MET 349 – Stringed Instrument Design and Manufacture

 

Instructor:

Mark French

138 Knoy Hall

rmfrench@purdue.edu

desk:  765-494-7521

mobile:  765-714-9382

 

Text:

 

Technology of the Guitar

Springer

ISBN

 

 

Syllabus

 

This class meets for lecture once each week and for lab twice each week.  Initially, labs will be divided between CAD work and fabrication in the guitar lab.

 

The central task for the semester is designing and building solid body electric guitars.  You will work in teams of 5-7 people and each team will do its own instrument.  Each team must complete one instrument for each team member.

 

You will be allowed to buy commercially available necks if you choose.  In the past, making necks took more time than was reasonably available.  Each design must have an electronic component in addition to the usual pickups, volume and tone controls.  Some teams choose to add a headphone amp.  Others have tried to make a separate amplifier, though this has been a challenge.

 

The teams will have a parts and materials budget of $200 per instrument.  There are four allowable suppliers:  Mighty Mite, All Parts, Stewart MacDonald and Guitar Fetish (no, I don’t know who names these companies).  This is funded through purchase cards you will get from Boiler Copy.  The purchase cards cost $300 each and the difference between the purchase card cost and your budget is used for consumable materials, bits, blades and replacement parts.

 

No parts orders will be placed until all teams have 2D layouts completed and approved.  There will be one parts order from each supplier.  Successful manufacturers plan their operations carefully; if additional orders are required because of poor planning, a tax of 15% will be assessed on each additional order.  Additional orders required for reasons beyond the control of the build teams will not be taxed.

 

 

 

Week

Date

Lecture Topic

Reading

Homework

Homework Due Date

1

Intro, notes and scales

Ch 1

Ch 2.1

 

Intro to CAD lab

 

Intro to Guitar Lab Safety

 

2

Scales and Chords

Ch 2.2

 

Instrument Preliminary Design

 

CNC Laser Operation

 

3

Fret Layout

 

HW #1:

 

1 - Find the notes that make up:

·         C major scale

·         D major scale

·         A minor scale

2 – Find the notes that make up:

·         C major chord

·         D major chord

·         A minor chord

·         F major chord

·         G major chord

·         E minor chord

3 – Completed Bill of Materials

·         One list per build group

·         Include part numbers, estimated prices, quantities and suppliers

·         Names of all group members

 

Aesthetic Elements of Instrument Design

 

 

3D Printer Operation

 

·          

4

String Tension

Ch 2.3 – 2.6

HW #2:

 

Calculate the fret layout for the following scale lengths:

1.    25.5 inch guitar

2.    24.75 inch guitar

3.    34 inch bass

4.    600mm classical guitar

13.7 inch mandolin

No Lab – Career Fair

 

Basic CNC Router Operation

 

5

Sound, quantifying sound

 

HW #3:

The frequency for A4 is 440 Hz

1 - Find the notes for a major scale starting at A2 and the corresponding frequencies.

2 - Repeat for a major scale starting at C2

3 – Make a table of the locations (measured from the nut) of the frets for an instrument with a 22 inch scale length.

4 – If a sound has an RMS pressure of 0.50 Pa, what is the sound pressure level in dB?

5 – If a sound has an SPL of 110 db (really loud), what is the RMS pressure?

6 – If a steel string with a diameter of 0.012 inch is tuned to 330 Hz, what is the tension?  Assume E=29*10^6 psi and a weight density of 0.3 lb/in^3. Scale length is 25.5 in.

