Phase Tech EA-3

Commentary

A transistor-type phono equalizer amplifier developed by inheriting the design philosophy and musical expression of EA-1.

The circuit configuration employs an all-stage symmetrical non-feedback amplifier.

The first stage consists of a low-noise voltage-to-current conversion circuit with the complimentary service connection of a phase-correction FET (field-effect transistor). Since carefully selected elements are used and the operating point is determined by the self-bias operation, no bias circuit is required. This eliminates the inflow of noise and the deterioration factor of sound quality, enabling the original low-noise operation of the element.

The second stage consists of a current amplification and voltage conversion circuit. The RIAA impedance element connected to the current output point gives the reproduction characteristics. This makes it a CR type equalizer circuit with no RIAA deviation up to the ultra-high frequency range, giving excellent transient characteristics.
This circuit employs a circuit technique that achieves high precision without being affected by current variation errors and parameter variations of the amplifying element that depend on the output voltage. This circuit realizes excellent electrical characteristics comparable to those of a feedback amplifier despite being a non-feedback amplifier.

The output buffer circuit uses an input bootstrap circuit to ensure high input impedance over a wide range, while the Darlington-connected output element provides sufficient current amplification and powerful drive for devices connected to the next stage.

The power supply section uses an independent power transformer on the left and right and a shunt type local power supply. It provides an ideal power supply without parameter fluctuation due to power supply load, and channel separation is improved by minimizing circuit current loop.
In addition, a large R-type transformer is used for the power transformer to minimize magnetic vibration and leakage flux by operating with a margin due to low magnetic flux density.

The internal layout uses symmetrical dual monaural construction to achieve uniformity of the left and right channels.

The power transformer is mounted directly to the brass round bar machined foot via a 5 mm thick baking plate, which is an insulator with high electrical and magnetic resistance, so that the vibration generated by the power transformer is not propagated to the chassis and is directly released to the ground.

The chassis structure is vibration free, resonance free and interference free.
The amplifier is mounted on an electromagnetically floating sub-chassis so as not to be affected by signals other than music signals and vibration. In addition, the chassis base and top cover are plated with copper on 1.2 mm and 1.6 mm thick steel plates, respectively, and coated with paint to ensure rigidity and reduce magnetic distortion.
The front panel is made by cutting out aluminum of 6 mm thickness.

Equipped with a full-fledged active subsonic filter with a cutoff frequency of 20Hz/40Hz.

Machined gold plated terminals are used for input / output terminals.

Model Rating

Type	Phono equalizer amplifier
Input Sensitivity / Impedance	MM : 2.5mV/47k Ω MC : 0.12mV/470 Ω
Gain	MM:38dB MC:65dB
Input conversion S/N ratio	MM:-124dBV MC:-144dBV
Maximum allowable input	MM:125mV(1kHz) MC:6mV(1kHz)
Rated output voltage	200mV(1kHz)
RIAA curve deviation	20 Hz to 20 kHz ± 0.2 dB
Output impedance	100 Ω
Channel separation	100 dB or More (20 Hz to 20 kHz, Both MC and MM)
Subsonic filter	20Hz/40Hz, 18dB/oct.
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	7W
External dimensions	Width 305x Height 90x Depth 310 mm
Weight	5.1kg
Attachment	Power cable