Предусилители — ModWright Instruments LS 100

The LS 100 is a single-ended valve preamplifier from ModWright Instruments of the United States, operated through pushbuttons and a ten-function remote with no toggle switches. It combines a line stage, a built-in headphone amplifier and a slot for an optional internal phono board in one large aluminium chassis with a perforated top plate and blue backlighting. At launch the line stage alone cost USD 3,750, rising to USD 4,600 with the phono card or USD 4,900 with an internal DAC card.

Key specs that matter

Line gain is 11 dB, input impedance is 38 kilohm and output impedance is 300 ohm. Frequency response runs from 20 Hz to 100 kHz within 1 dB. Maximum input signal is 10 Vrms and maximum output reaches 37 Vrms. The headphone amplifier delivers 1.5 W into loads from 32 to 600 ohm. The case measures 451 mm wide, 445 mm deep and 165 mm high, and the unit weighs 11.3 kg.

Engineering and use context

A single gain and buffer stage, which inverts phase, is built around two 6SN7 driver valves. Rectification is handled by a 5AR4 valve, and ModWright states that 5U4GB and 5V4GB types can be fitted in its place. Connections include five standard RCA inputs, XLR inputs wired single-ended, a monitor input with tape output, and a home theater bypass input for a surround processor. Main outputs are provided as RCA pairs plus XLR sockets, again single-ended internally, so the balanced connectors do not make the circuit balanced. The optional phono card is built for either moving-magnet or moving-coil use, not both, with 48 dB or 63 dB of gain, uses one 12AX7 and one 12AU7 valve, and offers loading choices of 50, 100, 500, 1K and 47K ohm plus 100 pF. The front-mounted headphone socket is fed from the valve driver stage. Two large knobs handle volume and balance, blue LEDs confirm the selected source, and at power-up the unit mutes itself while the volume control turns to its off position.

Pairing

With its moderate output impedance and large output swing, the LS 100 copes with lengthy interconnects and with power amplifiers of ordinary input sensitivity. A balanced power amplifier will receive a signal on its XLR input, but not a differential one. The bypass input allows the stereo system to share front speakers with a home cinema processor.

Alternatives

The ModWright LS 300 is a balanced valve preamplifier from the same maker that sits above the LS 100 in its range.