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The Focusrite magic: warmth plus transparency
Focusrite's ISA Two mic preamp has a distinguished heritage. Since its 1985 introduction, the transformer-based Focusrite pre amp has become something of a legend - and a benchmark for transparency. But there's something else going on. That something is a subtle warmth, courtesy of transformer core saturation. It's this apparent contradiction of warmth plus transparently open and unrestricted high frequencies, that identifies the Focusrite "sound" that continues to be in demand in top studios worldwide.
Engineering it right
The Focusrite ISA Two has some innovative thinking under its bonnet. Just what engineering innovations contribute to a superior-sounding mic preamp? For one thing, to eliminate the audible rolloff exhibited by preamps limited to the audible bandwidth, Focusrite ISA pres operate over a much greater range (10Hz-135kHz, in the case of the ISA Two). There's also the ISA topology that gives you up to 80dB of undistorted gain. How about variable input impedance, which lets you fine-tune the amount of "character" in your signal - from pristine transparency, to vintage warmth.
The Neve connection
Rupert Neve selected the Lundahl LL1538 as the input transformer for the legendary Focusrite ISA 110, and it's still the best microphone input transformer available - Focusrite specifies it in every one of their ISA Series mic pres. Mr. Neve also perfected the Zobel network (found in Focusrite's ISA circuit), which is responsible for the broad-bandwidth, ruler-flat frequency response exhibited by ISA preamps.
Focusrite ISA Two Dual-mono Mic Preamp Features: