Monday , 20 February 2017
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Proteus 4040 Integrated Amplifier Review

Review By Georgallou Efthemious

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This amplifier has forced me into a little introspection. It’s not a vintage unit, my usually preferred component, but a recent conception utilising a circuit design rooted in the 40’s. It’s an entirely British product made by English Valve Amplifiers Ltd, a small company based in East Sussex and owned by Geoff Kremer. The pedigree is all there. Geoff  has been a valve amp and reel to reel tape deck engineer since 1968.  He has had experience with numerous exotic and prestigious amplifiers, vintage and current, transistor and valve from the UK, Japan and the States. In fact, all the ones many aspire to own. Geoff formed EVA ltd in 2010 to manufacture and market valve amps, but still continues his servicing work as well.

I’ll cut to the chase. Any device that is blessed with the sound quality produced by the Proteus 4040 is a rare find. It’s simply an excellent integrated design which will rival any, high-end pre/power amp combination for detail and accuracy. The HF is sweet, the midrange has that unique valve lucidity and the LF is firm, deep and controlled. What is also extraordinary about this design is that, far from using the latest software to control high-tech gizmo circuits, the Proteus 4040 uses output transformers conceived in 1947. Neither does it utilise silver-wound transformers, Black Gate capacitors or other internal exotica – just very good quality readily available components. However, the enormous mains and output transformers are hand-wound custom units.

Geoff is understandably very passionate and knowledgeable about amplifier design and construction, with appropriately firm views regarding extravagant claims for individual circuit components. I have transcribed on my website, RedDiamondAudio.net a short interview I recorded with him which covers his approach to amplifier design.It’s full of good sense, grounded but controversial views, and is well worth a read.

Technicals.
The Proteus 4040 is an entirely hand-built integrated amp a built-in MM phono stage. It produces 40 watts RMS per channel in full Class A, triode mode. The two KT120 output valves for each channel are in a push-pull cathode biased configuration. Driver valves are 12BH7 dual triodes, 2 per channel. The power supply delivers 250 Watts of 600volts HT and is split in two to deliver HT separately to each channel, whilst a valve regulated HT supply provides for the line and phono stages. The output drivers are ‘Long Tailed Pairs’ DC coupled to a voltage gain stage with minimum feedback. The output valves are automatic cathode biased, so there is never any need to constantly adjust the bias settings. Also this method offers a degree of protection should a valve fail and each channel is fused for added safety. All the components used are high quality “off the shelf” items. It has never been deemed necessary to use anything else.

The mains input is filtered to eradicate spurious spikes and noise. The mains is also passed through a blocking circuit to remove any DC which can cause the mains transformer to hum and overheat. All the valves except the output valves have DC fed heaters.

The Line and Phono stages share a similar Cascode arrangement of double triodes for low noise and good stability. There is no feedback employed in these stages. The phono RIAA system is fully passive and accurate to within 1dB. There are 4 line inputs and an output for recording in addition to the phono input.

The output transformers are manufactured to the Williamson design specification in East Sussex by Precision Windings Ltd of Bognor. The components are mounted on an electronically isolated aluminium sub chassis using silver plated feed through insulators. This enables the various components and associated wiring to be placed on both sides of the plate and helps reduce the effects of stray capacitance and crosstalk. It also allows for efficient cooling and easy servicing. All the circuits employ point to point wiring with the exception of two very small PCB’s for the input switching relays and LED’s, and the HT protection / timer system. Each pair of input sockets at the rear have their own small LED indicator which is illuminated when that pair is selected. The wire used is Alpha, PTFE sheathed, silver plated copper multi stranded.

Apart from the HT and LT rectifiers, the heater regulator, the LED display and HT protection, there are no solid state devices. The entire amplifier is valve based.

There is a “standby” mode which reduces the valve HT supply to a trickle. This 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. This is coupled to a HT timer circuit which delays the application of the 600 volts to the valves when switching on from cold.

Speaker impedance loading is nominally set at 8 ohms, but can be changed to 2, 4, 8, 16 ohms by internal jumpers. Any impedance between 2 and 26 ohms in two ohm steps can be requested for manufacture.

