Analog Guitar Amplifier

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ANALOG

GUITAR

AMPLIFIER

U N I V E R S I T Y O F W Y O M I N G E C E D E PA R T M E N T D E S I G N E R : A L E X S O V E R O S K I A D V I S O R : P R O F. F E R R E - P I K A L U N D E R G R A D R E S E A R C H D AY P R E S E N TAT I O N

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ANATOMY OF AN AMP

• Power Amplifier _• _{External Effects}

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VACUUM TUBES VS TRANSISTORS • Old vs New • Thermionic Emission vs Silicon Doping • Different Characteristics

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VACUUM TUBES VS TRANSISTORS Asymmetric (Harmonic) Distortion Inp ut Out put

Design and Construction of Tube Guitar Amplifiers, 3rd_{Ed. Robert Megantz. 2012, Self Published.}

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TECHNICAL SPECS – PHYSICAL

• Final Product: 13”x7”x9”, approx. 13 lbs.

• Design is for a standalone amp “head” to connect to external speaker

• Original Proposition: 30”x10”x12”, approx. 50 lbs.

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TECHNICAL SPECS – ELECTRICAL

• Preamp designed using triode

tubes for even distortion:

≥30dB over 60Hz to 2kHz at maximum gain

• Tone control section design

based on Fender’s Tone Stack design

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Effects signal (Wet) can be blended with internal signal (Dry) via

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• Power stage consists of

triode-based phase splitter with pentode-based push-pull output: ≥30dB over 30Hz to 10kHz at maximum volume

• New addition: Presence Control allows control of power amp’s negative

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TECHNICAL SPECS – ELECTRICAL Power supply section comprised of step-up transformer with rectifying diodes

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THE DESIGN PROCESS – RESEARCH

• October – November 2016

• Investigated vacuum tube

operation

• Obtained valid tube models for

simulation in LTspice

• Researched typical circuit

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THE DESIGN PROCESS – SIMULATION

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THE DESIGN PROCESS – SIMULATION Output Current Output Voltage Input Voltage C ur r e n t ( A ) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 16 14 12 10 8 6 4 2 0 -2 -4 -3 -8 -10 V ol t a g e ( V ) Time (ms) 218.80 218.84 218.88 218.92 218.96 219.00 219.04 219.08 219.12 219.16

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THE DESIGN PROCESS – PROTOTYPING

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THE DESIGN PROCESS – PROTOTYPING -7.3V 260V 375V 320V 320V 300V 6BQ5 6BQ5 12AX7 12AX7 12AU7 12AU7 12AX7 12AX7 T1 2to1CT C14 0.1u C13 0.1u C12 .01uF C11 6.8uF 5k Pres C10 0.022uF 250k Vol 100k Dry C9 0.047uF 100kWet C8 0.47uF RET C7 0.047uF SND C6 0.047uF C5 0.01uF 1MEG Gain 10k Mid 250k Bass 250k Treb C4 0.047u C3 0.1u C2 250p C1 12.7uF IN SPK1 8 R41 100k R40 1.8k R39 1.8k R38 10 R37 220k R36 220k R31 47k R32 2.7k R33 1MEG R34 10k R30 7.5k R29 33k R28 470 R27 1MEG R25 5.1k R23 27k R22 22k R18 100k R19 390 R20 47k R17 1k R16 100k R12 1MEG R15 15k R14 390 R13 470k R11 1k R10 50k R5 100k R4 100k R3 1.25k R2 22k R1 1MEG

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THE DESIGN PROCESS – FINAL CONSTRUCTION

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FINAL RESULTS • Output gain comes mostly

from current instead of voltage

• Performance is best at higher frequencies, some oscillation at lower ones

• All control knobs are functional

• Some controls operate noisily

• Design is physically smaller than original proposition

Cost Analysis

2 x Electro-Harmonix 12AX7 tubes $30

1 x Electro-Harmonix 12AU7 tube $17

2 x JJ EL84 tubes $26

Power Transformer – Hammond 290EX $82

Output Transformer – Hammond 1760E $41

Custom resistors/capacitors for power supply ≈$20

Tube sockets / potentiometers / quarter-inch jacks ≈$20

Folded Aluminum Chassis ≈$20

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RESEARCH RESOURCES

• Valve Amplifiers, 4th _{Ed. Morgan Jones. 2012, Elsevier Ltd.}

• Design and Construction of Tube Guitar Amplifiers, 3rd _{Ed. Robert Megantz. 2012, Self}

Published.

• How to Gain Gain, 2nd _{Ed. Burkhrad Vogal. 2008, Springer-Verlag.}

• Koren SPICE Tube Models, obtained from