Welcome to Part 3 of the Mod.It.Yourself series where we have previously looked at the basics of Tools and Techniques in Part 1 and how to mod the Diode Clipping in a pedal in Part 2. Part 3: Switches will look at an important component in the pedal modder’s toolkit. Switches are mechanical devices that allow an instantaneous flip to either turn part of a circuit on or off (break the circuit), or introduce a new part to the circuit. The latter function is useful in doing reversible modifications, or mods that use the original stock component. This part of The M.I.Y series will explain a bit about common switches and some ideas on how to use them in your own pedal mods.

The two most common mechanical switches used in modifying pedals are the push button switch and toggle switch [above]. Both of these switches use common nomenclature for their components that must be understood before selecting them for your next project. Below is a look at some of the more common names of switches that are used for pedal mods and an explanation of their specs:

Each switch is named with respect to the functions of their contacts, i.e the part of the switch that is in contact with your wire, component, PCB etc. Also called a lug or pin. The two terms are poles (denoted by P) and throw (denoted by T). A pole is the number of switch contact sets of pins/lugs, and are labelled SP- for single pole, DP- double pole, 3P- for triple pole etc. The diagram [below left] shows the poles of a 4PDT switch.

Most switches used in pedals have three pins per pole. The center pin is common ie. is always connected to either outer pin of the three. Moving the toggle either up or down selects [above right] between these two connections or conducting positions. These positions are known as throws and are denoted -ST for single throw or -DT for double throw. A single throw switch only has two pins with the third pin shorting to ground, thus having only one position.

Common switches used in modifications are single pole double throw (SPDT) or double pole double throw toggle (DPDT) switches, and true bypass foot switches are known as triple pole double throw (3PDT). So using this knowledge of switches, here are a couple of mods you can try on your next pedal designs or mods.

KILL SWITCH

To get a stuttering effect made famous by guitarists Tom Morello and Buckethead in stompbox form, you can make use of a type of push button switch called a momentary switch. By using a push-to-make momentary or “normally open”, when pressing the switch you are breaking the circuit thus creating a staccato effect. To do this, all you need to do is cut the wire that goes from the output of the PCB to the bypass switch. Wire each of these two ends to a normally open SPST momentary switch and you have a momentary kill switch [diagram below]. The effect signal will stay on until you step on the switch, cutting all volume of your signal. By pressing at rhythmic intervals, you can create unique guitar rhythms heard in many RATM riffs. Momentary switches are great for these “stab” like effects and can be used for feedback loops, or wiring to a potentiometer in a delay pedal to get that spaceship, oscillation sound.

DIODE  CLIPPING SWITCH

As previously discussed in Part 2 of the M.I.Y series, we can mod a pedals’ clipping diodes to create a different tone of the distorted sound. We could use different diode material , symmetry, combinations etc to get our desired sound. But what if you liked two diode sounds and wanted to switch between them? Using an SPDT switch, you can do just that and is a common feature on many effects pedals.

The schematic [above left] shows the clipping diode structure of many distortion pedals – a hard clipping pair at the output of the IC. One end of the pair shunts to ground, while the other end is in the signal path. If this end on the signal path (A) is wired to the common pin of the SPDT switch, we can then switch between two differing pairs of diodes. Wire the end of two pairs to ground, and the other end to (B) and (C) of the switch and you can select between your favourite clipping tones [above center]. The symmetry of the clipping can be controlled using this switching layout as well – just use different symmetrical pairs for (B) and (C).

You can also use this principle to switch between two components of differing values ie. the output capacitor to provide more/less bass into the circuit. Remove the initial capacitor from the PCB where one pad will have one wire running to (A) and two wires from the other pad to one end of either capacitor you wish to switch between [above right].

Hopefully this info and diagrams will give you ideas on how to mod your next pedal, or to modify your next pedal build. Also, I would suggest getting a multimeter with a continuity test function. By putting either probe on any two connections, a beep or sound should be heard. This is very useful to test your new connections.

Happy modding,

C.

After reading Part 1 of the M.I.Y series: Tools and Techniques, you should have a good grasp of what is required to get into your pedal and start modding. But before we flick on the soldering iron, I thought I’d write a few points about the diode, the key component to Part 2 of the M.I.Y series: Diode Clipping.

A diode is an electronic component that allows electricity to flow in one direction, much like a valve does letting water go one way but not the other. Diodes can be seen in nearly all effect pedal schematics and are noted as this symbol (left). They are integral in creating that overdrive or distortion sounds in your favourite dirt pedals, and come in different packages, materials and sizes. Each diode has a positive side (anode) and negative side (cathode). This polarity is what resembles a valve, and dictates the flow of electricity.

