COUNTERPOINT SA-5000
¥ 1,000,000 (around 1990)
Commentary
The best counterpoint preamplifier developed as a culmination of hybrid technology.
The preamp has equipped with cables with various capacities and inductive characteristics, and with resistance loads such as volume and balance control, which can obscure the signal purity. The RIAA demodulation network circuit also requires severe handling. The SA-5000 maintains the performance of the vacuum tube by reducing the load on the vacuum tube by receiving a buffer between these load conditions and the vacuum tube.
Specifically, a wide-band current amplifier composed of FET / bipolar transistors is used as a buffer in all vacuum tube stages. This buffer has a role other than signal amplification to reduce the load, so that not only the true value of vacuum tubes can be displayed, but also various types of distortion can be reduced and reaction speed can be increased.
For signal amplification using a general vacuum tube, the grid side was used as an input. However, for voltage amplification stage of Phono and Line of SA-5000, a cathode input is used to maintain signal transfer and reduce distortion.
In addition to perfectly matching the vacuum tubes, by utilizing the complimentary service characteristics of the cathode input of one vacuum tube and the cathode output of the other vacuum tube, the distortion is canceled without using global feedback.
Two types of output can be selected : direct and buffer.
In the case of the direct output, the signal is output from the output tube only through the output capacitor. In the case of the buffer, it is output through the buffer amplifier of the line driver. The buffer output has a lower impedance than the direct output, so that stable transmission characteristics can be achieved even when the cable to the power amplifier is extended.
A total of seven vacuum tubes are used, including the 3-pole 6DJ8, which excels in amplifying minute signals.
Each of these tubes has been aged for 160 hours on the original Counter Point check board. In addition, microphonic noise is checked by the computer of Audio Precision, and noise, distortion and amplification capability are checked again in the mounted state. After aging for a total of 200 hours, the tubes are used.
The power supply unit is a separate unit structure, eliminating interference with the power supply unit.
The power supply unit consists of 6CA4 rectifier tubes and constant voltage regulators, and is made of the same chassis material as the main unit.
DC power is supplied to this unit when the ready switch of the main unit is turned on. The main unit is designed to be always energized except for the high voltage supply of the heater, reducing stress to the vacuum tube and extending the life.
The toroidal transformer used in the power supply was designed and manufactured in our factory in San Diego, California, and is an original hand-wound product.
A chassis structure is adopted in which the mounting method of the board is thorough.
The main audio board is a 250x400mm, 3-mm-thick cold-rolled steel copper-plated sub-chassis with 13 screws in a floating structure that insulates the signal path from all physical vibrations, and components with vibrations are placed outside the board to eliminate microphonic noise caused by switches and relays.
The main chassis is made of the same solid aluminum as the front panel, and the copper-plated steel material of the sub-chassis can shield electromagnetic interference over a wide range of frequencies from 10 Hz to gigahertz.
With a total of 16 green LEDs on the audio board and one red LED on the control board, you can check the operation status of each part at a glance.
A 3-stage level control for the buffer output can be used to reduce the noise level during high-volume playback with high-efficiency horn speakers, or to reduce the total volume prior to volume adjustment.
In addition, it is equipped with a balance trimmer in which left and right channels are independent, so you can precisely adjust the balance of left and right channels.
Equipped with an MC load selector, 100 Ω, 300 Ω, 47k Ω, or any other resistance value can be selected by plugging a resistor onto the board.
Switching between MM and MC is done by the internal switch.
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Model Rating
| Stereo control amplifier | |||
| Input sensitivity | Phono MC : 31 μ V Phono MM:1.3mV Line:37mV |
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| Input impedance | Phono MC : 47k Ω, 300 Ω, 100 Ω, user set value Phono MM : 47k Ω Line : 15k Ω |
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| Maximum input level | Phono MC:10mV Phono MM:400mV Line:12V |
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| Output impedance | Direct output : 3.5k Ω Buffer Output : 75 Ω Tape Output : 10 Ω |
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| Maximum output level | 32Vp-p (1% THD, 20 Hz to 20 kHz) | ||
| Gain (1 kHz) | Phono MC:84dB Phono MM:52dB Line:23dB |
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| Distortion Factor (IHF) |
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| Frequency characteristic |
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| Signal-to-noise ratio (10 hz to 500 khz) | Phono MC : 80 dB (0.5 mV reference, EIA-WTD, 55 μ V noise) Phono MM : 76 dB (5.0 mV reference, EIA-WTD, noise 30 μ V) Line : 90 dB (0.5 V standard, EIA-WTD, noise 15 μ V) |
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| Vacuum tube used | For Audio Amplification 6DJ8x4 pieces 6DJ8x2 for High Voltage Regulator 1 x 12AX7 for High Voltage Regulator Error Amplifier Rectifier 6CA4x1 |
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| Recommended fuse | Power Supply : 2-1/2A AGC 3 ag Size / Fast Blow Type High Voltage : 1A8AG Size, Fast Blow Type |
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| Pwer | 88 V ~ 133 V AC, 50Hz/60Hz | ||
| Power consumption | 55W (standby) 80W (operating) |
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| External dimensions | Body : Width 483x Height 130x Depth 322 mm Power Supply : 148 mm W x 130 mm H x 315 mm D |
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| Weight | Body : 12.7 kg Power supply : 5.5 kg |
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