Luxman L 58A (1979)
A high-performance integrated amplifier featuring Luxman’s proprietary Duo-Beta circuit and MOS FET output stage, released in 1979.
Overview
The Luxman L-58A is an integrated amplifier manufactured by Luxman and released in September 1979. It delivers 100 watts per channel into 8 ohms across both channels with a total harmonic distortion of 0.015% or less. The amplifier supports multiple inputs including phono (MM and MC), tuner, auxiliary, and main in, with dedicated sensitivity and impedance ratings for each. It features a comprehensive set of built-in controls such as tone adjustment with selectable frequency bending points, subsonic and high-cut filters, tape monitoring, and speaker selection.
Specifications
| Continuous effective output | 100W + 100W (8 Ω, both channel operation, 20 Hz to 20 kHz) |
| Total harmonic distortion factor | 0.015% or Less (8 Ω, 100W, 20 Hz to 20 kHz) |
| Cross modulation distortion factor | 0.015% or Less (8 Ω, 100W, 60 hz : 7 khz = 4 : 1) |
| Frequency characteristic | Phono MM, MC-1 : 20 Hz to 20 kHz ± 0.2 dB; Tuner, aux1, 2, main in : 10 Hz to 100 kHz -1dB |
| Input Sensitivity / Impedance | Phono MM : 1.5mV/50k Ω; Phono MC-1 : 1.5mV/100 Ω (direct to equalizer); Phono MC-2 : 0.05mV/2 Ω ~ 0.15mV/40 Ω (Automatic gain adjustment type head amplifier operates); Tuner, aux1, 2 : 220mV/20k Ω; Main in : 220mV/820k Ω |
| Signal-to-noise ratio (IHF-A Input short) | Phono MM : 80 dB or more; Phono MC-1 : 80 dB or more; Tuner, aux1, 2, main in : 100 dB or more |
| Tone control | LUX System NF Type with Bending Point Frequency Switching; Low-pass curve point : 150 Hz, 300 Hz, 600 Hz; High-frequency bending point : 1.5 kHz, 3 kHz, 6 kHz |
| Output Level / Impedance | Pre out : 220mV/220 Ω |
| Attachment | Subsonic Filter (15 hz, off, 30 hz); High-Cut Filter (9 khz, 0 ff, 15 khz); Low Boost Switch (70 Hz, off, 150 Hz); Tape monitor switch; Tape dubbing & rec off switch; Speaker selector; Headphone jack |
| AC outlet | Switched : Route 3, max300W; Unswitched-1 line, max200W |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Power consumption | 300W (Electrical Appliance and Material Control Law) |
| External dimensions | Width 466x Height 181x Depth 378 mm |
| Weight | 15.3kg |
Design
The L-58A uses Luxman’s original Duo-Beta circuit, which combines two negative feedback loops to improve performance. The power amplifier section employs a pure complimentary symmetry differential push-pull circuit with FETs (2SK163 N-channel and 2SJ44 P-channel) at the input stage. The output stage uses MOS FETs (2SK134 and 2SJ49) with a transition frequency of approximately 500 MHz and operates with a bias current of 300 mA or more, creating a "notchless class A" amplifier without switching operation. The preamplifier’s equalizer stage uses a cascode input bootstrap circuit with four FETs and a SEPP output stage with four transistors, while the MC head amplifier uses parallel-connected N-channel FETs in a DC amplifier configuration with automatic gain adjustment. The tone control circuit includes a buffer amplifier and uses a cascode-connected source follower with FET input, and can be bypassed when not needed. The power supply uses high-capacity block capacitors combined with film capacitors for improved sound quality, and the preamplifier uses a fast-switching transistor for constant voltage regulation. The chassis is hollowed out beneath the PCB, and the cabinet is made of real wood with minimal shielding using ultra-thin aluminum foil.
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