Prentiss Effects

I was recently commissioned by a couple of guys at my church to build some Strymon favorite switches. These are pretty easy to build and are a great place to start if you're getting into building pedals. Not much to say about them other than that so let's get into the build.

Parts

Build Procedure

Step 1 - Prepare and drill the enclosure

This step is pretty straight forward. I purchased a powder coated enclosure (link above) so it didn't need any prep work before I started drilling. If you buy an unfinished enclosure then you'll want to sand and paint it before this step.
There are only 3 holes to drill in this enclosure; footswitch, LED, and jack. Measure each of your parts so that you don't use the wrong drill bit size and you're all set. I use a step bit like this one so I don't have to change bits when I'm drilling.

I was surprised that I couldn't find a drilling template for one of these so I made one myself. If you want to use it just save this image and print it at 100%. Do not select "Fit to Page" or it won't scale properly it needs to be original size.

Strymon Favorite Switch -1590LB Drill Template

Step 2 - Installing the Hardware

Now we're going to take all of the hardware and fit it in the enclosure. Since it's so few parts, we're just going to be soldering directly from one piece to another. I quickly discovered that some parts are easier to put in first with my drill template. I recommend starting with your LED bezel, then the TRS jack and finally the DPDT switch.

Hardware All Mounted

Step 3 - Soldering it all together

Today we're going to be looking at the Friedman BE-OD, a distortion pedal that was designed to emulate the Friedman Brown Eye Amplifier. If you're wondering how it sounds, just go check out the demo done by Pete Thorne here. While he makes everything he plays sound great, this pedal was really easy to dial in for various guitars because of the powerful EQ controls and internal gain trimmer. The gain itself is really nice, you can get a wide range of sounds from it, although you can't really get super low gain sounds unless you're rolling off the volume on your guitar. But if you're using this pedal then you're probably not looking for low gain anyway.

This pedal was built using the Thermionic Distortion PCB from PedalPCB. I really liked working with it because it's laid out really well and designed for top mounted jacks in a 125B sized box. The board version I have uses 1/8W resistors (my first time with those) but the updated one uses standard 1/4W. First, we're going to look at the theory behind the pedal and then I'll talk more about the build process and board itself.

Theory

It only seems natural to use the schematic from the Thermionic Distortion build doc, since that's the board I used, and the guys over at Pedal PCB were really cool and gave me the go ahead. I've gone and marked it up into 7 blocks that we'll be examining. While it looks like a lot, the building blocks are fairly simple. The signal path consists of 4 cascading gain stages like a tube amplifier might use, some power filtering, and various filters to shape your sound. So let's dive right in.

Power Supply

Let's talk about the power supply. This one might seem more intense than most pedals and that's for good reason. High gain pedals tend to get noisy, especially if they're not filtered properly. Here, D1 is acting as a reverse polarity protection diode in case the pedal is hooked up to the wrong power supply. The resistor that follows, R30, is a current limiting resistor that will blow if the pedal starts drawing too much current.

Then we have the voltage filtering. C20 is smoothing the majority of any DC ripple that existed in the power supply. It's followed by three 100nF caps which are used to filter the power between pins 8 and 4 of each of the ICs to prevent any noise in the signal path.

Lastly, there's a voltage divider created by R32 and R33 which is buffered by an op-amp in order to make sure each gain stage receives a constant current.

Input Gain Stage & Tight Control

This is a really simple stage. First we have an anti-popping resistor, R1, for when the pedal is switched on. The signal then goes through the input capacitor, C1, and through a low-pass filter, formed by C2 and R3, which removes any high frequency noise.

After all of that we get to the first gain stage. This gain stage is made using a non-inverting op-amp configuration which means we can calculate the gain with this equation:

2nd Gain Stage

The other interesting part is that there's a cap in series with the Rin resistor. This forms a high-pass filter with a corner frequency of ~72Hz, so all of your bass will pass through. Then there's a set of LEDs used for soft clipping and a 47pF cap to smooth out some of the treble content. Overall, this looks a lot like the tube screamer clipping section. The major difference is that it uses LEDs (a common TS mod) and the corner frequency on a Tube Screamer is much higher, cutting out a lot of bass (~720Hz). This section doesn't need as high of a cutoff frequency because the tight control in the previous stage is allowing you to choose it yourself.

