AudioAficionado.org - VAC Signature Preamplifier Mk IIa ....

I thought I'd start a new thread on this lovely piece. It should be home in about 3-4 weeks. Anyone use VAC gear?

Signature Preamplifier Mk IIa

a/k/a "Renaissance Signature"

"That’s pretty much how it goes with VAC gear – whatever it is connected to sounds about as good as it’s going to get! ... This is the only preamp I have used, bar none, which does not in some manner mangle the music by reducing dynamics, veiling detail, portraying a compressed soundstage, or sounding flat. I can see, or shall I say hear, clearly why Kevin Hayes prefers to refer to his creations as instruments as opposed to components. The level of refinement is extreme. The Signature Preamplifier Mk 2 is suitable for the most exquisite of audio systems, and thus is recommended without reservation!" - Doug Schroeder, DaGoGo, March 2010

The culmination of eight years' research and development, this is VAC's finest preamplifier. Its new and unique circuit follows VAC's "first principles" design philosophy, wherein we look beyond conventional wisdom to discover what a preamplifier really must do to preserve musical life. As usual, the answers are distinct from anything you've seen or heard before.

Through its principal outputs, the Signature Preamplifier contains no coupling capacitors from input to output. No coupling capacitor hinders the purity and detail developed by the hand-wired direct-coupled Class A1 triode tubes. Additionally, no loop negative feedback is used; the output interface is completely stable and free from dynamic interactions with the load. In addition to five standard line inputs (four when phono is fitted), a fully balanced input is provided. Fully balanced outputs are present, as are dual standard RCA outputs. Balancing is achieved by differential triodes driving a special output transformer. This design ensures a true balanced signal, capable of driving even the most cruel professional studio equipment, something impossible with cathode followers and totem circuits. In addition, the transformer output may be used with unbalanced loads. In this manner, galvanic loops and interaction between source & power amp feedback loops are eliminated, allowing for the most liquid, dimensional sound.

The line stage also offers a fully buffered tape loop and VAC's Cinema Bypass mode, which allows your high-end stereo system to integrate seamlessly with home theater. The Cinema Bypass input is a fixed gain input that allows your source component to control volume, and passes this signal through to the stereo power amplifiers without further processing. It allows a cost-no-object stereo system to integrate seamlessly into a home theater context when needed, without any degradation of two channel performance from traditional stereo sources. The Cinema Bypass input may also be used with stereo components that have their own level control, such as d/a converters.

The optional phono stage is a zero-feedback design incorporating six low noise triode tubes. Sensitive and quiet, it is capable of handling even low output moving coil cartridges. A rear panel switch allows engagement of wideband transformers to provide a proper and balanced load to low output pickups. Electrostatic decoupling prevents the heater circuits from "talking" to each other, a common cause of lost detail. Indeed, a completely separate power transformer and filter circuitry are dedicated to the phono stage, eliminating any disturbance of the delicate phono signal by the powerful line stage. Variable load switching is provided.

The laquered aluminum remote control is standard. Uniquely, our remote system is implemented with electromechanical switches and controls. This approach is considerably more costly than the usual digital interfaces, but has several major advantages. First, no VCAs, relays, or transistor switches (switched ladder networks) are used in controlling volume. This is mandatory for sonic purity. Second, VAC's careful implementation avoids the use of microprocessors, which generate significant noise signals that, while sometimes not audible directly, can do damage to the sound. Third, the front panel controls are direct and intuitive to use, their positions indicating at a glance exactly how the unit is set.

The VAC logos are backlit with an elegant blue in normal operation, but display red when the mute is activated. These are set in the heirloom-quality sculpted 3/8" fascia. The liberal use of sound deadening material compliments the 1/4" thick CNC-machined aluminum chassis, creating a solid mechanical foundation.

Internal parts are specified from the finest and most exotic materials, as extreme measures and the most careful "voicing" are required to reach this unequaled pinnacle of perfection.

Basic specifications:

Inputs: 3 sets RCA line input, 2 sets balanced/RCA selectable inputs; optional 1 MM and 1 MC (or additional line input if phono is not fitted); 1 set RCA tape monitor input; 1 set RCA cinema bypass input
Outputs: 2 sets RCA, 2 set balanced XLR (EIA "pin 2 hot" studio standard); 1 set RCA tape output
Optional MM/MC phono stage with user adjustable loading
Absolute phase is correct from all inputs to all outputs
Dimensions: audio chassis 18" wide x 5.5" high x 14.5 deep (plus knobs & connectors); power supply 18" x 3.9" x 14.5" plus connectors
Shipping weight: 61 pounds total (with phono)
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Line stage:
Two 12AU7 twin triodes and two 8416, 7308, 6922, E88CC, ECC88, 6DJ8, or 12DJ8 twin triodes
Gain: 12 dB
Frequency response: flat over audio band; -3 dB bandwidth 5 Hz - 210 kHz
THD: <0.009% @ 1 kHz, 1 V RMS
Maximum output: > 8 V RMS
Output impedance: 96 ohms, 20 Hz - 20 kHz, static (i.e., not dependent upon feedback)
Recommended output load: >300 ohms
Channel separation: >80 db
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