Audio Database

Image of C-21
Commentary

This is a simple preamplifier with a monofunctional to achieve high-quality sound.

The equalizer amplifier uses a 2-stage differential, class A SEPP current mirror circuit.
Various characteristics are improved by this circuit with emphasis on reducing distortion and improving SN ratio.
In addition, carefully selected elements such as precision small metal film resistors with a resistance error of ± 0.5% and temperature characteristics of ± 100 ppm / ℃, and polypropylene capacitors with a capacitance error of ± 1% are used for the equalizer elements.
A high voltage of ± 37 V is applied to this circuit to ensure a dynamic margin of 300 mV maximum allowable input for sensitivity of 2.5 mV.

In order to demonstrate the performance of various cartridges, 6 load resistances and 6 load capacities can be independently selected, and a total of 36 cartridge loads can be set.
The load resistance position of 100 Ω is suitable for direct connection of MC cartridge with large output voltage.

The flat amplifier section uses two stage differential amplification as well as the equalizer section.
A low-noise transistor is used in the first stage, and a current mirror circuit is used in the intermediate amplifier stage. Together with the use of carefully selected elements, we have secured characteristics of 10 Hz to 100 kHz + 0 -0.2 dB in frequency characteristics, 0.005% in distortion factor, and 100 dB in SN ratio.

The power supply consists of a large L/R independent winding transformer as a preamplifier and a constant voltage power supply to eliminate mutual interference between channels.
In addition, two L/R-independent read relays are used for the muting circuit, and the function switch has a special design incorporating a spacer to prevent interference between channels. These features emphasize the quality of stereo playback.

The volume uses a 32-step attenuator type with silver printed contacts.

The output stage of the flat amplifier is equipped with gain control by 22 contact attenuator independent of L and R.
The contact point is treated with silver-palladium.

Model Rating
Type Stereo preamplifier
Circuit system Equalizer amplifier : Differential 2-stage current mirror amplifier Class A SEPP
Control Amplifier Section : Differential 2-Stage Current Mirror Amplification Class A SEPP
Input terminal Phono : 2.5mV/100 Ω, 10k Ω, 25k Ω, 50k Ω, 75k Ω, 100k Ω
Cartridge Load Capacity : 100 pF, 150 pF, 200 pF, 300 pF, 400 pF, 500 pF
AUX1, 2, Tape Play : 150mV/50k Ω
Phono maximum allowable input 300 mv (1 khz, 0.01% harmonic distortion rate)
Output terminal Tape Rec : 150mV/1k Ω
Output (RL : 50k Ω) : 1V/450 Ω (Rating), 20V/150 Ω (MAX)
Harmonic distortion factor (20 Hz to 20 kHz) Phono : 0.006% (at 1 V output, Volume-20dB, gain control 0 dB)
AUX : 0.005% (at 1 V output, gain control 0 dB)
Frequency characteristic
Phono: 20 Hz to 20 kHz ± 0.2 dB
AUX: 10 Hz ~ 100 kHz + 0 -0.2 dB
3 Hz ~ 300 kHz + 0 -1.0 dB
Signal-to-noise ratio (IHF, A-network
Short circuit)
Phono : 80 dB at 1 V output
AUX : 100 dB at 1 V output
Phono Subsonic Filter 15 Hz, 6dB/oct.
Semiconductor used Transistor : 36
Diode, Others : 47 pcs
Power supply voltage 100 V, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law) 10W
AC outlet Power switch interlock : Route 3
Power switch not linked : 2 systems
External dimensions Width 420x Height 81x Depth 357 mm
Weight 6.3kg