Luxman SQ-505X (1971)
A solid-state stereo integrated pre-main amplifier released in July 1971 with high-fidelity specifications for its era.
Overview
The Luxman SQ-505X is a solid-state stereo integrated amplifier combining a preamplifier and main amplifier in one chassis. Manufactured by Luxman and released in July 1971, it was designed for high-performance audio systems. It features a fully transistorized signal path with advanced design choices aimed at minimizing distortion and noise, including direct coupling across all stages and ultra-low noise components in the preamp section.
Specifications
| Continuous output (both channels, 8 Ω) | 30W + 30W |
| Continuous output (single channel, 8 Ω) | 35W |
| Total harmonic distortion | 0.04% or less (8 Ω, 30W) |
| Cross modulation distortion | 0.04% or less (8 Ω, 30W, 70 : 7 kHz = 4 : 1) |
| Output bandwidth | 5 Hz to 50 kHz (-3dB, 0.04% THD) |
| Frequency characteristic | 10 Hz to 60 kHz (within -1dB) |
| Input sensitivity (Main In) | 430 mV (8 Ω, 30W) |
| Input impedance (Main In) | 50k Ω |
| Damping factor | 30 (8 Ω) |
| Damping factor | 60 (16 Ω) |
| Residual noise (Main Amp) | 1 mV or less |
| Preamplifier Frequency characteristic | 10 Hz to 50 kHz -3dB (Aux1) |
| Preamplifier Total harmonic distortion | 0.05% or Less (1 kHz, 1 V, Aux1) |
| Preamplifier Input sensitivity | Phono1, 2 : 2 mV; Aux1, 2, 3 : 80 mV |
| Preamplifier Input impedance | Phono1 : 30k Ω, 50k Ω, 100k Ω; Phono2 : 50k Ω; Aux1, 2, 3 : 30k Ω |
| Preamplifier Signal-to-noise ratio | Phono1, 2 : 63 dB or more; Aux1, 2, 3 : 80 dB or more |
| Preamplifier Maximum Allowable Input (1 kHz, Phono) | 300mV |
| Tone control | LUX System NF Type with Bending Point Switching; Low Bend Point : Defeat, 150 Hz, 300 Hz, 600 Hz; High Frequency Curve Point : Defeat, 6 kHz, 3 kHz, 1.5 kHz |
| Preamplifier Residual noise | 25 μV or less |
| Preamplifier Crosstalk (1 kHz) | Phono : -60dB or less; Aux : -65dB or less |
| Filter | Low-cut : 70 Hz (-6dB/oct.); High Cut : 6 kHz (-6dB/oct.) |
| Low booster | 100Hz (6dB/oct) |
| Attachment | Attenuator (-18dB); Speaker switch (2 systems); Premain isolation switch; Tape monitor (2 systems); Recording output terminal (2 systems) |
| Semiconductor used | Transistor : 31; Diode : 2 pcs; Varistor : 4 pcs |
| Power consumption | 130W (8 Ω simultaneous load at maximum output) |
| External dimensions | Width 450 x Height 160 x Depth 268 mm |
| Weight | 10.5kg |
Design
The main amplifier uses a dual power supply system with all stages directly coupled, eliminating capacitors in the signal path. The complementary output stage employs PNP-type power transistors in a pure output configuration to prevent crossover distortion. The first stage uses two differential amplifier circuits. The preamplifier’s equalizer stage is a three-stage direct-coupled circuit using a PNP-NPN-PNP transistor configuration and incorporates ultra-low noise 2SA493 silicon transistors throughout all preamp stages. Tantalum and Mylar coupling capacitors with low leakage current are used to reduce switch-on shock noise. The unit features a friction-type double volume control for tone adjustment, allowing ganged operation with independent fine-tuning capability.
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