How to Mod a PedalAt some point this thread will have to end.
I'm not a tone
connoisseur, i don't have the funds to buy top of the line amps/guitars. Unfortunately, I don't even have a band right now and my playing skills is not up to par. But I want to share to everyone what I've learned in the past few months of modding and building pedals. Most of you may not know me and being almost a noob here, my intention is just to share information.
My Modded Pedals
Before You Mod a PedalThere are lots of way to improve your tone before resorting to modded or boutique pedals. Here are some tidbits that I learned over the years.
- Guitar. Check your guitar first. Send it to a luthier for a good ol' general setup. You may want to upgrade your no-name (or manufacturer stock) pickups to decent branded ones. DiMarzio, Seymour Duncans, Bare Knuckles, Elegee, etc, will do just fine. You may also want to disconnect the tone knob from your guitar's circuit (or you can replace the tone knob pot with a "no load" pot).
- Strings and Picks. Make sure that the strings loaded in your guitar are still ok. Replace them if necessary. There's a trick that I do when I was still in high school, I would get a pot and boil water, dip in the wound strings for a minute and wipe it with dry cloth. You may want to use heavier guage strings. Picks do affect your tone. I use 1.14mm Dunlop tortex picks for years. It never failed me.
- Cables. It's probably the cheapest and most effective upgrade. For years I've been using the cheap cable that came with my guitar. For 500 pesos (I think) you can buy Klotz cable which is way much better the more common, no name cables. Also the shorter the cable is, the better. I use Fender Tone Master Instrument cables, and IMO they are the best cables out there (that my wallet can afford).
- Pedals and Pedal Board. I have a few dozen of pedals but I don't have a working pedal board. I noticed when you start chaining two or more pedals in series you will loose some clarity in your guitar's tone (especially with pedals that uses input buffers). That's why when I jam with friends or play with my old band I'd bring only one pedal (and sometimes a wah pedal when i'm not lazy). There are times that I don't even bring a pedal with me. I'll just use the amp's distortion and back off the guitar's volume knob to dial in clean tones. (A EQ pedal can also improve your overall tone).
- Amp. There are lot's of decent solid state and cheap tube amp out in the market. Even though some will swear on their expensive amp, for me it's not a big deal. It's not like you will be playing infront of Eric Johnson or your d*ck is at stake when you have bad tone. Just make sure that you don't play with a blown speaker and dial in some mids.
- ETC. I prefer to stay away from unnecessary devices. The shorter the signal path is, the clearer tone your guitar will have.
- Fingers. Enough said.
Tone is also subjective. It differs for person to person. Modding your pedal does not always equate to a better tone. I've seen many mods on youtube that sounds nasty for my taste. You may also want to try backing down the gain a little bit, in which at loud settings may sound very effective (Thanks Nathan!).
ToolsThe things that you will need when performing modifications.
-Guitar
-Amp
-Guitar Cables
-Soldering Iron and Lead
-Resistors and Capacitors
-Jumper Cables
-Screw Driver
-Scissors
-Multimeter (optional)
-Audio probe -
http://www.diystompboxes.com/pedals/debug.html-Pedal Schematics or Pedal Mod guides
-Electrical tape
I bought this device (I forgot the name of this gizmo, it's the black device with a big Omega character) where you can hook it up to your circuit and change the value of the resistor with a turn of a dial. I also made a "dial in a capacitor value" device from 12 capacitors with different values, a pcb and a 12 position rotary switch (the device with lots of orange wires). The audio probe is useful for troubleshooting your pedal (there might be some instances that no sound will come out when you test it).
I buy capacitors and resistors in packs. It's way much cheaper and time saver to buy in bulk (especially if you are planning to mod a couple of pedals).
Basic ReferencesYou must learn how to read capacitor and resistor values before proceeding. Just google it and you'll find tons of resources on the internet. Here are some
Resistor Values -
http://www.dannyg.com/examples/res2/resistor.htmCapacitor Values -
http://www.kpsec.freeuk.com/components/capac.htmBasic Tone ModsMost big manufacturers will use cheap components. That's why before I mod my pedal, I will try to replace all capacitors with MKTs, mylars or silver micas. You can also further reduce the pedal's floor noise by replacing those nasty 1uF polarized electrolytic capacitors with MKTs or tantalums. When I performed my first pedal mod, I tried to replace the 100nF and 1uF caps with precise metal film caps. It a little bit pricey (ranging from $2 to $10 each) but they do sound good (you will have problems squeezing them in your pedal's confined space).
Huge Yellow Cap
More Yellow Boxed Caps
I love modding dirt pedals because with minimal component change, you can immediately notice the difference when you test it. The first thing to look for are the high pass and low pass filters in the pedal's schematics. You can also calculate what frequencies to attenuate and what component values to use. Refer to the references below.
High Pass Filter -
http://en.wikipedia.org/wiki/High-pass_filterLow Pass Filter -
http://en.wikipedia.org/wiki/Low-pass_filterBut I'm too lazy to perform calculations that's why I do it by ear. By using my DIY "dial in a capacitor" and my "dial in a resistor" (forgotten the product's name) devices, I would remove a capacitor and a resistor installed on the pedal's PCB, replace it with the dial device using the stock values. Then I'll connect the pedal to a guitar and amp (with guitar cables or with an audio probe), point all knobs on the pedal to 12 o clock and test the tones by ear. Choose your prefered tone by playing a few power chords and by incrementing/decrementing the values of the capacitor and resistor.
