Ir. Menno van der Veen "Modern High-End Valve Amplifiers based on toroidal output transformers"

Elektor Electronics (Publishing)
Dorchester, England
© 1999 Ir. Menno van der Veen
ISBN 0-905705-63-7

About the author (xiii)
Introduction (xv)
1. Why Valve Amplifiers?
1.1. What's special about valve amplifiers? (1)
1.2. How do valves work? (4)
1.3. What types of valves are there? (8)
1.4. Why do we need an output transformer? (10)
1.5. How is a valve amplifier constructed? (10)
1.6. How is this book organized? (12)
1.7. Where can I learn more? (13)
2. Output Transformer Specifications
2.1. The transformer turns ratio a (15)
2.2. Class A and Class AB operation (16)
2.3. The relationship between the primary and secondary impedances (17)
2.4. The primary winding inductance Lp (18)
2.5. The primary winding leakage inductance Lsp (19)
2.6. The primary winding internal capacitance Cip (21)
2.7. The winding resistances Rip and Ris (22)
2.8. Summary and conslusions (23)
3. The output Transformer, Valves and Loudspeaker
3.1. Loudspeaker impedance (29)
3.2. Triodes, pentodes and the ultralinear mode (31)
3.3. The effect of rp (32)
3.4. Calculating the damping factor (33)
3.5. The -3dB high frequency limit (35)
3.6. High frequencies in the output valve (38)
3.7. Summary and conclusions (39)
4. The Output Transformer in the Complex Domain
4.1. Calculations in the complex domain (43)
4.2. The real and imaginary components at different frequencies (46)
4.3. The phase angle (47)
4.4. Differential phase distortion (47)
4.5. The limitations of complex analysis  (48)
4.6. Summary and conclusions (49)
5. Frequency-Domain Calculations for Toroidal Output Transformers
5.1.  The power valve as a voltage source (51)
5.2. Matching the valve and transformer impedances (52)
5.3. The equivalent circuit of the transformer (52)
5.4. The transfer function (53)
5.5. The -3dB frequency range (55)
- The lower -3dB frequency (57)
- The upper -3dB frequency (56)
5.6. The tuning factor and the frequency-decade factor (57)
- Introducing the tuning factor (57)
- Tuning factor examples (58)
- Introducing the decade factors (61)
- Frequency decade factor examples (62)
5.7. New toroidal wide-bandwidth output transformers (62)
- General description (62)
- Specifications (64)
- Secondary impoedance (64)
- The quality factor and the quality decade factor (64)
- Winding resistances (65)
- Calculating the -3dB bandwidth (65)
5.8. Summary and conclusions (66)
6. Theory of Overall Negative Feedback
6.1. Defining the transfer function (67)
6.2. Defining our example amplifier (68)
6.3. Defining the phase splitter and preamplifier sections (70)
6.4. The complete amplifier under load, with no overall negative feedback (71)
6.5. Applying overall negative feedback (72)
6.6. Stabilization in the frequency domain (75)
6.7. Comments about the damping factor (77)
6.8. Summary and conclusions (78)
7. Output Transformer Low-Frequency Tuning
7.1. Measuring the primary inductance (79)
7.2. Calculating the primary inductance (82)
7.3. Exploring the core (83)
7.4. Output transformer distortion calculations (84)
7.5. How the valves affect the distortion (86)
7.6. How bad is nonlinearity? (89)
7.7. The sound of a valve amplifier (90)
7.8. References (91)
8. Special Output Coupling Techniques
8.1. From pentode to Super-Pentode (93)
8.2. The Ia-Vak-Vgk formula (93)
8.3. Local ultralinear feedback (95)
8.4. Specialist SSCR toroidal output transformers (96)
8.5. The power issue (98)
8.6. Cathode feedback techniques (98)
8.7. Combining cathode feedback with ultralinear feedback (100)
8.8. Toroidal cathode feedback output transformers (101)
8.9. Experiments with cathode feedback and ultralinear configurations (101)
8.10. From the pentode and triode to the Super-Pentode (102)
8.11. The next logical step: unity coupling (105)
8.12. Experimental results with the VDV1070-UC toroidal output transformer (107)
8.13. Summary and conclusions (108)
8.14. References (109)
8.15. Transformer specifications and wiring diagrams (109)
9. Single-Ended Toroidal Output Transformers
9.1. Ypu can't argue about taste (113)
9.2. The basic circuit diagram of an SE amplifier (114)
9.3. Characteristics of a single-ended power valve (115)
9.4. Calculating the operating point (116)
9.5. Properties of single-ended output transformers (120)
- Low frequency behaviour and power (121)
- High frequency behaviour (122)
- Fine tuning the high frequency response (124)
- The insertion loss Iloss (124)
- Maximum allowable primary direct current (126)
- Phase distortion and differential phase distortion (126)
9.6. Summary (127)
10. Building a Push-Pull Valve Amplifier: the Phase Splitter
10.1. Avoiding core saturation (129)
10.2. The function of the phase splitter (130)
10.3. Phase splitter circuit diagram (131)
10.4. Requirements and adjustments: the supply voltage (132)
