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 978-1-4614-1920-4

 

 

Syllabus

 

This class meets for lecture twice each week and for lab four times 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 design its own instrument.  Each team must complete one instrument for each team member.

 

You will each have a body blank and a neck kit to start with.  In addition, each team will have an extra body blank and an extra neck kit to make a prototype instrument

 

The teams will have a parts and materials budget of $200 per instrument.  The body blank and neck kit were $98, so there is a remaining budget of $102 for parts.  I do have some parts in the guitar lab.  If any of them can be used for your guitars, I’ll donate them.

 

There are three allowable suppliers:  All Parts, Stewart MacDonald and Guitar Fetish (no, I don’t know who names these companies).  Parts purchases are funded through price cards you will get from Boiler Copy.  The purchase cards cost about $300 each and the difference between the price card cost and your budget is used for consumable materials like glue, 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.

 

Lecture Schedule

 

Week

Date

Lecture Topic

Reading

Homework

Homework Due Date

1

6/16/14

Intro to class

Selection of build groups

History of the guitars

Ch 1

 

6/18/14

Intro, notes and scales

Ch 2.1

 

2

6/23/14

Scales and Chords

Ch 2.2

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

6/30/14

6/25/14

Instrument Preliminary Design

 

3

6/30/14

Fret Layout

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

5.    13.7 inch mandolin

7/7/14

7/2/14

Aesthetic Elements of Instrument Design

 

4

7/7/14

Sound Pressure Level,

String Tension

Ch 2.3 – 2.6

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=205 GPa and a density of 7850 kg/m^3. Scale length is 647.7mm.

 

7/14/14

7/9/14

Real strings and inharmonicity

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

HW #4:

1 – A steel G string has a diameter of 0.43mm.  If the scale length is 647.7mm, find the inharmonicity for the open string and the string being played at the 12th fret.  Assume E=205 GPa and a density of 7850 kg/m3.

2 – What changes in length would be needed for the frequencies to be correct at the 12th fret and the 18th fret?

3 – A Nylon G string has a diameter of 1.023mm and E=1.95GPa.  Find the tension assuming it is an ideal string and density is 1100 kg/m3

4 – Find inharmonicity for the open string and the string being played at the 12th fret

7/17/14

5

7/14/14

Electronics

Resistance and impedance

Input and Output Impedance

 

HW #5:

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

 

7/21/14

7/16/14

Op-Amps

 

 

6

7/21/14

Installing headphone amp in guitar

HW #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 ?

 

7/28/14

7/23/14

 

7

7/28/14

 

7/30/14

Exam

Open Book, Open Notes

 

8

8/4/14

 

 

 

 

Review for Exam

 

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

 

 

 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

Grading

 

Exam:              20%

Homework:     15%

Guitar:              55%

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

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

Final Product: 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