s video “How and WHY to Solder Correctly,” and ExpertVillage.com’s “How to Solder: Removing Solder.”)

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How to make your Russian Big Muff Pi deliver tones from Queens of the Stone Age to David Gilmour


The Big Muff Pi is a timeless classic in the fuzz-pedal world. It’s been heard on numerous recordings and been offered by countless boutique pedal manufacturers in one form or another over the years. There are several different versions of it, but for this article we’re going to talk about the newest Russian version (black box).

While it is a good-sounding pedal in stock form, as DIY’ers we have to ask ourselves how it can be improved. What are its shortcomings? What kind of modifications would turn this great fuzz into an amazing fuzz? Let’s look at the circuit and break it down in layman’s terms.


Click to download high-res schematic


The signal comes in and passes through R1 and C1 before hitting the first stage, a basic transistor signal boosting stage. Once the signal is boosted, it goes through C3 and uses a potentiometer connected as a volume pot in order to control the gain. The signal goes through C4 and R8 before hitting the next stage, which is boosting the signal but also clipping the signal quite a bit via the diodes (D1 and D2) in conjunction with C6. The signal then goes through C7 and R13 before hitting the next stage, which is nearly identical to the preceding stage. After this stage, the signal goes into the tone control, which pans between a high-cutting section and a low-cutting section. This explains why when you turn the tone control down the sound is very bassy, while turning it up cuts the bass, and it gets very bright. After leaving the tone control, the signal goes through C12 and enters into the final signal boosting stage before exiting through C13 and going out of the volume control into the pedal’s output.

Modifications
A common complaint is that the stock big muff tone control takes out too much of the mids. In a band situation this can make the guitar tones seem to disappear a bit. In order to bring the mids back in, I like to change the tone stack, so it’s more like a traditional high-cut type of control. In addition, I like to control the bass frequencies so they aren’t so overwhelming. Here are the changes I would make:

Click to download high-res schematic

• C1: 1uf
• R8: 22k
• R13: 22k
• Remove R19 completely; do not replace it with anything.
•  In place of R18, connect a 20k potentiometer as shown in the schematic. This requires drilling a hole and mounting the new pot. Alternatively, you can wire in a 20k trimpot and just set the pot to taste. This modification will allow you to have separate bass and treble controls.
• C12: .01uf (make larger if you need more bass)
• R22: 1M
• C9: 1uf
This will make it nice, big and full—something closer to a Queens of the Stone Age type of tone. We can also make the gain control more useful in lower gain applications: simply connect a .001uf cap between lugs 2 and 3, shown as C3A on the schematic. For a creamier, Gilmour-ish tonality, jumper R1, and connect a .001uf cap in parallel with R24. If you want more of a higher gain, open-sounding distortion, make all the same changes, except make C1 a .01uf and C12 a 1uf. For an extra bit of creaminess, replace R12 and R16 with jumpers.

I prefer poly film or metal stack film capacitors whenever possible. This isn’t absolutely necessary, just a tonal preference. If you use electrolytics, make sure you get bipolar electrolytics. You can get any of these parts from smallbearelec.com, mouser.com, or digikey.com, among other places. I do not recommend Radio Shack-type caps, though; sometimes the parts are so large you can have trouble fitting them in the pedal.

If you happen to like the scooped-mid sound of the Big Muff, but still want a separate bass and treble, I would make the following modification to the tonestack:

Click to download high-res schematic


All of the changes in the previous mods still apply, the only thing we are changing is the tonestack, shown in blue on Schematic 3. Some DIY’ers also like to experiment with different types of NPN transistors, which do indeed give a bit of a different sound. They’re inexpensive as well, so it can be very fun. These modifications can be done to any Big Muff-style pedal; just cross-reference the schematics shown here with the particular schematic you have for your pedal. I guarantee you’ll have a killer-sounding tonal twist on a classic fuzz pedal.

Have fun!



Brian Wampler
Brian Wampler is an author, effects designer/builder and operates IndyGuitarist Custom Effects - IndyGuitarist.com and Wamplerpedals.com. His books include How to Build Effect Pedals, How to Modify Effect Pedals, and Advanced DIY Effect Pedals available at GuitarTone.net.

Mods that will take your MXR Distortion Plus to a bigger, meaner level

Many years ago distortion pedals were much more limited than they are today. MXR released a simple hard clipping device called the “Distortion Plus” in the late seventies. Randy Rhoads, among others, used this pedal to achieve more distortion in his amps. Guitarists everywhere mistakenly thought that this little device was the secret to Randy’s tone. Since then, there have been many, many different versions of this type of circuit. Let’s take a look at it a bit closer; there are a great many mods that can be done to turn it into a tone monster.

