Audio Database
E-405
Commentary

In order to overcome the limitation of the pre-main amplifier, the pre-main amplifier is composed by combining a pre-amplifier and a power amplifier which are substantially independent.

The output stage of the power amplifier is a 5-parallel push-pull configuration with 10 output elements. Each element has a Pc (collector loss) of 130W, so that sufficient power can be sent even under low load.
The drive stage that drives the output stage employs a two stage cascode direct-coupled circuit of cascode push-pull and MOS FET cascode push-pull. The cascode connection improves high-frequency characteristics, while the MOS FET minimizes distortion at small outputs.

All amplifier stages, including the preamp section, are directly connected. In addition, a selector switch and an input terminal are provided so that the preamp section and the power section can be separated and used as an independent amplifier.
When DC voltage is applied for some reason, it is amplified as it is and a large DC appears in the output, which may damage the speaker. Therefore, we have adopted the "DC servo method" to cut unnecessary DC components and stabilize the DC drift of the amplifier itself due to temperature changes.
The 0 DC voltage is maintained by detecting the DC voltage appearing at the output and returning it to the input.

As a function of the power amplifier section, it is equipped with a large power meter that can monitor output voltage.
Output power can be monitored with a logarithmic compression type peak meter located in the center of the panel.

There are two speaker outputs, which are controlled by a large relay, and two A + B outputs are arranged in parallel. This allows for bi-wiring in which the low and medium / high sound networks are separated.

The high-level flat amplifier in the preamplifier section, to which normal signals other than analog disks are input, employs a cascode bootstrap differential method composed of a low-noise dual FET and transistor, thereby preventing mirror effect distortion due to changes in impedance and volume adjustment volume of the input device as well as high S/N.
It also has a XLR-type balance connector.

It is equipped with an equalizer amplifier with a dedicated input circuit that takes into consideration the characteristics of each MM type and MC type cartridge.
Considering that the output voltage and output impedance of the MM cartridge are high at MM input, the cascode bootstrap differential input circuit is composed of FET and transistor which can maintain high input impedance over the whole frequency band.
On the other hand, at the MC input, the signal voltage is low, so S/N improvement is the most important theme. Therefore, we have constructed a cascode bootstrap differential input circuit using carefully selected elements with little inherent noise.
These switching are performed by relay 1 and relay 2, and at the same time, the amplification degree suitable for MM/MC is selected.

The preamp section has a power supply section that is completely independent of the power amplifier.
A low-leakage flux toroidal transformer is used for the power transformer, which is rectified by a high-speed diode and then stabilized by a ± / dual tracking series regulator.

In order to configure the shortest and straight signal path, relays are installed in the signal path where switching is necessary, and a logic relay control method is adopted to electronically control these relays for switching.
The relay uses a sealed type relay developed especially for audio equipment. The contact is a crossbar twin type with low contact resistance and high durability.

It is equipped with a remote commander that can adjust the input source and volume.
To prevent deterioration of sound quality, the relay is switched electronically for input switching, the logic circuit is controlled only by the commander, and the volume is adjusted by rotating the motor with a manual volume.

For the tone control, we have developed and installed a tone control using an addition type filter. By using a high-quality element with an emphasis on sound quality, we further eliminate the influence on characteristics and sound quality.
In addition, an ON-OFF switch is provided to pass the circuit when it is OFF.
The principle of this circuit is that the original flat signal passes straight through, the characteristics are created as needed, and the signal is added or subtracted from the flat signal.

The Recording Selector is installed independently of the Input Selector, enabling you to record FM while listening to CDs.
It also has a copy switch that allows independent dubbing between sound recording devices.

It features a mode switch to mix left and right sounds, a subsonic filter to cut out ultra-low-frequency noise such as analog disks, a compensator switch to enhance bass sound at low volume, and a headphone jack.

Model Rating
Type Integrated stereo pre-main amplifier
Continuous average output (both channel operation
20 Hz to 20 kHz, Distortion Factor 0.02%)
4 Ω load : 250W/ch
8 Ω load : 170W/ch
Total harmonic distortion factor (both channel operation) 0.02% (4 ~ 16 ohm load, 0.25W ~ continuous output, 20 hz ~ 20 khz)
IM distortion factor 0.01%
Frequency characteristic
Main Amp Input: 20 Hz ~ 20000 Hz + 0 -0.2 dB at Rated Output
0.5 Hz ~ 150000 Hz + 0 -3.0 dB (at 1W Output)
High Level Input: 20 Hz ~ 20000 Hz + 0 -0.2 dB at Rated Output
Low Level Input: 20 Hz ~ 20000 Hz + 0.2 -0.5 dB (at Rated Output)
Damping factor 150 (8 Ω load, 50 Hz)
Rated input / input impedance
Input sensitivity Impedance
At rated output EIA (at 1W output)
AD Input(MC): 0.14mV 0.011mV 100 Ω
AD Input(MM): 4.38mV 0.335mV 47k Ω
High Level Input: 143mV 10.8mV 20k Ω
Balanced Input: 143mV 10.8mV 40k Ω
Main Amp(unbal): 1.47V 110mV 20k Ω
Main Input(bal): 1.47V 110mV 40k Ω
Disk Max Input
(1 kHz, 0.005% distortion factor)
MM Input : 300 mVrms (Rec Out)
MC input : 9.5 mVrms (Rec Out)
Rated output / output impedance Pre Output : 1.47V/200 Ω
Tape Rec Output : 143mV/200 Ω (from AD)
Headphones : 0.36 V, Applicable Impedance 4 ~ 100 Ω
Gain Main Input → Output : 28 dB
High Level Input → Pre Output : 20 dB
AD Input (MM) → Tape Rec Output : 30 dB
AD Input (MC) → Tape Rec Output : 60 dB
S/N, input conversion noise
Input short / A-correction EIA S/N
S/N at rated input Input reduced noise
Main Amp Input: 124dB -121dBV 102dB
High Level Input: 110dB -127dBV 83dB
Balanced Input: 98dB -115dBV 83dB
AD Input(MM): 89dB -137dBV 80dB
AD Input(MC): 74dB -150dBV 78dB
Tone control Bass : Turnover frequency 300 Hz, ± 10 dB (50 Hz)
High tone : Turnover frequency 3 kHz, ± 10 dB (20 kHz)
Loudness compensator +6dB(100Hz)
(Volume -30dB)
Subsonic filter 17 Hz, -12dB/oct.
Attenuator -20dB
Power meter Logarithmic compression type peak level display
Direct reading of output at dB scale and 8 Ω load
Load impedance 4 ~ 16 Ω
Semiconductor used Transistor : 85
FET : 22
IC : 30
Diode : 65 pcs
Pwer 100V/117V/220V/240V, 50Hz/60Hz
Power consumption No input : 90W
Electrical Appliance and Material Control Law : 390W
8 Ω load rated output : 620W
External dimensions Width 475x Height 180 (Including Legs) x Depth 375 mm
Weight 25kg
Attachment : Remote Commander RC-3
Remote control system Infrared pulse system
Pwer DC 3V
Dry battery SUM-3 (IEC Designation, R6), 2 units
Maximum external dimensions 64 mm wide x 149 mm high x 18 mm deep
Weight 140g (including dry batteries)