The Fredenstein HD Reference microphone preamplifier utilizes a completely new approach to microphone level amplification. Many in the recording industry are now using 96 kHz or 192 kHz sampling rates while tracking, but still using equipment, which cannot provide the frequency response or bandwidth provided by modern A/D converters. The HD Reference overcomes these limitations and yields a new sound quality. Especially for wider bandwidth sources, like acoustic instruments, voices, and drums, the HD Reference is simply unequaled. It is the preferred choice for classical recordings as well.
The HD Reference was preceded by the HD Pre which was designed for the 500 Series racks, but that format does have limits regarding available voltage and current plus imposes some restraints on the available physical area. Never the less, the HD Pre set new levels of performance in all of the important parameters pertaining to mic pre-amplifiers. The HD Reference surpasses the HD Pre due to higher voltage power supplies +/-24V rather than +/- 16V, higher current (?? vs +/- 150mA), and even more discrete transistors (from 54 in the HD Pre to 64 in the HD Reference).
The HD Reference also goes a step further by allowing a full featured Remote Control called The Commander that can access every function on the front panel. The HD Reference and Commander are connected with a conventional XLR cable, that can be routed though a patch bay if necessary. With 920kHz bandwidth available, it makes little sense to risk losing that fidelity with a mic driving 100 feet or more of mic cable. With the HD Reference placed close to the microphones and short mic cables in use, the engineer can realize the benefit of bandwidth.
The HD Reference also has a few added features, such as a display that shows gain in dB next to the knob that allows one to set gain in accurate 1dB steps, which is great for setting up stereo pairs. We also added more choices to the High Pass Filter (Off, 39Hz, 82Hz) and more choices to the Input
Impedance (200K, 1K, 300, 232).
In terms relating to audibility, the HD Reference is very very fast, clean and true to the source, with very low noise. And for the technically inclined, it does this without negative feedback and, maintains outstanding performance at any and all gain settings, which is rare indeed.
Besides incorporating a fully discrete signal path and a Class-A balanced output stage, the HD Reference uses a revolutionary current amplification circuit, which neutralizes internal transistor capacitance (Miller Effect) that limit frequency response and slew rate in conventional voltage amplifiers. As a result, the HD Reference features an unprecedented bandwidth of over 900 kHz.
The HD Reference may also be unique in the world of mic pre-amps in needing moderate sized heat sinks that one might expect to see in a small power amp. The output stage is also really Class A, running on 48 volts and can drive +29 dBm (60 volts peak to peak). And this implies appreciable idle current, and some heat generated.. No problem driving long lines and still sounding fine though, thanks to that available current...
The HD Reference does not use input or output transformers. These would prevent the pre-amp from having the amazing specifications and performance that it is capable of. The F601A Mic Pre has both an input transformer and output transformer that can be inserted or bypassed. The F609, F676, F200, V.A.S and Artistic Mic Pre's all have transformers and each has special applications in where they excel and compete with well known vintage pieces.