Onkyo Model 732 amplifier

Model 732 with newly discovered amplifier design

Amplify the input signal without any distortion. This is the most fundamental theme that runs through all efforts when designing an amplifier. But what is distortion and how is it produced? If these questions are not answered it is impossible to create a really excellent amplifier. Of course, every amplifier is designed to reduce distortion. In an ordinary amplifier the distortion is measured by feeding a sine wave into the amplifier. However, this wave form is very rare in real music. Usually live music has many loud and abrupt sounds. They are an integral part of good music but it is this very dynamic sound that causes much distortion due to the poor transient response of many amplifiers. Even if an amplifier has a Total Harmonic Distortion of, for example 0,01% at 1 kHz it does not mean that this amplifier can reproduce music with low distortion. If we consider the "live signal" we find it very complicated and man, without some help cannot analyse it very satisfactorily. That is the reason Onkyo resorted to electronic computer technology to analyse each signal. This computer technology was combined with extensive listening tests in an effort to discover just what distortion is and how it is caused. The result of this research enabled Onkyo to establish a new method for the design of an amplifier. Consequently, model 732 has precise equalization, big phono overload capacity, direct coupling, differential amplifier and pure complementary SEPP circuitry.

 

Equalizer Stage

Transient response is a problem left unsolved by many preamplifiers because their calculations depend on the input being a sine wave. However, this simple wave is quite different from the complex signal produced by live music. As is well known, live music contains many very abrupt and impulsive sounds and has an unbelievably wide dynamic range. The dynamic signal causes distortion in all circuits and must be taken into consideration when designing equipment.

This means that model 732's reproduction is faithful to the original music because it avoids the distortion caused by poor transient response. CAD (Computer Aided Design) is used in model 732 because it is impossible to analyse dynamic music signals with ordinary measuring instruments. By comparing extensive listening tests and the measurements of computers Onkyo was able to discover just what the distortion was and through this research established a new method of designing an amplifier.

In a preamplifier precise equalization is extremely important. To avoid distortion that is caused by saturation in this equalizer stage model 732 has a big phono overload capacity of 320 mV at 1 kHz and 1500 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 75 dB

 

Power Amplifier Section

An unbelievable amount of effort has been expended in an endeavour to reduce distortion of any kind in the amplifier section of model 732. for this purpose model 732 has pure complementary SEPP, direct coupled and differential amplifier circuitry. The power amplifier circuitry was analysed by a computer but this analysis was not restricted to the audible range. It was extended beyond that range because live music contains many signals in this inaudible range. Onkyo found that the very low frequencies have a very important bearing on the music even though they cannot be heard. Ordinary amplifiers that do not take these very low frequencies into consideration cause a lot of distortion because this disturbance in the very low frequencies causes Intermodulation DIstortion throughout the whole range of the signal. The statistics for this amplifier are very impressive. It is capable of delivering a continuous power output of 56 watts per channel at 8 ohms. The distortion of model 732 is rated at less than 0,02% at 10 watts, 1 kHz. The same low rate of distortion is maintained regardless of whether model 732 is used at full power or played very softly.

The use of a differential amplifier means that this model is extremely stable. Instability in an amplifier will put DC voltage on the loudspeaker terminals and this will lead to distortion . Fluctuations in the power supply.

 

Specifications

Type:  All Silicon Transistor Integrated Stereo Pre-Main Amplifier

Circuit:  Direct-Coupling and Differential Amplifier, Pure-Complementary SEPP System

Semiconductors:  54 Transistors; 20 Diode; 2 Thermistor; 4 Posistor

Main Amplifier (8 Ω  load in case of no indication)

Dynamic Power: 

150 W at 8 Ω  IHF

200 W at 4 Ω  IHF

RMS Continuous Power (Both Channel Driven)

56 W + 56 W at 8 Ω  (1 kHz)

68 W+ 68 W at 4 Ω  (1 kHz)

Total Harmonic Distortion

Less than0,1% at rated output 1 kHz

Less than 0,03% at 0,5 W output 1khz

Less than 0,03% at 10 W output 1 kHz

Intermodulation DIstortion (SMPTE 70 Hz ; 7 kHz = 4 : 1)

Less than 0,05% at 34 W output

Frequency Characteristic :  10 Hz - 80 kHz (+0 -1 dB at normal output)

Power Bandwidth:  10 Hz - 100 kHz (IHF -3 dB, T.H.D. 0,2%)

Signal-to-Noise Ratio:  better than 110 dB (IHF A Network Shunt)

Damping Factor:  100 (DC - 20 kHz)

Load Impedance:  4 ihm - 16 Ω

Input Impedance:  100 k Ω  (10 Hz - 50 kHz)

Gain:  27 dB

Rated Input Voltage:  1 V

Input/Output Characteristics:  in-phase

Output Terminal:

Speaker:  A, B, C, A + B

Headphone

Pre-Amplifier

Input Sensitivity/Impedance

Phono 1 (1,03 kHz) :  2,0 mV / 50 k Ω , 30 k Ω

Phono 2  (MM) :  2,0 mV/ 50 k Ω

Phono 2 (MC) :  83 µV / 80 k Ω

Mic :  1,8 mV / 50 k Ω

Tuner, Aux 1, 2 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)

Frequency Response

Phono 1, 2 :  30 Hz - 15,000 Hz (±0,5 dB)

Tuner, Aux 1, 2 Play :  10 Hz - 70,000 Hz (+0 -1 dB)

Max. Allowable Input Phono

MM :  320 mV (1 kHz), 1500 mV (10 kHz ) rms

MC :  13 mV (1 kHz), 60 mV (10 kHz) rms

Signal-to-Noise Ratio (IHF A Network Input Shunt)

Phono 1 :  better than 75 dB

Phono 2 (MM) :  better than 75 dB

Phono 2 (MC) :  better than 55 dB

Mic:  better than 69 dB

Tuner, Aux 1, 2 Play:  better than 90 dB

Output Voltage:

Pre-Out 1, 2 (100 k Ω  at load) :  1 V (Rated output); 4 V (Max. Output)

Output  Impedance:

Pre-Out 1, 2 :  2,2 k Ω

Tone Controls (2 dB/step Switch Type)

Treble :  ±10 dB at 100 kHz, 30 kHz

Bass :  ±10 dB at 100 Hz, 30 Hz

Turnover Frequency

Treble :  2,5 kHz, 8 kHz

Bass ;  400 Hz, 125 Hz

Filter

High Filte (-3 dB) :  7 kHz 12 dB/oct

Low Filter (-3 dB) :  70 Hz 12 dB/oct

Muting:  -20 dB

Loudness :  VR -30 dB , 6 dB (at 100 Hz)

Transient Killer Operation Time

When SW is turned On :  3 sec

When SW is turned Off :  0,5 sec

Power Requirements:  AC 100, 110, 120, 220, 240 V  50/60 Hz

Power Consumption:  80 W

Dimensions (W x H x D):  437 x 136  x 355 mm (17,5" x 5,4" x 14")

Weight:  12,5 kg (27,5 lbs)