Physics 1010

Line 2 Amp Audio Converter

Physics 1010-007 Project

By:

Clay Boitnott and Sara Wiscombe

Instructor: David Schaffer

MWF 12:00-12:50

 

What We Built For Our Project:

For our project, we built a passive electronic device that converts a high output, low impedance, balanced audio signal (known as a “line level” audio signal) into a low output, high impedance, unbalanced audio signal (known as an “instrument level” audio signal).  The purpose of such a device is to allow a computer (specifically the audio output of a computer soundcard) to “play guitar” through an actual electric guitar amplifier.

Figure 1. The Completed Device.

What It Is:

When one records a guitar track, one typically records the sound coming out of a guitar amplifier with a microphone.  This signal goes directly into the computer.  The problem with this method is that once you record something, you are stuck with the sound and tonality of the initial recording.  You can’t change any settings on the amplifier after the fact.  However, if one could record an electric guitar’s output signal-unamplified-directly into the computer and send the unprocessed recorded guitar signal from the computer directly into the guitar amplifier, you would be able to re-record a guitar track with an identical performance and any amplifier settings you choose at any time you desire.  The device that we built allows us to do exactly this.

Figure 2. Typical Device Operation

How We Built It:

Figure 3. All the Components Ready for Assembly

There is a kit that is available for purchase that includes all necessary components required to assemble a complete “re-amping box”.  We purchased and completed this kit.  Building the device mainly consisted of assembling a complete circuit board and assembling all of the components and audio cable connector jacks required for operation into a metal enclosure.  Building and assembling a complete circuit board required the soldering of input/output jacks to the circuit board, soldering a transformer to the circuit board, soldering four resistors to the circuit board, grounding the device to the enclosure, installing a switch that changes where the ground signal leads to, and installing all of these electrical components into the aluminum enclosure that the kit we purchased included.  Go to http://www.diyrecordingequipment.com/line2amp-manual/#3 for the complete set of instructions that we followed in order to complete the project.

Figure 4. The completed circuit board with four resistors, a transformer (not pictured), an input jack (top left), an output jack (top right) and a ground lift switch (bottom left).

What We Learned:

Building this device has taught us a lot about the way that electricity works, and we feel that we now have a better understanding of electricity in general.  This project has taught us a great deal about electrical impedance and resistance.  There are four resistors that are contained within the unit.  The purpose of these resistors is to impede the electrical current that is flowing through the circuit.  This is just one of the ways that the unit converts the audio signal between a computer and an amplifier. We have learned about Ohm’s Law–which is one of the principles that our resistors utilize in order to function.  Without Ohm’s simple math equation we would not be able to build the resistors to the specifications necessary for this unit to function properly and effectively.  The unit is built with a useful ground lift switch that allows the unit to alternate ground to two different places.  Some devices ground differently than others.  Having two places in which to ground ensures that any incoming signal from any device can be properly grounded when functioning with the unit we built.  Improper grounding produces excessive amounts of noise in the signal—which is absolutely unacceptable for recording audio.  This project has taught us quite a lot about the actual, real world applications of simple ideas (such as adding resistance or impedance to an electrical circuit and the way that electricity actually flows through the circuits).  This is a device that we will use in our home recording studio for years to come.  Every time we use it, we will think of the lessons that it has taught us about electricity and the way that the world around us really works.

Figure 5. The Completed Unit (lower right) in the studio