3rd Gain Stage

The signal first goes through a coupling capacitor to remove any DC offset from the previous stage. This capacitor also acts as part of a high pass filter in tandem with the overall impedance of the next stage to limit the amount of bass passing through.

Next we have an inverting op-amp configuration. This is actually simpler to calculate than the non-inverting op-amp. So let's take a look at the equation.
Now, if you're wondering why we have a negative amplification, it's because we're using an inverting op-amp configuration. It's flipping the phase of the signal, not reducing the amplification of our signal. So we really have an amplification of 10 for all intent and purposes.

There's also some more clipping diodes and another smoothing capacitor like the 2nd stage has. One cool thing is the additional 22k resistor. It's not a part of the gain calculation, it's actually acting as a "knee-softening resistor". It helps to smooth out the conduction of the diodes in the feedback loop, which makes the drive more tube-like.

4th Gain Stage

For the fourth gain stage we have another inverting op-amp configuration. This one's interesting because the feedback resistor is a combination of the 10k resistor and the 100k trim pot. The math is pretty similar to the previous gain stage:
That's really all there is to this stage. Nothing real crazy

Presence, Hard Clipping, and Treble Control

The Presence control is a simple RC low-pass filter, but it's really useful. The 2.2k resistor sets up a maximum corner frequency of 7238Hz. When the control is all the way down we have a total resistance of 12.2k which translates to a corner frequency of 1305Hz. You really get a lot of tonal variation out of that control.

Next we have a hard clipping phase. Again this is really simple, just two LEDs that run to the 4.5V bias reference (VREF). This is the kind of clipping you'd expect to see in a distortion pedal. We're using VREF instead of ground because our signal hasn't run through a coupling capacitor yet, so the AC part of the signal is still centered around 4.5V. By using LEDs the signal will clip at a higher voltage threshold which gives another character to the gain compared to some standard silicon diodes with a lower threshold. By varying the trim pot in the 4th gain stage you can change how these diodes clip. This is used to simulate the way a power amp distorts when changing the master volume.

Lastly, we have another low-pass filter that's forming the Treble control. Now since the Presence control is taming the high end before this stage, we don't really need to set up a maximum threshold. With the Treble control all the way down we have a corner frequency of 338Hz which is crazy. At this point the control is basically being used to cut off any excess treble that is not tamed by the Presence control.

Bass Control and Volume

The bass control is the trickiest part. It's active filter based on a bridged-T feedback network. Now that means something to someone, but that someone is not me. From what I've found, it involves very long equations and some complicated math that uses a bit too much greek for my liking. I'll break it down as best as I can.

A bridged-T feedback network is basically a low-pass filter mixed with a high-pass filter. It's usually a passive filter that creates a notch (cuts the frequencies) but when it's in a feedback loop it becomes a boost.

This filter is designed to boost the bass frequencies around 70hz. The two capacitors are used to form a ratio that determines how dramatic of a boost there is. The resistors are typically the same value; this is convention and helps in getting more predictable outcomes. They, in conjunction with the capacitors,help determine the frequency that is being boosted.

There's a lot of interplay between these components and it can change a lot by messing with one value. For the most predictable results you'll want to change values in pairs. For instance, changing the 22n to 10n and the 220n to 100n moves the frequency to about 150hz. If you leave those capacitors alone and change the resistors to 3.3k then you get a mid boost around 700hz (a factor of 10 higher). Generally speaking, decreasing the value the parts will shift the boost upwards in frequency and increasing the values will shift it downwards in frequency.

For a bit more information (and some complex equations) on how this works check out this site. Just know that the explanation is for a passive configuration. The active configuration is what turns it from a frequency cut (notch) to a boost. I simulated this section in LT Spice (a circuit simulation software) to figure out how it works and I highly recommend doing that before changing any part values. Simulating it will give you an idea of what to expect when you change a part and how it plays with the other pieces of the circuit

The potentiometer is used to limit how dramatic the boost is. At its lowest value it will boost 70hz the most because it's essentially out of the circuit. When it's all the way down, it's at its maximum value and is limiting how much the filter can actually do it's job which reduces the boost.

