iFi audio iCAN Pro - Q&A !!!!!!!!

[AMR/iFi audio]

Hi there,

 

On the iCAN Pro dedicated Head-fi.org thread, some technical questions were asked. Lots of them in fact and that's something we couldn't ignore. No Sir! We've put a fair amount of time to give a properly technical and informative answers. We thought that these are worth sharing here as well.

 

Therefore without further ado and to your pleasure, these are said questions, with links to our replies:

1.)

I noticed your specs seem to reference "short duration" peak power rather than continuous power. What is the actual normal use power rating? For 200ohm headphones? Is it adapting (such as by impedance matching), based on the headphone connected?

 

Our answer to Q1 is

here

.

 

 

 

2.)

Many higher end headphone amps have a lower output impedance, often 3, or even less than 1. The IC pro has a much higher one. what is the reason/benefit of this design? As a result, should only headphones of a specific ohm rating be used? How about for optimal performance?

 

Our answer to Q2 is

here

.

 

 

 

3.)

The detailed specs do not discuss use of an output transformer. Is this a unique design? it would great to understand the innovation. Is it something similar to the Chord Mojo's gain stage (conceptually)?

 

Our answer to Q3 is

here

and

here

.

 

 

 

4.)

What is the impact of using a non balanced source? Do you still get the benefit of balanced output, or does half the circuit (including the corresponding power) go unused as is the case with some other amps? Currently, my favorite DAC is the Chord Mojo.

 

 

Our answer to Q4 is

here

.

 

 

 

5.)

Most other amps seem to require lots of power and use a giant desktop PC style power cord, perhaps to have a heavy enough gauge and shielding in order to avoid noise and interference. What is the technology that enables the pro to avoid these issues/requirements and use a small cord and wallwart (a great thing by the way)?

 

Our answer to Q5 is

here

.

 

 

 

6.) I noticed you spec JFets rather than the more commonly used Mosfets. What is the difference?

 

Our answer to Q6 is

here

.

 

 

 

7.) the description references that 3d sound and xbass are implemented in an analog manner. When these are switched off, are the related sections of the amp circuit physically bypassed, or is there some processing taking place all of the time?

 

 

Our answer to Q7 is

here

.

 

 

8.) Do you have frequency response charts? The lower registers are very important to me and I am curious as to performance in that area.

 

 

Our answer to Q8 is

here

.

 

 

9.) Your advertising materials highlight that ifi products leverage technology from the higher end AMR line of products. In the case of the ican pro amp, what are some of the technology that has trickled down?

 

 

Our answer to Q9 is

here

.

 

 

10.) Many amplifiers, including headphone amps, are really heavy. Presumably because parts, like transformers and heat sinks, are necessary for great sound. However, technology (and corresponding miniaturization) marches on. What technologies are responsible for your ability to keep the size and weight so low?

 

 

Our answer to Q10 is

here

.

 

 

 

11.) Do you consider the ifi ican pro to be in the same tier as the Audeze King? In other words, what segment of the personal audio market is the pro directed to? Performance is relative, and it would be interesting to understand against whom you benchmark.

 

 

Our answer to Q11 is

here

.

 

 

12.) Were the published specs based on tube, tube plus, or solid state mode? Assuming only one of these, how do the specs change for the other modes?

 

 

 

Our answer to Q11 is

here

.

 

 

 

 

 

 

---------------------------------------------------------------------------------------

 

And, of course, if you have ANY questions regarding our iCAN Pro, please don't hesitate and post them here!

[YashN]

These Head-Fiers sure ask a lot of pointed questions, but the answers make for great reading.

[AMR/iFi audio]

These Head-Fiers sure ask a lot of pointed questions, but the answers make for great reading.

 

Yes, they do

 

But in a while we'll publish our HF answers here as well.

[YashN]

Yes, they do

 

But in a while we'll publish our HF answers here as well.

 

Great!

[AMR/iFi audio]

Q#1A: I noticed your specs seem to reference 'short duration' peak power rather than continuous power.

