Предусилители — Kondo Audio Note Japan M7 Heritage

The M7 Heritage is a stereo valve preamplifier from Kondo Audio Note Japan with built-in phono and line sections. It revives the M7 of the late 1980s, a preamplifier that appeared together with the ONGAKU power amplifier and became known alongside it, especially in Europe. The new version keeps the character of the original design while using current parts and engineering and adapting it to present-day systems.

Key specs that matter

Two unbalanced RCA phono inputs present 47 kohm. The line section accepts three RCA pairs and one XLR input at 50 kohm, while output is taken from two RCA pairs and an XLR socket, all specified for loads of at least 20 kohm. Line gain is 25 dB and phono gain from input to line out is 63 dB. Response extends from 10 Hz to 280 kHz within 0 and -3 dB into 100 kohm, RIAA deviation is plus or minus 0.3 dB from 30 Hz to 20 kHz, and THD is 0.07 percent at 1 kHz and 1 V on the line stage. Noise stays below 0.15 mV on line and 5 mV on phono. Tubes are two ECC803S, six 6072 and one EZ81 rectifier. The chassis is 438 x 160 x 330 mm, weighs 15 kg and draws 38 W.

Engineering and use context

The phono stage opens with an SRPP circuit on ECC803S, a long-plate version of the 12AX7, and continues with a 6072 plate follower inside a two-stage feedback loop, after which a cathode follower lowers the output impedance and keeps RIAA error small. Built as a module, it combines the benefits of hand wiring with signal paths as short as a circuit board would give, and decoupling capacitors are fitted close to the module to shrink the signal loop. The line stage is also modular, with paralleled 6072 plate followers direct-coupled to cathode followers, giving an output impedance of 500 ohm and a low cut-off at 18 Hz. The supply uses the rectifier valve with a transformer and choke mounted to limit vibration, three kinds of decoupling capacitor, and a shunt-type DC heater circuit that holds 12.6 V within 5 percent from a 91,000 uF capacitor bank. Parts include Kondo silver foil and electrolytic capacitors, silver lead resistors, SSW wiring, custom transformers and RCA jacks, and a copper main chassis. The XLR sockets carry an unbalanced signal.

Pairing

With its high phono gain, a moving coil cartridge can connect directly without a step-up device. The low output impedance of the line stage suits long interconnects to power amplifiers such as the ONGAKU.

Alternatives

The Kondo G-70i is a line-only preamplifier with four RCA inputs and a 6X4 rectifier, meant to be used with a separate phono amplifier.