After all that complicated filtering, the signal runs through another cap and resistor and then to the volume knob which is just a standard voltage divider configuration. This is a pretty standard volume control for most pedals.

Pedal PCB Shoutout

Sources:

Jack Orman's RC Filter Calculator - http://www.muzique.com/schem/filter.htm
Op-Amp Basics - http://www.electronics-tutorials.ws/opamp/opamp_8.html
Soft Knee Resistors - http://www.diystompboxes.com/smfforum/index.php?topic=82764.0
Bridged-T Filters: - http://www.johnhearfield.com/RC/RC4.htm

Hey guys, I'm gonna be taking a look at the TC Electronic Hall of Fame 2. I was super excited when Amazon accidentally leaked this a while back. They were finally going to be adding shimmer and multiple TonePrint settings! I was already a fan of the original Hall of Fame, having used it for about the past 3 years, so these were updates I was really looking forward to. I ordered one off of amazon as soon as they popped online and two days later it was at my doorstep. If you're looking for a quick rundown of what I think and the new features then #scrollharder down to the bottom and there will be one. But now we're gonna dive in.

Algorithms

The new Hall of Fame looks like it has less algorithms, but that's not the case. Some of the less commonly used ones were removed from the front (such as the gated reverb) but are still accessible from the TonePrint editor. The original algorithms, such as Spring and Room, are mostly the same. They have subtle differences from the original due to incorporating the MASH technology. Also, they all seem to have a slightly longer decay than the original which I personally like since I get a bit more range to work with.

Let's talk about the shimmer algorithm. This is one I definitely wanted and wished the original had and now it's here. You can't say anything cliche about it because there's nothing "natural" about a shimmer reverb. Overall, I'm really pleased with how this turned out. Other shimmer reverbs I've played take too long to build into that sound and it feels uncomfortable to me, but this does not have that issue. The octaves bounce back into the signal fairly quickly and builds that nice choral sound you expect from a great shimmer. You do occasionally get a bit of modulation if you do some super complex chord voicing but it disappears in the mix when playing live. I will say that it still falls a bit short of the Strymon Shimmer that made this setting popular, but only just. That being said, I can get into that shimmer setting in the editor and tweak the small things that I want to change, but I can't really do that on the Strymon stuff (at least not that I know of). In the end, I think it's a great shimmer and easily the best at this price range.

MASH

So this is the new big thing from TC and...it's actually really cool. I was worried at first that this would be super gimmicky and not actually very useful. It turns out that it's really easy to work with and easy to operate, effectively, in a live setting. By holding down the footswitch and varying the pressure you use, it acts as an expression pedal. There's a little rubber grommet underneath the pad of the footswitch that helps you feel how hard your pressing and it's quite easy to operate. The parameters it controls also changed based on which setting your using. In the shimmer mode, it controls just how much shimmer is in your signal and the decay time of the reverb.

I know TC gets a bad wrap on their footswitches, but that's really just from one bad batch they had. This one feels really sturdy and I don't have any concerns about it going bad on me.

But the real magic of the MASH function comes into play with my favorite thing about this pedal. The...

TonePrint Editor

The editor got a fantastic upgrade in this version. In the original, you could control parameters for the modulation, the reverb, and what the decay and tone knobs controlled (up to two parameters for each). In the new version, you can assign up to three parameters to each control knob (that's one more knob guys!), and you have additional access to a bunch of parameters for the octaver. Lastly, you get to dial in how you want your MASH to work. That part is really cool because you can set it to fade things in and out depending on the pressure for cool crossover effects. It's also really simple to set up the mapping for your mash. You can pick a parameter from a drop down menu (up to three) and then scale it on a little graph to decide how it changes as you press down.

Summary

TC has made another great reverb for the money. The algorithms are really well designed and deliver where it counts in the mix. Having multiple TonePrint options makes the pedal incredibly versatile and customizable with the editor (which has gotten a nice upgrade). The shimmer setting doesn't quite get you the "chorus of angels" sound that folks like Strymon are known for, but it's still very good. Lastly, MASH function is well thought out and easy to use, rather than gimmicky, and the footswitch is very sturdy and holds up well in live use.

