SAE X10-A Hypersonic Class A Power Amplifier - Excellent Working Condition
SAE X10-A Hypersonic Class A Power Amplifier - Excellent Working Condition - This is a low production Rare SAE X-10A amplifier, rated at 100 W/channel into 8 ohms or 150 W/channel into 4 ohm loads RMS. Distortion is 0.02%, 20Hz. to 20kHz. It exhibits clean & detailed sound commensurate with its unique appearance. DALAUDIO recently tested, cleaned and serviced this amplifier. Please see all photos of internals. It is a very clean unit as the physical condition is excellent.
Interestingly, there is not a lot of generally available reliable or verifiable material on the internet regarding this amplifier. There are folks that love it, would love to find one. Conversely there are comments on various forums where folks state that the X Series Amps "were never really a class A amp at all", and would look the other way on purchasing. Curious, I decided to research the X Series further. Here are some important details I found that you may want to take into consideration before purchasing or passing on this rare find.
My observations: The X-10A runs cool. Each channel does have a decent amount of heatsink material and cooling surface area, but not what you might expect with a 100 Watt Class A Amp. As a general rule Class A typically runs hot even at idle with no load as the output devices (transistors or tubes etc) are drawing current most of the time. AB type amplifiers are a bit more linear with heat as the they run hotter when the load increases and are relatively cool at idle. Without getting into the whole biasing science, the rated class A power for an AB Class amp is a function of the standing bias current in the output stage. So I was curious about how these amps operated and decided to look further. After looking into the amplifier, I found the following:
- Large Toroidal Amplifier
- Large TRW - Schottky Diodes (on the amp boards power rails - not the bridge rectifier which is also large)
- Large 15,000 uF 80V capacitors
- Unique Ceramic Resistor "network" on the amp boards
- Toshiba 2SB554 PNP and 2SD424 NPN P/P Transistors (complementary pair) x 2 Pairs per channel
- There is no power switch on the unit as it was intended to be powered on with the X Series Preamp
- The amp was manufactured in February of 1981 (or passes QC) by SAE USA. The "2-81" sticker is still on the bottom.
SAE Information: It appears the X Series was SAE's late 1970s design effort to capture the high end of the emerging audiophile market. The SAE Hypersonic X Project was headed by Barry Thornton as Director of Engineering, who is is a fairly well known and is also a very clever Audio Engineer.
The unique "Class A" power amplifier technology was developed at SAE and marketed under the title "Hypersonic Class A." Patents were issues to Barry Thornton in 1979, for unique design with the following patent abstract: "A high fidelity audio amplifier having a pair of cooperating active amplifying devices includes two diodes, each of which is connected in a distinct signal pathway directly associated with an active amplifying device so that the amplifier achieves true Class A operation over the full range of normal input signals. The amplifier can achieve true Class A operation using bipolar transistors, field effect transistors, or vacuum tubes as the active amplifying devices. "
During the same timeframe Barry delivered a presentation at AES (Audio Engineering Society) entitled " AES Paper 1664; AES Convention 66; May 1980 A Power Class A Technique with Open Loop Stability" - Outlining his efforts at SAE while creating this Hypersonic X product line. The paper is still available for download for AES members or for Non Members at a fee of $33, if one so desires.
Bottom line: For almost two decades, SAE made some of the best known home audio amplifiers. In the early Seventies, if one wanted the best in solid-state amplification, SAE was considered. Today SAE still lingers in the minds of audiophiles old enough to remember these products. The X-series was SAE’s entry into the high-end audiophile market. The official product line included a preamp and three different sizes of power amps (X-10, X-15, and X-25). Unfortunately not a lot of them were produced, and they're pretty uncommon today.
Specifications from a X series Amplifier Manual:
- Rated Power: 100 W/channel into 8 ohms or 150 W/channel into 4 ohm RMS
- THD: 100W RMS 0.02 / 150W 0.15
- Intermodulation Distortion: from .25W to full output - 0.02
- Damping Factor: 60
- Clipping Headroom (dB) .5
- Frequency Response: 20Hz. to 20kHz
- Signal to Noise: 100 weighted
- Input Sensitivity: 1.42 @ rated output , 1W -.14
- Relay Protected: Thermal/Overload