Audio Database

PMA-740
Commentary

Stereo pre-main amplifier with non-feedback 0 db amplifier.

Equipped with a non-feedback 0 db power amplifier that eliminates negative feedback loops.
This system is an application of the non-feedback technology developed in POA-8000, and uses a direct distortion servo circuit. The direct distortion servo circuit compares the input signal with the signal obtained from the output side (main signal + distortion component) to detect only the distortion component, and then applies the inverted phase of this distortion component to the input side.
This action drives the static distortion into the 0 region, and the noise appearing at the output side of the amplifier is treated as a difference from the input signal and is removed in the same way as the distortion component.
As a result, there is no signal feedback and no time delay, so the dynamic distortion which affects the auditory quality is suppressed. In addition, since there is no NFB circuit, it is not affected by the back electromotive force from the speaker, so the increase and generation of the distortion when the speaker is connected are suppressed.

A Pc150W power transistor is used for the power amplifier section.

In order to cope with the high dynamic range of digital sources, we have adopted a large transformer with multiple shields, a large capacitor of 20,000 μ F, and a fast recovery diode for the power supply.

The equalizer section is equipped with a unique super-equalizer to achieve a wide bandwidth.

Built-in high-speed protection circuit.

Model Rating
Type Pre-main amplifier
Power Amplifier Unit
Circuit system Non-feedback 0 db power amplifier system
Rated output (both channel drive
Sine wave continuous output, 20 Hz to 20 kHz)
120W + 120W (6 Ω)
105W + 105W (8 Ω)
Input Sensitivity / Impedance 150mV/30k Ω
Total harmonic distortion rate (20 Hz to 20 kHz) 0.005% or Less (at Rated Output -3dB)
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1) 0.0025% or Less (at Rated Output Equivalent Amplitude Output)
TIM distortion factor Below the measurement limit
Slew rate ± 200 V / μ s or more
Output Bandwidth (IHF, both channel drives) 5 Hz ~ 80 kHz (THD 0.03%)
Frequency response (at 1W output) 4 Hz ~ 150 kHz + 0 -3dB
Output Impedance (1 kHz) 0.1 Ω
Output terminal Speaker AORb : 6 Ω ~ 16 Ω
Speaker A + B : 12 Ω ~ 16 Ω
Headphone : 410mW/8 Ω
Preamplifier Section
Circuit system Super equalizer system
Input Sensitivity / Impedance Phono MM : 2.5mV/47k Ω
Phono MC : 0.2mV/100 Ω
Tuner, DAD/Aux, Tape : 150mV/30k Ω
Maximum Output / Rated Output 10V/150mV
RIAA Deviation (MC) 20 Hz to 100 kHz ± 0.3 dB
Total Harmonic Distortion Factor (at 1 khz, 8 v output) Not more than 0.002%
<General>
SN ratio (IHF-A, input short circuit) Phono MM : 86 dB (at 2.5 mV input)
Phono MC : 70 dB (at 0.25 mV input)
Tuner, DAD/Aux, Tape : 106 dB at 150 mV input
Tone control Bass : ± 8 dB (100 Hz)
Treble : ± 8 dB (10 kHz)
Muting -20dB
Loudness property Low frequency : + 7 dB (100 Hz)
High frequency : + 6 dB (10 kHz)
Pwer 100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law) 195W
External Dimensions (including legs, knobs, terminals) Width 434x Height 112x Depth 398 mm
Weight 10.2kg