Let's build the Madbean Turnabout (a.k.a. JHS Andy Timmons clone). I got the chance to play the JHS @ (Andy Timmons) at the Chicago Music Exchange a while back and it sounded pretty freaking good. It had a nice, thick overdrive/distortion and the clipping options made pretty drastic changes which was cool. So when a vero layout based on the pedal showed up, I knew I had to make it. I'll go through the fairly simple circuit theory that this pedal uses and then quickly go over my process for building this pedal. Lastly, I'll say a couple words about how knowing the theory behind this pedal helped me to troubleshoot an issue I had.

Please note: the circuit used here is from the Madbean Turnabout which is similar to, but not exactly the same as the JHS @. There are only two significant differences which I'll point out as they come up.

The Theory 

Something I like about this circuit is that it's pretty straightforward from a theory standpoint. Nothing crazy, just basic building blocks that result in great tone. We'll be using the schematic from the Madbean website for this but taking it one block at a time. I've gone ahead and marked up a copy of the schematic based one what the blocks are for our analysis here:

Power Section

This is a pretty standard power section. The 100uF and 10uF caps do some DC filtering to get rid of residual ripple from the power supply. A pair of 22k resistors forms a voltage divider to bias the op-amps for the signal path.

1st Gain Stage

The first gain stage is very simple. It's a standard non-inverting op-amp configuration like you might see in a Tubescreamer. The difference here is that it doesn't include diodes in the feedback look for clipping. A low pass filter, centered at 723.8Hz is made with R5 (1k) and C4 (220nF) which could be fun to play with in order to change up how the mid frequencies are affected.

If you look at the gain range for this section, then using the equation for a non-inverting op-amp we get 2 at the low end and 101 with the drive knob all the way up.

2nd Gain Stage

The second gain stage is another basic building block. It's set up in an inverting op-amp configuration. In this case R6 and R7 set the gain for this stage at 100. Nothing super fancy is happening here, you could tweak those resistors to mess with the gain but it's probably not worth doing since you already have the gain knob in the first stage.

Note: The coupling capacitor, C7, is different between the Madbean and JHS pedals. In the JHS version this is a 2.2uF cap as opposed to the 1uF in this circuit.

Clipping Options

The clipping options on this pedal are pretty cool. The pedal uses an on-off-on SPST toggle switch. In the center position the contacts of the switch don't connect. Since the LEDs are outside of the switch, they are able to conduct and clip the signal. When the switch goes to either of the other two positions, the diodes and/or MOSFETs have a lower clipping threshold than the LEDs so they conduct and clip the signal instead of the diodes.

Note: This is just how the Madbean Turnabout configures it. Changing clipping diodes is a great way to achieve new sounds from a circuit. The JHS Andy Timmons has a similar 3 way toggle, but they use LEDs for their 50W mode, BAT41 diodes for the 25W mode, and no diodes for their 100W mode. You can try all sorts of combinations with your own setup. Just make sure they have lower forward voltages than whatever the combination in your middle position is or the middle position will start clipping first.

Tone Controls & Output Stage

Summary

References

Prep

It's never fun to sit down to start soldering and realize you don't have something you need half-way through. Get these items together before you start and have them close by for when you need them:

1. Soldering Iron (I keep mine in the back corner of my desk at all times)
2. Solder
3. Solder Sucker or wick
4. Tip cleaner or damp sponge for cleaning your iron
5. Wire Cutters
6. Wire Strippers
7. Needle nose pliers
8. Containment device (blue-tack, rubber bands, piece of cardboard. Anything that keeps your components held flat against the board when you flip it over to start soldering)
9.  Trash can (for tossing away bits, cutoffs, solder blobs and other things that take up desk space while you're working)
10. Third Hands (helpful for populating the board)

That all may seem intuitive, but it wasn't for me. Having a trash can was especially hard for me to remember. It really helps when you have a clear work space and you're not trying to work around all the bits you've stripped from your wires.

Setting Up Your Soldering Iron

Now that you have your tools you have to make sure they're ready. Heat up your soldering iron. I have a variable temp one that I set at around 350°C for soldering and I crank it up a bit more for desoldering. Once it gets hot, melt a bit of solder over the tip in order to tin it. Then wipe off any excess by dabbing it in your tip cleaner. Now, you have your soldering iron ready to go and we can begin.

