What makes A.N.T. Audio so very special?

Alex Nikitin who for 9 years worked as Chief Engineer for Creek Audio explains: 

Good sounding circuits can be developed in many different ways. Sometimes a new circuit idea appears, sometimes a fine tuning and a careful selection of components for a well known circuit can produce great results, sometimes a particular device, like the famous 300B valve shapes a whole range of designs.

The Kora 3T phono stage is a combination of rarely used but generally known topology with a particular type of a field-effect transistor (FET). The topology in itself is known from valve electronics and I've used it successfully in many of my previous solid-state designs, with both bipolar transistors and FET's, starting from about 1980. However I was taken by surprise when I tried a particular FET in my phono stage circuit in February of 2008. To my knowledge nobody had used that device in phono stages before, probably not even in audio applications in general - at least I've never met an audio circuit with this particular FET. I did came across a number of these devices by accident, as I bought them for a non-audio application.  One day, after measuring some of their parameters (not listed in the datasheet) I decided to try these in my FET-only phono stage circuit that I was developing.

I did not expect much - my main interest was just to see, if it was at all possible to use these devices in the audio field. When  hooked a crude bread-boarded circuit to my usual vinyl setup, in place of my then current design (which was already considerably better than my previous best and well-respected phono stage I designed for Creek Audio around 1995-1996 - the Creek OBH-8SE.   I was completely unprepared to what happened next - this simple, only 3 FET per channel circuit easily bettered my best previous efforts. Pretty soon I discovered that the circuit can be precisely tuned for the best sound with a particular cartridge by changing a DC operating point of the FETs in a certain range by adjusting a simple rear panel pot.

I then built several prototypes and sent these out to few friends with good vinyl experience. After a while one of them, from the US, asked me, if I could make another version for him, using the best premium components and the best building techniques available to me. I did that for him and his response was that he could not believe the quality of the sound and a musical nature of that small box. In his opinion it sounded better that his previous best choice - a custom modified EAR no less!

The result of this development was the Kora 3T phonostage - produced in two versions the "Special Edition" and the "Limited Edition".  Both share exactly the same electrical circuit, the difference made only by component quality and the selection criteria of the FET's used.  Later in the year, on request from some of my friends and customers I've started the development of the MC version. In September I've met Dave Cawley at Heathrow Show and he did encouraged me to put more effort in the MC design. So by November 2008 the Kora 3T MC was born, both in SE and LE variants. Higher gain required for MC forced me to add one more FET per channel but I've kept the "3T" in the name even thought "4T" might be more appropriate.

I can add few words about the circuit I've used - it is a single-ended class A voltage amplifying stage and an output follower, EQ is passive, there is no global feedback. But these are all technical terms and such techniques are used by many manufacturers. What makes the Kora 3T design unique is a marriage made in heaven - between a particular topology and a particular device, a rare combination of properties resulting in a top quality sound. And sorry, no, I am not going to tell you what device it is. There should be some mysteries in this world.

Hi Fi World July 2009

In a review of six phonostages, the most expensive being £2,000, they said "The first podium position goes to the A.N.T. Kora 3T Ltd.  I loved the sheer musicality of this unassuming little box, it entices the listener into the music in a totally unforced way that's as effortless as it is beguiling."  The review goes on and on.

The even better news?  The wallwart has been banished and we now supply a lovely desk top power supply with all versions.

 

A.N.T. AUDIO KORA 3T Moving Coil

The new Kora 3T MC phono stage is optimised for Moving Coil cartridges with the output from 0.3 mV to 0.6 mV. It shares it's topology and basic features with MM version: single-ended class A, passive RIAA equalisation, local negative feedback (what is called “Zero Negative Feedback” by some manufacturers), low output impedance, excellent stability and frequency response. Two versions of the Kora 3T phono stage are available, sharing exactly the same circuit but different in components quality and price. The table below gives a brief overview of these versions. All units are hand built, thoroughly tested in our workshop near London and carry a 1 year warranty. The “Limited Edition” version is supplied with measurement results for each unit.

