YAMAHA HA-1 separate Phono equalizer a long-running famous product from 1977 to 1983
Playback equipment is amazing. Excellence was the secret of popularity.
From the current phonoiko to hear this kind of sound
I feel like I can't.
Independent and developed bed amplifier section
2 positions for MC, for MM the through position of
Switch with front switch
Basic spec
MC.LOW position 10Ω
MC.HIGH position 100Ω
Gain 34db 10Ω
　　14db 100Ω
Bypass possible
size
w150mm, H67.5mm, D 352mm
Weight 3.2 kg

An MC equalizer amplifier that employs a pure current signal transmission system and a pure current servo amplifier system.
A unique pure current signal transmission method is used to prevent the weak signal of the MC cartridge from deteriorating at the contact point.
The output signal of the cartridge is connected to the input terminal of the amplifier through the head shell, the signal cable inside the arm, and the output cable. However, most of the metal joints between them have non-linearity which acts like a kind of diode. Therefore, the small signal is distorted by the influence of the non-linear part of the diode characteristics. Therefore, in HA-1, the bias is applied to the signal of the microvolt order which is caught in the non-linear part of the diode characteristics of the metal joint part, and pure signal transmission is achieved by using the linear region of the diode characteristics.

The circuit configuration of the HA-1 is non-feedback first stage amplification (voltage-to-current conversion : pure current transmission) -SRPP circuit (consisting of the first stage and SRPP circuit) - inverted amplification RIAA equalizer (current-to-voltage conversion) set in a dedicated head shell.
The FET on one side of the first stage of the High gmFET SRPP circuit is sealed inside the head shell and the other side is sealed inside the main body. The signal converted from voltage to current by the amplifier inside the head shell is transmitted to the main body on the power supply current for operating the amplifier inside the head shell. In this way, the current of several tens of mA required for operation of the amplifier is supplied to the transmission system that used to supply AC current of microampere order in the past, so that the very small signal of the MC cartridge is released from the adverse effect of non-linear.

The signal converted from voltage to current in the first stage is input to an inverting equalizer amplifier, and is extracted as an RIAA-equalized voltage. This inverting equalizer amplifier has the same transfer characteristics as the CR-type equalizer, and is highly accurate within ± 0.2 dB of RIAA deviation over a wide range of 20 Hz to 100 kHz.
The HA-1 has a gain of 63.5 dB at a rated output of 150 mV for a rated input of 100 μ V. In addition, it has a built-in RIAA compensation circuit so that it can be connected directly to the Aux terminal of the amplifier.
If the main amp has a volume for adjusting the level, you can directly connect it to the main amp for more pure sound quality.
The HA-1 has a black box structure in which almost all circuits are modularized by the first stage amplifier module, inverted RIAA amplifier module, constant voltage power supply module, constant current power supply module, etc.
The HA-1 is equipped with a newly developed pure current servo amplifier.
The pure current servo amplifier was developed with attention paid to the degree of influence (element sensitivity) of the amplification method and power supply of the amplifier on sound quality. The signal current does not flow to the power supply or ground line at all, and a constant current is always supplied to the power supply line. Therefore, it is not affected by the L/C/R / C / R components of the power supply or wiring, or non-linear characteristics due to current changes.
All parts are selected based on sound analysis, including electrolytic capacitors and tantalum coated resistors in polypropylene cases for audio equipment, SE capacitors for RIAA constant setting, and glass epoxy printed circuit boards.
When the HA-1 is operating, the DC voltage supplied to the first stage amplifier in the head shell is supplied to the hot side of the input pin jack. In the event of a short circuit or when a cartridge is connected to the normal head shell, the protective circuit operates to protect the cartridge.
It uses a short type muting circuit that does not involve a relay in the signal path during playback.