DENON PMA-750
¥ 69,800 (around 1981)
Commentary
This pre-main amplifier is equipped with a non-feedback 0 dB amplifier that realizes 0 dynamic distortion and an ultra-wide band super equalizer.
The basic circuit is the same as that of the high-end model PMA 770. It consists of two amplifiers including a direct-DS (distortion servo) no-feedback 0 dB and an MC/MM super equalizer equipped with a real drive circuit and a direct-A system.
In addition, a k ンデンサーレス configuration is adopted in which no coupling capacitor is interposed between all signal paths from the MC input terminals to the speaker outputs.
Equipped with an MC/MM super equalizer, it achieves broadband characteristics of 20 hz to 100 khz ± 0.2 db.
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 a dual-FET differential amplifier with direct DC servo system.
The power amplifier section uses a non-feedback 0 db amplifier.
In this method, the static distortion caused by the nonlinear amplification characteristic of the power transistor is driven to the 0 region by the effect of the direct DS circuit, and high sound quality is achieved.
The circuit configuration consists of a 3-stage current mirror with a low-noise FET at the first stage. Low impedance is achieved by a complimentary service and emitter follower, and it is completely separated from the power amplifier stage. The power amplifier stage is a push-pull stage with a high-speed power transistor to improve individual characteristics and realize high signal speed.
The output stage is equipped with DENON's unique 0 cross linear bias circuit to eliminate the switching distortion caused by the cutoff of the power transistor and to achieve both the quality of class A amplifiers and the high efficiency and high output of class B amplifiers.
It is equipped with a real drive circuit that reduces distortion of the amplifier when the speaker is mounted.
This suppresses the increase in distortion caused by the phase difference between voltage and current due to the load resistance of the speaker that changes with frequency, and reduces the distortion to approximately 1/50 near the speaker fo.
In the in-chassis construction, the equalizer amplifier and power amplifier sections are laid out separately to reduce mutual interference.
Equipped with tone control, subsonic filter, loudness control switch and Rec out selector.
It is also equipped with a direct couple switch and a mode switch capable of stereo reverse and monaural playback.
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) |
100W + 100W (4 Ω) 80W + 80W (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 : 310mW/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 : 0.25mV/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:88dB Phono MC:72dB 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) | 200W |
| External dimensions | Width 434x Height 132x Depth 407 mm |
| Weight | 12kg |