 

Music has a relatively high so-called ‘crest factor’ or ratio between peaks and average power, usually 10:1 – meaning for music mainly looking at the ‘peak power’ is somewhat relevant. Sine-waves as used for equipment objective testing have a peak to average ratio of 1.414:1, meaning they stress equipment greatly and may create overheating.

 

Comparison of Sinewave & Music Crest Factor

 

 

The iCAN Pro omits any protection circuitry that is directly connected to the audio path, as this often causes sonic degradation. To avoid a risk of blowing out the output stage in case of overload (which may occur with sinewave testing) we have integrated current limiting circuitry into the power supply.

 

This circuitry allows short term unrestricted peaks, but will progressively limit available current to protect the device based on temperature and clipping of the amplifier, all the way to an eventual complete shut-down of the iCAN Pro if overload is sustained, to avoid damage to either iCAN Pro or headphone.

 

Q#1B: What is the actual normal use power rating? For 200ohm headphones? Is it adapting (such as by impedance matching), based on the headphone connected?

 

Power = Voltage X Current.

 

Voltage directly proportional to the input signal is what almost all amplifiers deliver (exceptions exist), current flowing is determined by the load.

 

Even if the amplifier is unconventional (e.g. current output types), the actual power is always dependent on the load (Headphone/Speaker) impedance. This applies to any amplifier of the ‘voltage output’ and ‘current output’ type.

 

In theory it would be possible to design an amplifier that delivers constant output power regardless of load impedance, but there is at this point in time no known headphone that would actually show any benefit from such a design.

 

Too low or too high load impedance both result in max output power allowed with that particular load lower than the absolute max capable by that amplifier.

 

For the iCAN Pro the power supply voltages to output stages limit the output voltage to 11.5V for single ended headphones and 23V for balanced headphones. The long term current limit for the iCAN Pro is around 1A peak per channel, which means with sinewave testing around 700mA is available, which in case of the balanced connection is shared between the signal phases.

 

Short term current can be much higher, the absolute maximum is certainly more than 7000mA for several milliseconds; it is not the easiest number to measure.

 

All this means the maximum long term sustained power with sinewaves with balanced connections will be 8,000mW into a 64 Ohm load and for single-ended connections it will be the same 8,000mW with a 16 ohm load for maximum power.

 

For short term peaks the main limitation is the length of the peak, we test with music that has relatively long, high level peaks at clipping to determine the equivalent sine-wave power.

 

For lower load impedances than those stated above the power will be limited by available current, for higher impedances it will be limited by available voltage. It should be noted that this behaviour is not unique to the iCAN Pro but applies actually to each and any amplifier under the sun.

 

Finally, if using 200 ohm headphones the power is limited by available voltage only (again, this happens with all amplifiers) so you would get around 660mW with a single-ended connection and around 2,640mW for balanced connection.

 

As most headphones tend to deliver > 100dB/mW SPL these power levels are insanely high, basically like driving a high-sensitivity horn speaker like AvantGarde with amplifiers having a kilowatt or more power!

 

If the 200 ohm headphone was 100dB/mW the single-ended connection would produce 128dB at full power and the balanced connection would produce 134dB at full power. These are extremely high SPLs and permanent hearing damage is a real danger at SPL levels this high.

 

Very few headphones will ever require even a small fraction of the power available from the iCAN Pro, having such large extra reserves allows it however to for example drive very inefficient headphones such as HiFiman HE-6 or AKG K-1000 with authority.

 

Carpe diem with these hungry headphones

[AMR/iFi audio]

Q#2: Many higher end headphone amps have a lower output impedance, often 3, or even less than 1. The IC pro has a much higher one. what is the reason/benefit of this design? As a result, should only headphones of a specific ohm rating be used? How about for optimal performance?

 

The iCAN Pro has relatively low output impedance. So we're not sure where you get the impression the output impedance is high?

