The M9Phono pre-amplifier - WELLINGTON AUDIO



The M9Phono pre-amplifier

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The M9 is unusual in most respects it's main features are, over to Andy Grove for the full low down,

The M9 Phono stage uses a new concept, that of the "Virtual Component". Real reactive components, whether inductors or capacitors exhibit losses due to DC resistance, hysteresis and other energy storage effects such as dielectric absorption. The M9 Phono stage uses a specially designed "RIAA Transformer", where the usually unwanted leakage inductance between primary and secondary is utilised as a component in the RIAA equalisation. This inductance is essentially loss less, and has no stray capacitance associated with it, which is the downfall of conventional inductor RIAAs as used in the original M10, and requires such circuits to function at a low impedance level of 600ohms requiring cathode follower drive, or suffer severe problems with unwanted resonance's. In contrast to this the M9 Phono operates at 50 kOhms, unheard of until now.

To keep the size and cost to a reasonable level the circuit still requires some silver foil capacitors to function. The forthcoming M10 Phono, however, will utilise the "Virtual Component" concept throughout. The RIAA transformer is hand made with the finest nickel-iron alloy core and a very large number of turns of extra fine silver wire. The fine tolerances gained from the careful crafting of the transformer ensure an accurate response, however the surrounding capacitor and resistor values are then tuned to give a response within +/- 0.1dB within the RIAA specified frequency range.

The Philips SQ E80F is used as the input valve, it is a low noise, low microphony pentode, specifically designed for audio. It is used as a transconductance element, and impresses a current proportional to it's input voltage upon the LCR RIAA network, the signal is passed via the aether to the secondary of the RIAA Transformer and thence to an E80CC double triode which is used for second stage amplification.

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The overall gain from phono input to single ended line output is 60dB, 66db to balanced outputs.

The line stage uses one ECC82 and one 7044/E182CC and is transformer coupled via a nickel-iron cored silvered wired output transformer to the outputs. The volume control/attenuator is a hand assembled shunt attenuator, where the signal only traverses a single extremely high quality resistor before reaching the input to the line stage. All switch contacts and other components are in the shunt leg of the attenuator.

The power supply unit is housed in a separate chassis, this minimises hum interaction from the mains transformers and is necessary due to the size of both the supply itself and that of the line and phono stages, housed in the audio chassis. The power supply itself uses two stabilised units using a 6X5 rectifier, an ECL82 stabiliser and an OB2 reference glow tube. The stabiliser is of proprietry design and uses a similar technology to that of the M10 power supply.

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AG, January 3, 2005

What I found really interesting when playing 1950's mono records through the M9 transformer RIAA correction, is the way that records which were obviously cut with the original choke anti-RIAA correction system suddenly stand out in terms of dynamic integrity, medium and timbral vividness, this truly leaves anything digital standing as the medieval medium we all know it was, despite advances in CD transport and DAC technology.

The M9 is designed as a proper record collector's control centre and features a stereo - mono switch and the most direct and cleanest signal path possible, with no tape input or loop, it is really designed to maximise the quality of all LPs made with the RIAA curve, whether mono or stereo.

The line stage is used a 5814a/12AU7WA/ECC82 first stage and a 7044 second stage with each channel amplified by one side of these double triodes, the 7044 is coupled to a specially designed fully silver wired output transformer on a core made from 55% nickel AN Super Perma double c-core providing both balanced XLR and single-ended RCA outputs.

The volume control is an in house designed and hand made stereo attenuator with silver contacts and 1/2 watt Audio Note™ tantalum resistors throughout.

On the input side the M9 also offers some novelty in that, apart from the MM phono input, it has 3 line inputs one of which is a transformer coupled XLR balanced CD input, to allow for fully balanced connection to our best transformer coupled DACs.

That is pretty much it; the M9Phono is available to order only at £ 69,500.00 including Vat.

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