DENON PMA-550

Commentary

This pre-main amplifier is equipped with a super equalizer to take advantage of the cartridge performance.

The basic configuration consists of two amplifiers, an MC/MM super equalizer amplifier and a non-switching A power amplifier. In addition to this simple configuration, a complete DC configuration is adopted from the MC input terminal to the SP output terminal without using a coupling capacitor in the signal path.
This fully capacitor-less configuration is realized by installing DENON's direct DC servo system in both the equalizer and power amplifiers to shut out DC drift and achieve the sound quality inherent in DC-configured amplifiers.

The EQ section is equipped with a super equalizer for use with cartridges capable of wide-band playback.
The amplifier consists of an NF-type DC amplifier with newly developed low-noise dual FET and a CR-type equalizing filter. The first stage is parallel differential amplifier with dual FET of direct DC servo system.
As a result, in addition to the ultra-wide range, we have obtained a high gain equivalent to that of a head amplifier for MC. It is also compatible with low-output MC cartridges.
In addition, it is equipped with the dual listening mechanism of the cartridge, and not only the switching of MC/MM can be used, but also the comparison trial listening of 2 MC or 2 MM can be operated by the push button on the front panel.

The power amplifier section is equipped with a direct DC servo type high gain non-switching A power amplifier.
It consists of a low-impedance buffer amplifier with a first stage low-noise FET parallel differential + IC high-speed operational amplifier, a driver stage of a 3-stage differential current mirror, and a high-speed power transistor 2 parallel push-pull output stage. Direct DC servo is applied from the output terminal of the power amplifier to the first stage of the buffer amplifier. This improves the characteristics of the amplifier such as high speed, high gain, high stability, and low distortion factor.
The bias circuit is DENON's unique 0 cross linear bias circuit and high-speed thermal feedback circuit. This eliminates switching distortion, which is the advantage of non-switching systems, and realizes highly stable operation.

The tone circuit has real-time tone control.
It is composed of only the passive elements necessary for tone control and does not have an amplifying function, so the distortion factor and S/N problem of the tone circuit itself are improved.

The power supply is equipped with a large toroidal transformer with an emphasis on leakage flux and voltage fluctuation, and a 44,000 μ F block capacitor.
This power supply section is located in the center of the left and right independent power amplifier sections, and adopts the layout of power current pure radiation construction method which makes wiring the shortest distance and L/Rch the equal distance.

It is equipped with functions such as a direct couple switch, Rec out off function, an equalizer subsonic filter which is effective only when playing records, and a loudness control function.

Model Rating

Type	Pre-main amplifier
<Power Amplifier Unit (Tuner in → SP out)>
Rated Output (Double-channel Drive, Sine Wave Continuous Output, 20 Hz to 20 kHz)	140W + 140W (4 Ω) 100W + 100W (8 Ω)
Input Sensitivity / Impedance	150mV/40k Ω
Total Harmonic Distortion Factor (20 Hz to 20 kHz, Rated Output -3dB)	Not more than 0.005%
Intermodulation distortion factor (60 Hz : 7 kHz = 4 : 1, equivalent to rated output)	Not more than 0.008%
Output Bandwidth (IHF, both channel drives)	5 Hz ~ 400 kHz (THD0.035%)
Frequency response (at 1W output)	1 Hz ~ 400 kHz + 0 -3dB
Output Impedance (1 kHz)	0.1 Ω
Speaker output	AORb : 4 Ω ~ 16 Ω A + B : 8 Ω ~ 16 Ω
Preamplifier Section (Phono In → Rec Out Excluding Input Sensitivity / Impedance)
Input Sensitivity / Impedance	Phono MM : 2.5mV/50k Ω Phono MC1, 2 : 0.125mV/100 Ω Tuner, AUX, Tape : 150mV/40k Ω
Maximum Output / Rated Output	10V/150mV
RIAA deviation (MM, MC)	20 Hz to 100 kHz ± 0.2 dB
Total Harmonic Distortion Factor (1 khz at 9 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 : 73 dB at 0.25 mV input Tuner, AUX, Tape : 108 dB
Tone control	Bass : ± 8 dB (100 Hz) Treble : ± 8 dB (10 kHz)
Subsonic filter	18 Hz, 6dB/oct.
Loudness control	100 Hz : + 7 dB, 10 kHz : + 6 dB
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	255W
External dimensions	Width 434x Height 132x Depth 407 mm
Weight	13.5kg