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19 July 2010:


The Proteus ~ An Introduction

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The Proteus ~ 30 watts/ch integrated amplifier

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The Proteus is a hand built all valve integrated amplifier designed around the traditional engineering values and beliefs of quality, excellence Proteus Diamond intergrated amplifier.and reliability. Only the finest materials and components are used in its construction from the solid stainless steel chassis to the hand wound transformers, attention to detail has been of the utmost importance. The styling is 'Art-Deco' and attempts to get away from the "box" and the current machined billet aluminium look.

From the outset, the way the amplifier performs and sounds has been the main design criteria. Particular attention has been paid to the way the Proteus behaves at low listening levels. Most of the time we listen to music at 5 Watts and below, an amplifier should be capable of delivering the full spectrum of frequencies and dynamics at these lower power outputs.

All the hand wired circuits are carried on an electronically isolated aluminium sub chassis whilst its layout is based on a traditional point to point method of assembly using silver plated feed through insulators enabling the various components and associated wiring to be placed on both sides. This helps reduce the effects of stray capacitance and crosstalk, it also allows good cooling properties and easy servicing. Apart from the HT and LT rectifiers, the heater regulator and the LED display, there are no solid state devices, the entire amplifier is valve based.

The heart of any valve amplifier is the output transformer and power supply

The output transformers are hand wound adopting design and manufacturing methods used over fifty years ago and therefore, are over twice the size of those used by many manufactures of today. Their frequency response extends from below 5 Hz to over 50 kHz with massive reserves of current capacity to handle peak power excursions.

The power supply will deliver over 250 Watts of HT to the output stages and a fully regulated secondary supply feeds the pre amplifiers and phono stages. Each stage of the amplifier has its HT supply separately smoothed and de-coupled to improve inter channel distortion and stability. A standby circuit is switched in when the amplifier is not in use. This reduces the HT supply to a trickle which helps prevent cathode poisoning of the valves and reduces the power consumption of the amplifier by about two thirds. The standby function also ensures the amplifier is maintained at a minimum working temperature.Proteus Diamond intergrated amplifier.

A conventional push-pull output stage with KT90 valves is used in pure class 'A' triode mode with automatic cathode biasing so there is no need to continually adjust the amplifier to get the best out of it or when there is a change of output valves. The output stage is driven by a simple "long tailed pair" phase splitter and DC coupled double triode voltage gain stage driver with minimal negative feedback resulting in an unconditionally stable output regardless of load. The resulting output is better than 0.08% THD at 5 Watts and delivers a maximum of 32 Watts RMS. *See note at the end of this literature.

The above driver stage is driven via a Vishay "Blue Velvet" volume control by a wide band dc coupled line stage preamplifier which has a high input impedance to help negate source mismatching effects and all its inputs are selected by relays. A line level output is provided for recording purposes. The MC phono stage uses two cascade coupled double triodes per channel providing excellent signal to noise ratio and uses an accurate, passive RIAA equalisation circuit.

* The Peak Power Myth

The 'peak power' output is often given by some manufacturers in order to make it appear an amplifier is more powerful than it actually is. This peak power is the absolute maximum amount of power an amplifier can produce at any instant, it is not a useful representation of the amplifiers"..the Proteus still thoroughly managed to charm all those who heard it. "
HiFi Critic
ability to deliver the quoted amount energy continually. A true and useful guide to the amount of actual power an amplifier can produce is the RMS (Root Mean Square) value and represents the measured power delivered to a load (speaker) continually. The maximum power a pair of KT88 valves connected in push-pull triode mode and operating in pure Class 'A' and with an HT of 425 volts is 27 Watts with 1.5% THD. Class 'A' ensures the valve operates over the most linear part of its inherent characteristics to deliver the lowest distortion levels for a given power output. Under class 'B' operation a pair of KT88 can deliver 65 Watts but at much higher distortion levels, typically in excess of 6%. These 'classes' are the method adopted by a designer to enable a particular valve to operate in a way suiting the requirements of the amplifier, this is accomplished by the type and level of biasing employed. Data source; GEC KT88 original data sheet from 1956.


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