Unmatched impedances provide the best amplifier and speaker performance.

 

 

The precise value depends on the connection (balanced connection has double the impedance of single-ended and the 3.5mm connections include a network to match high sensitivity IEM's, but the maximum output impedance for any connection is around 4 ohms balanced or 2 ohms unbalanced.

[AMR/iFi audio]

Q#3A: The detailed specs do not discuss use of an output transformer.

Output transformers are mainly used with tube amplifiers. They require great care in design and manufacturing to avoid adding distortion and frequency response limitations. Where they are essential, they must be used and designing good ones is no small task.

Impedance matching transformer matches 5000 Ω amplifier to 8 Ω speaker for maximum efficiency.

The Retro Stereo 50 Amplifier uses a full classic EL-84 tube amplifier and hence an output transformer is required. No off-the shelf item offered adequate performance, regardless of price, so we developed our own. In the end, we went through 20 prototypes before we had an output transformer that delivered the combination of objective measured performance we required and the quality of subjective performance listening to music we desired.

 

 

Q#3B: Is this a unique design? it would great to understand the innovation. Is it something similar to the XXXXX gain stage (conceptually)?

 

The circuitry in the iCAN Pro is quite unique. It is not a cookie cutter, cut & paste from some textbook or a manufacturer’s design note. With the greatest respect to others, conceptually it has no parallels – except in classic professional studio equipment using tubes, like for example from the legendary R.E.D.D.37 & 51 tube recording consoles.

REDD.51 tube recording console, Studio Two/Abbey Road

However, the circuitry is not a mere rehash of the best classic British or German studio gear either.

All tube circuits have their own challenges, so we use the tube where it makes the greatest difference, in the first stage, though it may be switched out for a J-Fet instead for a completely solid-state circuit path.

The tube or J-Fet is followed by a second fully discrete gain stage using a combination of bipolar transistors and mosfet selected and operated to achieve very specific goals in terms of linearity, gain etc.

 

The result is a circuit that very much behaves like a modernised, transformer-less and direct-coupled version of classic recording gear. So much of the common sonic colouration traits found elsewhere from coupling capacitors and transformers do not exist in the Pro iCAN.

[AMR/iFi audio]

Q#4: What is the impact of using a non-balanced source? Do you still get the benefit of balanced output, or does half the circuit (including the corresponding power) go unused as is the case with some other amps?

 

If an unbalanced source is used, the iCAN Pro includes a circuit that creates an inverted replica of the signal so after this circuit the signal has been transformed to balanced signal. This uses a very minimalist non-feedback circuit composed out of J-Fets and Bipolar transistors. After this circuit the signal is amplified fully-balanced.

 

iCAN Pro signal path

If the headphone uses unbalanced wiring, the circuit actually has no additional stages, that is the single-ended signal is used as the positive half of the balanced circuit but also forms in effect the single-ended signal path.

 

In order to take advantage of the balanced circuit, headphones require balanced wiring. In this case and with a true balanced source (such as the upcoming iDSD Pro) the signal remains fully balanced from the DAC Chip to the headphone with no added unnecessary stages. Only for a single-ended signal does the circuit create a balanced signal from a single-ended input by adding an inverted polarity signal path.

[AMR/iFi audio]

Q#5: Most other amps seem to require lots of power and use a giant desktop PC style power cord, perhaps to have a heavy enough gauge and shielding in order to avoid noise and interference. What is the technology that enables the pro to avoid these issues/requirements and use a small cord and wallwart (a great thing by the way)?

 

Small correction, the iCAN Pro does not use a ‘wall-wart,’ but a 15V/3.5A (52.5W) external power ‘brick’ instead and it can actually be powered with any DC voltage from 9V to a maximum of 16V (18V will activate protection circuitry).

 

Internally the iCAN Pro uses latest high frequency mosfet technology to power the system. The incoming voltage uses a 1.2MHz converter to create a low voltage DC bus that can provide up to 44 Watt power. A separate 1.2MHz converter creates the 6V needed to heat the Tubes.

