Here's what Lehle say about the Sunday Driver SW II:
The LEHLE SUNDAY DRIVER SW II is a compact high-end preamp for all types of electric and acoustic instruments - a preamp for electric and acoustic guitars and basses, not to mention other stringed instruments (such as violins, cellos and double basses) to realize their full musical potential. The switchable version expands on the classic LEHLE SUNDAY DRIVER II with a soft-touch foot switch, to activate and deactivate the pedal.
The LEHLE-Switch works with a microcontroller and an intelligent True-Bypass-Relay-Circuit with active pop suppression circuit, thereby allowing the LEHLE SUNDAY DRIVER SW II to switch even faster than mechanical switches, noise-free and without wear.
The easy-action mushroom-shaped button characteristic of LEHLE products is mounted in the cover, so that your foot pressure is transmitted indirectly, via a spring. Thus the electronics board is not exposed to mechanical loads, making the LEHLE SUNDAY DRIVER SW II virtually indestructible and guaranteeing years of trouble-free switching.
When ON, its circuit is based on a discrete Class A circuit with JFET technology and provides two modes of operation, selected by a mode selector switch with gold-plated contacts: "D" stands for Driver: in this mode, your guitar signal is amplified, with absolutely no modification, at the input impedance of a guitar amp, efficiently eliminating losses on the route through leads and effects; the signal remains strong and clear, retaining its full dynamics. The second setting "S" - as in Sunday - multiplies the input impedance by five, bringing out previously inaudible details and, as gain increases, giving your guitar a characteristic and unmistakable warmth that has given this preamp its name - the result is a sound as mellow as a sunny Sunday afternoon.
Even at the maximum +18 dB gain setting, the LEHLE SUNDAY DRIVER II always stays clean and absolutely free of background noise, thanks to its studio-standard overall dynamic range of 130 dB. To exploit the dynamics of tube amplifiers to the full, the input voltage is also rectified from the power supply socket, then filtered, stabilized and transformed to 30 V.
When OFF, the LEHLE SUNDAY DRIVER SW II provides two different modes of operation: in TB (= True Bypass) mode, the input and output are linked via relay, with zero tonal loss. True-Bypass mode is the best option if you have a small setup with short cable routings and for when a treble booster or old-school fuzz pedal is placed after the LEHLE SUNDAY DRIVER SW II.
If you have long cables or a complex effects board configuration, switch to TS (= True Sound) mode, and the LEHLE SUNDAY DRIVER SW II is active as a buffer, without amplifying or modifying the signal in any way. In this mode, the LEHLE SUNDAY DRIVER SW II operates as a totally neutral line-driver equivalent to mode D with the gain pot turned all the way to the left. The Bypass mode option enables you to effortlessly and tone-fully integrate the LEHLE SUNDAY DRIVER SW II into any setup, no matter how complex. And not just on Sundays!
- High-end preamp, buffer and booster
- Discrete Class A input stage
- 130 dB dynamic range thanks to 30 V technology
- Choose between two sound modes
- Neutral, studio quality sound
- Switchable boost up to +18 dB
- Choose between Buffer and True-Bypass operation
- Balanced output can be used as a DI box