OTTO / SANYO DCA-650 (around the early 1970s)
Taking advantage of good material, excellent pre-main amplifier which pursued the realization of naked property.
The DCA-650, uses a good transistor a small quality of high input capacitance f T. In addition, phase correction is not used only one place between the pre-main, yet the smallest minimum value of 10pF (usually 50 ~ 100pF) has been reduced to. In addition, it is banished as much as possible about the stray capacity (stray capacitance). To improve the slew rate by these measures, it has to allow the faithful amplification more input signal. In addition, in order to correspond also to those who prefer a soft sound in a bad source and the software of the record, it is equipped with a slew rate of the switching mechanism.
Main amplifier part has adopted the whole page hardwired-connection Pure complementary OCl circuit using a differential amplifier circuit in the first stage. To screen the transistor of the perfect pair of symmetry is used, compensation is also enough to do that, we have to achieve DC balance without satisfactory. The circuit and does not have a bypass capacitor that is inserted into the first stage of the differential circuit and the drive stage for the purpose of increasing La gain in order to apply a deep NF. Bypass capacitors, AC-drop the emitter to the ground as it would eliminate the local negative feedback due to the emitter resistance, gain This way is obtained but will be unstable in the circuit basis. The DCA-650, and at the same time to improve the stability by applying a local negative feedback to eliminate these bypass capacitor, stretched out naked property, has achieved the same effect as when using a higher transistor of f T. The stability of the circuit has been checked in detail from below 0.1Hz by drawing precisely the Bode diagram or Nyquist plot to more ultra-high-frequency 10MHz. This is not in preparation for applying a deep NF as usual, it is for obtaining still absolute stability to the phase correction circuit for improving the slew rate to minimum. The pure complementary circuit of the output stage is AB class operation by passing a sufficient idling current of 40mA, the cross-over distortion can be ignored, we are notch distortion also drove to a minimum. NF is, until the gain is 20kHz low flat naked characteristics, have been subjected to 35dB and shallow.
How to take the lead and ground point of the power supply, pay attention to how to draw the pattern, and the crosstalk to a minimum take into account at the same time so as not to those distorted crosstalk components. This distortion of the high range at the time of full power has been greatly improved.
The heat sink has adopted a large heat sink of silver.
It equipped with a current limiter circuit for protecting the power transistor for a load of short-circuit and over-current. Also, if there leakage of DC current to the speaker looks like a fuse operates.
3 seconds when the power is ON by three using the circuit transistors, one second muting will operate when the power is OFF. This will not prevent a shock noise when the power is turned on.
Equalizer circuit of the preamp section, high voltage utilization rate because it has adopted a three-step direct coupling system of the PNP-NPN-PNP, the final stage is the output impedance at the emitter follower is kept low. For this reason it does not or fall allowable input of high frequencies by NF. In addition, this circuit can be possible to reduce the RIAA deviation, multiplied by the NF to direct current. Circuit configuration has become a simple, small phase correction circuit that 8pF in order to increase the slew rate has been inserted into one. In addition, multiplied by the high pressure of the 70V power supply to ± 35V, allowable input is 400mV (RMS, 1kHz), it has achieved a large value of 2880mV (15kHz). The transistor of the final stage in a large transistor of T05 type of Pc, which is housed in the can case, has become a thing to withstand really 500mW. The equalizer element and are used to screen those with less secular change and environmental change. For example, the capacitor is using a special Mylar type frequency characteristic is also good none the leakage current compared to such as tantalum.
Tone control of the preamp section is equipped with NF type of tone control after the amplification stage of the two-stage direct connection, it has become a active filter is followed by the configuration of the low-pass to the back.
Volume has been used to place a high input impedance, it is also taken into consideration so as not to change the S / N at any point of the volume.
Power unit are supplied in separate windings and a main portion, + and - independent have been constant voltage by the voltage detecting servo-type constant-voltage circuit using two transistors, respectively. This circuit has become a ripple filter combination.
As Buzz measures, it has a high-frequency manner down to the chassis at the input terminal. The circuit has been prepared which also serves as a buffer circuit to avoid destabilization when mounting the MC-type cartridge. This will have been shut out of interference like shortwave broadcast and amateur radio. In addition, we try to not accept the ham by the wiring not to make a loop in the input circuit.
Microphone amplifier part has substantially the same three-step direct connection type as the equalizer amplifier.
Main amplifier section
Music power 130W
Effective output (distortion rate of 0.1%) 55W / 55W (8Ω, single-ch drive, 1kHz) 45W + 45W (8Ω, both ch drive, 1kHz) 43W + 43W (8Ω, both ch drive, 20Hz ~ 20kHz)
Harmonic distortion rate 0.1% (at the time of an effective output) 0.05% (at the time of 1W output)
Intermodulation distortion 0.1% (at the time of an effective output) 0.04% (at the time of 1W output)
Output bandwidth (IHF, distortion rate of 0.5%) 5Hz ~ 80kHz
Frequency characteristic 7Hz ~ 100kHz
Damping factor 60 (1kHz, 8Ω)
SN ratio (IHF-A network) More than 110dB
Input sensitivity / impedance 1V / 50kΩ
Residual noise 0.3mV (8Ω)
Through late 5,10,20V / μs
Preamplifier section
Input sensitivity / impedance Phono1 / 2: 2.5mV / 50kΩ Tuner, Aux1 / 2, Tape PB1 / 2: 140mV / 60kΩ Mic: 2.5mV / 50kΩ
Phono maximum permissible input 400mV (RMS) 1100mV (pp)
Mic maximum permissible input 500mV (pp)
SN ratio Phono1 / 2, Mic: 70dB Tuner, Aux1 / 2, Tape PB1 / 2: 90dB or more
Output level / impedance Tape rec1 / 2: 140mV / 1kΩ Tape rec (DIN): 35mV / 80kΩ Pre out (rated): 1.2V / 1kΩ
Harmonic distortion rate 0.04% (at the time of rated output)
Phono RIAA deviation 30Hz ~ 15kHz ± 0.5dB
Frequency characteristic Tuner, Aux, Tape PB: 10Hz ~ 60kHz
Tone control
Bass:
Treble: ± 10dB (50Hz, turnover 250Hz) ± 10dB (100Hz, turnover 500Hz) ± 10dB (10kHz, turnover 2.5kHz) ± 10dB (20kHz, turnover 5kHz)
Subsonic Filter 20Hz, 12dB / oct
Low filter 70Hz, 12dB / oct
Loudness control + 8dB (100Hz)
General
power outlet Switch interlock: Two lines, 150W Switch non-linked: 1 system, 200W
Power-supply voltage AC100V, 50H / 60Hz
External dimensions Width 420 × height 130 × depth 330mm
weight 10.2kg
Source:
http://audio-heritage.jp/SANYO/amp/dca-650.html
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