This DC Bus voltage supplies a bank of further converters also operating at 1.2MHz that produce the high voltage for the tube (or solid-state) circuit which operates from 60V. More converters produce the power supplies for the power output stage at +/-16V. All output voltages are then filtered with multiple inductor/capacitor filters to remove any noise.

 

Separate supplies exist for left & right channels, so a total of six converters produce the actual audio power supply voltages.

The iCAN Pro Power Supply Section.

By operating at 1.2MHz instead of 50/60Hz, in the power supply we can use radically smaller size parts. As the operation is literally 20,000 times faster, only 1/20,000th of the size of traditional power supplies is needed for identical performance. These high frequencies can represent challenges, we have taken great care in the mechanical and electronic design to address these challenges.

As you can see, with the greatest respect, AMR/iFi is different compared to most. As we have digital, analogue, signal and power technology ‘pillars.’ What looks small and unassuming on the outside beneath is a wealth of hi-tech. We also ask our customers to look inside and learn for themselves to arrive at their own conclusions. Rest assured, our gear is ground-up and is far from ‘run of the mill.’

[AMR/iFi audio]

Q#6: I noticed you spec JFets rather than the more commonly used Mosfets. What is the difference?

As for tube vs. J-Fet vs. mosfet vs. bipolar transistor, these are all different amplification devices. They have all different parameters and all are subject to limitations and have undesirable traits. No device is ideal for all applications or uses. One of the key skills of a good design is to select the right device for the right application.

A Short History of Amplification Euphoria

1. The tube

Of these four active devices we have available, the tube is the oldest and is now over a century old.

Lee de Forest, the father of the radio, invented the ‘Audion’ tube – the first electronic amplifier device in 1906

Among the very desirable traits of tubes are a very high input impedance, a high level of inherent linearity for a given gain, the fact that the tube is a depletion device (it produces the highest current it can with 0V between input and common terminal) which allows simpler circuits and the fact that all parasitic (unwanted) effect are essentially constant with signal level and frequency.

 

The downside is relatively low absolute gain, a high internal impedance combined with a low current capacity and the need for very high voltages to operate, as well as the need to provide extra power to heat up the cathode to a dull red glow temperature. As a result, tube equipment has mostly disappeared from common use, yet especially for input stages they are often still without equal.

 

The iCAN Pro uses genuine USA made General Electric New Old Stock Tubes

2. The J-Fet

Perhaps surprisingly the J-Fet is the second oldest amplification device and the first solid-state amplification device. It was patented in 1926 by Julius Lilienfeld and he put a working theory of operation in place by the mid-1930’s.

The 1926 J-Fet Patent

 

While not actually a tube, interestingly, the J-Fet shares many traits with it.

It has a very high input impedance, a moderate level of inherent linearity for a given gain, the fact that the J-Fet is a depletion device (it produces the highest current it can with 0V between input and common terminal) which allows simpler circuits and the fact that if enough voltage is applied all parasitic (unwanted) effect are essentially constant with signal level and frequency.

 

The downside is merely moderate gain, a high internal impedance combined with a low current capacity and the need for relatively high voltages to operate. Like tubes, J-Fets are often used in Input stages and while they do not equal tubes, if applied correctly they can come quite close. Compared to generic transistors (Bipolar and Mosfet) J-Fets are difficult to make, have a process that is variable and requires selection and cost is around 100 times that of Mosfets and Bipolar Transistors.

3. The Bipolar Junction Transistor

In 1948 William Shockley invented the Bipolar Junction Transistor which rapidly became the device of choice for modern electronics and for three decades remained the device of choice in the design of discrete and integrated circuits.

Electronics rapidly became miniaturised and energy efficient. Instead of the huge, hot running wooden tube radios there were battery powered pocket radios that could drive headphones and could be certainly carried everywhere. Portable audio became possible with the bipolar transistor. Nowadays, the use of the BJT has declined in favour of MOS(fet) technology in the design of most circuits and IC's.

