Audio Database

PMA-790
Commentary

A pre-main amplifier designed for digital sources with strong construction centered on a non-feedback 0 db power 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.

In the PMA 790, the direct distortion servo circuit, which is the core of the non-feedback system, has been thoroughly polished and the slew rate of the circuit itself has been improved in order to be compatible with digital sources. In addition, the signal system has been made highly pure by removing all the coupling capacitors from all the signal paths from the input terminal to the speaker terminal for the MC cartridge to make it a complete DC configuration, thereby greatly improving the signal transmission speed.

The circuit configuration of the voltage amplification stage of the power amplifier section is such that the influence of the power amplification stage does not reach the voltage amplification stage by making the first stage a three stage current mirror using a low-noise FET and making the impedance low by using a complimentary service emitter follower.
The final output stage is a parallel push-pull configuration using a Pc130W power transistor and a direct class A configuration using DENON's original 0 cross linear bias circuit to eliminate switching distortion.

The power supply uses a 600 VA class large toroidal transformer, a 66,000 μ F large capacitor and a fast recovery diode.

The first stage of the equalizer amplifier is 2-parallel differential amplification using four low-noise FETs to obtain a high SN ratio. In addition, the cascode bootstrap is used to suppress the increase in distortion caused by the impedance rise in the mid - and high-frequency range in the case of MM cartridges to realize a wide bandwidth.
In addition, the MC input has two positions of High and Low to support various cartridges.

Equipped with a dual listening mechanism that allows you to freely switch between two cartridges for trial listening.

Equipped with wide-band real-time tone control with limited quality degradation.

Equipped with 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)
240W + 240W (4 Ω)
200W + 200W (6 Ω)
150W + 150W (8 Ω)
Input Sensitivity / Impedance 150mV/47k Ω
Total harmonic distortion factor 0.002% or Less (20 Hz to 20 kHz, Rated Output -3dB)
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1) 0.0015% or Less (at Rated Output Equivalent Amplitude Output)
TIM distortion factor Below the measurement limit
Slew rate ± 350 V / μ s or more
Output Bandwidth (IHF, both channel drives) 5 Hz ~ 80 kHz (THD 0.015%)
Frequency response (at 1W output) 1 Hz ~ 300 kHz + 0 -3dB
Output Impedance (1 kHz) 0.1 Ω
Output terminal Speaker AORb : 4 Ω ~ 16 Ω
Speaker A + B : 8 Ω ~ 16 Ω
Headphone : 590mW/8 Ω
Preamplifier Section
Circuit system Wide-band equalizer system
Input Sensitivity / Impedance Phono MM : 2.5mV/47k Ω
Phono MC high : 0.25mV/100 Ω
Phono MC low : 0.125mV/100 Ω
Tuner, DAD/Aux, Tape : 150mV/47k Ω
Maximum Output / Rated Output 12V/150mV
RIAA Deviation (MC/MM) 20 Hz to 100 kHz ± 0.2 dB
Total Harmonic Distortion Factor (at 1 khz, 8 v output) Not more than 0.001%
<General>
SN ratio (IHF-A, input short circuit) Phono MM : 90 dB at 2.5 mV input
Phono MC : 75 dB at 0.25 mV input
Tuner, DAD/Aux, Tape : 110 dB at 150 mV input
Tone control Bass : ± 8 dB (50Hz/100Hz)
Treble : ± 8 dB (10kHz/20kHz)
Subsonic filter 18 Hz, 6dB/oct.
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) 380W
External Dimensions (including legs, knobs, terminals) Width 506x Height 168x Depth 451 mm
Weight 20kg