On-board Components

Time to solder components in. I have an order I follow which makes things go smoother and quicker and it goes thusly.

1. Jumpers - These go first. Since they're so thin I use the stash of resistor, capacitor and diode cutoffs that I have to get them in before anything else. By doing this first I can keep them tight to the board. 
   
2. Resistors - These are the next in size (generally) so I go ahead and populate the board with all the resistors (held in a set of  third hands). Then I can stick something like a piece of cardboard over the top, flip over the board and solder everything together in one go.
   
   
   If you're using blue tack to hold everything in place then you should be good to go. If you're using a piece of cardboard then you can also use a couple of rubber bands around the edges to hold everything in place under tension. I tend to push down in the spot where I'm soldering on accident and let the resistors start falling out in other places. In this case I weighed the board down with a couple of spare tools (as seen above). The end result looks like this:
   
3. Diodes - This is a little trickier. At this point I solder in the diodes that I won't be socketing (like power protection). They're about the same size as resistors so it's pretty straightforward and uses the same technique. You'll notice the diode in the top center of the previous photo. I did that at the same time in this case since it was the same size as the resistors. 
4. Sockets - I do any DIP (Dual In Line) sockets first. These are the ones you'll be using for ICs in most cases. Then I work on any SIP (Single In Line) sockets which are usually diodes, transistors, or filter resistors/capacitors.
   
   
   For putting on SIP sockets, break off however many you need and stick them onto the bigger piece in the spacing you need. This will let you use the big section you took them from to position the sockets in the board without them falling out. 
   
5. Ceramic and MCC Capacitors - These are the small yellow and orange capacitors. They're pretty tiney so putting them in first makes things easy. (MCC stands for Monolithic Ceramic Capacitor...so yes I was a bit redundant)
   
6. Film Capacitors - The box and greenies go next. I generally work from lowest value to highest since they increase in size as you go (especially with the greenies). 
   
7. Electrolytic Capacitors - These are super nice because you can put all the caps in, flip the board, and then the caps hold the board up while you solder (if you do them one height at a time)
   
   
   Note: In the last picture there's an MCC in the bottom right corner that magically appeared. Well that's what happens when you don't read the build doc thoroughly enough and you realize you're gonna be putting a tiny cap in after all your electrolytics. If that kind of thing does happen to you, then just push the component in and bend the legs outward from the holes so that it holds the component in place and keeps it close to the board.

Off-board Wiring (Pots and Switches)

This is where things get a bit tricky for me. I like to use PCBs with board mounted pots. That way I can use a drill template and I don't have to deal with offboard wires. That procedure typically goes like this:

1. Drill Enclosure - I drill the enclosure with a template (usually provided in a build guide like the Aion Electronics documents do).
2. Mount pots and switches - Put all the pots in the enclosure and screw them on tight enough that they'll hold. You're gonna want them to be able to move a bit to line up with the PCB so don't tighten them too much.
3. Align PCB with hardware - Take your PCB and fit each of the legs of the pots and switches into their corresponding locations. 
4. Solder - Now you can go in and solder all of your connections. Then solder in your wires for your switches and such and you'll be left with a fully working board that now lines up perfectly with your drilled enclosure. 

If you're working with a PCB that doesn't have board mounted hardware (or a veroboard layout) I follow a similar procedure.

1. Drill Enclosure (optional) - I say it's optional because sometimes I just want to try out a circuit before deciding if I'm gonna box it. If you do want to box it then go ahead and drill an enclosure using a generic drill template. They're all over the internet.
2. Measure and Cut Wires - This is the tedious part. I figure out how long my wires need to be based on how they'll have to be run in the enclosure (a little extra wire is always better) to get to the pots and swtiches.
   Pro Tip: when you're soldering the wires in place, put the opposite ends in the closest socket to hold it and bend it in place for you while you're soldering. 
3. Solder to the Board - I solder the wires to the board next. Then I'll group them and bend them to whatever shape I need so they're close to the pots.
4. Solder to the Pots/Switches - I usually have a third hands hold the pot and the board. Then I can manipulate the wire to whatever configuration I need to make the solder join. 
5. Test Fit - I then test fit everything to make sure I didn't go short on any wires.

