Pioneer SMT-804 (circa 1965)
At 13kg, it sits on the rack heavy and solid. Solid-state had arrived, and Pioneer wasn't playing around.
Overview
The Pioneer SMT-804 Solid State Stereo Amplifier came out around 1965 at an original price of ¥57,500. It landed in the mid-60s shift from tubes to transistors, when Japanese manufacturers were proving they could engineer with both precision and ambition. It is an all-transistor stereo pre-main amplifier. That means a full integrated design, with preamp and power amplifier in a single chassis.
At 13kg, it has serious internal construction, and not only in mass. There are 25 transistors and 10 diodes or thermistors on board, which was dense circuitry for the era. The DIN-standard tape recorder interface and dual equalization options (NARTB for tape head, RIAA for magnetic cartridge) show it was designed for a full stereo chain. Input sensitivity runs from 1.5mV for the tape head up to 250mV for tuner and auxiliary sources. No reviews or user testimonials survive in the documentation. The range of connections, the bass and treble tone controls and the loudness compensation switch suggest it was aimed at serious home listeners who wanted both fidelity and flexibility.
Specifications
| Manufacturer | Pioneer |
| Product type | Stereo pre-main amplifier |
| Rated output | 40W + 40W (16 Ω), 27W + 27W (8 Ω) |
| Music Power (IHF) | 45W + 45W (16 Ω), 30W + 30W (8 Ω) |
| Frequency response | 10 Hz ~ 70 kHz ± 1 dB (Main Amplifier Output 500 mW) |
| Input sensitivity (for rated output) | Tape head: 1.5mV, MAG: 2.5mV, X'tal: 70mV, Tuner/Aux/Tape playback: 250mV, Mic: 2.5mV |
| Signal-to-noise ratio (Volume Max, Tone Flat, IHF) | Tape head: 55dB, Aux: 62dB |
| Equalizer | Tape head: NARTB, MAG: RIAA |
| Tone control | Bass, Treble |
| Filter | Low filter and High filter |
| Loudness control | ON/OFF enabled |
| Output terminal for speaker | 8 Ω ~ 16 Ω (With Phase Selection Switch) |
| Stereo headphone jack | Yes |
| Tape rec | DIN standard tape recorder and reconnector |
| Residual noise | 1.5 μW or less |
| Protection circuit | Six transistor configuration, relay, reset lamp |
| Semiconductors used | Transistor 25 pcs (2SD45x4, 2SB347x2, 2SB345x2, 2SB379x2, 2SB54x6, 2SB283x2, 2SC147x2, 2SB129x2, 2SB55x2, 2SB26x1), Diode/thermistor 10 pcs (SE-1.5ax4, D-1Bx4, D-2Bx2) |
| Power supply voltage | 100 VAC / 117 V (Switching Type), 50Hz/60Hz |
| Power consumption | 220W maximum, 59W (no signal) |
| Dimensions (W x H x D) | 390 x 137 x 354 mm |
| Weight | 13kg |
Key Features
All-Transistor Configuration
The SMT-804 was built entirely without vacuum tubes, a big step for the mid-1960s. That meant faster transient response, less maintenance, and no tube drift or microphonics. The 25 discrete transistors across the signal path allowed complex gain staging and buffering. Residual noise is 1.5 μW or less, a good figure for its time.
Single Ended Push-Pull (SEPP)-OTL System
The circuit is a Single Ended Push-Pull (SEPP)-OTL (Output TransformerLess) design. It avoids the coloration and bandwidth limits of output transformers. Complementary transistor pairs drive the speaker load directly, which improves high-frequency extension and reduces phase distortion. OTL demands precisely matched output devices and stable biasing. A frequency response of 10 Hz to 70 kHz ±1 dB suggests Pioneer pulled it off.
Mesa Silicon Transistors in Output Stage
The output stage uses mesa silicon transistors, an early form of planar transistor technology with better reliability and thermal stability than the earlier alloy-junction types. They handle the Music Power output of 45W + 45W into 16 Ω (IHF standard), leaving headroom for musical peaks without clipping. Part numbers like 2SD45 and 2SB54 turn up across multiple stages, so device selection was not arbitrary.
Electronic Protective Circuit with Relay
Protection was not an afterthought. The SMT-804 has a six-transistor electronic protective circuit. When it detects a fault, a relay disconnects the speakers and a reset lamp lights, so you can see that something has tripped.
Bridge Rectification with Silicon Diodes
The power supply uses a bridge rectifier with silicon diodes, a modern approach at the time that improved efficiency and reduced ripple compared to selenium rectifiers or half-wave designs. It also has a switching-type power supply that handles both 100 VAC and 117 V inputs, so the amplifier could run on different regional voltages. Maximum power consumption is 220W, which reflects the demands of the OTL output stage. Idle draw is 59W.
Collectibility & Value
The Pioneer SMT-804 is described as rare and scarce, with few units appearing on the market. A Yahoo Japan auction listing from February 26, 2024, showed a current bid of 4,999 ¥ (approximately $31 USD), though final sale prices may vary significantly based on condition and completeness. No data exists on common failures, maintenance requirements, or spare parts availability. That makes restoration a challenge for technicians unfamiliar with early Japanese solid-state designs.
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