But how does a diode contribute to that overdrive sound? If we look at an audio signal (represented as a sine wave) we can distort the signal by “clipping” the tops and bottoms of the wave. This clipping produces harmonics that we hear as overdrive.

Image source: www.geofex.com

If a signal is clipped evenly on both top and bottom of the wave, this is referred to as symmetrical clipping and is used in pedals such as the Ibanez Tubescreamer. If a signal is clipped more heavily at one peak than the other, this is called asymmetrical clipping as heard in the BOSS SD-1 Overdrive. The more heavily a peak is clipped, the more a sine wave moves closer to a square wave, and closer to distortion and fuzz.

Image source: www.diystompboxes.com

The location of clipping diodes has an effect on the sound as well. Soft clipping involves having two diodes connected on the feedback-path of an opamp or a transistor (Tubescreamer). Hard clipping is when two diodes shunt to ground, creating distortion as in the ProCo RAT. The material of the diode also affects the clipping. Silicon diodes have been described as being “sharper” and “tighter” whereas germanium diodes are described as being more”compressed” or “spongey”. You can also use LEDs (light emitting diodes), Zeners, Schottkys, MOSFETs etc… the experimental possibilities are endless.

So with all of that in mind, let’s crack open a pedal. We will need [1]:

• A pedal (I will be using a BOSS SD-1),
• A selection of diodes,
• Single in-line break away sockets (purchased from any electronics store),
• The schematic of the pedal (that can be found at the resources listed in Part 1 of the series).

Firstly, unscrew the back so we can get to the PCB. You should be able to see a trace side, full of tracks and solder joins [2]. Carefully lift up the PCB so we can see the component side, and look for a set of diodes [3]. The markings (e.g D3, D4, D5) should correspond to your schematic. Desolder these diodes, marking down their original orientation, and clear the holes. Solder in a socket for each hole from where the diode was removed [4] and place the PCB back into the pedal. We can now experiment with different diodes, and combinations of diodes, and immediately hear the difference between them.

Place the diodes (using the same polarity as you marked down earlier) back into the sockets, power up the pedal, plug in and play. No need to close the pedal back up, it will just be a bit noisier. Now remove the power, remove the diodes and try another combination. Power, plug and play – hear the difference. Now try a symmetrical configuration, then asymmetrical.

In the place of one diode, try a MOSFET like an MPF102 (note in [1] how I bent only the ground pin to remove). Or you could try germanium and silicon diode in series, a silicon and LED, two silicons in series, two germaniums in series etc. To solder diodes in series, ensure that the cathode is soldered to the anode [5]. Using diodes in series increases headroom and volume but sacrifices a bit of gain. Use MOSFETs for “tube-like response” and LEDs (reds are great) for crunch and higher gain. When you find a combination you prefer, desolder the sockets and solder in your killer selection. Close the pedal back up and you now have a diode clipping modded pedal. Common mods include placing different diode combinations on switches, or a symmetrical/asymmetrical diode switch. But we may leave that till next time…

Happy modding.

C.

I modded this pedal for Matt, the bassist/guitarist in local Sydney post-punk band Hira Hira. He would use the Muff as his fuzzed bass sound, and whilst liking the sound, wanted something more bass-friendly. The Big Muff is a great fuzz for bassists looking for a heavier tone so I tweaked this one for use with bass and now offer it as the cubisteffects T-34 Big Muff Bass Mod.

Bassists seek out one Big Muff in particular – the Green Sovtek Russian Big Muff, or “The Tank”. The nickname is apt as it is rumoured to have been built with scrap pieces of tank plating. One of the most formidable weapons in World War II, the T-34 Soviet medium tank blitzed its way through the German forces. Known for its combination of ruggedness and firepower, the T-34 and the Green Sovtek Big Muff have a lot in common.

The tone of the Russian fuzz is similar to the Civil War Sovtek Muff but has more gain, is less smooth sounding and has a touch more aggression. This is ideal for the percussive attack of bass players. A number of selected components are responsible for the bass friendly bottom end the Green Big Muff produces. I have used this pedal as a template, and inspiration, to come up with a number of modifications to tailor the pedal for bassists - to emphasise the depth of a bass’ tone whilst creating a high gain Muff sound. All of this for a fraction of the cost of a vintage Russian Muff. The Green Sovtek Big Muff shares many similarities to the current Big Muff products and these modifications are offered for the NYC Big Muff (as pictured) or the current Black Russian Big Muff.