Off-board Wiring (Footswitch, LEDs and Jacks)

Now that the board is all set we can get the rest of the hardware mounted and wired up. If your PCB has a space for your LED then you can line that up and solder it in place. If it's off board then you can follow what I do. Follow whatever your favorite true bypass wiring diagram is. I like this one. I won't be showing you how to wire your footswitch (because there's a few different ways), just the order that I run the wires for all of off-board wiring.

NOTE: At this point you should have a board that you're able to test. I would recommend testing it out first with a testing rig before boxing it up to make sure it works. Remember "Rock it before you box it".

1. Mount the hardware - I first mount all of the hardware in the enclosure (jacks, footswitch, power jack, LED bezel) to make sure nothing is accidentally grounding out or touching anything else.
2. Run your ground wires - Pretty straight forward. I run all of the ground wires and solder them up before I do anything else.
3. Run your power wires - This will basically be the 9V wire from your board and the positive terminal of the LED (unless you board has the LED built in
4. Run your signal wires - Your input and output jacks are next along with soldering the in/out wires from your board to the footswitch. 

Congratulations, you now have a fully built pedal. If you have any questions then feel free to ask. Also, check out these other resources for off-board wiring. This is just how I do it. I learned from a bunch of places and these are some of them.

http://tagboardeffects.blogspot.com/2012/02/offboard-wiring.html
http://madbeanpedals.com/tutorials/downloads/MBP_FootswitchWiring.pdf
http://madbeanpedals.com/tutorials/downloads/Making_a_Prototyping_Rig.pdf
http://effectslayouts.blogspot.com/p/general-layout-notes.html

This post is an in depth look at the Ernie Ball VP tone suck mod. It works on all passive Ernie Ball volume pedals and can also be applied to other passive volume pedals. I'll go over why people experience "tone suck" (hint: it's because of impedance) and a step by step on how to install a buffer that prevents this.

I've been looking into making a replacement PCB with these mods built in. If this is something interesting to you then please go fill out this form and let me know.

Now, let's get started!

What it does and why it works #NerdTime

In audio level signals, we look at optimizing voltage transfer to maintain our signal. As the ratio drops, our high end begins to roll off as well. The Ernie Ball VP (and JR) is basically the volume circuit from your guitar and an added output jack for the tuner before the volume pot. The problem with this configuration is that the volume pot in the volume pedal puts a load on your signal which combines in parallel with the input impedance of your amp or the next pedal in your chain and lowers your voltage transfer ratio. Let's look at the math of how that all works.

For starters, your guitar has a high output impedance. Sources vary a lot on what that range is, but Jack Orman and Jack Deville seem to agree that it's somewhere between 10k-40k (and they're both really smart so we'll trust them). I'll use 15k for our purposes. Now standard practices tell us that in order to optimize voltage transfer we want the input impedance of the next object in our signal chain to be at least 10x greater than our output impedance. In fact, the higher we can make the input impedance, the better the transfer will be and less high end will be lost. The reason for this is that your guitar's output impedance can be thought of as a series resistance and the following input impedance as a resistance to ground which creates a voltage divider.

So let's say that we normally have a guitar going into a pedal with a 500k input impedance. That gives us a circuit that looks like this:
We can then look at the voltage divider equation to figure out our ratio. Upon inspection, we can state that if our input signal is assumed to be 1V then we really only need to look at the resistance ratio to figure out our voltage transfer ratio. So by plugging in those numbers we get the following:

So we're going to be seeing about 97% of our signal go through. Great! That 3% that we're losing is coming from our high-end because higher frequencies are effected more by impedance. So the frequencies we're losing are ones we can't really hear.

Now if we add the volume pedal into the signal chain we get a different result.

The pot in the volume pedal is essentially a parallel resistance to our pedal's input impedance. This means that our overall resistance value is going to be lowered. If we do our calculation again then we get this result:

Now we're seeing that we're losing about 8% of our signal. At this point we can start to hear some of that "tone-suck" people talk about, but probably not enough for us to freak out about much. But let's add in that tuner.

When we add in the tuner to the circuit we get a new diagram and equation because of all the parallel resistances. The diagram looks like this now:
Let's go through the equation simplifying along the way:

We're now losing 11% of our signal and that high end is really starting to go away.