 

Replica of the first functional bipolar transistor from 1947

Compared to tube and J-Fet, the Bipolar Transistor was a radical departure and practical electronics had to be nearly re-invented to suit it. The bipolar transistor is actually a current driven device, meaning it has a low input impedance and it is an enhancement device (meaning it passes no current with 0V between input and common terminal, requiring more complex circuitry. Parasitic effects are wide and varied and all are highly signal level and frequency dependent and linearity is quite poor.

However bipolar transistors can handle much higher currents than Tubes or J-Fets, work well with very low voltages, are easy to manufacture with good consistency and at very low cost, so they displaced tubes and J-Fets could barely carve out a niche where bipolar transistors could just not work well.

4. The Mosfet

The newest amplification device is the Metal Oxide Semiconductor Field Effect Transistor a.k.a. Mosfet. Invented in 1960 it was meant to displace the bipolar transistor by giving a device that worked much like a bipolar transistor but with high input impedance.

The 1963 Mosfet Patent

Problems in manufacturing initially caused higher cost and it was a long time before Mosfets became viable alternatives as linear (audio etc.) amplifiers to the J-Fet and Bipolar transistor. It was however discovered that Mosfets could be made very small and that they made good switches, which drove the revolution in digital integrated circuits and in the end led to modern computers which use chips that combine literally millions of tiny, tiny Mosfets to form the logic.

As a linear amplifier the Mosfet does less well, even in the 21^st century, very few types are particularly suitable for the job. Operated at low voltages, the Mosfet has high input resistance but very high and signal variable input capacitance which causes a very specific type frequency dependent distortion that rises with frequency a lot more than bipolar transistors. Linearity is also quite poor, but the more modern types have huge levels of gain allowing very large amounts of negative feedback to be used to overcome the non-linearity.

There you have it, a brief rundown of each amplification device and the pros and cons – as you can gather, in the end no device is perfect and using the right device for the right job in the right circuit can give an excellent outcome. Get it wrong and the results are dire!

[AMR/iFi audio]

Q#7: The description references that 3D sound and XBass are implemented in an analog manner. When these are switched off, are the related sections of the amp circuit physically bypassed, or is there some processing taking place all of the time?

There are no ‘additional sections’ in the circuit insofar that there no additional stages used.

All functions are realised using passive components; resistors (Vishay MELF), capacitors (TDK C0G Types) and custom made audio inductors. If the function is disabled, these components are completely switched out of the circuit.

Q#8: Do you have frequency response charts? The lower registers are very important to me and I am curious as to performance in that area.

 

The iCAN Pro is direct-coupled and uses modified DC Servo technology to eliminate any DC offset that has extremely low gain for audio signals and even subsonic signals. As a result, the low frequency response is in effect flat to near DC, the -3dB low frequency response should be at 0.25Hz by design, however our AP2 only measured reliably down to 10Hz, where it shows a perfectly flat line.

 

As we cannot measure reliably at frequencies as low as 0.25Hz we have rated the iCAN Pro conservatively as having a -3dB point of 0.5Hz for low frequencies, at high frequencies the -3dB point is above 500kHz. In the 20Hz – 20Khz the frequency response is basically a pure flat line.

 

You can find some measurements in this review, however they merely illustrate the limitations of the test system used, which is notably inferior to either AP2 or the capabilities of the iCAN Pro:

 

“[PMR Reviews] iFi Pro iCAN” - thatonenoob’s Review of iFi Pro iCAN

[AMR/iFi audio]

Today we have a story for you all. It's about 'em tubes. Yes, again. But please bare with us, this tale really is special. You'll see soon enough...

 

 

The (5670) electron valve. It matters. - Part 1/3

 

Every audio aficionado likes 'em Electron Valves and for a number of reasons. The two most obvious ones are their influence on the sound itself and highly appealing aesthetics. Some of you might dislike the look of glowing glass and since this matter is highly subjective one, we won't focus on it. The rest though, well, that's a completely different story.