Here''s the stock circuit:


The signal enters where C1 and C2 intersect. C1 is a low pass filter, throwing some highs to ground pre-clipping. C2 allows mainly mids and highs through into the clipping section. The R1 limits the signal going into the opamp and R5 sets bias for the opamp.

R4, C3, R2, and R3 control the gain and frequencies getting boosted and clipped in a traditional “non-inverting” method of opamp circuit. R3 is labeled as a gain control, however you’ll notice that it changes the tonality depending on its setting. This is because it is changing the frequency response of the opamp at the same time. With the gain control all the way up it only clips frequencies 723hz and higher, though it is at max gain. In its minimum gain setting it is boosting and clipping almost all frequencies (3.4hz and higher) though it has much less gain. This is why it sounds muddy and undefined when the the gain is lower and why it thins out when you turn the gain up.

After the signal is boosted it exits through C4 and then through R6. D1 and D2 clip the signal using a “hard clipping” method while C5 works with R6 as a low pass filter to filter out 6db worth of frequencies 15.9khz and above, which the human ear can’t really distinguish too much. Most likely this was to filter out some odd harmonic overtones and/or noise. A much better use would be to wire a 100k pot in series with a .0022uF cap in place of C5. This will act as a tone control.

D1 and D2 are 1n34a type Germanium diodes in the stock version. This leads itself to a bit of a fuzzy compressed tone with not much volume left over after being clipped.

The signal exits via the 10k pot on the output.

The Dod OD250 and YJM308 circuits are almost identical to this and these mods will work for these pedals as well.

Here some of my favorite mods that I like to make to this type of circuit:

  • Use an SPST switch to insert a .01uf cap in parallel with a .001uf cap in place of C2. This will give a ''more/less compression'' type of function, or a ''smooth/open'' tonality. For a more dramatic effect, make the .01uf a .047uf or so.
  • Add an SPST switch around C3 to add more bass by adding a .33uf cap in parallel with C3.
  • Change R2 and C3 to a 1k/.22uf for the same high gain frequency response but more gain potential
  • Change R4 to a 1m audio taper pot for better response through gain adjustment.
  • Add an SPST switch to add in diodes in parallel with R4. I have 1n34a and 1n4001 diodes shown here, though any can be used.
  • Change D1 and D2 to 1n34a and 1n4001 diodes (in series) in place of each stock diode for louder output as well as better dynamics.
  • Change C5 to a .0022uf and wired in series with a 1m audio taper pot to act as a tone control.
Here''s the schematic with the mods in place:

These mods will make your pedal into a much bigger, fuller, nicer (or meaner) sounding distortion or overdrive. While not all of the mods are necessary, I encourage you to experiment to find what you like and don’t like and tailor your own pedal to your needs.

Happy Soldering!

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The Boss Blues Driver is one of those pedals that everybody has owned or at least played through once. I’d venture to say it’s nearly as popular as the


Boss BD-2 Mods
The Boss Blues Driver is one of those pedals that everybody has owned or at least played through once. I’d venture to say it’s nearly as popular as the beloved Tube Screamer. While many players like the sound of the stock pedal just fine, many other guitarists like the basic tone but just want it better—more organic, responsive and dynamic. Some feel that there are just way too many high frequencies in the pedal, making it sound brittle, especially with a single coil guitar into a clean, Fender-type amp. Luckily, there are modifications we can do to make the pedal much better.


The Circuit

Larger Image
Before we get into the mods, let’s break down the circuit a bit and see what is going on. Looking at the schematic we see that it is essentially two cascaded discrete opamps, which are then followed by a standard opamp for gain recovery, bass boosting, and buffering of the signal. Of course, this is after it goes through a discrete buffer.

In layman’s terms, a discrete opamp is similar to the IC chip version. It does the same thing, just in a simpler fashion that some feel is more responsive and less “sterile” feeling and sounding. It uses two FETs facing each other followed by a bipolar transistor. There are two of these types of gain stages in the BD-2, controlled by a dual gang 250k pot wired as a variable resistor. Just like the IC opamp circuits, there is a resistor/capacitor pair going to ground that will also help set a frequency to clip. This pair will also help set the gain, though they are fixed values in the BD-2. R31 and C22 are the pair for the first stage, while R15 and C9 are the pair for the second stage.

We know that EQ before clipping determines the clipping feel, tonality, and response (distortion/overdrive) quite dramatically. For example, if we want a fuzzier type of distortion, we want to increase the bass before it is clipped. Then, we clip the signal as much as possible without creating a lot of noise or oscillations.

