Luxman SQ-505X (1971–c.1974)
The SQ-505X is a solid-state stereo integrated pre-main amplifier, preamp and power amp in one chassis. Luxman released it in July 1971. One source puts production as running to 1974. The release date is corroborated and the end date is not, so treat the tail of the run as approximate. It sold in Japan at ¥69,500 and belonged to a small family. The SQ-507X is its better-known sibling, and the two are routinely listed together today. The manual for the 507X describes that model as an upgraded SQ-505X with the output raised from 30 to 50 watts per channel, which shows where the 505X sat in the lineup.
The design is unusually well documented because the service material survives. The main amplifier runs a dual power supply with every stage directly coupled, so there is no capacitor in the signal path. The output stage is a pure complementary arrangement of PNP power transistors, intended to kill crossover distortion. The first stage uses two differential amplifier circuits. The preamp's equalizer is a three-stage direct-coupled circuit in a PNP-NPN-PNP configuration, built around the low-noise 2SA493 silicon transistor. Tantalum and Mylar coupling capacitors were chosen for low leakage to suppress switch-on thump. Tone control is Luxman's NF type with selectable bend points: defeat, 150, 300, or 600 Hz on the low end and defeat, 6k, 3k, or 1.5k on the high. The double volume pot is a friction type, ganged for normal use but separable for fine trim. Around back and across the front you get two tape-monitor loops, two recording outputs, two speaker systems, a pre/main isolation switch, an −18 dB attenuator, a low-cut filter at 70 Hz, a high-cut at 6 kHz, and a low booster at 100 Hz.
The numbers are modest by later standards and honest for 1971. Output is 30 W per channel into 8 ohms with both channels driven (35 W single-channel). THD and intermodulation are both under 0.04%. Power bandwidth is 5 Hz - 50 kHz, and damping factor is 30 into 8 ohms and 60 into 16. Phono sensitivity is 2 mV with switchable 30k/50k/100k loading on Phono 1. S/N is 63 dB on phono and 80 dB on the line inputs, and the whole thing draws 130 W at full output. It has thirty-one transistors, two diodes and four varistors. It measures 450 × 160 × 268 mm. The weight is reported as both 10.5 kg and 9,800 g in different sources, so no winner here - call it roughly ten kilos.
Reception is thin in the print record but warm among owners. A Dutch collector's unrestored example was still running after 45 years. A restored unit that surfaced had its wood case refinished and its capacitors and transistors replaced. Most of what's said about the 505X today lives in forum threads rather than magazines, and one owner's comparison to an Accuphase is exactly that - an owner's claim, not a measurement. No period review from our approved sources has surfaced, so the contemporary critical record is missing.
One caution for anyone shopping: the 507X manual is often what turns up when you search for 505X documentation, and its specs are not this amp's. The 50 W figure belongs to the 507X.
Known specifications (from the manufacturer's service documentation):
- Continuous output: 30 W + 30 W (8 Ω, both channels); 35 W (8 Ω, single channel)
- THD / IM distortion: less than 0.04% (8 Ω, 30 W)
- Output bandwidth: 5 Hz – 50 kHz (−3 dB)
- Frequency response: 10 Hz – 60 kHz (within −1 dB)
- Damping factor: 30 (8 Ω) / 60 (16 Ω)
- Phono input: 2 mV sensitivity, 30k/50k/100k Ω selectable (Phono 1)
- S/N ratio: 63 dB (phono), 80 dB (line)
- Tone control: LUX NF type, selectable bend points (150/300/600 Hz low; 1.5k/3k/6k high)
- Semiconductors: 31 transistors, 2 diodes, 4 varistors
- Power consumption: 130 W
- Dimensions: 450 × 160 × 268 mm
- Weight: 10.5 kg (one source gives 9.8 kg)
- Original price: ¥69,500 (Japan, July 1971)
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.