TRIO KA-7500

Commentary

This pre-main amplifier was developed under the policy of delivering the real thing to those who want the real thing.

The equalizer amplifier section uses a 3-stage direct connection circuit consisting of 1 stage FET differential amplifier and 2 stages PNP + NPN class A amplifier.
10 at low-noise for first stage differential amplification^-9By using an FET with A or less and extremely low gate leakage current, the input capacitor is eliminated and connected directly to the input, eliminating various causes of distortion and noise. This ICL method can greatly improve phase characteristics and transient characteristics, reduces disturbance noise in the ultra-low frequency range caused by the capacitor, and ensures a wide dynamic range with a maximum allowable input of 260 mV by applying a high voltage of ± 25 V.
Second, a 2-stage class A amplifier circuit consisting of PNP + NPN is used to improve the bare gain. Since a sufficient amount of feedback is applied to the low-frequency range, it can obtain both low distortion and excellent equalizer characteristics.

For the power amplifier part, all stages are directly connected OCL circuit by first stage PNP differential + class A amplification + constant current + pure complimentary service power Darlington.
In addition to the final transistor and complimentary service, the pure complimentary service Power Darlington Block is an original device of Trio. In addition to this device, the Power Darlington Block is equipped with a limiter protection, which is unique to Trio. In this device, the high power is obtained while the no-signal current is adjusted within the Power Darlington Block, and the stability is greatly improved. In addition, the bias of the power transistor is stabilized by making the load circuit of the pre-driver constant current. This stabilizes the bias of the power transistor. The pre-driver load circuit can be used as a stabilized power supply. Thus, the power supply before the pre-driver can be used as a stabilized power supply. It has a wide bandwidth, low distortion rate, and stable characteristics that are not affected by power fluctuations caused by sudden large signal input are obtained.

The power supply section uses a power transformer with good regulation and two large capacitors of 15,000 μ F.

The protection circuit is a triple protection configuration. It is equipped with an ASO detection type limiter method for protecting the power transistor, a relay for protecting the speaker, and a surge prevention for the power switch circuit.

The tone amplifier is a ± 2 power supply system using a low-noise operational amplifier. Since it is a selective NFB type tone control, the CR element is in the NF circuit and not in the signal system, so the SN ratio is good and the distortion factor is low.
In addition, since the CR element is removed in the tone defeat position, the buffer amplifier has excellent characteristics such as DC stability, distortion and phase.

Equipped with a large power meter that employs a logarithmic compression circuit.
The meter uses a current sensitive meter of 400 μ A. The meter has an easy-to-read W display and a range switch of 15 dB from 0.01W to 100W.

The volume section uses a 22-contact attenuator volume and a 3-step attenuator of off/-10dB/-20dB.

Equipped with a subsonic filter.

There was a carrying handle as an option sold separately.

Model Rating

Type	Integrated amplifier
Power Amplifier Unit
Effective output (both channel operation)	80W + 80W (8 Ω, 20 Hz to 20 kHz) 85W + 85W (8 ohm, 1 khz) 110W + 110W (4 ω, 1 kHz)
Music Power (IHF)	240W (8 Ω) 380W (4 Ω)
Total harmonic distortion factor	0.1% (at rated output) 0.04% (8 Ω at rated output of -3dB)
Cross modulation distortion factor	0.1% (8 Ω at rated output)
Output Bandwidth Characteristics (IHF)	5 Hz to 40 kHz
SN ratio (using IHF and A-curve)	100dB
Input Sensitivity / Impedance	1.0V/50k Ω
Damping factor	30
Optimum load impedance	4 Ω ~ 16 Ω
Preamplifier Section
Input Sensitivity / Impedance	phono1/2 : 2.8mV/50k Ω Tuner, aux, tape play : 150mV/50k Ω
SN ratio (IHF-A curve)	Phono : 77 dB (5 mV input) Tuner, aux, tape play : 90 dB
Output Level / Impedance	Tape rec pin : 150mV/600 Ω
Maximum Allowable Input (1 kHz, Distortion 0.1%)	phono:260mVrms
Frequency characteristic	Phono : RIAA deviation ± 0.3 dB Tuner, aux, tape play : 20 Hz to 20 kHz + 0 -0.5 dB
Tone control	Bass : ± 10 dB (100 Hz) Treble : ± 10 dB (10 kHz)
Subsonic filter	20 Hz, 12dB/oct.
High filter	10 kHz, 12dB/oct.
<General>
Power outlet	Power switch interlock : 2 systems Power switch not linked : 1 system
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption (Electrical Appliance and Material Control Law)	180W
External dimensions	Width 430x Height 149x Depth 376 mm
Weight	16kg
Sold Separately	Carrying Handle D-7 (1 set, ¥ 3,000)