Description: hybrid (tube/FET) stereo preamplifier with one phono input, six line-level inputs, and two tape loops. Frequency response: 30Hz-40kHz ±0.3dB (RIAA phono), 5Hz-50kHz ±0.5dB (line). Distortion: 0.01% at 2V output. Input impedance: 47k ohms standard, with user-adjustable resistance and capacitance (600pF as supplied) (phono); 50k ohms (line). Output impedance: 250 ohms (main), 850 ohms (tape-out). Recommended load: 60k-100k ohms in parallel with 100pF (20k ohms minimum and 1000pF maximum). Phono stage gain: 67dB to main out, 46dB to tape-out. Phono…
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In the real world, "knowledge is power" means that if I know more about something than you do, I am better able than you to control it or use it to my own advantage. This is no less true in high-end audio, where a gut-level understanding of how a component works can free its owner from the constraints and frequent inaccuracies of instruction manuals, folklore, advertisements, and the nugatory, nullifidian nonsense in the mainstream audio press assuring you that most of what you know damn well you are hearing is really only a figment of your imagination.
Many years ago, Life magazine did a…
Any electric source, like a battery, has electrons pent-up behind its negative terminal, just waiting to go somewhere, while the positive terminal, with a deficiency of them, is sitting there saying "Hey, come to me, baby!" The difference between their density at the battery terminals is called the battery's potential difference, or electromotive force (EMF), and is measured in volts (V). When the battery is connected to the ends of a conductor, the pressurized electrons zip into the negative end of the wire, knock several million electrons out of orbit, and take their place around the first…
Controlling Current Flow
While sticking a wire across a battery makes for an enlightening illustration, it isn't really all that good an idea. Wire is such a good conductor that it will pass as many electrons as the battery can supply. In fact, it will pass so many that friction between them will cause the wire to heat up, and if the wire is thin enough, it will melt. If it's too thick to heat, it will simply "short-circuit" the battery, so that no potential difference (voltage) can exist between the battery terminals, in which case the battery will become extremely agitated, heat up,…
While sticking a wire across a battery makes for an enlightening illustration, it isn't really all that good an idea. Wire is such a good conductor that it will pass as many electrons as the battery can supply. In fact, it will pass so many that friction between them will cause the wire to heat up, and if the wire is thin enough, it will melt. If it's too thick to heat, it will simply "short-circuit" the battery, so that no potential difference (voltage) can exist between the battery terminals, in which case the battery will become extremely agitated, heat up,…
Separating AC and DC
Some resistors have much higher resistance to current flow in one direction than in the other. When they do, we cease to call them resistors and refer to them as diodes or rectifiers because they put things right. (It doesn't make sense to me either.) Their main application in audio is the conversion of the household AC supply into DC, which is needed for amplification.
Some resistors have much higher resistance to current flow in one direction than in the other. When they do, we cease to call them resistors and refer to them as diodes or rectifiers because they put things right. (It doesn't make sense to me either.) Their main application in audio is the conversion of the household AC supply into DC, which is needed for amplification.
One rectifier, in series with the AC supply, will pass every half cycle of the AC input but will block the other half (fig.5). Amazingly, this is called half-wave rectification. To get DC from both…
An alternative way of expressing that transition frequency is as a charge/discharge time constant, in microseconds (µs). The time constant is calculated by multiplying the resistance by the capacitance. To convert from time constant to frequency, or vice versa, just use the magic 160,000. Divide the known quantity into it, and that's it.
Another interesting property of a charged capacitor is that it produces what's called an electrostatic field, in which the negative energy from packed electrons actually radiates for some distance from the negatively charged plate, and will attract…
Transformers
A transformer is two or more inductors placed so that one picks up on the other's magnetic fields. The source winding, to which input is fed to the transformer, is called the primary winding, or just primary; the output winding is the secondary. Usually, the windings are wrapped around opposite legs of a closed-M-shaped laminated magnetic-metal core (fig.11). Varying electrical currents in the primary sets up magnetic fields in the core, and these are induced into the secondary winding, which responds by putting out an AC voltage into any electrical circuit connected across…
A transformer is two or more inductors placed so that one picks up on the other's magnetic fields. The source winding, to which input is fed to the transformer, is called the primary winding, or just primary; the output winding is the secondary. Usually, the windings are wrapped around opposite legs of a closed-M-shaped laminated magnetic-metal core (fig.11). Varying electrical currents in the primary sets up magnetic fields in the core, and these are induced into the secondary winding, which responds by putting out an AC voltage into any electrical circuit connected across…
AC on DC
This isn't a kinky sexual situation, it's what we end up with at the output of an amplifying stage. Consider: The input signal, representing soundwaves, is alternating current, varying positively and negatively above and below zero voltage. But because an amplifying device can only pass current in one direction, its output signal is not AC, it's varying-current DC. Fig.13 shows what it would look like if we plotted output voltage against time. Note that the sinewave has no zero-voltage point on the vertical scale. Instead, it is superimposed on a DC voltage---called a DC offset…
This isn't a kinky sexual situation, it's what we end up with at the output of an amplifying stage. Consider: The input signal, representing soundwaves, is alternating current, varying positively and negatively above and below zero voltage. But because an amplifying device can only pass current in one direction, its output signal is not AC, it's varying-current DC. Fig.13 shows what it would look like if we plotted output voltage against time. Note that the sinewave has no zero-voltage point on the vertical scale. Instead, it is superimposed on a DC voltage---called a DC offset…
Transduction
This formidable-sounding word simply means changing one form of energy into another. A cartridge transduces the little mechanical squiggles in a record groove into electrical signals, and a loudspeaker transduces amplified electrical signals into soundwaves.
This formidable-sounding word simply means changing one form of energy into another. A cartridge transduces the little mechanical squiggles in a record groove into electrical signals, and a loudspeaker transduces amplified electrical signals into soundwaves.
Transduction is possible because certain interactions between electrons or between magnetic fields create physical forces. There are two approaches in general use: electrodynamic and electrostatic.
Electrodynamic (dynamic for short) transducers are based on two properties of magnetism: 1) Magnetic poles…
For a soundwave, its frequency equals 1100 ft/s divided by its wavelength. The rate at which a physical object vibrates---that is, the number of vibrations per second---depends on the mass (inertia) of the object and on its flexibility or compliance---the ease with which it is free to move back and forth. The higher its mass or the higher its compliance, the lower its natural vibrating frequency.
The frequency of the object's natural vibration rate is called its resonant frequency, and when a body with resonant properties is struck or otherwise set into vibration, the regular series of…