Trio (Kenwood) KA-8700 Stereo vahvistin

Ihan siisti ja täysin ehjä vahvistin. 100V japanilainen versio ja 230V muuntaja mukaan.

Commentary

This pre-main amplifier was completed by condensing technologies such as two power supplies on the left and right, DC amplifier, and high-speed amplifier.

The MC head amplifier uses a push-pull complimentary service configuration for all stages, and a newly developed ultra-low-noise transistor is used for the first stage to high SN.

A newly developed dual FET is used in the first stage of the equalizer amplifier, and the SN ratio is improved by lowering the impedance of the whole circuit.

The circuit configuration consists of the first stage current mirror load cascade connection FET differential amplification + constant current load Darlington connection A class amplification + complimentary service push-pull output. By cascading the constant current section, the load is A class amplification, and by using transistors in the operation range with good linearity, low distortion factor is realized.

The tone control section is equipped with a unique NF-CR type tone control using an operational amplifier.

The circuit has no gain and phase inversion, and can be inserted anywhere regardless of the impedance before or after the circuit.

The power supply consists of four 10,000 μ F electrolytic capacitors and two large power transformers.

By making the left and right sides independent, dynamic crosstalk is eliminated, and sound image is positioned sharply.

The power amplifier section is a 3-stage differential direct-coupled ICL / OCL / DC sub amplifier using a cascade connection FET differential amplifier at the first stage.

The final stage employs parallel push-pull transistors with excellent high-frequency characteristics and a wide stable operating range. The first stage employs a single-chip dual FET that is resistant to temperature changes to prevent drift. At the same time, the current flowing through the common source of the first stage FET is kept constant regardless of ambient temperature changes, so that the current flowing through the FET is hardly affected by temperature changes.

A class A amplifier stage for handling small signals is installed on the back of the front panel. The equalizer amplifier and MC head amplifier are constructed by connecting directly to the input terminal of the rear panel. They are strictly shielded from the power supply of the center and class B amplifier.

The grounding point from the equalizer to the inlet of the power amplifier uses a copper B-Earth. The B-Earth is U-shaped and shields the wires in the small signal path.

It is equipped with peak meter IC which can respond to instantaneous signal of 10 kHz wave.

The meter uses a 50 dB logarithmic compression type.

Model Rating

Type Integrated amplifier

Rated output

(phono → sp terminal, both channel operation)

20 Hz to 20 kHz : 110W + 110W (8 Ω)

1kHz: 150W + 150W (4 Ω)

115W + 115W (8 Ω)

Total harmonic distortion factor (8 Ω)

Phono → sp terminal : 0.015% (at rated output, 20 Hz to 20 kHz, Volume-20dB)

Tuner, aux, tape → sp jacks : 0.015% (20 Hz to 20 kHz at rated output)

0.008% (1 kHz at rated output)

0.008% (20 Hz to 20 kHz at 1/2 Rated Output)

Cross modulation distortion factor Tuner, aux, tape → sp connector : 0.003% (at rated output, 8 Ω, 60 hz : 7 khz = 4 : 1)

Frequency characteristic Tuner, aux, tape → sp jacks (straight DC on) : DC ~ 450 khz -3dB

Tuner, aux, tape → sp jacks (straight DC off) : 18 Hz to 450 kHz -3dB

Output Bandwidth (IHF) Tuner, aux, tape → sp terminal : 5 Hz ~ 70 kHz (8 Ω at 0.03% distortion rate)

Damping factor 100 or more (tuner, aux, tape → sp jacks, DC ~ 20 khz, 8 Ω)

Input Sensitivity / Impedance phono1 (MM) → sp Terminal : 2.5mV/50k Ω

phono2 (MC) → sp Terminal : 0.1mV/100 Ω

Tuner, aux, tape → sp terminal : 200mV/50k Ω

Phono maximum allowable input

(1 kHz, 0.015% distortion factor) phono1 (MM) → rec out : 230 mV

phono2 (MC) → rec out : 9 mv

Phono RIAA deviation 20 Hz to 20 kHz ± 0.2 dB

Signal-to-noise ratio (IHF-A) phono1 (MM) → sp terminal : 90 dB

phono2 (MC) → sp terminal : 70 dB

Tuner, aux, tape → sp connector : 105 dB

Output Level / Impedance Tape rec pin : 200mV/330 Ω

Tone control

(tuner, aux, tape → sp jacks) Bass : ± 7.5 dB (100 Hz)

Treble : ± 7.5 dB (10 kHz)

Loudness control + 9 dB (100 Hz, tuner, aux, tape → sp jacks, Volume -30dB)

Transient response Rise time : 0.8 μ s (tuner, aux, tape → sp terminal)

Slew rate : ± 150 V / μ s (tuner, aux, tape → sp terminal)

Power outlet Power switch interlock : 2 systems, 100W

Power switch not linked : 1 system, 400W

Power supply voltage 100 VAC, 50Hz/60Hz

Rated power consumption 280W (Electrical Appliance and Material Control Law)

External dimensions Width 440x Height 153x Depth 407 mm

Weight 17.5kg