YAMAHA HX-10000

Commentary

Phono equalizer amplifier developed by Yamaha to commemorate the 100th anniversary of its founding.

In consideration of sound quality and usability when combined with two player systems or a two arm player system, two phono inputs are provided. Four independent MC head amplifiers (Phono 1 and Phono 2) are provided. After that, two equalizer amplifiers for both Phono 1 and Phono 2 are sent by selecting a phono selector.
This is designed to minimize the switching contact at the microvolt order minute signal level represented by low-impedance low-power MC cartridges. The output of the MC cartridge is directly connected to the MC head amplifier through only cartridge load selectors independent of Phono 1 and Phono 2.
Equipped with a 4 mc head amplifier, two player systems with different cartridge specifications, such as Phono 1 with high impedance MC and Phono 2 with low impedance MC, can be fixed and used at all times under optimum input conditions.

In order to enjoy the high quality of the MC cartridge, the head amplifier for the MC cartridge is mounted separately instead of the step-up transformer or the gain variable of the equalizer amplifier itself.
A simple circuit design has been made. The circuit configuration consists of four parallel input complimentary service push-pull using eight ultra-low-noise transistors at the first stage, and complimentary service push-pull at both the voltage amplification stage and the output stage. All stages are complimentary service push-pull with a total of three stages of amplification.
Especially for the first stage transistor, an ultra-low noise type with minimum base spreading resistance is adopted, and equivalent noise resistance is reduced by using it in four parallel.
In addition, since all stages are A-class push-pull operation, transistors are equivalently working in parallel and there is an effect of oscillation, and low-noise characteristics are realized in the whole MC head amplifier.

Since the equalizer amplifier has the function of equalizing the RIAA characteristics of low-pass down and high-pass up, it is necessary to have a circuit configuration with sufficient gain and peak margin and high thermal stability.
In the first stage, a differential input cascode bootstrap using two high-Gm dual FETs achieves a wide bandwidth and high gain with a low distortion factor.
By using the first stage dual FET in parallel, the cartridge mounting S/N has been improved.
On the other hand, power MOS FETs are used in the power stage to drive heavily loaded RIAA devices, and a complimentary service push-pull configuration provides low impedance drivability with room for RIAA devices.

The MC head amplifier (Phono 1, Phono 2) and the equalizer amplifier (L/R) are each constructed with independent circuit boards to eliminate mutual interference between the MC head amplifier and the equalizer amplifier and to pursue performance through optimization.
Each unit amplifier board is firmly fixed to the internal chassis with five 8mm-diameter brass shavings posts at five corners and centers in order to eliminate the influence of vibration on sound.
To further improve vibration resistance and protect against external noise, we have prepared an aluminum housing made of non-magnetic extruded aluminum material, and four unit amplifier substrates are stored in four aluminum housings.

Uses a highly rigid 2-box chassis that separates the power supply part, which tends to generate internal electrical and magnetic noise, from the amplifier part, and stores each part in an independent box.
The amplifier and power supply are separated by 3 mm thick extruded aluminum material to prevent the magnetic loop centered on the power transformer from affecting the amplifier.
The chassis is made of extruded non-magnetic aluminum material that does not cause metal fatigue due to mechanical bending. The front panel is 9 mm thick, the top and bottom are 5 mm thick, and the rear panel is 3 mm thick. The rigidity is increased by using different materials for the front panel, top and bottom are 5 mm thick, and the rear panel is 3 mm thick. They are firmly fastened together with screws.

In addition to a large transformer with low leakage flux contained in a shield case, the power supply section is equipped with an aluminum electrolytic capacitor for audio in the Chemi-Con for smoothing. Six units of 10,000 μ Fx are installed as the main unit, and in addition, six units of 4700 μ Fx, eight units of 1000 μ Fx, and 12 units of 470 μ Fx are installed.
The increase in power supply impedance is suppressed by using a plurality of parallel and step-by-step.

Since power feeding using wiring materials tends to cause an increase in power supply impedance due to routing and induction noise due to inadvertent formation of a current loop, we have adopted a motherboard method that minimizes the use of internal wiring materials.
On the mother board, constant voltage circuits for the MC head amplifier and the equalizer amplifier are mounted together. After fixing it to the lower part of the internal chassis with brass shavings post, each unit amplifier board ± B power supply is connected through the internal chassis directly with connector.
This makes it possible to provide high-quality power supply with less loss by connecting rigidly at the shortest distance.

6-position cartridge load selectors are provided independently for Phono 1 and Phono 2 so that various cartridges such as MC and MM can be used under optimum input conditions.

In order to prevent interference from the power supply between unit amplifiers with different gains, three constant voltage circuits are installed : the primary regulator for the equalizer amplifier and the Phono 1 / Phono 2 independent / secondary regulator for the MC head amplifier.
Like the amplifier section, all discrete parts are used.

A 2% class high-precision polypropylene film capacitor is used for the RIAA element of the equalizer amplifier, a mica capacitor and a polypropylene film capacitor are used for the phase compensation capacitor, and a 10 μ F film capacitor is used for the output coupling capacitor to prevent leakage of the DC component.
All signal resistors, including RIAA elements, are equipped with 1% class, high-precision square metal-coated resistors.

Both unit amplifier boards and power supply motherboards use glass-epoxy double-sided boards that are highly reliable in mounting parts.

Gold plated OFC (oxygen-free copper) bus bars are embedded at important points on the board to reduce the impedance of the ground line.

The output muting relay circuit linked to the power switch uses an audio-only relay filled with gold-clad contact and nitrogen gas to prevent deterioration of the signal contact due to oxidation and to obtain high reliability and stability.

The phono input and output terminals are made of gold-plated brass pin jacks, and the ground terminal is also made of gold-plated brass.

The AC power cord uses a 10 mm diameter OFC (oxygen-free copper) cable.
In addition, polarity display is attached.

Model Rating

Type	Phono equalizer amplifier
Input Sensitivity / Impedance	MC High Gain : 60 μ V/10 Ω, 30 Ω MC low gain : 200 μ V/30 Ω, 100 Ω MM : 2.5mV/47k Ω · 100 pF, 47k Ω · 330 pF
Maximum Allowable Input (1 kHz, 0.01% THD)	MC high gain : 3.4 mV MC low gain : 12 mV MM:120mV
Output Voltage / Impedance	150mV/470 Ω
Maximum output voltage	5 v (20 Hz ~ 20000 Hz, 0.01% THD)
RIAA deviation	± 0.2 dB (20 Hz to 20000 Hz)
Total harmonic distortion factor (20 Hz ~ 20000 Hz, 3 V Output)	MC:0.002% MM:0.001%
S/N ratio (IHF-A corrected)	MC : 88 dB (250 μ V input short) MM : 93 dB (2.5 mV Input Short)
Input reduced noise level	MC : -160dBV (250 μ V Input Short) MM : -145dBV (2.5 mV Input Short)
Channel Separation (1 kHz)	MC:50dB MM:86dB
Power supply voltage	AC100V 50Hz/60Hz
Power consumption	20W
External dimensions	Width 475x Height 130x Depth 432 mm
Weight	20kg