Understanding Hi-Fi Circuits (1957) -- Article Index and Intro

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1. The Approach to Hi-Fi: The background of audio. Early advances. Triode versus pentode. Use of positive and negative feedback.

2. Special Output Stages: Push-pull triodes. Tetrode or pentode. Ultra-linear. Grid drive. Effective plate resistance. Cathode followers. Unity coupling. Modified ultra-linear. Circlotron. Comparative qualities of output circuits.

3. Feedback and Damping: Loop gain and feedback factor. Negative and positive feedback. Cyclic blocking. Avoiding overload blocking. Effects of feedback. Stability of gain. Frequency response. Output impedance. Stability margins. Phase margin. Gain Margin. Maximal flatness. Loading. Multiple-loop feedback. Phase correction methods. Variable damping.

4. Inverter and Driver Stages: Direct-coupled transformers. Parallel-fed transformers. Tapped AF choke. Split-load inverter. Paraphase. Output-coupled paraphase. Floating paraphase. Long-tailed inverter. Cross-coupled inverter. Extra push-pull drive stages. Positive feedback drive. Comparative qualities of phase inverters.

5. Input Stages: Thermal noise. Noise voltages. Hum. Cable microphony. Microphonic tubes. Distortion. Bootstrap pentode input. Transistors.

6. Matching: Input circuits. Output circuits. Minimum distortion. Transistors.

7. Equalization: Phono and tape equalization. Disc and tape standards. Methods of equalization. Passive equalizer. Separate sections. Feedback type. Single triode stage. Single pentode stage. Two-triode stages. Relative properties of equalizer circuits.

8. Speaker Distribution and Crossovers: Kinds of reproducer. Intermodulation. Multiple-unit speakers. Peaky highs. Balance. Crossovers. Inductors and capacitors. Channel separators. Feedback separators.

9. Loudness and Volume Controls: Fletcher-Munson Curve. Position of controls in circuit. Circuits. Continuously variable or stepped. Feedback types.

10. Tone Controls: Tone-control functions. Response. Simple step circuits. Practical considerations. Feedback and peaking types. Variable-slope rolloff.

11. Overall View of Hi-Fi

This guide is based on the this 1957 book:

THE whole subject of high fidelity has "come of age" in one or two short decades. With such rapid progress along such varied avenues, some confusion was to be expected. Also the assessing of hi-fi performance is so much a matter of taste, while its circuitry is generally regarded as completely scientific. Whatever may be under discussion, each enthusiast naturally claims that his favorite, whether it be a whole system, an amplifier, preamplifier, or even a part of a circuit, is the best.

The hi-fi enthusiast is by nature a perfectionist. But getting the best is not so simple a matter as putting together all the "best" parts. A high fidelity system must be "integrated," or considered as a whole. To questions often asked, there is no such simple answer as "The split load type is the best phase inverter." But neither is the story terribly complicated. This guide divides the whole audio or high fidelity system into sections, and explains the "facts of life" pertinent to each section. Your selection for the best of a particular circuit should depend on your choice of output stage and the feedback performance you expect. This, in turn, depends upon the kind of amplifier you want. This principle is equally true, whether you buy the amplifier complete, or make it yourself.

In most sections there are at least two approaches--one simple and one complex--each with some merits over the other.

The best compromise will depend on a number of circum stances: your budget, your taste in programs, how critical a listener you are, and in what way. This guide aims at helping you unlock the answers to all these often-perplexing questions for yourself, whether you are an engineer, a technician, a musician, or just someone who would like to enjoy good music of your own choice.

Best listening, folks!

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