 

Our latest headphone amplifier - the Pro iCan - is loaded with a pair of GE5670 JAN double triodes. OK, there's a ton of valves out there. Therefore this question is in order: why we use this one specific type from this specific manufacturer? Now that's a story to be told. Here we go then.

 

 

Behold the WE396A double triode by Western Electric. These small critters were introduced in 1946 and shortly replaced by their 6922 variants. The former is the pinnacle, almost unfindable these days. The scenario isn't that grimm when it comes to the latter type. But as it turned out, there is one sonically as good model and made to very strict specifications - the GE JAN 5670 NOS type. It was under the radar of the audiophiles' scope for many years.

 

 

GE stands for General Electric manufacturer, which is self-explanatory. Said company was responsible for Electron Valves production for decades and is well-known for the quality of its products.

Moving on, JAN is the service branch of the US Armed forces and said three letters stand for Joint Army & Navy. Electron Valves marked as JAN were made for the Army/Navy (the airforce had to have their own naturally) and had to pass the most rigorous testing procedures at that time.

 

The Russian parallel system was OTK, which means "Отдел технического контроля" or technical control department. Even the Russian system was very decent as one does not wish for Mach 3 Jet Fighters at 100 million ruble a pop to be falling out of the sky on account of poor Electron Valves. This translated into modern money would be ~350 Million USD - the same as the F-22 Raptor today! And yes, it used Electron Valves for a lot of critical electronics.

 

It packed a targeting Radar so powerful it was a crime to even turn it on except in combat or exercise. It would kill small mammals at several 100 feet (microwaved to death).

 

 

Side Note: The Mig-25 Foxbat (a Mach 3+ jetfighter that scared the poop out the USAF at the time and inspired the Clint Eastwood film, ‘Firefox’ was no cheap junk (even if it was not as rad as the Firefox).

 

 

Germany/Europe never had an equivalent system, they got either JAN electron valves with US equipment (including export versions) or German Postal electron valves (CCa, C3g, D3a etc.) made in...Germany.

 

The British Empire had (surprisingly) its own inter-service system for military electron valves, it came into force in 1941. The British generally used civilian electron valves (and later transistors) that were tested and certified for military use. British Military electron valves are identified by the letters CV (Common Valve) and a number.

 

Generally JAN/OTK marked electron valves are more rugged, have very tight technical parameters and much less variation, yet are at the same time compatible with civilian types. German/European Postal electron valves in general were dedicated designs with the singular exception of the Cca and equally ruggedised. British and Chinese used selected (or not) civilian electron valves for military applications.

 

 

Stay tuned, there's more...

[AMR/iFi audio]

The (5670) electron valve. It matters. - Part 2/3

 

In many ways the 5670 when introduced was a revolutionary electron valve. Ostensibly an RF device for VHF use, thanks to a usable frequency range to 800MHz it also offered good linearity, low harmonic distortion and low-noise in audio applications. Yet the 5670 electron valves never really went into audio gear much. Why?

 

First, being a relatively expensive electron valve to make made them less attractive for mass production.

 

Second, they saw wide military equipment use, including fire control computers and communication systems.

 

 

So before the late 80's the US Military & Nato stockpiled most of the production. Production of the 5670 ended in the 1980’s almost completely, so stockpiles were retained until the equipment they supported was removed from inventory in the latter part of the 90’s.

Third, and in addition, the 5670 uses a non-standard pinout. If one looks at 12AX7, 12AU7 or 6DJ8/6922, all of these have an identical or very similar pinout. The 5670 pinout is radically different. Electrically and in terms of internal design it is very similar to the 6DJ8/6922 which became very popular in American high end audio gear, but one can't plug it into a 6922 socket.

 

 

Well, physically it's doable, mechanically the 5670 will plug into a 6922 socket, yet the result may be deadly for the Preamplifier/Amplifier as heater and anode pins are mixed up, shorting out the high voltage power supply. Just don’t go there girlfriend.

