Richard Kuehnel "Guitar Amplifier Preamps"

Pentode Press, Seattle,
3rd printing
© 2007 by Richard Kuehnel
ISBN 0-9769822-2-6

1. Introduction (1)
2. Triode Voltage Amplifier Design (3)
The Vacuum-Tube Diode (3)
The Vacuum-Tube Triode (4)
Characteristic Curves, Load Line, and DC Operating Point (7)
Voltage Amplification (9)
Plate Dissipation (9)
Remowing DC from the Output (11)
Self-Biasing (12)
Equivalent Circuit for Audio Frequencies (14)
Combining Two Self-Biasing Circuits (18)
Plate Resistance, Transconductance, and Voltage Amplification Factor (20)
The Input Load of the Next Stage (23)
3. Input Circuit Design (27)
Series Impedance Networks (27)
Shunt Impedance Networks (29)
Inverted-L Networks (31)
Gamma Networks (31)
Pi Networks (37)
T Networks (40)
Converting Between T and Pi Networks (42)
Double Inverted-L Networks (43)
Gamma-Pi Networks (46)
Three Factors that Constrain Input Circuit Design (47)
4. Guitar Characterictics (51)
Lumped Impedance Characteristics of Pickups (53)
Distributed Impedance Characteristics of Pickups (53)
Guitar Volume and Tone Controls (53)
Guitar Cable Characteristics (56)
Designing the Preamp to Match the Guitar (59)
The Impact of Guitar Characterictics on Amplifier Design (60)
5. Preamp Frequency Response (61)
Miller Capacitance (61)
The Complete AC Circuit (63)
Approximate Gain for Middle-Range Frequencies (65)
Low-Frequency Gain (66)
High-Frequency Gain (68)
Simplyfying Frequency Response Calculations for Complicated Circuits (71)
6. The Selection of a Plate Load Resistor Value (73)
The Implications of Increasing Preamp Gain (73)
The Effect of the Plate Resistir Value on Nonlinear Distortion (77)
Practical Example: A Preamp with a 390k Plate Resistor (77)
7. Pentode Voltage Amplifier Design (81)
Screen Grids and Screen Circuits (81)
Adjusting Characteristic Curves to a New Screen Voltage (84)
AC Equivalent Circuit (84)
Sharp-Cutoff versus Remote-Cutoff Distortion (86)
Appriximate Gain for Middle-Range Frequencies (88)
Low-Frequency Response (89)
High-Frequency Response (90)
Screen Circuit Impedance  (90)
Microphonic Noise (94)
8. Cathode Degeneration (97)
Using a Cathode Resistor without a Bypass Capacitor (97)
Cathode Impedance (98)
Bypass Capacitor Size (99)
Cathode Degeneration as Negative Feedback (101)
The Effects of Negative Feedback (103)
9. Headroom, Distortion, and Tube Noise (105)
The AC Load Line (105)
Determining Headroom (107)
How the Location of the DC Operating Point Affects Nonlinear Dynamics (110)
Second Harmonic Distortion (110)
Intermodulation Distortion (115)
Shot Noise (116)
10. advanced Design Example: The Ampeg B42X Preamp (119)
DC Operating Point and Load Line (119)
Estimating the AC parametes Graphically (122)
Unloaded Gain, Miller Capacitance, and Cathode Degeneration (123)
Strategy for Determinng Frequency Response (124)
The Input Circuit (124)
Bright Channel Input Network Response (125)
Normal Channel Input Network Response (126)
Miller Capacitance for the Sceond Stage (128)
Grid-to-Grid Gain (129)
Middle-Range Frequency Response (130)
Low-Frequency Response (130)
High-Frequency Response (133)
Effect of the Volume Control on Gain and High-Frequency Response (135)
Closing the Ultra-Lo Switch (136)
Closing the Ultra-Hi Switch (139)
The Total Response of the B42X Preamp (141)
Headroom (146)
11. Using Two Triodes in Parallel (149)
Dual-Triode Output Impedance (151)
The DC Operating Point (152)
12. Real-World Resistors and Their Impact on Preamp Design (155)
Lead and Wiring Resistance (155)
Skin Effect (157)
Paasitic Inductance and Capacitance (157)
Dielectric Materials (159)
The Effect of Parasitic Capacitance on the Preamp Circuit (159)
Wiring and Lead Inductance (161)
Carbon Composition Resistors (166)
Other Types of Resistors (167)
Frequency Characteristics of Carbon Composition Resistors (168)
Distributed Capacitance Between Wires and Leads (171)
A Real-World Example (174)
Lead Inductance (177)
Comparison with a Metal Film Resistor (179)
Resistor Noise Characteristics (180)
Noise Specific to Carbon Composition Resistors (181)
Carbon Composition Resistor Nonlinearity (183)
13. Real-World Capacitors and Their Impact on Preamp Design (185)
Leakage and Dielectric Absorption (185)
Resistive and Reactive Characteristics (186)
Typical Capacitor Specifications (192)
The Effects of a Capacitor's Impedance on a Preamp (193)
14. Appendix A: series and Parallel Resonance (197)
Series Resonant Circuits (197)
Parallel Resonant Cicruits (198)
15. Appendix B: Dielectric Constants and Dissipation Factors (203)
16. Appendix C: Philips EF86 Data Sheet (205)
17. References (217)
18. Index (221)

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