COUNTERPOINT SA-220
¥ 850,000 (around 1990)
Commentary
This is a stereo power amplifier developed by taking advantage of both the tube type and solid state type.
The SA-220 uses a triode 6DJ8 for the voltage amplifier and output stage driver, which is well known for its low internal resistance and linearity. Moreover, by using a constant current source cathode follower circuit for the driver stage, the distortion factor is much lower than that of a simple resistance load type cathode follower.
The output stage consists of eight 125W rated output MOS-FETs for each channel with a high bias current to expand the class A range. The output stage is removed from the NFB loop to maintain the natural overtone structure and dynamism. As a result, stable driving is possible without oscillation due to the inductance fluctuation of the speaker.
It can also be used as a monaural power amplifier with bridge operation by switching the internal switch.
A 1 kva transformer is used for the power supply part.
This transformer was manufactured in Counterpoint's own factory based on its unique winding technology. As with other transformers, it uses only high-grade parts such as Lederstein's 1% metal coated resistor, metal-containing polypropylene capacitor, and metal oxide coated high-precision power resistor. It also uses copper-coated FR-4 epoxy laminate material for the substrate.
The chassis is made of copper-plated steel, which has proven shielding capabilities in high-end electronics, and blocks all interference over a wide range of frequencies from 10 Hz to gigahertz.
Equipped with APC (Advanced Protection Circuit), a newly designed protection circuit incorporating an analog computer.
This circuit constantly monitors the output stage and calculates its energy consumption. If the output stage deviates from normal operating parameters, a mute circuit is activated to protect the playback system.
The APC does not use the conventional current limiting method, it does not affect the audio system.
Equipped with XLR connector for bridge connection.
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Model Rating
| Type | Stereo power amplifier | ||
| Effective power |
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| Input impedance | 100k Ω / 100 pF | ||
| Total harmonic distortion factor | 0.5% (200W, R. M.S., 8 Ω) | ||
| Frequency characteristic | 1.2 Hz to 200 kHz | ||
| SN ratio (input short) | -84dB (400 to 80 khz, UNWTD, stereo, 8 Ω, 1W standard) | ||
| Damping factor | 6.0 | ||
| Gain | 30dB | ||
| Vacuum tube used | 6DJ8x4 for audio amplification Phase Tube 6DJ8x1 Rectifier Tube 6CA4x1 |
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| Power consumption | 200W (idle) | ||
| External dimensions | Width 480x Height 113x Depth 480 mm | ||
| Weight | 31kg |