EF-1 Solid State Phono-Equalization Preamplifier

Introduced August of 1995

The EF1 is a highly refined phono preamplifier designed to faithfully reproduce live musical performances, and to maintain their sonic excellence over the years.

The EF1 is a separate phono equalization preamplifier, designed to provide the added gain and RIAA equalization required by modern phono cartridges. The EF1 features low noise circuitry and selectable gain (40, 46, and 52 dB) to accommodate the full range of phono cartridges from low output moving coil to high output moving magnet types. A buffered output stage results in a low output impedance for the EF1.

First and foremost, the EF1 is an instruments for the reproduction of recorded music. The primary design objective was to create circuits which were capable of recreating the emotional impact of experiencing live music. A number of critically important considerations entered into the design process.

Field Effect Transistors (FETs).

More important than the total amount of distortion of an audio circuit is the character of the distortion. Odd-order harmonic distortion products are amusical, whereas even-order distortion products are part of the natural overtones. FETs have been selected for the active devices in the EF1 because, like tubes, and unlike bi-polar transistors, they produce almost no odd-order harmonic distortion.

Minimal Negative Feedback.

Negative feedback is an engineering technique used to reduce measured distortion. While feedback does achieve this goal, it also introduces aberrations in the transient response characteristics of the circuit. The EF1 uses conrad-johnson's unique auto-linear gain block which achieves low distortion with zero loop feedback by exploiting the symmetrical distortion properties of n and p channel fets.

Quality Parts.

The EF1 conform to the unmatched standard of parts quality for which conrad-johnson's Premier products are internationally known. Capacitors are polystyrene or polypropylene "by-passed" by polystyrene, including all power supply create circuits which were capable of recreating the emotional impact of experiencing live music. A number of critically important considerations entered into the design process.

Low Dynamic Impedance Power Supplies.

DC power supplies are an inseparable part of the audio signal path, and require as much care in design as the audio circuits. An ideal power supply would have zero ac impedance, so that the power supply voltage could not fluctuate with the audio signal. conrad-johnson products feature discrete dc regulated power supplies designed for vanishingly low impedance even at high audio frequencies. For the EF1, a primary line regulator filters and stabilizes the input voltage, isolating all circuits from power line fluctuations and noise. This regulated supply in turn delivers stabilized dc current to two separate secondary regulators for each gain stage. These regulators employ discrete devices and the highest quality polypropylene and polystyrene capacitors in circuits designed to provide a low impedance at all audio frequencies, for an extremely stable source of dc current.