DENON PMA-970

Commentary

Pre-main amplifier developed with POA 3000 and PRA 2000 PRA technologies.

In order to shorten the signal system, we have adopted a two amplifier configuration consisting of an equalizer amplifier and a power amplifier, so that the tone circuit cannot be used as a servo circuit at the front of the power stage.
In addition, the direct DC servo circuit removes all capacitors from all signal paths from the MC input to the SP output to achieve a complete DC configuration.

A direct DC servo circuit that realizes a capacitor-less configuration for all stages is used for the equalizer amplifier and power amplifier.
In the direct DC servo system, stability in the ultra-low frequency range is ensured by shutting out minute latent DC drift. Moreover, since this circuit has an extremely simple configuration with only the parallel connection of the first stage FET differential amplifier and servo elements, characteristic degradation due to the servo circuit does not occur.

The equalizer amplifier section is equipped with a non-feedback real-time equalizer with two DC linear amplifiers.
This circuit consists of two stages of DC linear amplifier with newly developed low-noise dual FET and a CR-type equalizing filter. The first stage is a dual-FET parallel differential amplifier with direct DC servo system, which fundamentally eliminates DC temperature drift while improving S/N and distortion factor. In addition, high-frequency characteristics are also improved. In addition, a newly developed cascode differential bootstrap and a dual-transistor current mirror circuit are used together in order to reduce potential distortion and noise. In the voltage amplification stage of the next stage, the Darlington local feedback circuit is a class A push-pull circuit, which greatly reduces distortion. The CR-type equalizing filter of the SEPP output stage is driven with low impedance. The CR-type equalizing filter of the SEPP output stage is driven with low impedance. The CR-type equalizing filter is a thoroughly low-impedance type and uses a non-feedback type real-time equalizer system to obtain excellent SN ratio. In addition, high-precision elements carefully selected by a computer are used for the CR element.
The latter amplifier, to which the signal from the equalizing filter is sent, has the same high-grade circuit structure as the former amplifier. ± 60 V is supplied to the former amplifier and ± 32 V is supplied to the latter amplifier from independent stabilizing power supply respectively. In addition, a high-output, high-speed, and high-voltage transistor of Pc300mW ・ fT100MHz is used to realize a high output and wide dynamic range of clipping level 18 V.

The equalizer amplifier section is a high-gain type equalizer focusing on the MC cartridge from the beginning, which brings out the power of the MC cartridge.

The power amplifier section uses the circuit technology of the real bias circuit used in the power amplifier POA-3000, and realizes high power with class A operation.
A real-bias circuit has three functions : setting and stabilizing control of a fixed bias, supply of a high-speed bias according to the magnitude of the signal, and peak-hold-reset operation in response to an unfavorable change in the signal. The circuit operates by detecting the input signal at a high speed, and then supplying the amount of bias necessary to maintain class A operation in the bias balanced drive circuit of the FET differential based on the detected signal. At this time, the bias current is stably controlled so that it does not fluctuate even if the power transistor generates heat. Therefore, the best condition is always maintained. In addition, the bias current rises faster than the signal current, and in order to eliminate cutoff due to time delay, a small amount of fixed bias current flows even when no signal is present. This enables the bias to rise faster than the signal current even when a high-frequency music signal with a fast rise comes in, and ensures class A operation.
For the output transistor, newly developed high-speed power transistors (fT : 100 MHz, Pc : 120W) with excellent high-frequency characteristics are connected in parallel with two parallel push-pull connections on one side per channel to improve the linearity of hFE at high output.

The buffer amplifier of the power amplifier section has a circuit configuration of "first stage low noise FET parallel differential cascode bootstrap direct DC servo + differential current mirror balanced drive + pure complimentary service push-pull". The pre-driver stage has a 3-stage differential current mirror output, which drives the class A power stage with low impedance.

The power supply uses a large toroidal transformer (7.6 kg, 145 mm φ x height 121 mm) and a 66,000 μ F large capacity block capacitor (63.5 mm φ x height 120 mm).
The voltage amplifier of the class A power amplifier is supplied from a stabilized power supply of ± 23 V, the power supply is supplied from a separate winding of ± 60 V, the equalizer amplifier is supplied from a separate winding of a stabilized power supply, and two DC linear amplifiers are supplied with ± 60 V and ± 32 V.
In addition, the large toroidal transformer suppresses leakage flux by strict multiple shielding.

Equipped with a protection circuit that also functions as a muting operation when the power switch is ON.
It also has a DC protection circuit to prevent damage to the speakers due to DC output, and a temperature protection circuit to prevent damage to the transistors due to abnormal temperature rise of the radiator.

The tone control employs a newly developed real-time tone control that eliminates harmful capacitors from the signal path.

In order to prevent mutual interference between circuits, the power supply and signal amplification system, which occupy approximately 1/3 of the internal volume, are shielded by shield processing.
In addition, all input / output terminals are directly connected to the shortest printed circuit board, and the various modes are operated by remote switches controlled by front panel knobs to minimize wire routing.

The side wood has a Brazilian Rosewood-like mirror finish and the front panel has a champagne gold hard anodized finish.

Equipped with a headphone jack with direct position.
In addition to High/Low impedance switching, Direct is also installed. Unlike general resistance division type, it is directly connected to the output stage and can drive low output impedance.

Equipped with a subsonic filter, loudness control and muting.

LED display is used for the input selector.

Model Rating

Type	Pre-main amplifier
Power Amplifier Unit (Tuner in-SP out)
Circuit system	Direct DC Servo System DENON Class A Circuit
Rated Output (Both Channels Driven, Sine Wave Continuous Output)	100W + 100W (8 Ω, 20 Hz to 20 kHz) 80W + 80W (4 ohm, 1 khz)
Input Sensitivity / Impedance	150mV/40k Ω
Total harmonic distortion factor	0.003% (20 Hz to 20 kHz)
Intermodulation distortion factor (60 hz : 7 khz = 4 : 1)	0.005% or Less (at Rated Output Equivalent Amplitude Output)
Output Bandwidth (IHF, both channel drives)	5 Hz ~ 100 kHz (THD 0.02%)
Frequency characteristic	1 Hz ~ 400 kHz + 0 -3dB at 1W Output
Signal-to-noise ratio (IHF-A)	108dB
Output impedance	0.08 Ω or less
Slew rate	250 V / μ s
Rise time	0.6 μ s
Output terminal	Speaker AORb : 4 Ω ~ 16 Ω, A + B : 8 Ω ~ 16 Ω (With Impedance Switching Switch) Headphone : Stereo headphone (Impedance switchable : Low/High/Direct)
Preamplifier Section (Equalizer Amplifier)
Input Sensitivity / Impedance	Phono1/2 mm : 2.5mV/50k Ω Phono1 MC : 200 μ V/100 Ω Tuner, Aux, Tape1/2 : 150mV/40k Ω
Maximum Output / Rated Output	18V/150mV
Phono maximum allowable input (1 kHz)	MM:300mV MC:23mV
RIAA deviation	MM/MC : 20 Hz to 100 kHz ± 0.2 dB
Total harmonic distortion factor	0.001% (at 1 kHz, output 10 V)
Overall Characteristics
SN ratio (IHF-A, input short circuit)	Phono1/2 MM:90dB Phono1 MC : 75 dB at 250 μ V 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	Low frequency : + 7 dB (100 Hz) High frequency : + 6 dB (10 kHz)
Muting	-20dB
<Others>
Pwer	100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	305W
External Dimensions (including Knob, Rubber Leg, Terminal)	Width 506x Height 168x Depth 451 mm
Weight	23kg