Pioneer A-09

Commentary

Pioneer engineers have kept the idea of "If we can express our will to the maximum in the fixed condition of pre-main amplifier" warm for 6 years. It uses simple circuit design for "straight sound". In addition, it is the highest quality pre-main amplifier which was born by incorporating all the technologies such as Exclusive C7 philosophy and technology.

Symmetrical twin monaural structure is adopted.
A shield box with a large current circuit power block on the left and right sides and a small signal input block in the rear center is placed around the central power supply section. The symmetrical structure with independent left and right channel circuits provides excellent separation.
In addition to the length of the left and right signal paths and the configuration of parts, the temperature, magnetic field distribution, and vibration environment inside the main body that affect the operation of elements and circuits are made uniform, and the occurrence of left and right electrical and mechanical characteristic errors is suppressed.

A pre-power isolated structure has been adopted to achieve the purpose of a separate amplifier, in which circuits with different roles of voltage amplification and current amplification operate properly, while maintaining the advantages of a pre-main amplifier, in which excellent balance and compactness can be obtained by connecting two amplifiers directly.
The preamp circuit (from the input terminal to the voltage amplification stage) including the volume is shielded by a non-magnetic aluminum box. Moreover, this box is supported by a chassis through vibration control rubber. It adopts a floating structure. The power supply section is also separated from the rectifier circuit by making the pre-section and the power section independent of each other. This realizes complete separation.
As a result, delicate input signals are isolated electrically and physically so as not to cause deterioration of sound quality due to circuit interference from the power section, fluctuation of the power section and vibration of the power section. This structure can be called a separate amplifier in a set.

It is equipped with advanced direct construction which is a further development of direct construction which makes the signal path as short as possible.
The signal switching relay and volume unit are controlled from the front panel right after the input terminal. The input block is located at the rear. In addition, the 16 power transistors of the power block are also located at the rear so that the shortest length is realized.
The signal is routed directly from the input block to the power amplifier and processed at once at the rear of the amplifier. As a result, the paths between pre-power and power speaker terminals, which tend to be noise sources, are greatly shortened.
In the input circuit, a signal switching relay is placed immediately after the input terminal to greatly improve crosstalk between each source. In addition, the buffer amplifier mounted on the same substrate as the relay drives low impedance, thereby realizing excellent channel separation by reducing impedance of the circuit.

The power amplifier section is operated in pure class A operation. By expanding the exclusive super linear circuit developed by Pioneer to the final stage of large current, the low distortion of 0.05% is achieved despite the final stage non-feedback configuration, and the high damping factor of 200 is also achieved.

The newly developed high-precision, integrally molded silent chassis is used for the chassis.
Through in-depth research, we have developed a special resin material that is resistant to changes over time and has excellent anti-torsional and anti-shock properties. It supports the main body securely and at the same time, it has a shape that matches each block and efficiently disperses and absorbs internal and external vibrations.
Since it is non-magnetic, electromagnetic induction noise and magnetic distortion are greatly suppressed.

The power supply section uses a stack type electrolytic capacitor with low flux noise developed like a pure A-class amplifier, and a power transformer with low magnetic flux density, sufficient capacity, and excellent regulation characteristics to keep flux noise low.

The volume uses a hand-made attenuator type with the same basic structure as the one used for Exclusive C7.
Each step consists of carefully selected carbon resistance and high-precision contact points. Unlike conventional sliding resistance devices, which change the sound volume, it is less affected by temperature and humidity. It eliminates the sound quality change due to contact resistance and the level difference between left and right, enabling stable control.

In order to maintain the design with the highest priority on sound quality, the attached functions such as tone control, balance, and loudness are omitted, and the speaker output is also single-system. This reduces the subtle influence of circuits and switches, and minimizes the effect of wiring steps and signal paths.
In addition, the earth side of each input source is also switched simultaneously, and a separate earth design is adopted to eliminate signal interference between connected devices from the earth side.

The Phono equalizer has a single-chip dual FET input configuration.

One balanced input is mounted on the input terminal, and highly reliable gold-plated terminals are used for all terminals.
The speaker terminal is a large vise type.

It uses a large-capacity extra-thick type OFC power cord that suppresses the influence of external noise by drawing it from directly under the power transformer.

It uses a high-grade type pure aluminum machined rotary knob and carefully selected resistors and capacitors.

The concentrated arrangement of power transistors separates the part that absorbs the generated heat from the part that effectively diffuses it, and adopts a new heat radiation structure that takes into consideration the position and shape of the heat sink and the air flow path.
The aluminum heat sink uses a new type that reduces resonance by changing the length of the fin.

Model Rating

Type	Stereo pre-main amplifier
Rated Output (Both channel drive)	35W + 35W (8 ω, 20 Hz-20 kHz, 0.05%) 70W + 70W (4 Ω)
Damping factor (8 Ω)	150 (20 Hz to 20 kHz) 200(1kHz)
Input Sensitivity / Impedance	Phono MM : 2.5mV/50k Ω CD, Tuner, Line, Tape : 150mV/50k Ω Balance : 150mV/600 Ω
Phono maximum allowable input	MM : 150 mV (1 kHz, 0.05%)
Output Level / Impedance	Tape Rec : 150mV/1k Ω
Frequency characteristic	Phono MM : 20 Hz to 20 kHz ± 0.2 dB CD, Tuner, Line, Tape : 1 hz to 150 khz + 0 to 3 db
S/N (IHF, A-network Short circuit)	Phono MM:87dB CD, Tuner, Line, Tape : 109 dB
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	220W
External dimensions	Width 440x Height 198x Depth 480 mm
Weight	28.8kg