Posts Tagged ‘diy’

“Powering Your Board” article in Premier Guitar

Posted by Terry

premier guitar magazine cover December 2011

I had the opportunity recently to contribute an article for Premier Guitar magazine. It covers some of the most common issues that come up when deciding how to power all of the pedals on your pedal board and keep your rig low noise at the same time. It’s titled “Powering Your Board” and you can read it here.


Strymon Tech Corner #3 – Volume Pedal as an Expression Pedal

Posted by Terry

In this third edition of our tech corner series, I’ll explain a simple and easy way to use a volume pedal as an expression pedal. This cool little trick was shared with us by our good friend Chad. This article will be the last on expression pedals specifically, although there are many other interesting diy projects we can do in the future with the EXP input on Strymon gear.

If you’ve got a volume pedal hanging around that doesn’t get much use or better yet one already on your board, you can use it as an expression pedal with one special cable. It’s called a TRS (tip/ring/sleeve) insert cable and the purpose of this cable is normally to break out a TRS insert jack (commonly found in mixers) to the separate send and return signals. Luckily we can take advantage of this wiring to convert our volume pedal into a standard 1/4″ TRS equipped expression pedal.

One example of this type of insert cable is the Hosa STP-201 seen below.
1/4" TRS input cable

Once you have a TRS insert cable, simply plug the TRS plug into your exp input, the “ring” plug into the volume pedal input, and the “tip” plug into the volume pedal output. That’s all there is to it! Now you can use volume pedals like the popular Ernie Ball VP Jr or the new Dunlop DVP-1 as expression pedals for your Strymon gear and most other gear featuring expression pedal control. What is actually going on here is that we’re taking advantage of the design of a passive volume pedal and re-wiring it as an expression pedal with this cable. Note that your volume pedal needs to be passive, not active and the impedance (value of the resistance) in the volume pedal’s potentiometer isn’t critical. One thing that may be a little bit different about using the volume pedal as an expression is that if the volume pedal uses an audio taper potentiometer you won’t get a linear sweep of expression pedal values from toe to heel. In other words, much of the action will happen at one extreme of the pedal.

As you can see, the expression pedal schematic from Tech Corner #1
expression pedal schematic
is functionally identical to using a volume pedal with a TRS insert cable.
Schematic diagram for a volume pedal used as expression pedal

Here is a video walk-through:

Hopefully this has been a useful trick to get you rocking that expression pedal.

Happy shredding,

Strymon Tech Corner #2 – Build your own expression pedal

Posted by Terry

Recently, I ended up with a broken crybaby wah. I was already lucky enough to own a 70′s thomas organ crybaby which I love, so sacrificing this second newer crybaby for a project seemed like a fun idea. Since the crybaby chassis is extremely rugged and I like the action of the pedal, I set out to turn it into an expression pedal for my El Capistan. This article assumes that you have experience soldering and using basic tools like wire strippers, etc. Of course, always observe proper safety precautions and wear safety goggles while working on any type of electronics.

crybaby wah sitting on green felt
Here’s my wah on the workbench.
crybaby wah pedal with back cover removed
First, opening up this box couldn’t be easier. Just remove the 4 thumb screws from the back plate and remove the plate.
crybaby wah pedal with electronics removed
Then, unscrew the two jack nuts from the input and output jacks and also remove the single screw holding the PCB (printed circuit board) to the chassis. Unplug the cable connector, remove the PCB and set aside.
crybaby potentiometer and switch with wires desoldered
Connect your treadle pot to a standard 1/4″ TRS (tip/ring/sleeve) jack according to the schematic in tech corner #1. Desolder all wires from the pot and switch and set aside.
crybaby wah pedal with original electronics removed and re-wired as an expression pedal
The “sleeve” of the jack is ground, so first connect that to the pin of the post closest to the footswitch. Then, connect a 1k resistor to the wiper (center pin) of the pot. Connect the resistor to the “tip” of the jack. Lastly, connect the pin of the pot closest to the jack to the “ring.” You’ve got an expression pedal!

Watch the youtube video for a walkthrough of the build process and an El Capistan demonstration with our completed diy project:

Happy shredding,

*All product names used in this article are trademarks of their respective owners, which are in no way associated or affiliated with Strymon or Damage Control, LLC.

Strymon Tech Corner #1 – Anatomy of an expression pedal

Posted by Terry

Welcome to the first post of our new Strymon Tech Corner series! I will be posting technical articles on music electronics as part of our blog at least once a month. Pete, Dave and Gregg from our team may also write an article here and there when they can get time away from their PCB layout programs and DSP emulators. Hopefully you’ll find these posts helpful and informative.

In this first edition I’ll be going through the inner workings of the common expression pedal. Once we know how one works, then comes the fun stuff … tearing them apart, modding, etc, etc. But that will be left to next month’s article :)

expression pedal from moog

We knew from day 1 that we wanted some of our pedals to feature expression pedal inputs. So, the question was “what’s the standard?” That is, do all manufacturers make their expression pedals the same way? Luckily the answer is yes … mostly.

Expression pedals work by feeding a control voltage to a device, such as a guitar pedal or synthesizer. The voltage is read by the device and then used to change some type of parameter. The voltage range depends on the design of the pedal or synth. Our Strymon pedals, for example, read control voltages from 0 to 5 volts DC. Turns out that this is a fairly common voltage range, especially in music electronics where MIDI (a 5V system) is still popular and widely used after over 25 years. The expression pedal itself, however has nothing to do with the voltage range. It’s only function is to manipulate that range and control the control voltage. The way almost every expression pedal out there works is that it takes a reference voltage from the device it’s connected to, divides that voltage down by a certain amount and then feeds it back to the device. In electronic terms, this is most commonly accomplished with a TRS (tip / ring / sleeve) 1/4″ cable where the reference voltage is on the “ring,” the control voltage is fed back to the device on the “tip” and the “sleeve” is ground.

Here  is what a standard 1/4″ TRS plug looks like:

As you can see from this 1907 diagram, TRS has been around for a long long time ;)

Here is the schematic for a typical expression pedal:

As you can see, the simplest and most common method is to use a passive potentiometer. A reference voltage from the device would enter the expression pedal jack on the ring. Then that voltage gets connected across a 10k load which is the resistive element of the potentiometer. When you move the expression treadle up and down there is a mechanical mechanism that physically turns the treadle potentiometer or “pot” as it’s commonly known. You can visualize the arrow at pin 1 of the treadle pot moving from pin 3 to pin 2 as one moves his/her foot back and forth on the pedal. This is what varies the voltage at pin 1. This is the control voltage which then travels out of the pedal on the tip of the jack. R2 is only present as a current limiter and not applicable to this discussion.

The Moog EP-2, Roland EV-5, and M-Audio EX-P all work in this manner, and therefore, work with our pedals. The nice thing about this standard design is that the control voltage is very stable and the value of the potentiometer in the expression pedal doesn’t matter so much. The Line6 EX1 is the only one we’ve see that works differently, with only a simple resistor divider and a mono cable. The nice thing about their solution is that it uses a mono cable. Two disadvantages are: 1. The expression pedal input circuit is highly dependent on the value of the potentiometer in the expression pedal.  2. Their products won’t work with other manufacturer’s expression pedals and vice versa.

Watch our video for more info and audio demos with our Brigadier delay and Orbit flanger.

I hope you’ve enjoyed this first edition of the Strymon Tech Corner. Tune in next time where we’ll make our own D.I.Y. expression pedal from a broken crybaby wah!

Happy shredding!

*All product names used in this article are trademarks of their respective owners, which are in no way associated or affiliated with Strymon.

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