EA-300 Phono Preamplifier By Phasemation

The Phasemation EA-300 is a notable step up from the EA-200 model. The design is a class A circuit with zero-feedback, and using all discrete parts. Amplifying with zero-feedback increases the cost but the results are spectacular. A load feedback amplifier compares the input and output signals and the difference (supplement signal) is amplified as an input signal which makes it possible for amplification at a low cost. However, a zero-feedback circuit amplifies the input signal itself, which makes a big difference. In terms of sound quality, with music impression, dynamics, and shading expressions, there’s no substitute for zero-feedback, so all Phasemation phono preamplifiers use this approach.

Substantial Functions

• 1,Two systems for input can be connected; and two arms can be connected.
• 2,Low Cut SW (20Hz): Prevents swing of speaker (woofer) for a bent record
• 3,Stereo/Monaural playing curve switch RIAA playing curve for Stereo, DECCA (UK) for MONO1 and COLUMBIA (USA) for MONO2

Accomplishment of Solid chassis and Dual monaural pattern
Because the fine weak signal of phono amplifier has to be protected, a solid chassis structure not to be influenced from others and a simple signal transmission are required.

a) Solid chassis structure
1) For the chassis base and top cover making of a 1.6 mm steel plate, copper plating and finishing are conducted. It achieved reduction of magnetic distortion and secured the high strength of rigidity. The front panel and top cover are made of aluminum; furthermore, for the front panel 10mm thickness board is used.

2) Mechanical earth/Direct grounding construction of power supply transformer
Magnetic vibration and generation of leakage flux is reduced as much as possible, because the R-core type power supply transformer operates with the margin made by low magnetic flux density.
In addition, this transformer is assembled directly to the foot to be cut from steel material through the 5mm thickness bakelite board that is an insulator having high electric and magnetic resistances. As a result, the vibration that the power transformer originates is discharged into the earth at once without transmitting to the chassis.

b) Dual monaural pattern
1) It builds the dual monaural layout of the same pattern of the left and right, and actualizes a uniformity of the left and right channels at a high level.

2) It supplies an ideal power without the parameter change due to the power supply load by right and left independent power supply transformer and shunt type local power supply. The channel separation over 100dB (20Hz to 20kHz) has been achieved by minimizing the loop of the circuit electric current.

Introduction of High Quality Parts
The following evaluated high sound quality parts are adopted for the RIAA impedance elements and the audio signal main portion which strongly influence a sound quality of a phono amplifier.

1) Metal film resistors with some margin of the rated value
2) Parts having high sound quality such as a high quality film capacitor

The following parts are adopted for the power circuit in order to prevent the decrease in speed of recovery in high current range, which has made it structure a very low noise power supply.

1) Newly adopting SiC diode made by ROHM which is evaluated as high sound quality because of small switching noise
2) Low noise Zener diodes for composing of extremely low noise power supply

Ongen Publising
Audio Excellence Award 2015 Bronze Prize