Technical - Maya Classic Integrated Hi-Fi Amp
Twin paralleled KT88 Gold Series beam tetrodes drive custom designed multi-section output transformers in single ended mode.
These transformers, each with a massive 2.5" stack of high grade silicon steel gapped laminations, are provided with screen grid taps wired via high quality, precious metal power relays and the output configuration may be switched on-line by the user between triode and ultra-linear mode.
A unique design feature of this triode stage is Transfer Characteristic Matching (TCM) (patents pending). This technique inversely models the inherent non-linearity in the output stage valves, and so drastically reduces harmonic distortion. The driver stage TCM characteristics are automatically adjusted when the user changes from triode to ultra-linear mode to optimise overall linearity in each configuration. Shielded precious metal reed relays are used to allow this on-line reconfiguration of the driver stage.
Each channel uses a low noise double triode configured as a SRPP (Shunt Regulated Push-Pull) front end. This topology has been found to offer excellent gain/noise performance with wide bandwidth and extremely low distortion. The input stage is dc coupled to the driver stage to minimise overall phase shift, and to present a wide stability margin when the (optional) corrective feedback facility is selected.
Passive Input Stage
The entire passive input stage is contained within a specially designed Faraday Cage to minimise pickup of hum and noise.
Four line level inputs are provided, via colour coded gold plated phono sockets. These inputs are wired in ptfe sleeved, silver plated cables to an array of shielded, precious metal reed relays. The relays allow source selection and signal routing via a selectable tape in/out loop with a further set of gold plated phono sockets. Stereo/mono selection is provided. The signal is then routed, via ptfe/silver shielded cable to the Alps volume control at the front panel through heavy wall copper tubes. Individual conduits are provided for the signal leads of each channel, and also for the corrective feedback signals for each channel. A further conduit contains the various coil switching signal leads for the signal routing relays.
These novel design techniques result in minimal corruption of the original source material, and contribute towards the impressive s/n ratio and sound purity of the Maya Classic.
Variable corrective feedback, adjustable from the front panel in the range −3dB to −20dB may be switched in or out by a front mounted rocker switch. Signal switching is by means of precious metal shielded reed relays. Feedback source may be user selected either directly from the output transformer secondary, or externally via gold plated phono sockets. This allows the user optionally to derive the feedback signal directly from the speaker terminals, thus compensating any non-linearity which may be introduced by the loudspeaker interconnect cables.
The dual rectifier power supplies have been designed for minimum impedance, maximum noise rejection and high energy storage. Twin mains transformers are equipped with multiple primaries to allow voltage selection to suit any mains supply. Separate, centre tapped secondaries at 6.3v feed the heaters for each channel. High tension windings are fed to fast recovery silicon diode bridges. The two separate HT sections are series wired to present a 420v HT line using no less than four choke/capacitor filter sections, to achieve a ripple of less than 0.1%. A further rectified and smoothed output is derived from a separate secondary winding to provide relay coil switching.
The construction of the Maya Classic is unique.
A sub-frame, machined and fabricated from heavy gauge aluminium alloy carries all user selection rocker switches at the front, and the mains IEC inlet and protection fuse at the rear. The Power Modules, one for each channel, are secured at either side of the sub-frame. Between these two Power Modules is located the central Signal Module.
The two Power Modules are built up as a series of layers or decks. Each bottom deck, which fits to the sub-frame, carries two low-noise smoothing chokes fitted using resilient anti-vibration mounts. The next deck above this forms the ledge upon which the side covers fit. The top deck carries a mains transformer at the front, and an output transformer at the rear. Fastened just below the top deck are the rectifiers, smoothing and bypass capacitors and associated power supply components. At the rear of the top deck, behind the output transformer, are located the LF output terminals for connection to the loudspeaker bass section terminals. For ease of access and maintenance all wiring to each power module is connected via heavy duty silver plated plug-in connectors.
The Signal Module carries the actual amplifier circuitry. A heavy gauge aluminium chassis plate provides the mounting for all the amplifier active and passive components. On top of this is fitted a polished black acrylic top plate to which are affixed the valve holders. These special valve holders are machined in-house from solid brass castings, polished and plated with a heavy layer of 24 carat gold. High quality ceramic bases with gold plated pins are resiliently mounted within the holders. All signal wiring is hand wired, using ptfe sleeved silver plated wire.
The Signal Module is divided into separate fully shielded compartments, or Faraday Cages, containing respectively the passive input stage, the front end pre-amplifier, the driver stage and the power output stage.
At the front and rear of the Signal Module are mounted solid brass fascia plates, again plated with a heavy layer of 24 carat gold. The front plate is pierced to accept the spindles for the three rotary controls (Corrective Feedback, Volume Level and 4-way input source selector). The rear fascia plate carries the phono sockets for signal inputs, tape in/out connections, two pairs of speaker terminals for wiring to loudspeaker HF terminals (when bi-wired), remote Corrective Feedback (CFB) inputs, and CFB source selection switches.
The side covers, which fit to each power module, are machined to tolerances of closer than 0.05 mm from 6mm thick, high density phenolic laminate. The individual components of the covers are then pinned and bonded in purpose built jigs, before being hand veneered using selected book matched hardwood veneers from sustainable sources. After veneering, the covers are sealed with four coats of selected lacquer, each coat being allowed to dry naturally before it is rubbed down by hand in readiness for the next application. A final coat of high quality satin lacquer results in a deep durable finish which enhances the natural grain of the wood beneath. This results in components which are absolutely stable through the most severe variations in temperature and humidity, whilst presenting a real hard wood finish of the highest quality.