Preamplifier Section
Equalizer Stage
One problem that is not taken care of by many preamplifiers is transient response because their measurements depend on the input being a sine wave. Unfortunately, this simple wave is not the same as the comlex signal produced by live music. The real dynamism of live music comes from its many abrupt and impulsive sounds. It is this dynamic sound that can cause distortion due to poor transient response in all circuits if nothing is done to prevent it in the design of the equipment. In the equalizer stage in particular this problem of transient response must be handles because this is the input stage for the music signal. If the signal is distorted in this first stage it gets worse and worse until the distortion destroys all listening pleasure.
Precise equalization is one of the very important features of a preamplifier. To avoid any distortion that might come from saturation in this equalizer stage model 725 has a big phono overload capacity of 200 mV at 1 kHz and 930 mV at 10 kHz. The phono overload capacity gets larger with the rise in frequency so that it is the same as that of the RIAA equalization curve. RIAA deflection is ±0,5 dB from 30 to 15,000 Hz. The signal to noise ratio is better than 70 dB.
Tone Control
The Tone Control is put in model 725 so that each individual can adjust the tone to fit his own taste in music. The Tone Control has click stops and each stop represents 2 dB up or down. High grade components have been selected for the Tone Control so there is always exact response, low distortion and high stability.
Transient Killer
Model 725 has been equipped with the Transient Killer to prevent the usual disturbing noise that you hear when an ordinary amplifier is switched on or off. The Transient Killer in this model guarantees that there will be no irritating sounds to disturb your music enjoyment every time you turn the set on.
Power Amplifier Section
Model 725 is the fruit of Onkyo's tireless efforts to reduce distortion of any kind in the amplifier section of its equipment. Distortion is reduced in model 725 because of the quasi complementary SEPP, direct coupled and differential amplifier circuitry. The computer was used to analysis the very complex music signal and this analysis extended outside the audible range. This extensive measurement was necessary because Onkyo found that the very low frequencies have a distinct influence on the music even though they cannot be heard by the human ear. Ordinary amplifiers do not take these very low frequencies into consideration and consequently cause a lot of Intermodulation Distortion.
The statistic for this amplifier are very excellent. It is capable of delivering a continuous power output of 22 watts per channel at 8 ohms. The Total Harmonic Distortion of model 725 is rated at less than 0,05% at 10 watts, 1 kHz.
whether used at full power or very low output the same low distortion rate is maintained. Stability is enhanced by the use of a differential amplifier, instability in an amplifier will put DC voltage on the loudspeaker terminals which will causes excessive distortion.
Fluctuations in the power supply voltage and temperature can also cause distortion but these fluctuations are solved by the differential amplifier. The OCL circuitry is an added reason why this model has less distortion, a flatter response over the whole frequency range and especially good damping in the lower frequency range.
Top Panel Connectors and Large Heat Sink
Model 725 has all its connectors centralized on the top panel so that connecting and disconnecting is simplified. This is especially true if the amplifier is placed against a wall. Instead of having connectors in the rear panel this model uses the rear panel as a large Heat Sink which helps to protect the power transistors as well as the rest of the amplifier. This is important because of the change in the capacity of the transistor. However, because of the large Heat Sink in model 725 it always stays cool no matter how long it is used at full power.
Multi step-up terminals
The design of model 725 is unique in that its preamplifier and main amplifier can be used separately. This design opens up new possibilities for the music lover because model 725 can easily be the base of a multi-amplifier stereo system if either model 624 or 613 is added. These two model are dividing amplifiers and they do the job of separating and amplifying the signals before they are passed on to the tweeter, mid-range speaker, and woofer. If only one extra unit is added your system is up-graded to a bi-amplifier system. If two units are used your system will become a tri-amplifier system. The top panel of model 725 makes connecting and disconnecting very easy because all the terminals are located on the top of the unit and not in the back as is the case with most units.
Specifications
Type: All Silicon Transistor Integrated Stereo Pre-Main Amplifier
Circuit: Direct-Coupling and Differential Amplifier, Quasi-Complementary SEPP System, Transistor 29, Diode 18, Therminator 2
Main Amplifier (8 Ω load in case of no indication)
Dynamic Power:
70 W (IHF) zt 8 Ω
100 W (IHF) at 4 Ω
RMS Continuous Power
22 W + 22 W (8 Ω , 1 kHz) Single Channel Driven
27 W + 27 W (4 Ω , 1 kHz) Single Channel Driven
Total Harmonic Distortion
At Rated Output (1 kHz) : less than 0,1%
At 0,5 W Output (1 kHz) : less than 0,05%
At 10 W Output (1 kHz) : less than 0,05%
Intermodulation Distortion: less than 0,05% at 10 W output (SMPTE 70 Hz : 7 kHz = 4 : 1)
Frequency Characteristic: 15 Hz - 70 kHz ( +0 -1 dB at normal output)
Power Bandwidth: 10 Hz - 100 kHz (IHF -3 dB T.H.D. 0,5%)
Signal-to-Noise Ratio : better than 100 dB (IHF-A network)
Damping Factor: 60 (DC - 30 kHz)
Residual Noise: 0,001 µW (IHF input shunt)
Load Impedance: 4 Ω - 16 Ω
Input Impedance: 100 k Ω (10 Hz - 50 kHz)
Gain: 22 dB
Rated Input Voltage: IV
Input ?Output Characteristics: In-phase
Pre-Amplifier
Input Sensitivity/Impedance
Phono 1 : 2,4 mV / 50 k Ω and 100 k Ω
Phono 2 : 2,4 V / 50 k Ω (1,03 kHz)
Tuner, Aux-1, Aux-2 and Play : 100 mV / 100 k Ω
Total Harmonic Distortion : less than 0,05% at 1 V output (1 kHz)
Intermodulation Distortion : less than 0,05% at 1 V output (1 kHz) (SMPTE 70 Hz : 7 kHz = 4 : 1)
Frequency Response:
Phono 1, Phono 2 : 50 - 15,000 Hz (±0,5 dB RIAA Characteristics
Tuner, Aux-1, Aux-2, Play : 10 - 60,000 Hz (+0 -1 dB at 1 V output)
Max. Allowable Input (Phono): 200 mV (at 1 kHz); 930 mV (at 10 kHz)
Signal-to-Noise Ratio (IHF A Network Input Shunt)
Phono 1, Phono 2 : 75 dB
Tuner, Aux-1, Aux-2, Play : 90 dB
Output Voltage? Impedance
Pre-Out 1, Pre Out 2 (100 k Ω at load) : IV (rated output);. 4 V (max output) 2,5 k Ω
Rec Out: 100 mV (rated output open terminal voltage) 30 k Ω (phono)
Tone Control (2 dB/step switch type)
Treble : ±10 dB at 10 kHz
Bass : ±10 dB at 100 Hz
Filter:
High : 6 dB/oct at 8 khz
Low : 6 dB/oct at 70 Hz
Muting: -20 dB
Loudness: 6 dB at 100 Hz (VR -30 dB position)
Input/Output Characteristics: in-phase
Transient Killer Operation Time: 3 sec when SW is turned On
0,5 sec. When SW is turned Off
Power Requirements: AC 110/120/220/240 V, 50/60 Hz
Power Consumption: 30 W
AC Output: Switched, Unswitched
Dimensions (W x H x D): 313 x 366x 136 mm (12,%" x 15,6" x 5,4")
Weight: 8 kg (17,6 lbs)
No comments:
Post a Comment