In order to prevent this high end loss, we add a buffer in between the input and the split. This turns our high impedance guitar signal, 15k, into a low impedance signal, 10-1k (1). If we plug that value into our crazy tuner equation then we the following:

Boom! We have all audible frequencies and then some to annoy the dog with! This is why the buffer is so useful. It lowers your impedance so drastically that it doesn't matter what comes after, you're going to have a great voltage transfer. Tone Suck Gone! Now let's take a look at doing the actual mod.

Step by Step

Now we'll look at the process of modding your volume pedal with a buffer at the input. I put the buffer on a toggle switch when I do it. This lets me turn off the buffer and still use my volume pedal which makes it so I can use that power jack for something else if I need to. Also, some people use their volume pedal with a Y-split TRS cable as an expression pedal. This won't work if there's a buffer in the circuit. So by putting the buffer on a toggle, it still allows you to use it as an expression pedal if you wanted to.

Aside from the standard tools. You will need the following:

• 1x Completed Buffer Circuit (I use a Klon based buffer, but any good buffer will do)
• 1x DPDT Toggle Switch
• 3x LEDs (of your favorite color)
• 1x 330Ω resistor

The resistor and LEDs are not strictly necessary. Once you have the buffer in place, the actual signal benefits of the mod are done. But  let's be honest, you gotta put LEDs in there so people know you have a super modded volume pedal of awesomeness!

Step 1

Turn over your volume pedal and remove the two screws underneath the black faceplate. Then remove the nuts holding the jacks in place so the faceplate can be removed.

Step 2

Take the faceplate and drill a hole between the input and output jacks for the power jack. Then drill a hole directly above for the toggle switch. Be sure to measure the size of each hole first as they will be different. Go ahead and put the toggle switch and power jack in place when you're done, making sure the toggle moves vertically when switched (I'll go over why later).

Step 3

Solder a wire between the top two lugs of the toggle switch. This will allow you to bypass the pedal when the toggle is in the down position. I do it this way so that if you unplugged your power jack to use on a different pedal and your foot slid off the front of your volume pedal, you can't knock the toggle into a position that would kill your signal.

Step 4

Take the circuit board that the jacks are mounted on and desolder the input jack. You may only need to desolder the tip for this to work. Be patient and don't stay on the solder joint for too long or you may burn the PCB trace.

Note: It may be easier to clip off the tip connection from the jack and then desolder the bit still in the pcb by essentially pushing it through with your soldering iron. This does risk burning the PCB but it can be useful.

Step 5

Bend the tip of the input jack so it doesn't make contact with the pcb and solder a wire from the tip to the middle of the right side of the toggle. Then solder a wire from the other side of the middle of the toggle to where the input jack used to be soldered.

Pro Tip: If you don't have a set of soldering "third-hands" then you can clamp the wire down on the jack using some blue tack or a bobby pin.

Note: If you had to cut the connection to the jack then you will still need to bend it a bit. When you're soldering the wire to the tip, scratch the metal a bit with a knife or some sandpaper to help the solder flow better. You may also want to do the bobby pin trick to keep the wire from sliding around while you're soldering.

Step 6

Find where you want to place your buffer circuit inside the pedal and tape it in place using double sided tape. I place mine above the input jack on the faceplate. Then solder the input and output wires from the buffer to the remaining two lugs on the same sides as each input/output jack.

Note: At this point if you don't want to add the LEDs, you can solder your power and ground buffer connections to the power jack (make sure to connect your power jack's ground to the chassis ground or you'll get hum) and you're done.

Step 7 (Adding LEDs)

Pick three LEDs (same color is usually best) and a 330Ω resistor. I personally love green and blue LEDs for this, but I've seen some awesome purple ones too. You will be putting one in each bottom corner and one in the top center (angled slightly upwards). We're going to take advantage of the ground connections from the jacks in the bottom two corners and solder the bottom LEDs to them in the next step.

Step 8

In the bottom left corner, take the negative end of your LED and push it through the ground connection of the jack while heating that joint with your soldering iron to make the solder flow. Get the LED right up next to the solder joint and make sure that it's a firm connection. Repeat this process in the bottom right corner. 

Step 9

Take the negative lead for the LED in the top center and do the same process you did for the previous LEDs, but push just enough of the negative lead through in order to center it. 