The T-34 Big Muff Bass modifications also improve on the original hardware and bypass design. What you get in the end is a pedal with a bass sound that has some clean tone mixed with fuzz and a flexibility not seen in any standard Big Muff. This flexibility allows you to pull a number of sounds from the pedal; smooth long synth-like sustain or a splattery loose tone, a mid-frequency EQ’d fuzz for a better place in the mix or a +6dB volume boost.

The T-34 Big Muff Bass Mod has a number of standard, and optional, modifications to transform your standard Big Muff into a unique bass tone monster.

The T-34 Big Muff Bass Mod involves three hardware changes:

1. TRUE BYPASS – The pedal will have a 3PDT switch installed for true bypass.
2. DC POWER JACK – The stock 1.35mm DC power jack will be removed for the industry standard “Boss-style” 2.5mm DC jack. This allows daisy chaining  a multiple pedal setup easier.
3. LED – The stock LED is replaced with a high quality, superbright, waterclear red LED.

The T-34 Big Muff Bass Mod also includes several component replacements. These are to emphasise the low end of the pedal to make it bass friendly. Some ceramic capacitors values are increased to let through more bass. Also, the stock transistors are replaced with Fairchild SE4010 silicon transistors, which gives the pedal a vintage-like bite. I found that these transistors, within a certain Hfe range, complement the bass fuzz sound.  They come in the epoxy dot package, like the Sovteks, and are hand-sorted to ensure the correct current-gain is provided to the circuit. Another modification is done to the diodes in the first stage. This modification “opens up” the distortion, allowing more bass and volume to push through. Also, as you increase the Sustain, the bass response also increases.

Two more mods are also included. These mods have become legendary in the DIY community and are the handiwork of Jack Orman.

1. TONE BYPASS – A toggle switch is wired to the Tone circuit of the pedal and allows the choice of having the Tone circuit ON or OFF. This switch was found on the late 70′s Op-Amp Big Muff. By bypassing (or turning OFF) the Tone circuit, the pedal has an additional +6dB output. Using this in the bass mod, the tone sounds a touch brighter or has increased treble. It has a great raw fuzz sound that is great on bass. As the Sustain is increased, the attack gets more loose and Fender Blender-esque tones can be achieved.
2. MID CONTROL MOD - By altering the tone circuit, a pot can be used to control the amount of mids. This provides a better standing in the mix if turned up, or can provide a cut if turned down. Like the Tone Bypass, it alters the original sound of the pedal but does provide more flexibility and ability to achieve a different tone.
   NOTE: The Tone and Mids Control pot will not function when the Tone Bypass mod is engaged as it has been…bypassed.

ADDITIONAL OPTIONS

There are a number of additional options that are offered in the T-34 Big Muff Bass Mod. These added options incur an additional fee and can be seen in the Pricing page.

• The Diode Mod can be switchable (with a toggle switch as in the picture above). This gives flexibility between the Stock clipping and Modded clipping.
• The Tone Bypass Mod can be made footswitchable (the pedal would have two switches, ON/OFF and Tone Bypass) instead of a toggle switch. This setup allows the mod to act as a volume/treble boost.
• A Blend circuit can be installed, with a knob placed aside the Mid Control pot (as seen in the picture above). The blending of a dry signal with fuzz is an important option for bassists and is offered as an extra. A secondary circuit board will be installed in the pedal with a pot controlling the mix of the blend.

Below is a demo of the T-34 Big Muff Bass Mod.
Clip Details: Fender Jazz Bass > T-34 Big Muff >DOD FX-17 Volume Pedal > Fender Bassman
Settings: Rhythm 1 played clean with neck/bridge pickup 50%/50% and Rhythm 2 with neck/bridge pickup 50%/50% and T-34 Big Muff (V: 12 o’clock, T: 11 o’clock, Mid: 12 o’clock, S: 12 o’clock)
Lead 1 with neck pickup 100%, bridge pickup 0% and T-34 Big Muff (V: 12 o’clock, T: 11 o’clock, Mid: Max, S: Max) and cut in/out with volume pedal.
Lead 2 with bridge pickup 100%, neck pickup 0% and T-34 Big Muff (V: 12 o’clock, Tone Bypassed, S: 2 o’clock)
Recording: SM57 > Mbox2 > Reaper

T-34 Bass Big Muff Mod by cubisteffects

Also, here is a recording from local Sydney band Hira Hira. Matt’s T-34 modded Big Muff features in the latter half of the track. Nice work boys!

Children’s Letters to God by Hira Hira. Uploaded by cubisteffects

C.