 

2D CAD Layout

 

 

CNC Router Operation

 

 

 

6

Electronics

Resistance and impedance

Input and Output Impedance

 

Homework #4

 

1 – For a voltage divider where R1 is the output resistance of a pickup and R2 is the input resistance of an amplifier.  If Vin=12V, find Vout for these values:

a)    R1=1MΩ, R2=100kΩ

b)    R1=1MΩ, R2=1MΩ

c)    R1=100kΩ, R2=1MΩ

d)    R1=15kΩ, R2=500kΩ

 

2D CAD Layout

 

 

 

Body Prototypes

 

 

 

7

Op-Amps

 

Homework #5

 

2 – For a non-inverting pre-amp made using a TL061 op amp, What are the values of the feedback resistor for gain A=2, A=10, A=20?  Assume Rg=100

 

 

 

3D Models

 

 

Body Prototypes

 

8

Impedance Matching

Homework #6

 

Given a circuit diagram for a pre-amp

 

1 – A pre-amp is to be made using a TL061 op-amp and powered by a 9v battery.  If you have a pile of 50kΩ resistors, how do you set the input bias voltage to 4.5V?

 

2 – If the pre-amp gain needs to be 6 (i.e. A=6) and the ground resistance, Rg, is 1000Ω, what is the required value of Rf ?

 

3 – The input impedance is

 

 

If the input impedance needs to be 100kΩ and the input bias voltage needs to be 4.5V, what are the resistance values of RA and RB ?

 

 

3D Models

 

 

Initial Assembly of Prototype Instruments

 

9

Intonation

 

Note: The frequencies for the open strings on a guitar at standard tuning are:

 

E - 84.2 Hz

A - 110

D - 146.8

G - 196

B - 246.9

E - 329.6

 

 

3D Models

 

 

 

 

Verifying Dimensions and Alignment of Prototypes

 

 

 

10

Basics of Amplifier Design

 

 

 

Production Bodies

 

 

 

Production Bodies

 

 

 

11

String Mechanics

 

 

 

Production Bodies

 

 

 

Production Bodies

 

 

 

12

Inharmonicity

 

 

 

Wiring Harnesses

 

 

Wiring Harnesses

 

 

13

Dynamic Testing

 

 

Final Assembly

 

 

Final Assembly

 

 

14

Measuring Build Variation

 

 

Tuning and Intonation

 

 

Tuning and Intonation

 

 

15

Review for Exam

 

Homework #6

 

Use the real string equation for all 4 problems

 

1 – Calculate the frequency error for a 25.5 inch nylon G string (E=10^6 psi) with a diameter of 0.040 in, stopped at the 12th fret.  String Tension is 11.7 lb.  Calculate the error due to inharmonicity.  Assume that nylon is 1250 kg/m3.

2 – Calculate frequency error for a steel G string (E=29*10^6 psi).  String diameter is 0.023 in.  String Tension is 27.2 lb.  Assume steel is 7850 kg/m3.

3 – Calculate the saddle offset needed for the nylon string using frequency at the 12th fret

4 – Calculate the saddle offset needed for the steel string.

 

Note:  Use the metric system for all calculations.  If you need help converting units, so to onlineconversion.com

 

 

 

Dynamic Testing of Completed Instruments

 

 

Dynamic Testing of Completed Instruments

 

 

16

 

Exam

Open Book, Open Notes

Practice Questions:

 

1 – How far from the nut would the 12th fret be on a guitar with a 24 in scale length?

 

2 – If a string is 700mm, is made from steel and has a diameter of 0.4mm, what tension is required for it to be at a frequency of 150 Hz?

 

3 – What are the notes in an F major scale?

 

4 – What are the notes in an A# chord?

 

5 – The bias resistors, RA and RB, in a pre-amp need to create a bias voltage of 4.5V and the circuit is powered by a 9V battery.  The sum of the two resistances must be 440kΩ.  Find RA and RB

 

 

 

 

Last Day of Class

 

Instrument Grading

 

 

 

 

 

 

 

 

Grading

 

Exam:              20%

Homework:     15%

Design:            20%   completeness, accuracy, creative solutions to design problems, aesthetics

Construction:  20%   accuracy, organization, meeting build schedule, build process, jigs and fixtures

Final Product: 15%   accuracy, playability, finish, balance, sound, aesthetics

Peer Grade     10%  We added this after a class discussion in which we decided that peer ratings would capture important information that might be missed by the other grades