KM-7 DESIGN CONFIGERATION
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 singlecore wires with Teflon sheathing
Parts
⑴ Signal path resisters – Holco metal film resistors.
⑵ Non-signal path resisters – Holco metal film resisters.
⑶ Power resisters – RMG carton resisters.
⑷ Input attenuations – 2 mono ladder-type American Shallco 31-
step switches made to specifications with 1% tolerance Holo metal film resistors.
⑸ 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.
Specifications
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)