Modwright LS 100 Preamp

ModWright LS 100 Tube Preamplifier

Single-Ended Tube Preamp. More than It Appears. Less Than It Could Cost.

The LS 100 was designed to advance everything that made ModWright's earlier 9.0SE preamplifier well-regarded — sonics, aesthetics, and functionality — while staying at a price point that makes the ModWright house sound genuinely accessible. It is a single-chassis design, internal power supply, compact enough to share shelf space with a matching amplifier, and every inch a ModWright product in the way it is built and the way it sounds.

It is also quietly one of the most versatile preamplifiers in the line. A built-in headphone amplifier fed directly from the tube driver stage. An optional phono board — user-installable, no service visit required — that adds MM and MC capability. A Monitor input and tape loop. Home Theater Bypass. Two 12V remote trigger outputs. All of it controlled via pushbutton inputs and a 10-function remote, with no toggle switches anywhere on the front panel.

The LS 100 is the entry point to the ModWright preamplifier line. It does not behave like one.

The Circuit — Mu-Stage Design, Zero Feedback, Direct Coupling

The LS 100 uses a mu-stage — technically a mu-follower or mu-stage variation — as its single gain and buffer circuit. The mu-stage is a topology that has been well-regarded in tube preamplifier design for its combination of excellent linearity, low distortion, and the harmonic richness that characterises the 6SN7 triode when operated correctly. It is a circuit that prioritises natural tone and smooth dynamics over the kind of forced resolution that can make tube amplification sound unnatural.

Two 6SN7 driver tubes handle the signal. The 6SN7 is one of the most celebrated dual-triode types in audio — a large, robust tube with a long production history and a wide range of well-regarded NOS options for those who enjoy exploring what tube rolling can do. ModWright recommends the Sophia Electric 6SN7 as an output tube upgrade; for the rectifier, Mullard, Amperex, or Philips GZ34 made in Holland.

One 5AR4/GZ34 rectifier tube (5U4GB and 5V4GB also compatible) feeds a solid-state regulated internal power supply. The supply is internal to the main chassis — no separate power supply box — keeping the LS 100 compact without the penalty of inadequate power delivery. Star grounding and optimised layout are employed throughout to minimise the noise floor.

Zero global negative feedback. Direct-coupled input with a single ModWright custom coupling capacitor at the output for the cleanest signal path. Pure copper PCB traces. Extremely short signal paths and high-quality audio-grade components throughout. The 300-ohm output impedance is low enough to drive virtually any power amplifier without interaction — tube or solid-state.

The LS 100 is phase-inverting by design, consistent with the single-stage topology. This is noted in the owner's manual and easily accommodated by reversing speaker leads at the amplifier or speaker terminals.

Built-In Headphone Amplifier

The headphone amplifier in the LS 100 is not an afterthought. It is a Class A discrete solid-state unity-gain circuit that acts as an impedance-matching stage between the tube driver stage and the headphone output — allowing the 6SN7 stage to drive headphones directly, without an additional gain stage in the signal path. The result is headphone amplification that shares the tonal character of the tube preamp stage itself. Rated at 1.5 watts into loads from 32 to 600 ohms, it is capable of driving a wide range of headphones with authority.

Optional Phono Stage

The phono board is available as a user-installable upgrade via two 20-pin headers and sockets — no soldering, no service required. It adds MM and MC phono capability to the LS 100 without an external box or additional cabling.

The phono circuit uses a tube-JFET input stage followed by tube gain and buffer stages, with a 12AX7 (MC) and 12AU7 (MM) tube complement. Passive RIAA filtering. Internal dip switches for cartridge loading at 50, 100, 500, 1K, and 47K ohms, plus 100pF capacitive loading. Total preamp and phono gain is 66dB, variable via the volume control.

Note: the phono slot accepts either the phono board or an optional DAC board — not both simultaneously.

Connectivity and Control

• 5× RCA line inputs
• 1× XLR line input (wired single-ended)
• 1× RCA Home Theater Bypass input
• 1× RCA Monitor input
• 2× RCA main outputs
• 1× XLR main output (wired single-ended)
• 1× RCA tape output
• 2× 12V remote trigger outputs
• Headphone output (front panel)
• Selectable balance control (bypassable for cleaner signal path)
• 10-function remote: power, volume, mute, input select, monitor input, trigger outputs, balance

The balance control is selectable — it can be left in circuit for fine-tuning, or bypassed entirely for the shortest possible signal path. This kind of considered flexibility is characteristic of the LS 100's design throughout.

Press Recognition

Positive Feedback — Best of the Best Bob Levi Read the review

Audiophilia — December 2011 Reviewed alongside the KWA 100SE amplifier. Read the review

6moonsRead the review

Specifications

Questions about how the LS 100 compares to the LS 99, or whether the phono option is right for your cartridge? We're happy to help you think it through.