Pre amps >> KM-7  
Phono amps
Pre amps
KM -11AC
Hifi Fittings
Central Control System
Acoustic Room Design

    Modified from the prestigious Matiesse Reference Preamplifier circuit with a unique phono design to accommodate extremely low output MC cartridge to achieve high gain, low impedance and a wide and linear frequency response.
The phono stage
The original Matiesse circuit was modified by adding an interchangeable Ortofon T-3000 silver-wired (or any) step-up transformer at the forefront of the phono circuit to accommodate the modern low-output MC cartridge and then followed by a dual-gain stage high-mu Telefunken ECC83 and GEC A2900 with an RIAA compensation circuit.
The line stage
The line stage is a traditional 2 tiers amplification circuit, firstly by a Telephone ECC83 and then by a GEC A2900.
At the second tier of amplification, a damping control circuit is added to enable the preamplifier to accommodate different characteristics and requirements of a variety of power amplifiers and loudspeakers.
Design to avoid interference
To avoid interference and to achieve the best ‘signal-to-noise’ ratios, the amplifier and the power supply are separately housed into two different chassis.
The amplification circuit and its parts are sealed within a 6-facet chassis built with a combination of 0.8 mm high-purity copper and 6 mm aluminium alloy, the effect of which is to seal off all kinds of unwanted radio frequencies which might find their ways into the amplification circuit.
The 4 valves are mounted onto 4 Japanese high-quality gold plated ceramic socket bases with gold-plated pin-connectors and the latter are themselves mounted onto 2 heavy weighed high-purity copper dampers with a 3 micron gold-plate layer.
All signal paths are connected through WBT 99.99% purity silver single-core wires with Teflon sheathing.
Signal path resisters–Holco metal film resistors.
Non-signal path resisters–Holco metal film resisters.
Power resisters –RMG carton resisters.
Input attenuations–2 mono ladder-type American Shallco 31-step switches made to specifications with 1% tolerance Holo metal film resistors.
Input selections and damping controls–6 positions stereo switches made by Elma of Switzerland. All turning knots are of aluminium alloy and made by Sato of Japan.

Phono circuit
Gain -MC 78 dB (through Ortofon T-3000), 3-5 Ohm (mc transformer switchable)
      MM 58 dB, output impedance 47KOhm
Signal to noise ratio –Better than 80 dB
Line circuit
     Gain - Over 32 dB at 1mv
     Harmonic Distortion–Less than 0.02% at 1KHz
     Frequency response–10Hz–100KHz (variation within 0.1 dB)

  Technical Documents  

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