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Understanding field coils
"Field-coil drive units—in laymen's terms, powered drive units, which use an electromagnet to generate the magnetic field with which the voice coil interacts (by Lorentz Force)—date from the earliest days of electrical music reproduction." That is from the Audio Note website. "Not long after the turn of the 20th century, permanent-magnet technology was not sufficiently advanced to make a conveniently sized, and priced, speaker drive unit."

Field coils reportedly offer a calmer, more relaxed and graceful sound, delivering more information and improved…

Description: Two-way, reflex-loaded loudspeaker with field-coil electromagnets and external power supply. Drivers: 1" silk dome tweeter, 8" hemp-pulp mid/woofer. Sensitivity: 97dB/W/1m, specified at 6 ohms. Frequency response: 18Hz–23kHz, ±6dB, in-room. Minimum amplifier power: 8Wpc RMS. Cabinet construction: Birch ply with real wood veneer.
Dimensions: 31" (790mm) H × 14" (360mm) W × 10" (270mm) D. Weight 64lb (29kg).
Finishes: Real wood veneer in high-gloss finish. Olive, Palisander, Apple, Walnut, Makassa-Ebony, Black. High-gloss finish standard.
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Analog sources: Thorens TD 124 with Korf TA-SF9R tonearm/HS-A02 Ceramic Headshell/Kuzma CAR-30 MC cartridge. J.Sikora Standard Max Supreme turntable with KV Max 9" tonearm, Aidas Gold Web PL MC cartridge.
Digital source: Tascam CD-200 iL CD player, HoloAudio May DAC.
Preamplifiers: Tavish Audio Design Adagio, Allnic DT-5000 phono.
Integrated amplifiers: Unison Research S6, Riviera Labs Levante.
Power amplifier: Rogue Audio Stereo 100.
Cables: Interconnects: AudioQuest Pegasus and Firebird, Triode Wire Labs Spirit II (RCA). Speaker:…

I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier to measure the Audio Note AN-E/SPx Ltd. Field Coil's farfield frequency behavior and dispersion. I couldn't raise the loudspeaker as far off the ground as usual for the quasi-anechoic measurements, which meant that the first reflection from the floor occurred relatively early. I therefore placed the microphone at 1m rather than my usual 50". I used an Earthworks QTC-40 mike for the nearfield and corner-positioned responses. As instructed in the manual, I…

303 power amplifier: tech story
The transformer in the new 303's power supply is a low-noise, low-impedance toroidal, updated from its E/I laminated precursor. The rated power output from the new transformer is a modest 200VA. The new design builds on the original concept, though the new 303 has significant advantages. The new design can easily be configured for either stereo or monoblock use. This modern, cool-running, class-AB solid state amplifier provides a baseline 50Wpc into an 8 ohm–rated load in stereo, rising (not doubling) to 70Wpc into 4 ohms. In stereo at least, the 303…

I reviewed the original Quad solid state amplifiers in the early 1970s, a time when my reviewing style was considered too outspoken and confrontational by the established old guard of UK hi-fi publishers and manufacturers. At Hi-Fi News, its editor, the great John Crabbe had inherited an industry-friendly policy of not discussing the sound quality of audio electronics. In the US, this situation had started to change in 1962, when J. Gordon Holt launched Stereophile guided by the notion that hi-fi reviews ought to…

Quad 33 Description: Solid state, stereo preamplifier with built-in phono stage and headphone amplification. Inputs: three pairs single-ended (RCA), one balanced (XLR), one pair MM/ MC phono, switchable (RCA). Outputs: one balanced line-level (XLR), one single-ended line-level (RCA), one Pre-Out (RCA), one ¼" headphone, two 12V trigger. Input sensitivity (Vout = 695mV): 695mV (line/XLR), 3.2mV (MM phono), 460μV (MC phono). Input impedance: 10k ohm (XLR), 45k ohm, 100pF (MM phono), 100 ohms, 1.7nF (MC phono). Output impedance: 120 ohms (line), 2.35 ohms (headphone…

Analog sources: Linn Sondek LP12 turntable with Keel chassis, Karousel main bearing, Radikal motor control, Naim ARO tonearm, and Lyra Delos cartridge.
Digital sources: Naim UnitiCore network server and S/PDIF source. Roon Nucleus+. Naim ND 555 Streamer-DAC with two 555 PS (DR) power supplies, Ariston CD player used as a transport.
Preamplification: Townshend Allegri Reference (line), Naim SuperLine-SuperCap DR (phono).
Power amplifiers: Naim NAP 250 (2024), Constellation Revelation 2.
Loudspeakers: Fink Team KIM, BBC LS3/5a.
Cables:…

I performed a complete set of tests on the Quad 33 preamplifier with my Audio Precision SYS2722 system. Looking first at the 33's performance as a line preamplifier, all the inputs and outputs preserved absolute polarity, ie, were noninverting. The balanced input impedance was close to 20k ohms from 20Hz to 20kHz; the single-ended input impedance was 8.7k ohms at 20Hz and 1kHz, 8.2k ohms at 20kHz. The preamplifier's balanced output impedance was a low 111 ohms from 20Hz to 20kHz; the unbalanced impedance was 119 ohms from 20Hz to 20kHz; the headphone output…