TOM EVANS AUDIODESIGN PREAMPIFIERS
The role of a preamplifier is to act as a switch controlling the signals from the various source components in a system, and to provide adjustable gain to the power amplifiers. On the face of it, a straightforward task-a switch, a volume control, and a modest amplifying stage. A classic case of easier said than done.
We must not forget that anything added to (or left out of) the signal by the preamp is necessarily going to be increased by 20-35dB in the power amps.
Like The Groove phono stage, The Vibe has been in development for the last 12 years. Its basic specifications comprise:
*5 pairs of switched line inputs and 1 pair of buffered record outputs
*2pairs of outputs to power amplifiers
*Function switch from 'WASP' manufacturers of battlefield communication technology
*The DACT switched attenuator used in The Vibe has a tracking accuracy between channels of 0.05 dB, compared with an error of ± 10% from other manufacturers. It comprises an array of surface mount metal film resistors mounted on a gold plated spiral track giving 24 positions. It's main benefits are: minimal distortion over a wide bandwidth, short signal paths, stunning attenuation accuracy figures of 0.05dB between channels.
*Proprietary 'Lithos' regulation (unique to Tom Evans products) supplying all stages of the circuit
The output stage utilises current feedback technology. This approach is superior to voltage feedback designs as it offers far greater rise and recovery times (less than 10 nanoseconds). Using conventional voltage regulation, this approach is rarely used as power supply related noise creates a marked reduction in resolution and dynamic range. Historically feedback has been used to solve problems of inadequate circuit design. This is certainly the case using conventional technology. Intelligent use of feedback is a key feature of producing a more lifelike presentation, as it greatly improves linearity and bandwidth. The application of Tom Evans' proprietary Lithos regulation means that one is no longer reliant on the amplifier's ability to reject garbage, as this is disposed of long before it reaches any gain stage. Noise is therefore virtually eliminated with the added benefit of increased speed and resolution far in advance of most designs.
Because the gain stage is fully DC coupled to accurately reproduce a wide bandwidth, an added safety feature is a DC detection and isolation circuit. This protects both loudspeakers and DC coupled power amps from potential damage through failure of any source components. This circuit delays power up at 'switch on' for 8 seconds while it checks the system, then remains active at all times during the unit's use, and will immediately isolate the output if DC is detected. This only operates below 3Hz; its presence in the preamp is inaudible.
In addition to the current feedback technology, there are marked echoes of the award winning Groove phono stage (in terms of error correcton and the application of psychoacoustic principles) built into the design. The Vibe preamp again moves the goalposts for what is possible in reproducing recorded music.
Dimensions: Width-13 inches Height-3.5 inches Depth-7 inches
Add the optional Pulse power supply to the above described Vibe and things get even better. The Pulse consists of two identical boxes, one carrying the transformer while the other provides a large dose of Lithos regulation. These are joined to each other by a short lead, and are joined to the Vibe through the same multi-pin connector used by the stock power supply. Chris Thomas in Hi Fi+ opined that "Even without the Pulse, the Vibe is good enough to be compared to any sub-$17,000 pre out there....But add the Pulse and you are talking of an entirely different level of performance altogether." Shockingly good.
The Pulse power supply is a plug-in power supply substitution to the standard Vibe preamp. No modification to the Vibe is necessary other than disconnecting the stock power supply and replacing it with the Pulse power supply.
Prices:
The Vibe- $6000
The Pulse 2(optional power supply upgrade for Vibe)- $4950
Vibe/Pulse 2 combo- $10,950
Manufacturers warranty until November 2009