Now let's add the price factor to the mix. Military parts always cost at least 10 more in comparison to identical civilian parts. Which for 5670 model meant that no-one designed audio gear with these electron valves during the golden age of Valve Audio.

 

After the military blew out these stocks from their warehouses when the cold war ended (those cavernous places like the one shown at the end in Indiana Jones "Raiders of the Lost Ark")...

 

...still very few people used them, as they couldn't be plugged into existing gear due to the non-standard pin-out. Long story short, NOS 6922 became very popular and their rare cousins worth 100's of Dollars while no-one wanted the 5670.

 

 

For the last 25 years plus dealers and audiophiles have been depleting very limited 6922 NOS stocks and that's why today it is next to impossible to find decent electron valves of this sort. And what about the unloved but excellent 5670? It sat nice and snug in warehouses like the proverbial Ark of the Covenant waiting for someone to discover it. That would be first of all Eric Barbour of Vacuum Tube Valley Magazine (but his article was also widely ignored) and then us.

 

 

 

Stay tuned, there's more...

[AMR/iFi audio]

The (5670) electron valve. It matters. - Part 3/3

 

With new old stock 6922 and equivalent disappearing and getting more and more expensive, what happened to the unloved but excellent 5670?

 

5670 valves became somewhat popular when Shanling made CD-players and electron valve amps years back which used the Chinese 6N3, a Chinese copy of the soviet 6N3P (often incorrectly written as 6H3PI) which was the Soviet version of the 5670. As few people knew about the possibility to swap the 5670 for a 6N3 the good stuff mostly remained in storage.

 

Needless to say, now the 5670 cat is out of the bag as a workable NOS 6922 substitute, AMR/iFi Audio have bunkered the content of one of these military warehouses for future use. With either the correct socket wiring (which our Pro iCAN sports) or an adapter (like used for our NOS 6922 replacement) they will be hunted to extinction within a few years by all the ‘electron valve hounds’ of audiophilia... Grab 'em while you can.

 

 

So there you have it, GE JAN 5670 NOS is a marvelous piece of glass built to last (100,000 hours’ of lifespan are easily possible if the electron valve is operated conservatively), with marvelous sound quality. The very best among what's currently available for the money. Yes, you can go even higher. But it's not only just an expensive journey to be had; the money is the smallest issue actually.

 

The main problem is in availability and origin of the various Western Electric & Bendix 6N3 equivalents. Yes, counterfeits are out there, you've been warned.

 

Glass going on record

 

_____________________

 

Makers of 5670/2C51/ECC40 on record:

 

(we are not going to do a sonic ranking between the valves in each category - waaay too subjective).

 

Best

 

 

• WE USA (as 396A) (there are D and O getter versions) - probably the best of the lot but good luck in finding original 'good' ones from reputable sellers for £££
  
• Bendix USA (as 6385) - very rare and hyper expensive·
  
• GE 5670 USA - as used in AMR CD 777 SE/DP-777SE & iFi Pro Series/Tube2/iTube
  

 

Middle

 

 

• Raytheon USA
  
• Tung Sol USA
  
  
• Old Soviet 6N3P-EV OTK marked Stock
  

 

Worst

 

 

• Soviet Russia 6N3P civilian type (marked in Cyrillic so looks like 6H3П)
  
  
• China (as 6N3)
  

 

 

The 5670/2C51 has similar data and application as the later European ECC88 and variants, so European valve makers concentrated on that type of valve.

 

 

Some valves marked "England" have been sighted, these appear mostly remarked Russian units.

 

 

Sylvania also made a 5670 which was also seen remarked as ‘Mullard’ but it isn't a true Mullard as they never made this version of valve, just a rebranding job.

 

 

To conclude, with the AMR CD/DP-777 SE or iFi iCAN Pro/iTube/iTube2/NOS 6922, we would not spend our hard earned cash on anything but the WE396A or Bendix USA.

