Features Manley input & output transformers with pure nickel laminations in mu-metal case with flat frequency response 20Hz-25KHz frequency response Balanced Inputs & Outputs Fully differential all-tube circuitry using one each 5670, 5751, 7044, & 12AL5 per channel Independently regulated B+ and Heater supplies Description Product Description Includes 1 Year Free Extended Warranty. An industry standard for professional mastering studios, the Mastering Version of the Stereo Variable Mu Limiter Compressor employs metal-film resistors loaded onto beautiful Grayhill sealed gold-contact switches for absolute repeatability, accuracy, and reliability. 1/2dB steps ensure precise and subtle adjustments. This is what defines mastering. High Pass Side Chain mod now comes standard. Proudly from our beginning, we at MANLEY LABS have been closely involved with numerous mastering facilities around the world. For these most demanding engineers in our industry, we have created specialized products such as our all-tube tape repro head amps, digital converters, high-powered vacuum tube monitor amplifiers, through to custom monitoring consoles, all the way up to complete facility design and installation. The Mastering Version of our Variable Mu® Limiter Compressor incorporating detented and logable steps built with 1% metal film resistors on sealed gold-contact Grayhill switches is available. NO, we will not mod a "normal" unit to the Mastering Version. The High Pass Side Chain mod comes stock on all Manley Variable Mu limiter/compressors since 12/2009, on both regular and mastering versions. This mod adds two switches to the front panel, one for each channel, so that when engaged, the side chain will not respond to frequencies lower than 100Hz. (We standardly use 100Hz as the -3dB point. Other frequencies can be custom ordered.) This HP SC Mod can be used with music with heavy bass lines or bass-heavy mixes where you don't want the bass driving the whole action of the compressor.