TRIO KA-7002

Commentary

This pre-main amplifier uses solid-state circuit technology cultivated in KA-6000 and directly connected pure complimentary service circuit in all stages.

All stages are directly connected to the main amplifier section, eliminating the coupling capacitor. This makes it possible to amplify from direct current, greatly improving frequency characteristics, and making it possible to apply feedback more deeply. In addition, the output impedance does not rise in the low frequency range due to the output capacitor, and the output impedance is flat from the ultra low frequency range to the high frequency range.

In the asymmetric power supply system using an output capacitor, the upper and lower current paths are different. Since the output capacitor is used as the power supply for the lower transistor, the capacitance value is limited and the maximum output in the ultra-low frequency range is reduced. In the KA-7002, the power supply is vertically symmetric so that the output in the ultra-low frequency range is not reduced and stable output is achieved.
Since the operation of the transistor is exactly the same in each half cycle of the input signal, crossover distortion and switching pulse components that cannot be avoided in a quasi-output circuit can be circuit can be eliminated, reducing distortion at low complimentary service.

In order to improve DC stability, a differential amplifier circuit is composed of transistors with good temperature characteristics for the first stage and pre-drive stage. A zener diode is used to stabilize the supply voltage of the first stage circuit. In addition, 100% DC feedback is applied. This prevents DC from flowing into the voice coil of the speaker, causing mechanical orientation to deteriorate. In this differential amplifier circuit, since two transistors share the emitter resistance, a large amount of feedback is required and self-stability is high. In addition, since this differential amplifier circuit is a direct-coupled circuit, it has excellent phase characteristics and an improved damping factor for the speaker.

A 3-stage NF circuit is used for the equalizer amplifier section.

The tone control section is a 2-dB step switching type, and the turnover roll-off characteristic can be switched in two steps.
In addition, to eliminate slight waviness in the flat position, the flat position is turned off, and tone cancellation can be controlled with both the level knob and the defeat switch.

The protection circuit uses a PC detection method with a current limiter that prevents the input signal of the drive stage from being applied when a large current flows through the output transistor, thereby limiting the output transistor current.
This circuit operates reliably on both the positive and negative sides of the KA-7002, which uses a two power supply system, and solves the problem of the protection function of the direct connection circuit.

Equipped with a cut filter, it can cut noise caused by resonance of the arm, motor goroh, wow flutter, scratches, etc.
This filter uses a tantalum solid capacitor with a leakage current of less than 1 mA to prevent shock noise when the switch is activated.

Equipped with input / output jacks and control volume for 4-channel stereo.

In the past, the left and right output were balanced by setting the MODE to MIX and adjusting the sound source to the center of the left and right speakers. However, the KA-7002 uses Null Balance, which eliminates sound when the left and right are balanced.
This allows you to balance the entire amplifier circuit from the cartridge by operating Null Balance while playing monaural records.

The preamp and main amp can be used independently.

Model Rating

Type	Pre-main amplifier
Power Amplifier Unit
Music Power (IHF)	196W (4 Ω) 170W (8 Ω)
Effective power	80W/80W (single-channel operation, 4 Ω) 70W/70W (single-channel operation, 8 Ω) 68W + 68W (both channel operation, 4 Ω) 55W + 55W (both channel operation, 8 Ω)
Total harmonic distortion factor	0.5% (8 Ω at rated output) 0.05% (8 Ω at rated output of -3dB)
Cross modulation distortion factor	0.3% (8 Ω at Rated Output) 0.08% (8 Ω at rated output of -3dB)
Output bandwidth	2 Hz to 60 kHz (IHF)
Input sensitivity	Main in : 1V/50k Ω
Residual noise	0.24 mv (8 Ω)
Damping factor	45 (8 Ω)
Preamplifier Section
Input Sensitivity / Impedance (for rated input)	Phono1 : 2.5mV/30k Ω, 50k Ω switching Phono2 : 0.06mV/200 Ω 2.5mV/50k Ω Mic : 2.5mV/50k Ω Aux1/2, Tuner, Tape : 200mV/100k Ω
Recorded output	Tape rec A/B(Pin):200mV Tape rec A/B(DIN):40mV Dubbing A-B:200mV
Frequency characteristic	20 Hz to 50 kHz ± 1 dB
Maximum Input Voltage	310 mv (Phono1, P-P, 1 khz)
Tone control	Bass : ± 6 dB (100 Hz, turnover 150 Hz) ± 10 dB (100 Hz, turnover 300 Hz) Treble : ± 6 dB (10 kHz, turnover 6 kHz) ± 10 dB (10 kHz, 2 kHz turnover)
Turnover roll-off	Bass : 150 Hz, 300 Hz Treble : 2 kHz, 6 kHz
Loudness contour	+ 8 dB (100 Hz), + 3 dB (10 kHz)
Low filter	40 Hz, 18dB/oct. 80 Hz, 18dB/oct.
High filter	7 kHz, 18dB/oct.
Equalizer	± 0.1 dB to the RIAA standard curve
Signal-to-noise ratio	Phono1:70dB(2.5mV) Phono2:50dB(0.06mV) 70dB(2.5mV) Mic:70dB Aux, Tuner, Tape : 80 dB
<General>
Accessory circuit	3-speaker switching Tape monitor (2 systems) and dubbing Head amplifier for low output cartridge Input / output jacks for 4D stereo Control volume for 4D stereo Load impedance switching for MM cartridge Tone turnover Null Balance Audio Muting Premain and separate Output terminal for mono Power transistor protection circuit Stereo horn jack DIN standard recording and re-connector (2 systems)
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption (Electrical Appliance and Material Control Law)	15W (No signal) 275W at maximum output
External dimensions	Width 408x Height 134x Depth 280 mm
Weight	10kg