Source from Sound on Sound, http://www.soundonsound.com/sos/may03/articles/focusriteisa.asp
“Focusrite microphone preamps have a reputation for transparency and, when used with an appropriate source, warmth. In the case of the ISA428 this is obtained by using a circuit designed by Rupert Neve back in the early ’80s, which demonstrates his unique awareness of subjective as well as objective qualities in audio. A lot of audio equipment rolls off frequencies outside the recognised audio bandwidth, but this can have an audible effect on the higher-frequency harmonics of a signal. Therefore, to capture subtle musical nuances in the source the ISA428 operates over a very wide bandwidth. By pushing the high-end roll-off well outside the audio band the phase response across the audible range is far more linear, and this ensures the required accuracy.
All of the main inputs to the ISA428 are transformer coupled and, although this is an expensive option, it has the added advantage of providing signal gain without active devices. Lundahl 1538 transformers are used in the ISA428, which were specified by Rupert Neve, along with a bespoke ‘Zobel network’ to control the inherent high-frequency resonance of the transformer. This Zobel network is also used in the RED preamps and Rupert Neve tuned it by ear, which is probably an important element of the ‘Focusrite sound’.
Neve 1073LB 500 Series
Source from Sound on Sound, http://www.soundonsound.com/sos/dec11/articles/neve-1073lb-1073lbeq.htm
This module is based very closely indeed on the original 1073 microphone preamplifier design, using exactly the same architecture, the same class-A circuitry, and even the same hand-wound input and output transformers. However, the method of construction is obviously very different, simply in order to fit everything into the constrictive Lunchbox module format. For example, the original expensive and bulky multi-level gain switch has been replaced with a simpler one controlling relays to provide the functions instead. Some might argue that this re-engineering has an audible effect on the sound character that was undoubtedly influenced in part by the hand-wired looms and plug-in amplifier circuit board arrangements of the original units. While this may be true in a strict A-B comparison, it wasn’t something that I noticed or was concerned about. To my ears, the character that shouts ‘1073’ is still there, loud and clear!
Classic Audio Product VP28
This pair of preamps were hand built by us. This DIY kit is provided by Classic Audio Products. It employs 2 stage amplification design. Each contain two discrete opamp, namely, 2520, providing sounding API console in 70’s. It is best used to record drums, guitar amplifier and acoustic guitar.
“When I ran the guitars through the VP28, the guitarist on the session yelled, “Stop! What’s that?? That’s the best I’ve ever heard my guitar sound!” Okay, cool. Guitars through the VP28 – check. They sounded fantastic, and I was happy to use them for the rest of the project.”
Alembic F2B and F1X
If you are fan of David Gilmor, the guitarist of Pink Floyd, you must not miss his sound through this 1U preamp that powers his wall of speakers for two decades!
The Alembic appeared in the late 60’s inspired by the circuit on the Fender Dual Showman amps, which were known for their super clean powerful tone. The F-1X and F2-B carry 12AX7 tube in each section and controls for bass, treble mids and volume and a bright/normal switch.