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Design. The Avantgarde Acoustic PRE is a preamplifier of the company's new XA Series. The manufacturer plans to add a D/A converter and network audio player as well as a phonostage. Obviously the pre + amp combination was a top priority. The PRE was designed from scratch by Mathias Ruff, chief engineer of AA. When designing it Mathias made best use of several of his patents and solutions which, although built upon pre-existing knowledge from other manufacturers and designers, creates a unique new and complete value.
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The circuitry is placed inside a solid enclosure with special sub enclosure for certain bits as one of the main assumptions was vibration control and that applied to both the power supply and gain stage. Matthias also wanted to use the shortest cabling possible including power cabling. The PRE is a solid-state preamplifier with battery power supply. The circuit is built up of transistors and a discrete resistor ladder. There are no capacitors or DC servo circuits in the signal path. To protect other elements of this design Avantgarde came up with a very clever protection system called DC Flow (patented together with the volume control solution). There is only a single solid-state class A gain stage. This is conceptually similar to Soulution and TAD. There is no negative feedback loop.
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The enclosure consists of two parts – a 18.5kg outer shell and a 10.5kg inner chassis covering the power supply circuit but not the output transistors. This adds up to the impressive weight of 40kg which is really a lot for a preamplifier.
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Front and back. The enclosure is made up of precisely machined cast and milled aluminium components that also double as heat sinks. The front panel is exchangeable but there is always an aluminium base beneath the decorative dress plate. The front panel slips between upper and lower retainer elements which come together in nice handles.
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On the right side of the front there is a large volume control knob with nicely knurled surface. It is placed in the middle of a back-lit panel with small LEDs behind it. When the volume is changed a row of LEDs show the action and after a brief period they extinguish except for the one that indicates the precise chosen setting. The color of the back light changes to confirm operational status. Blue is for mute. White is for battery power. Orange is for battery charge. The selector toggles are back-lit too and their color is indicative too. The first toggle switch is for voltage. If it goes orange, the batteries are being charged. If not, the machine draws power from the batteries.
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The back panel proves that the PRE is a rigorously balanced device – there are XLR inputs and outputs exclusively, 5 of the former, 2 of the latter. There is a grounding post, trigger outputs and knobs that control the back-light intensity. Even though these all are linear inputs they are not identical. The first three are ‘classic’ with an input sensitivity of 775mV. The fourth has its sensitivity increased by 4.5dB, the fifth by 9dB. The last two might be useful when one uses low-output sources like phono stages for example.
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Interior. This is divided into three parts for the batteries and charger, power transformers and the preamplifier itself. The batteries are placed inside a very heavy aluminium casing which makes up the inner case. Three power transformers which charge five batteries (separately for the left and right channels, logic circuits and back light) bolt to the side wall. The preamplifier circuit is quite small and mounts to one PCB per channel facing each other with the back sides of the boards.
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The signal goes from the gold-plated inputs to transistors of the same type as those in the gain stage which here act as input buffers. Then the signal proceeds to the relays and attenuator. The latter is a patented discrete regulator built with relays and SMD resistors controlled by a logic chip that works in 48 x 1.5dB steps. From here the signal hits the gain stage, a very simple design of a single transistor in a round metal casing per side/phase. Next the signal hits the outputs via some parallel circuits of Sanyo and Black Gate capacitors (the latter are out of production so AA bought a large stock for future use).
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Remote. I need to mention the wand separately. It's heavy and made from aluminium but that alone is quite common. What's different here is its shape – an elongated cylinder with a diameter similar to that of the volume control knob and a similar knurled finish. There are three push buttons for volume up/down and mute and two small legs which prevent rolling. The remote operates on 2 x AA 1.5V batteries.
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opinia @ highfidelity.pl |
Tech specs according to the manufacturer:
Input impedance:10 kΩ
Input sensitivity: inputs 1-3 at 775mV; input 4 +4.5dB, input 5 +9dB
Electronic volume control switch (patent pending): 48 1x 1.5db steps
XLR inputs: 5
XLR outputs: 2
Triggers: 2 x 12V
Battery power supply: 5 x 2300mAh
Dimmer control for illumination: Yes
Remote control: Yes
Dimensions (W x H x D): 484 x 190 x 486mm
Weight: Outer unibody aluminium chassis with heatsinks 18.5kg, inner unibody aluminium core 10.5kg - total weight 40kg
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