Audio Database

PMA-770
Commentary

This pre-main amplifier was developed by introducing original technologies such as a non-feedback 0 db amplifier, direct A system, and super equalizer.

From the MC input terminal to the speaker output terminal, all stages are capacitorless (complete DC configuration) without using even a single capacitor in the main signal path. The signal path is made pure and high-speed.
This fully capacitorless configuration uses the direct DC servo circuit installed in the PMA 970 and PMA 950 to suppress DC drift and ensure stability in the ultra-low frequency range.

Equipped with an MC/MM super equalizer, this cartridge has excellent RIAA deviation characteristics of 20 Hz to 100 kHz ± 0.2 dB, exceeding the upper reproduction limit frequency of high-end cartridges.
It consists of an NF-type DC amplifier with newly developed low-noise dual FET and a CR-type equalizing filter. The first stage consists of parallel differential amplification with dual FET of direct DC servo system.

The power amplifier section uses a non-feedback 0 dB amplifier.
The non-feedback 0 db amplifier compares the signal obtained from the output side of the main amplifier (main signal + distortion component, etc.) with the input signal by the direct distortion servo circuit, and extracts components other than the input signal (distortion, noise, etc.).
This distortion component is amplified by the direct distortion servo circuit, inverted in phase, and applied to the input side of the main amplifier to cancel the distortion component and suppress the static distortion.
In addition, the non-feedback 0 dB amplifier has a direct path in which the signal flows in only one direction, so no dynamic distortion occurs. In addition, noise components other than static distortion can be cancelled as a difference in the input signal by the effect of the direct distortion servo circuit. In addition, a buffer (emitter follower) is designed to separate the voltage and power amplification stages. Moreover, the voltage amplification stage is not affected by the speaker because there is no NFB loop, and the miscellaneous amplification stage can be simply constructed because no extra amplification by NFB is required.

The circuit configuration of the power amplifier section is a three stage current mirror using a low-noise FET at the first stage. Low impedance is achieved by using a complimentary service emitter-follower, and it is completely separated from the power amplifier stage.
The power amplifier stage is the output stage of the high-speed power transistor 2 parallel push-pull, and direct DC servo is applied from the output terminal to the first stage of the voltage amplifier to suppress DC drift and stabilize the ultra-low range.
In addition, DENON's original 0 cross linear bias circuit is used for the output stage to eliminate switching distortion caused by power transistor cutoff.

Speakers are equipped with a real drive circuit to reduce distortion under real load.
In the Real Drive Circuit, a Real Drive Line with electronic elements is set, and the protection line is very close to the A. S. O. (Area of Safety Operating) line. Therefore, even if the speaker load operation line becomes large at high output, it does not interfere with the protection line, making it possible to perform high power drive to the limit of transistor performance.
This reduces the distortion factor at the actual load of the speaker to approximately 1/50.

The equalizer amplifier and power amplifier are separated by an aluminum radiator to eliminate mutual interference.
Input switching is a remote control to shorten the wiring.

The power supply uses a large toroidal transformer with an emphasis on voltage regulation and leakage flux, and a 44,000 μ F large-capacity capacitor.

Real-time tone control is used for tone control.
This is composed of only passive elements necessary for tone control, and there is no distortion factor or S/N problem of the tone circuit itself, and the effect on the main circuit is suppressed.

By operating the switch on the front panel, it is also possible to compare and listen to 2 MC or 2 MM.

Equipped with a Rec out selector, subsonic filter, direct coupling switch, mode switch for stereo reverse and monaural playback, and loudness control switch.

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)
140W + 140W (4 Ω)
100W + 100W (8 Ω)
Input Sensitivity / Impedance 150mV/47k 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) 0.002% or Less (at Rated Output Equivalent Amplitude Output)
Output Bandwidth (IHF, double-channel drive, THD 0.035%) 5 Hz to 100 kHz
Frequency response (at 1W output) 1 Hz ~ 250 kHz + 0 -3dB
Output Impedance (1 kHz) 0.08 Ω
Output terminal Speaker AORb : 4 Ω ~ 16 Ω
Speaker A + B : 8 Ω ~ 16 Ω
Headphone : 390mW/8 Ω
Preamplifier Section (Phono In → Rec Out Excluding Input Sensitivity / Impedance)
Circuit system Super equalizer system with direct DC servo
Input Sensitivity / Impedance Phono MM : 2.5mV/47k Ω
Phono MC : 0.125mV/100 Ω
Tuner, Aux, Tape : 150mV/47k Ω
Maximum Output / Rated Output 10V/150mV
RIAA deviation (both MC and MM) 20 Hz to 100 kHz ± 0.2 dB
Total harmonic distortion factor 0.002% or Less (at 1 kHz, 8 V Output)
<General>
SN ratio (IHF-A, input short circuit) Phono MM:90dB
Phono MC:73dB
Tuner, Aux, Tape : 110 dB at 150 mV input
Tone control Bass : ± 8 dB (100 Hz)
Treble : ± 8 dB (10 kHz)
Subsonic filter 18 Hz, 6dB/oct.
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) 290W
External dimensions Width 434x Height 132x Depth 407 mm
Weight 12kg