Phonostages — Line Magnetic AS-129P

The AS-129P is an all-valve phono stage from Line Magnetic, part of the company's Analog Sound series of Western Electric-inspired components. Line Magnetic, based in Foshan, China, builds reproductions and developments of historic Western Electric designs, and the Analog Sound series uses hand-wired point-to-point construction and Class A circuits. The AS-129P takes the Western Electric 129 as its starting point, and the maker describes it as an inheritance and improvement of that design. It has separate inputs for MM and MC pickups and offers six equalisation curves for records cut before and after RIAA standardisation.

Key specs that matter

The valve line-up consists of four 6J7 amplifying valves, one 5U4 rectifier and two 0A3, also known as VR75, voltage regulator valves. The moving-magnet input offers 47 kOhm or 100 kOhm loading and 40 dB of gain. The moving-coil input runs through a step-up transformer, a reworked replica of the Western Electric 618B with a permalloy core, suited to cartridges of 5 to 30 ohm, and total gain reaches 60 dB. Gain is adjustable. The equalisation choices are RIAA, NAB, AES, SP, COL and FFRR. Frequency response covers 10 Hz to 20 kHz. The chassis is finished in grey.

Engineering and use context

Before the RIAA curve was adopted in the 1950s, record labels used their own recording equalisation, and playing those discs through an RIAA-only phono stage alters their frequency balance. The six selectable curves let the AS-129P follow older label curves such as Columbia and Decca FFRR as well as modern RIAA pressings. The power supply is entirely valve-based. The 5U4 rectifies the high-voltage supply, and the two 0A3 gas-discharge regulators hold the voltage steady, which keeps supply variations away from the high-gain amplifying stages. Using a step-up transformer for moving-coil cartridges lets the valve circuit work with the same gain for both cartridge types, since the transformer raises the low voltage of a moving-coil cartridge passively, without adding an extra active stage and its noise. Permalloy, a nickel-iron alloy, is used in the transformer core for its high magnetic permeability at low signal levels. Parts are joined by hand-soldered point-to-point wiring instead of a printed circuit board, as in the period the design comes from.

Pairing

The AS-129P is intended to work with the AS-133 valve preamplifier from the same Analog Sound series, or with Line Magnetic's LM-129 preamplifier. Low-output moving-coil cartridges use the internal transformer, while moving-magnet cartridges connect directly to the MM input with the 47 kOhm setting.

Alternatives

The Line Magnetic LM-LP33 is a valve phono stage with inputs for both MM and MC cartridges.