The beautifully polished solid stainless steel casing is manufactured locally by a sheet metal working company specialising in exclusive car body fabrication. The Art Deco design is distinctive, stylish and elegant but the finish can be varied to suit individual taste during manufacture. It can even be ordered in a paint finish of ones choice. Each amplifier is made to order.

And the sound?

There are many, many good amplifiers out there, but this is a real “stand-out” beauty. When I first came across the Proteus, I had been trying a new high powered and expensive transistor amp from the States. It was good, (and incidentally, has been very favourably featured within the Wam reviews), but it just didn’t have that lucid, tangible midrange unique to valves and in abundance with the Proteus 4040. Those, oh so life-like female voices, musical instruments full of subtle harmonics never heard before, and the calm non-hysterical, musical presentation. The HF is sweet and soaring where it should be, with incredible clarity and without “graininess”. The LF, more unusually for a valve amp, is extended and tight, with double bass and drum skins felt as well as heard. Choral works are perhaps the most striking as there is so much location ambience.

I played a wide range of music (except rap, which I can’t deal with), and the quality was immediately apparent on everything. And you can listen for hours on end – always a good sign. If you are into rock at phenomenal levels and subtleties are less of a priority, it’s probably best to go for brute force megawatts, but like all the best amps I’ve come across, transistor or valve, high level is no compensation for quality. There is no need to pump up the volume to appreciate the detail and subtlety, it’s all there at the lowest levels too. This amp is almost like listening to a musical instrument in it’s own right, exciting and enthralling.

Fortunately for me, I still have the 4040 at home, and any Wammer is more than welcome to pop over for an audition. I’m based in Brighton and if you’re reasonably near, I can bring it to over to you. Unfortunately, I’m not the distributor of the amp or on commission from anyone, but would just like to see this small enterprising company have the success it deserves. Similarly, if you’ve come across any other equipment from a small scale UK manufacturer that deserves attention, let me know. It seems that these enterprises are quietly producing excellent equipment, with that all important personal service. They need to be discovered in favour of the big bully boys.
Good quality ancillary equipment was used for the review:
Avalon Diamonds, Wilson Sophia 2’s.
Garrard 401/Lorricraft plinth/SME V, Sony Biotracer PS-X75
Kondo Io-m, Dynavector Karat 17D II, Sugano era long-bodied Koetsu Onyx and Rosewood.
Step-up transformer: Yamamura
Cables : Siltech, Audio Note (GB), Kondo and QED (!)
Specifications

Valve complement
4 X KT120 Tetrode, output valves
4 X 12BH7 Double Triode, driver and input valves
1 X EL84 HT Pentode, regulator element.
1 X 2PN6 HT Double Triode, regulator driver.
6 X E813CC Planar Double Triode, line and phono stages.

All valve bases are CMC precision “machine turned” solid brass socket pins mounted in Bakelite holders.
Power Output: 40 Watts RMS.
Total Harmonic Distortion at 1 kHz into 8 ohms load
3 Watt <0.03%
5 Watt 0.05%
20 Watt 0.08%.
Frequency spectrum
4 Hz to 35 kHz.
Input sensitivities
Four switched line inputs-
215 mV at 180 K Ohm input impedance.
Overload margin into clipping – 3.7 V RMS

Phono Stage-
Standard phono input for moving magnet cartridges; 2.5 mV at 50 K Ohm input impedance.
Included, outboard 10:1 step up transformer for Moving Coil cartridges;
250 micro volts at 470 Ohm nominal input loading.
Three sets of loading plugs are supplied for; 100 Ohm, 50 Ohm and 20 Ohm. Other values may be ordered from PAD Ltd if required.
RIAA performance to within 1 dB accuracy.
Hum and noise – 86 dB.
Phono stage, Moving Coil
Input sensitivity 250 micro volts at 1 K Ohm
RIAA performance to within 1 dB accuracy.
Speaker impedance’s catered for:
Supplied nominally at 8 Ohms
2, 4, 8, 16 Ohms selected by internal jumpers.Any impedance between 2 and 20 ohms in two Ohm steps can be requested during manufacture.
Heavy Duty “Clutch Grip” insulated solid brass terminal posts will accept 4 mm plugs and or bare ended cable.
Mains consumption
Running 280 Watts
Standby 120 Watts.
Dimensions Size in mm; 609 wide, 305 deep, 230 high
Weight; 33 Kg.

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