 

_____________________

 

Note 1 - some background, the 5670/2C51 from a technological point of view, the "premium version" of the 6922electron valve. Better design, strong plates, lower microphonics etc etc...

 

So if you have the 6922, you can roll the valves in your non-iFi device and get better sonics but with the 5670/2C51 family using adapters, you are already running with the big guns.

 

Note 2 - the 5670 and 6922 have the same physical pins but are not directly interchangeable as they different fundamental designs.

 

The AMR CD/DP-777 SE use 6922 Pinout and adapters to convert the 5670 to 6922 pinout, so both 6922 and 5670 with adapter can be used. The iFi iCAN Pro/iTube/iTube2 have the sockets wired only for 5670, you cannot insert a 6922.

 

 

Moving on, one might think that if magnificent 5670electron valves as we use in our product are quite available, then something's off. But that's not the case. As we've said above, this electron valve has ‘flown’ under the radar for many years, 6922 and alike were much more popular. Yet popularity isn't an indication of what's good.

 

From a purely technical side, GE JAN 5670 NOS valves are the best ones we could find in large batches enough to be commercial.

 

1. Excellent consistency of electron valves between batches
   
2. Glass is thicker than usual,
   
3. Controlled warm-up
   
4. Tight specifications on grid current,
   
5. Low noise and microphonics and exceptional longevity
   

 

And since genuine military grade New Old Stock 5670electron valves are reasonably well available (unlike many desirable electron valves), it'd be a shame not to exploit their potential. Hence we exploit as much as we can, fully aware of what GE JAN 5670 NOS performs and sounds like.

 

 

At iFi Audio we always strive to find the best parts for tasks given. This is not lip service – we ruddy well mean it!

 

We experiment with lots of components from a number of manufacturers, measure, audition and once extensive research is gathered, we cherry-pick. If every component’s related decision would be as simple as it was with GE JAN 5670 NOS, our engineering lives would be much easier and we’d spend a lot more time in the pub!

 

In conclusion, this electron valve has an incredible price-to-performance ratio, it honestly doesn't get much better than this. We've been there, we've done that – we’ve got the t-shirt and the blinking key ring.

 

You're of course free to experiment with our Pro iCAN past warranty period. But it's highly unlikely that you'll find anything better for sane money. Please trust us on this one; our Skin, she does not joke around when it comes to sound quality.

 

[christopher3393]

Another positive iFi Pro iCan review: http://www.innerfidelity.com/content/ifi-pro-ican-mixed-tube-and-solid-state-headphone-amplifier#CwvMJFVuVbC8H6WO.97

[AMR/iFi audio]

Do you guys enjoy the music? We surely do and so does Dwayne Carter with out Pro iCAN! Here's the story:

 

http://www.enjoythemusic.com/magazine/equipment/0217/iFi_Audio_Pro_iCAN _Professional_Headphone_Amplifier_Linestage_Review.htm

 

Fabulous review!

[AMR/iFi audio]

GE5670 reserved for flagship AMR and iFi

Press release

 

We have some mixed news for lovers of the GE5670.

 

It is our understanding that we have tracked down and acquired the last known large-scale stockpile of GE5670 tubes.

 

 

 

The good news is that we have amassed a respectable inventory for AMR to use in their machines and for iFi to use in their flagship ‘Pro’ series for the foreseeable future (read: years).

 

The bad news is that once units in the supply chain of iTUBE2s and NOS6922s are all gone, there will be no more. The recent rise in the price of the GE5670 makes it even more the right decision to not continue with using the GE5670 in this product. Given that we need to reserve 2 pcs of the GE5670 for each Pro iDSD and Pro iCAN and for the AMR 777 machines too, priority must be given to these flagship products.

 

History of the venerable GE5670

 

For those wishing to delve into the history of the GE5670 and why we chose it over its ‘lesser’ cousin the 6922:

 

https://ifi-audio.com/portfolio-view/accessory-nos-6922-2/