Step 10

Solder one side of your resistor to the positive ends of your LEDs. I find it helps to angle the LED leads towards the center of the pedal and then bend the resistor lead to wherever it needs to go. Also, another time where blue tack or the bobby pin trick can be helpful. 

Step 11

Connect a wire to the other side of your resistor and run it to the power jack. Solder in the power connection from the buffer and the resistor at the same time to make it easier. 

Step 12

Connect your power jack's ground connection to the buffer ground and the chassis ground (you can use one of the input jack's like you did with the LEDs) and you're all done! 

There you go! You now have a tone suck free volume pedal with some awesome LEDs to prove it.


References

1. Jack Orman - http://www.muzique.com/lab/pickups.htm
2. Jack Deville - Mr. Black Pedals Blog - Buffers, Impedance, and Other Internet Lore
3. Endolith - How important is impedance matching in audio applications
4. Impedance Bridging -  https://en.wikipedia.org/wiki/Impedance_bridging
5. Voltage Divider Tutorial - https://learn.sparkfun.com/tutorials/voltage-dividers
6. Parallel Resistor Calculator - http://www.sengpielaudio.com/calculator-paralresist.htm
7. Voltage Divider Calculator - http://www.raltron.com/cust/tools/voltage_divider.asp

The Mod

Parts:

• Joyo Ultimate Overdrive
• 500K Log Potentiometer (link has a drop in replacement for the board mounted one)
• 1K5 Resistor
• 470K Resistor
• 100nF Capacitor

Schematic

Here is a schematic of the changes we'll be making. We'll then go step by step through how to perform the mod.

Steps 

When desoldering, it will probably be easiest to do it from the underside of the board. I recommend marking which components to remove on the underside. Then you can put the board back into the enclosure and use the enclosure to stabilize the board while you desolder.

1.  Desolder the drive pot and replace it with the 500K Log pot. This will give you a smoother  transition through the gain range of the pedal. Alternatively, you can solder a 330K resistor across the outside lugs of the gain pot per the original mod.
2. Solder the 1K5 resistor to the outside lugs of the Tone pot. (You may find it easier to do this on the under side of the board)
3. Solder the 470K resistor to the outside lugs of the Volume pot. (See note in step 2)
4. Remove C9, a 1uF capacitor, and replace it with the 100nF capacitor.
   Note: If you have a board version prior to "2010.11.24" then you'll need to replace C7, which is a 10uF, instead. 
5. If you're board has a version date of "2010.11.24" (which all the recent ones do) then you'll need to remove the germanium diode and turn it around. The silkscreening is wrong and means that only one half of your signal will be clipped if you don't change this. I put sockets on the underside so I can easily swap out different diodes to taste. 
6. Optional: The wires from the footswitch to the main board are cheap and prone to breaking. I recommend replacing all of them with some good wire so it doesn't die on you when you're playing live. 

What it does

The mod is fairly simple as far as theory goes. The original mod by Freekish Blues uses 3 resistors in parallel with the pots to lower their values and thus limit their range. By using a 330K resistor, the gain pot goes from 1M down to 250K. I prefer to just swap it for a 500K Log pot since this is the preferred value on the OCD. Also, the log taper makes it a smoother transition across the gain range so it doesn't need to be limited to just 250K. The volume pot gets reduced in the same way from 500K to 250K.

The tone pot is a bit more interesting. It forms a simple low pass filter with the 100nF capacitor. With the pot turned all the way up the cutoff frequency is originally about 16k. By reducing the value of the pot with the parallel resistor, we get a different cutoff frequency. The 1K5 resistor takes our tone control down to a value of 1.3K which is pretty cool since we can't just go buy a potentiometer of this value. By doing this the cutoff frequency becomes roughly 122K. Now, to be fair, you can't hear about 80% of those frequencies...but it is brighter. Also, since the tone pot is a log taper, you're going to have a really wide range of usable settings across the whole knob.

Lastly, the capacitor change just limits how much bass is allowed to pass through the circuit before hitting the tone control.

I hope you found this a helpful bit of info. If you did then leave a comment telling me what you found most useful so I can focus on those things in later posts. Also feel free to leave a link to any pics of your mods.