ICON AUDIO Stereo 40 MkIIIm (KT88)

The best value in a integrated amplifier


SKU: ST403-KT88

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Why does a VALVE RECTIFIER, TERTIARY TRANSFORMERS, and NO FEEDBACK make the Stereo 40 MK III so special?

It's nearly ten years since we introduced our Stereo 40, designed by David Shaw, founder of Icon Audio. During this time we have used our expertise to make other highly successful, award winning valve amplifiers, each one pure valve and hand-made such as our MB845 90w triode monoblocks. So we decided to incorporate some of our new ideas into a new ‘High End’ version of Stereo 40 whilst keeping it affordable.

A Valve Rectifier (centre valve) helps to give a very smooth sound, but normally adds to size and price. We have found a way of incorporating a valve rectifier whilst keeping the power and speed of our other designs. We found the excellent Western Electric design, the 274B to give the best results.

A Tertiary Transformer has an extra (third) winding which put simply, allows the output transformer to compare both the input and output, and ‘null’ distortion. Thereby dramatically improving the performance, so much so that there is no ‘global feedback’ used. We believe our expertly hand wound output transformers to be amongst the finest available.

Feedback is used in most amplifiers to improve the performance in terms of bandwidth and distortion. But too much can actually increase the ‘nasty’ higher order distortion giving an unpleasant ‘metallic’ quality. We normally use a minimal amount, but Stereo 40 MKIII is so good than none is necessary.
The Stereo 40 is designed to work with a wide range of output valves. You can choose between EL34 or KT88 (or even KT66/77, 6CA7, 6550). You can also choose between either “Ultralinear” or Triode* mode to give the maximum choice of operating conditions. Its almost like having two amplifiers in one!
The GEC British designed KT88 brilliantly illuminates complex recordings with great speed and verve, The EL34 offers a slightly warmer more laid back interpretation.

Close attention has been paid to the big power supply using eight large capacitors and a large “choke” in a traditional “Pi” configuration. This gives very low source impedance with a huge reserve of power available for large transients without clipping, whilst low ripple and hum, with the advantage that it is very resistant to RF noise coming through the mains.

This combination gives a very smooth and detailed sound stage which works well to bring out the colour and texture of older recordings and whilst not overemphasising the harshness of many modern digital recordings. In short an amplifier capable of resolving very high definition, that is very easy to live with that has plenty of power to control modern speakers.

The brand new design is finished with a fine metallic paint work that is easy to clean and is wear resistant. A 10mm solid alloy front panel with polished dark chrome alloy knobs. And our famous Plexiglas valve cover to create a stunning visual impression.

On the scales at 25Kg this amplifier is 9Kg heavier than the ST40i. No lightweight in quality or performance and should give many years of excellent service.

As each amplifier is prepared to your order here in Leicester. We can offer a range of upgrades including premium and “new old stock” valves, the superb Jensen “oil in paper” capacitors. 

Icon Audio is a small company established in 2000. Our speciality is pure valve amplification, loudspeakers and associated equipment. All our equipment is hand built and hand wired. It is our belief that in many ways valve amplifiers are superior for the reproduction of music.

Specifications and Features

  • • Comprehensive manual supplied
  • • Full instructions for valve change included
  • • All hand wired point to point
  • • No printed circuit or tag board to ‘colour’ sound
  • • Japanese Blue ALPS volume pot.
  • • Class A, all Triode front end
  • • Output circuit Ultralinear or Triode switchable*
  • • 4x EL34/KT88 precisely matched for best performance
  • • 1x 6SL7/6N9 first stage valve, 2x 6SN7 phase splitter
  • • 274B/GZ34 valve rectifier for ‘soft start’ and smooth sound
  • • No global feedback used
  • • Standby switch to save valve life and power
  • • 2x 40w RMS per channel output
  • • 2x 20 Watts RMS in Triode mode
  • • Signal to noise level -90db
  • • Freq response better than 20hz-20kHz +0 – 1db
  • • Power bandwidth 10hz-30khz
  • • Total harmonic distortion 0.15% at full output
  • • Suitable for 4 to 16ohm loudspeakers
  • • Supplied with attractive safety guard.
  • • Audiophile quality metal film resistors
  • • Rubicon/Nichichron power caps.
  • • Blue LED mains indicator
  • • Valve rectifier
  • • Choke regulated power supply
  • • Audiophile quality polypropylene audio caps.
  • • Silver TEFLON audio cable
  • • Custom hand wound Tertiary output transformers
  • • Ceramic valve holders for minimum noise/leakage
  • • Centre tapped heater circuit for minimum hum
  • • Gold plated Input & speaker terminals
  • • Four line inputs – CD, Tape, Tuner, Aux
  • • Tape monitor circuit with ‘Record Out’
  • • 250mv input sensitivity.
  • • 230/240volts 76w SB, 140w Min, 240watts max.
  • • 1.6A AS rear fuse
  • • CE, ROHSS and WEEE where applicable.
  • • 390mmW, 410D, 210H, 25kg
  • (a minimum of 30mm height should be added to allow for ventilation)


ICON AUDIO Stereo 40 MkIII Leaflet


SKU ST403-KT88
Shipping Weight 26.0000kg
Shipping Width 0.550m
Shipping Height 0.530m
Shipping Length 0.400m
Shipping Cubic 0.116600m3

1 Year Warranty

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