R31 and C22 in this first gain stage set a frequency of just a hair over 700hz. This is a normal frequency for most overdrives and distortion. If you want more fuzziness, increase this cap to .22uf (microfarad) or larger. If you want a tighter crunchier type of tone, make the cap smaller. If you plug in these values to my calculator at indyguitarist. com/filter.htm you will see the frequencies you can affect.

Boss BD-2 Mods
BD-2 tonestack (left) and Traditional Fender tonestack (right)

After this first gain stage, we go through what first looks like an odd tone filtering stage. It is actually a Fender-type 3-band tonestack with fixed values (with the treble on 0 and the bass and mid on 10). This is a really cool thing to mess with if you want to go hog wild, because you can add trim pots in place of R37 (use a 250k trim pot for treble), R50 (use a 1M trim pot for bass), and R51 (use a 25k trim pot for mids). In addition, you can change the ‘slope’ resistor, R36, to a 33k, C34 and C35 to a .022uf, and change C26 to a 470pf in order to get more of a Marshall type of tonality before the signal is clipped. When you are replacing these resistors with trim pots, just connect one hole to pin 1 on the trim pot, and the remaining resistor hole to pin 2 on the trim pot. Leave the third lug untouched.


The BD-2 EQ before clipping looks like this due to this filter:
Boss BD-2 Mods

Notice how there is a ton of bass present? That is before the majority of the clipping is happening, so it’s no wonder the pedal sounds fuzzy when the gain is turned up!

A good mod at this location is to make R50 a 100 ohm, and change R36 to a 47k. That will give you a much flatter EQ response.

After that the signal is clipped by diodes connecting to ground (D7, D8, D9, D10) with two diodes on each side and fed into another discrete opamp. This opamp is nearly identical, except the frequency response is a little different. There is more gain in the bass (set by R34 and C24, frequency is about 72hz) but it works exactly the same. Notice that since the bass is boosted yet again here it’s really no surprise that the BD-2 would be so fuzzy with the gain turned up.

C17, R25, and C19 form both a highpass and low-pass filter, which will get rid of some high harmonics about 5k or so, as well as to get rid of some of the bass content that was created by boosting the lows so much previously.

Boss BD-2 Mods
View full-sized, printable schematic

From here, the signal goes through a fairly standard tone control very similar to that of an old Fender tweed Princeton. It acts as a high-pass filter with the tone knob turned up, and a low-pass filter with the tone knob turned down. So, you increase the highs as you turn up the tone, and lose some bottom end once you are past about halfway or so. Changing C100 will change what high frequencies are filtered with the tone control up, and changing C101 will change what frequencies are filtered with the tone control turned down. The volume control is next before going into the next stage—the EQ stage.

The next stage is a simulated inductor, which is boosting the bass content at about 120hz or so by 6dB. Even though there are diodes in this stage (D1 and D3), they aren’t really clipping much at all like diodes usually do in an overdrive or distortion circuit—it is actually more to protect this opamp from being slammed with a loud and hard signal. It also does a little bit of filtering as well as help to output a low impedance signal. Changing these diodes to a different type will give a little bit different “feel.” However, it becomes a little less compressed if you use LEDs, and becomes a bit more compressed and filters out a bit of the highs if you use germanium type diodes. This is probably due to varying degrees of harmonics being ever so slightly clipped.

If you want to mess with the EQ, there are several ways to do it. You can try changing the cap sizes of C9 and C16, or changing R21. Changing the caps can get you many more frequency options just by subbing in various values. Increasing the resistance lowers the frequency and decreasing it raises the frequency to a point. You might even try subbing a 5k trim pot here just for fun!

From here it goes into the switching circuit and then to an output buffer. Even when it’s in bypass the pedal is going through three discrete buffers.

A lot of folks just want to know, “What do I change to make it sound better?” In that case, I’d recommend several different options. The Blues Driver mod that I probably do most often is the Brent Mason modification. This mod is very easy, and only requires changing a few parts. It was a modification that I did in response to Brent Mason’s request for better tone from his blues driver. It will give you a meatier, more “round” sound and excels at low to mid gain:

Boss BD-2 Mods

Another popular mod is the “Tweed” mod—designed to give you a bit more of the “woolly” tones from an old Fender amp.

Boss BD-2 Mods

All of these parts can be found at my favorite parts supplier, Small Bear: smallbearelec.com.

All in all, this is a great palette to work from for great tones. Let me know what you think—you can find my contact information at: wamplerpedals.com


Brian Wampler is an author, effects designer/builder, and operates IndyGuitarist Custom Effects: indyguitarist. com and wamplerpedals.com. His books include How to Build Effect Pedals, How to Modify Effect Pedals, and Advanced DIY Effect Pedals, and are available at indyguitarist.com.
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