Here's an example using a Boss DS-1 and Boss MT-2 Metal Zone schematics (By the way I've done these mods to my pedals).
DS-1 -
http://www.godiksennet.com/images/sch/DS1PG2.jpgMT-2 -
http://www.godiksennet.com/images/sch/mt2-06.jpgNote: I'll be using the schematics of a Boss DS-1 and MT-2 for most of my examples.
For the Boss DS-1, I replaced C3 (stock value 47nF) to 39nF. With this small change, I was able to add more mids. I also made this change to my Vox Satchurator, now it has more mids that before (and now it sounds better than my DS-1).
For the Boss MT-2, I replaced C29 (stock value 33nF) to 100nF. With this change, i was able to add more bass to my pedal.
You can experiment with different resistor and capacitor values on the high/low pass filter using the schematics as your guide. It's also a good idea to take note of the changes that you have made, just in case you want to revert back to the original/modded values.
You can also change the caps and resistors connected to the tone knob as you like.
The basic rule is (depending if its a high or low pass filter)
- low value capacitors are used to increase/decrease higher frequencies
- high value capacitors are used to boost/cut lower frequencies
Also be aware that some capacitor types have polarity. I remember replacing an electrolytic cap with a tantalum with the polarity reversed. It produced weird sounds on my pedal and it took me days to troubleshoot the pedal.
Clipping CircuitTo locate the clipping section of a dirt pedal, all you need to locate are the diodes connected in parallel (Metal Zone - D4 and D3, DS-1 - D4 and D5). You can experiment with different components (LED, germaniums, mosfet) for the clipping circuit. You can also add another diode in series to one of the clipping diodes for asymetrical clipping. You can also increase the distortion/gain of a pedal by locating the resistor and capacitor connected in parallel with the clipping diodes (Metal Zone R13 and C23) or in series with the distortion knob (DS-1 R13 and C8). Increasing the values of the resistor in this section increases the pedal's distortion. The capacitor dicates the range of the frequency that will be clipped. Be sure to test the distortion knob's range before soldering your prefered components. Experiment.
Switches, True By PassIt's an advantage if you can perform a true bypass mod on pedal. Unfortunately this mod is difficult to execute on Boss pedals. If you are a true bypass snob, you can rehouse your pedal and add a 3pdt heavy footswitch. Trace the pedal's input. Chances are, the first or second transistor in the circuit that you will encounter (DS-1 - Q6) will be the input gate.
Also with a help of a drill and installing some mini SPDT or DPDT switches to your mods, you can have more mod options at your finger tips. For example, on the Boss MT-2, using a DPDT switch, you can reinstall the caps C35 and C25 to the switch and wire them back to the PCB. You can disable these two caps with a flick of the switch, thus removing the harshness of the pedal. By flicking this switch again activates the caps as they were stock, retaining the factory default, hissy sound of the Metal Zone.
My Modded MT-2 and XT-2. I think it needs another switch.
Op Amp UpgradesYou can experiment with different opamps on your pedal. From costly Burr Brown chips to the famous JRC4558 chips. You don't have to replace the opamp unless, whatever capacitors or resistors you replace on the board, the pedal still sounds harsh or noisy. I tried replacing the stock JRC4558s on the Metal Zone using Burr Brown OPA2134 but it only increased the distortion of the pedal causing my other mods to fail. However, replacing the Mitsubishi M5128 chip in my DS-1 with an OPA2134 did remove the harshness of the pedal. Replacing an 8SIP chip with an 8DIP will require a chip adapter. Using an 8DIP socket and some wires, you can build your own chip adapter.
Always make sure that the layout of the pins are correct and does not short with the other pins. Always refer to the chip's datasheet that can be downloaded from the manufacturer's website. Also do not install an opamp in reverse orientation because this may destroy the chip. I manage to burn a $7 Burr Brown chip and a $10 AD712 chip by placing it in reverse.
You can also check this reference from Texas Instruments when choosing a substitute opamp.
http://focus.ti.com/logic/docs/crossreference.tsp?sectionId=451&familyId=1Biasing the OPAMP/FET TransistorYou can also modify the voltage that flows to the FET amplifier or input of an op amp. By doing this mod,you can clean up or add a little more distortion to your pedal. This is by changing the resistor value connected to the source of the FET Transistor (DS-1, R9) and/or the reference voltage that flows to the gate of the FET by changing the resistor that's connected to transistor's gate (DS-1, R6). On my DS-1, I increased R9 a little bit (to 100 ohms) to bias the gate to 4.2 volts, removing a little bit of distortion in the input amplifier stage. The same principle applies to op amps. By changing the reference voltage, you can have a cleaner or a distorted output from the op amp.
You can also increase/decrease distortion by changing value of the feedback resistor connected to the op amp.
Here's a good reference for op amps -
http://williamson-labs.com/480_opam.htmClosing Remarks 
There you go folks. When performing mods it's important to take short breaks in between, especially when testing your modded pedal. Sometimes I'll test the pedal the day after. This way I'll now that my hearing has not been impaired and my thoughts not clouded by the fumes of the soldering lead. It's a lengthy post but I hope you'll benefit from this. Good luck with your pedals.