Hi Fi World review click here

	“Special Edition” MC	“Limited Edition” MC
Load capacitor	Polystyrene 1%	Polystyrene 1%
RIAA network	Polystyrene 1% capacitors, 1% metal film resistors	Polystyrene 0.5% capacitors, selected resistors
FETs	Matched to <5%	Matched to <3% and selected for lowest noise
DC biasing	User adjustable	User adjustable
RIAA (50Hz-20kHz)	± 0.3dB	± 0.2dB
SNR (A-wtd ref. 1V)	>73 dB	>77 dB
Power Supply	High Performance 24V regulated	Ultra Low Noise 24V
Gain	62dB	62dB
Input impedance	100 ohm  1000pF	100 ohm  1000pF
LED colour	Blue	Blue Green (Emerald)
Availability	Production	Production
PSU supplied	PSU 03	PSU 04 Linear
Retail less sales tax	£430.44	£865.52

 

A.N.T. AUDIO KORA 3T Moving Magnet

The First phono stage from ANT Audio is something very special. Only three field-effect transistors (FETs) are used per channel (hence “3T” in the name), single-ended class A, passive RIAA equalisation, local negative feedback (what is called “Zero Negative Feedback” by some manufacturers), low output impedance, excellent stability and frequency response. All this helps to create sound quality unexpected from a solid state circuit, with either MM or MC (using a suitable transformer for low output types) cartridges. Because the circuit is so simple its performance depends mostly on the quality of the components and the precise tuning of the DC biasing. For that reason there are two versions of the Kora 3T phono stage made available, sharing exactly the same circuit but different in sound quality and price. The table below gives a brief overview of these versions. All units are hand-built, thoroughly tested in our workshop near London and carry a 1year warranty. The “LE” version is supplied with measurement results for each unit.

Hi Fi World review click here

	“Special Edition” MM	“Limited Edition” MM
Load capacitor	Polystyrene 1%	Polystyrene 1%
RIAA network	Polystyrene 1% capacitors, 1% metal film resistors	Polystyrene 0.5% capacitors, selected resistors
FETs	Matched to <5%	Matched to <3% and selected for lowest noise
DC biasing	User adjustable	User adjustable
RIAA (50Hz-20kHz)	± 0.3dB	± 0.2dB
SNR (A-wtd ref. 1V)	>77 dB	>83 dB
Power Supply	High Performance 24V regulated	Ultra Low Noise 24V
LED colour	Amber	Red
Availability	Production	Production
PSU supplied	PSU 03	PSU 04 Linear
Retail less sales tax	£282.61	£673.91

Power supplies

PSU 03 The audiophile switch mode PSU supplied as standard with SE & Classic models.  Unlike a lot of SMPS this unit is built to our specification with extraordinarily low RFI and no EMI at all.  These sort of SMPS's are often used in medical applications.  With an input range of 90 - 253 volts it will work from the low voltage areas of Japan to the high voltages in the UK, and everywhere else in fact!  Avaible separately to upgrade other manufactures equipment. Retail less sales tax £65.22	PSU 04 Supplied as standard with all Ltd. models this fully fledged linear power supply has virtually no RFI or EMI.  It has been designed with the best available components:  Panasonic FC low ESR capacitors, National Semiconductor LM317HVT regulator in low noise configuration, schottky rectifiers and a 2 ounce plated through printed circuit board.  The PCB is hand made near Cambridge in the UK.  Avaible separately to upgrade other manufactures and our SE and Classic units. Retail less sales tax  £160.87	This interior photograph of our 04 Ltd. linear power supply shows the Panasonic FC capacitors.  One way to get a very low output impedance is to use a large storage capacitor and  that is exactly what we do as you can see. There are two versions:  90-126V for 100/110/120 volt and 216-253V for 220/230/240 volt power.

David Price editor of Hi Fi World said of the Ltd. linear PSU " It's gorgeous.  Changes the sound surprisingly much actually. Makes it ..  more explicit.   Big difference through my system."

 

UK Dealers (more UK dealers wanted, call us?)
• Sound Hi Fi, PO Box 2001, Dartmouth, Devon, TQ6 9QN, Great Britain
Telephone 01803 833366 Fax 01803 839498 web site www.SoundHiFi.com

• Emporium Hi Fi,  The Old Tannery Bridge,  St Bungay,  Suffolk NR35 1HD tel 01986 895929  web site click here
 

German Distributor
• AMSHifi GmbH, Wallstadterstrasse 59, 68526 Ladenburg, Germany
web site info@amshifi.de Telefon: 06203 - 402 888 Fax: 06203 - 957 956

German Dealers
• Best of British Hifi Volker Dahmen, Letzenbergstrasse 24; 69231 Rauenberg - Malschenberg; Tel.:07253-279683; Fax:07253-279684; Handy:0174-3158745; Email: info@best-of-british-hifi.de  web site www.best-of-british-hifi.de
• KlangArt, Reinhold-T. Trottmann e. K. Preysingstraße 37, 94447 Plattling,  Telefon 09931 3087

Finland
• Highend Studio Finland Oy, Fredrikinkatu 27, 00120 Helsinki, tel +358-(0)9-4553 685 , fax +358-(0)9-4553 785  web site www.highendstudio.fi