KENWOOD L-08M
¥ 150,000 (1 unit, released in 1980)
Commentary
A monaural power amplifier that uses a Σ drive system between a preamplifier and a power amplifier, and between an amplifier and a speaker.
The L-08M is a model with a three dimensional design, and uses a design with a machine Nomi in which the entire body is a heat sink.
Sigma drive system is adopted, and sigma connection with speakers is possible.
The Σ drive method was devised to prevent distortion caused by the back electromotive voltage generated by the movement of the cone paper (voice coil) of the speaker. The concept of NFB, which had been completed in the amplifier until now, is expanded to the input terminal of the speaker by using four cables. By incorporating both the cable and the input terminal of the speaker as one of the internal wiring of the amplifier, the distortion of the speaker is suppressed. This method realizes an incommensurable high performance with a damping factor of 15000 at the 3m Σ cable.
First of all, a unique Σ cable is installed to connect the + side of the speaker to the feedback point of the power amplifier. This cable controls the input terminal of the speaker so that various kinds of distortion, including reverse distortion caused by the magnetic circuit of the speaker, are not generated. The Σ cable is also installed on the - side. The ground point and power loop of the - side cable are separated. This eliminates the potential difference between the input terminal of the speaker and the ground point.
The L-08M allows a Σ connection between the preamplifier and power amplifier.
In the conventional separate amplifier, there are various capacitances between the windings of the transformer. In the high-frequency region, the primary side and the secondary side are completely electrostatically coupled. In addition, the primary side of the preamplifier and the primary side of the power amplifier are in the same state as if they were connected through an AC cord. In addition, the home AC power supply, which has long indoor wiring, has a considerably high impedance. When the power amplifier drives the speaker, the voltage drop occurs and the secondary side voltage fluctuates. This electrostatic coupling and electromagnetic coupling due to voltage fluctuation create a current loop consisting of the power transformer of the power amplifier → the power transformer of the preamplifier → the ground of the preamplifier → the ground of the power amplifier → the power transformer of the power amplifier. The potential difference generated in the ground connection cable due to the current flowing in this loop enters the power amplifier and is amplified, and is input to the speaker with a distortion that cannot be ignored in the sense of hearing.
In the Sigma connection, the Sigma cable between the earth and the ground acts as an exclusive bypass for the power loop generated by mutual interference between the power transformers and does not affect the signal system. Therefore, when the pre-power and the power are connected, the potential between the earth and the ground is matched. This makes it possible to connect in accordance with the original purpose of the separate amplifier, enabling faithful signal transmission.
The voltage amplification stage has a configuration that employs a fully symmetrical upper and lower circuit.
The input stage consists of a single-chip, dual-FET source follower. The first stage amplifier consists of a single-chip, dual-transistor cascode output, and the second stage amplifier consists of a dual-transistor differential input cascode output. This circuit has superior temperature characteristics and is fully symmetrical in the upper and lower sides. This configuration realizes flat and bare frequency characteristics up to the ultra-high frequency range. This configuration ensures sufficient NF quantity in the high frequency range, which has been allowed to cause switching distortion due to the decrease in bare gain, and surprisingly low distortion rate is obtained over the entire band. In addition, transient characteristics are greatly improved and TIM distortion is suppressed.
It uses a super-large chimney type radiator and efficiently radiates the heat produced by the high power of 170W.
In addition, magnetic distortion is greatly improved by making it non-magnetic aluminum die-cast.
The input of the power amplifier goes between the hot input terminal and ground, and the output goes between the speaker terminal and ground. In conventional power amplifiers, the ground terminal of the NF loop that controls the output is shared with the ground terminal of the input. Therefore, a certain amount of current flows between the ground terminal of the input and the ground, causing the damping factor and distortion to deteriorate.
In the Σ drive system, feedback is directly applied from the input terminal of the speaker for both hot and ground. Therefore, only a small amount of current flows between the input and output ground, which is negligible compared to the load current. Therefore, the signal path is not interfered by current, and an excellent output waveform similar to the input waveform can be obtained.
The power supply for the power amplifier stage, which requires strong energy, is completely separated from the power supply for the voltage amplifier stage, which operates with constant current and minute current, including the basic transformer. This eliminates interference from the power amplifier stage to the class A amplifier stage through the power supply circuit, and transmits pure signals to the subsequent stage.
The L-08M was sold separately as an exclusive power transformer L-08PS.
The L-08PS is an enhanced power transformer with a built-in high-capacity transformer of 260 VA, which has the same capacity as the internal power supply. It can be added as many as you want using a one touch connector. This allows you to increase the capacity of the power supply to 520 VA, 780 VA, 1040 VA, etc., thus improving sound quality.
By adding L-08PS, the power up of L-08M becomes 220W (1 piece), 240W (2 pieces), 250W (3 pieces or more) at 8 Ω.
.JPG)
.JPG)
.JPG)
Model Rating
| Type | Monaural power amplifier |
| <Audio characteristics (Power in → SP out)> | |
| Rated output | 170W (8 Ω, 10 Hz to 100 kHz, 0.02% distortion) 250W (4 Ω, 1 kHz, 0.002% distortion factor) |
| Total harmonic distortion factor | 0.002% (20 Hz to 20 kHz at rated output) 0.002% (20 Hz to 20 kHz at 1/2 Rated Output) 0.0005% (at rated syth pain force, 1 kHz, 8 Ω) |
| Cross modulation distortion factor 60Hz:7kHz=4:1) |
0.001% (8 Ω at rated output) 0.001% (8 Ω at 1W output) |
| Frequency characteristic | DC ~ 500 kHz -3dB |
| Signal-to-noise ratio | 120dB |
| Damping factor | 20,000 or More (55 Hz) 15,000 or More (Sigma Cable 3m Tip) |
| Rise time | 0.7 μ s |
| Slew rate | ± 170 V / μ s |
| Input Sensitivity / Impedance | 1V/50k Ω (at IHF reference output) |
| Power Supply Unit and Others | |
| Power outlet | Power switch not linked : 1 system (300W) |
| Pwer | 100 VAC, 50Hz/60Hz |
| Rated power consumption | 250W (Electrical Appliance and Material Control Law) |
| External dimensions | Width 185x Height 235x Depth 369 mm |
| Weight | 12.5kg |
| Attachment | 5m ground wire Remote cord for 15m power supply |
| Sold separately : Dedicated Power Supply L-08PS (1 unit, ¥ 28,000) | |
| External dimensions | Width 140x Height 123x Depth 358 mm |
| Weight | 6.8kg |