Audio Database Accuphase C-250 270,000 yen(June, 1994 release) Description The stereo preamplifier which attained simple-ization a design and in respect of a circuit, and aimed at the preamplifier of a new time based on the original balance transmission technology of an Accuphase by each element selected carefully, and the engine performance and sound quality which kept being polished thoroughly. The original balance transmission system is adopted as line amplifier. Balance transmission is a system which sends simultaneously the positive/negative symmetrical signal which the phase reversed mutually, and it excels in the capability to remove the noise ingredient in adviser mode. C-250 consists of three differential amplifier fundamentally, and at the time of balance, from +-both the inputs of amplifier 1, a signal enters, and is amplified, and then it is inputted into amplifier 2 and amplifier 3. This 2-set Mino amplifier has a relation of tucking up its sleeves with a cord which feeds back each output to the other party, and sends out the symmetrical signal of +- by low impedance. This circuit is the ideal circuit system to which floating of the symmetrical signal of +- was carried out from the ground, even if it grounds one side of an output, both of amplifier carries out differential, and an Output voltage does not change. For this reason, it is that input and output only connect either to an earth line at the time of the usual imbalanced connection. The main circuits of C-250 consist of right-and-left a total of six unit amplifier, such as line amplifier, balance input-and-output amplifier, and balance output amplifier, and are arranged on the mother board. In order to prevent the mutual intervention of these unit amplifier, each is surrounded by thick aluminum knockout material, and it has a structure strong also against resonance by external vibration. A power-source part achieves right-and-left independence also with a power transformer and a right-and-left filter capacitor, and has monophonic composition completely electrically. Thereby, the cross talk between channels was canceled and the mutual intervention between amplifier is prevented. The small resistance object of the distortion is adopted especially as the volume controller. This resistance object is finished in the shape of a specular surface, and has become what was excellent in antiwear quality with low contact resistance. The brush in contact with a resistance object is a gilding many contact type, an external terminal and solid construction are used, a metal composition plane is abolished, and distortion by different-species metal contacting is reduced. Moreover, the rotary system has adopted not the method that a brush rotates but the structure which fixes this and a resistance object rotates, the internal point of contact decreases sharply, and becomes unnecessary [ contact grease ], and its durability is improving. adoption s The logic relay control system of the Accuphase original which adopted the seal type relay containing nitrogen gas for communication industry is in the input selector part. This system and a change installed the relay in the required place, and have controlled these electronically in the logic circuit. The microprocessor has managed fine timing and there is no noise at the time of a change. The amplifier only for headphone is carried and consideration is carried out also to the sound quality of headphone. The output to a speaker can be cut by a switch and it can carry out variable [ of the headphone output ] in main volume. The remote control which controls [ a change and ] the volume of input sauce is attached. Making the input selector into the relay change system, volume control has prevented the bad influence to sound quality by considering it as combination with a small motor with a clutch. Although C-250 is the composition only for a line, it can respond also to an analog record with an optional phone equalizer unit. Rating of a mode Form Stereo preamplifier Frequency response Balanced/Unbalanced Input: 20Hz-20kHz+0 -0.2dB THD 0.005% (with all the input terminals) Input sensitivity/input impedance (An Output power / output 0.5V) Balanced: 252mV/63mV/40kohm Unbalanced: 252mV/63mV/20kohm An Output power/Output load impedance Balanced/Unbalanced Output: 2.0V/50 ohm Tape Rec (at the time of AD input): 252mV/200 ohms S/N Input short-circuit, IEC-A compensation (at the time of a rated input) Balanced:97dB Unbalanced:119dB EIA S/N Balanced:96dB Unbalanced:97dB Input conversion noise (Input short-circuit, IEC-A compensation) Balanced:-109dBV Unbalanced:-131dBV maximum-except-take-off level (0.005% of distortion) Balanced/Unbalanced Output:7.0V Tape Rec(at the time of AD input): 7.0V Minimum load impedance Balanced Output: 600ohms Unbalanced Output: 1kohm Tape Rec: 10kohm Gain Balanced/Unbalanced Input->Balanced/Unbalanced Output: 18dB Power supply voltage AC100V, 50Hz/60Hz Power consumption 9W Dimensions At usually, the time: Width 475x height 140x depth of 401mm At the time of AD-250 extension: Depth of 414mm Weight At usually, the time: 13.8kg At the time of AD-250 extension: 13.9kg Option Exclusive phone equalizer unit AD-250 (\30,000) Attachment: Remote commander RC-10 Remote control system Infrared pulse system Power source direct-current3V Battery: UM-4(IEC name R03) 2 piece The maximum Dimensions Width 66x height 175x depth of 20mm Weight 190g (Battery included)