10.5. The capacitors (133)
10.6. Some remarks about grounding (134)
10.7. The filament supply (134)
10.8. Caution: high frequencies (135)
10.9. the phase splitter with a different supply voltage (135)
10.10. Examples of other types of phase splitters (136)
10.11. Summary and conclusions (138)
11. Building a Push-Pull Valve Amplifier: from 10 to 100 Watts
11.1. Decisions, decisions, decisions (139)
11.2. The basis circuit: general design (140)
11.3. The basic circuit: input requirements (140)
11.4. The basic circuit: adjusting the NGV (143)
11.5. Stabilizing the output valves (143)
11.6. Connecting the output transformer (144)
11.7. 10 watts using two EL84s with a VDV8020PP (PAT4000) (145)
11.8. 30 watts using two EK34s with a VDV6040PP (PAT4002) (146)
10.9. 70 watts using four EL34s with a VDV3070PP (PAT4004) (147)
10.10. 100 watts using four EL34s with a VDV2100PP (PAT4006) (149)
11.11. 80 watts using eight EL34s in triode mode with a VDV1080PP (PAT4008) (150)
11.12. Summary and conclusions (150)
12. Building a Push-Pull Valve Amplifier: the Power Supply
12.1. Safety (153)
12.2. The basic power supply circuit (154)
12.3. The stand-by switch and the on-off switching order (155)
12.4. The power supply circuit continued: what do you mean, it hums? (156)
12.5. The filament supply, NGV supply and indicators (157)
12.6. Power supplies specifications summary (158)
12.7. Summary and conclusions (158)
13. Building a Push-Pull Amplifier: Construction Hints
13.1. Why not use a printed circuit board? (161)
13.2. Designing a logical layout (162)
13.3. Placing the filament wiring (163)
13.4. Choosing the ground points (163)
13.5. Where should you connect the mains ground? (164)
13.6. Ventilation and cooling (166)
13.7. Minimum plate voltage distance (166)
13.8. More about the NGV (167)
13.9. The 100Hz (or 120Hz) square-wave test (168)
13.10. Summary and conclusions (170)
14. Valve Amplifiers using a Printed Circuit Board
14.1. General description (173)
14.2. Component lists (176)
14.3. The printed circuit board (176)
14.4. Construction hints (179)
14.5. Final checkout and adjustments (181)
15. Practical Aspects of Overall Negative Feedback
15.1. The basic principle of negative feedback (183)
15.2. Practical implementation of negative feedback (184)
15.3. The extra preamplifier (185)
15.4. Testing for correct feedback connections (187)
15.5. Dimensioning the amplifier (187)
15.6. The side effects of negative feedback (188)
15.7. Feedback terminology (189)
- The feedback factor (189)
- Feedback in decibels (189)
- Which feedback definition is correct? (189)
15.8. The subjective element (191)
15.9. Feedback and the frequency response above 20kHz (191)
15.10. Eliminating the effects of feedback on the high frequency response (192)
15.11. Feedback and the frequency response below 20Hz (194)
15.12. Summary and conclusions (195)
16. The UL40-S Stereo Valve Amplifier
16.1. Outline of the UL40-S (197)
16.2. The philosophy behind the UL40-S (198)
16.3. Feedback: yes or no? (198)
16.4. Output power and class A or AB1 operation (200)
16.5. More about the phase splitter and distortion (202)
16.6. AC balance and the 100Hz square wave test (203)
16.7. Logistic Earth Patterns: LEP (203)
16.8. High frequency filament circuits (204)
16.9. The standby switch and the status LEDs (204)
16.10. The specifications (205)
16.11. Output power and impedance (206)
16.12. Alternative choices forvthe power valves (207)
16.13. How does it sound? (208)
16.14. Output power, gain, and ... what's with the volume control? (210)
16.15. Summary and conclusions (212)
17. A Guitar Amplifier with a Toroidal Output Transformer
17.1. The circuit diagram of the VDV40 (213)
17.2. Assembly, adjustments and specifications (216)
18. The VDV100 Power Amplifier
18.1. The basic sircuit (219)
18.2. Why use local feedback? (221)
18.3. Construction and specifications (223)
18.4. Modifications (227)
- Modification 1: UL configuration with older-model transformers (227)
- Modification 2: Pentode configuration with a VDV2100PP (228)
- Modification 3: Ultralinear configuration with a VDV2100PP (229)
- Modification 4: Pentode configuration with local feedback and a VDV2100PP (229)
- Modification 5: Complete negative feedback (230)
18.5. Conclusion (230)
19. Experiments with the Specialist Series of Output Transformers
19.1. A valve amplifier for the Specialist cathode feedback transformers (231)
19.2. Coupling to the output transformer (235)
19.3. Which CFB transformer is the one for you? (236)
19.4. Summary and conclusions (237)
19.5. References (238)
20. The VDV-6AS7 (The Maurits)
20.1. How it came to be (239)
20.2. The audio circuit (239)
20.3. Some power supply details (243)
20.4. Subjective properties (245)
Appendix
A1. Bibliography (247)
A2. Where to obtain Vanderveen parts and serwices (250)

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