Pro iESL User Manual
Thank you for purchasing this Pro series iESL. The Pro iESL is an audiophile-grade 'energiser' for electrostatic headphones. It can also be used to match dynamic headphones to powerful loudspeaker ampli ers. While designed to match the iFi Pro iCAN, the Pro iESL can be used equally well with sufficiently powerful headphone ampli ers and also loudspeaker ampli ers via dedicated separate inputs. Note: The Pro iESL is not a headphone amplifier.
1 3 2 5 4 6 8 7 Input iCAN Pro OFF Impedance Electrostatic Balanced Dynamic Normal Speaker Normal Pro OFF 64Ω Custom/Pro 580V Pro + Normal 540V 1. 2. 3. 4. 5. 2 LED Input Selector AC Termination Adjustment Normal Bias Electrostatic Headphone Socket Dynamic Headphone Socket iESL 24Ω 16Ω 620V 500V AC Termination 96Ω 600V 640V Bias P.4 P.4 P.4 P.5 P.5 6. Pro and Custom Bias Electrostatic Headphone Socket 7. Custom Bias Adjustment (500V – 640V) 8.
9 10 11 12 13 Balanced Input DC 5-9V/0.5A R In L Loudspeakers Out R L ESL - link Pro Technology licensed from AMR-Audio, UK Assembled in China 9. Loudspeaker Inputs 10. Loudspeaker Outputs 11. Balanced Signal Input P.6 P.7 P.7 12. DC Power Supply Connection 13. ESL-Link ifi-audio.com P.7 P.
1. LED Green: power on (either via DC power supply or ESL-Link) Tip: There are 2-ways to power the iESL, see ESL-Link and DC power supply sections. 2. Input Selector Off iESL is off. Pro iCAN Pro iCAN via ESL Link. On this setting, the iESL will turn on/off with the iCAN Pro. Headphone Ampli er via rear XLR input loudspeaker Balanced Loudspeaker Ampli er via rear loudspeaker inputs On this setting, the Loudspeaker Output will turn off. 3.
4. Normal Bias Electrostatic headphone socket 6-pin socket for older Stax Headphones, 230V Bias Voltage 5. Balanced Dynamic headphone socket 4-pin XLR socket for dynamic headphones, including AKG K-1000 and any compatible wired headphone, including Audeze. 6. Pro/Custom Bias Electrostatic headphone socket 5-pin socket for modern Stax headphones, 500V to 640V adjustable Bias Voltage 7.
640V (Custom) Future option 8. Impedance Adjustment The impedance response can be adjusted from 16Ω to 96Ω. This impedance describes the load impedance for the driving amp with a "standard" electrostatic headphone connected. Lower impedance settings create a greater step-up and will produce a louder sound level at the same headphone ampli er volume setting. Lower impedance settings are a much more difficult load for the driving ampli er.
10. Loudspeaker Outputs Connect loudspeaker cables to your loudspeakers. Switching the input selector to loudspeaker turns off the loudspeakers and connects the iESL circuitry to the loudspeaker ampli er. Tip: While the iESL Input selector is OFF, or any input except loudspeaker is selected, the loudspeaker input is linked to the loudspeaker output and disconnected from the iESL circuitry. 11. Balanced Headphone Ampli er Input Connect this to any 4-Pin XLR equipped headphone ampli er you wish to use.
DO NOT CONNECT ANY OTHER EQUIPMENT! This is only reserved for the iFi Pro iCAN headphone ampli er using the supplied cable! Speci cations: Ÿ Maximum Output voltage: 640V RMS (16Ω/20V in) Ÿ 320V RMS (64Ω/20V in) Ÿ Frequency Response: 5Hz – 50kHz (-3dB) Ÿ Input Voltage (Pro iESL): 5V – 9V/1A max Ÿ Input Voltage (iPower): AC 85 – 265V, 50/60Hz Ÿ Power Consumption: < 1W 213(l) x 206(w) x 63.3(h) mm Ÿ Dimensions: 2.5kg (5.
Notes on Electrostatic Headphones Electrostatic headphones require very high voltages for operation. For example, Stax are around 101dB @ 100V, compared to around 105dB @ 1V for a common inefficient full size headphone. On top of that, they need a 'bias voltage,' usually 580V for modern Stax.
Depending on the impedance control setting the Pro iCAN and Pro iESL combo can deliver between 320V RMS (910V PP) to 640V RMS (1820V PP). These are very high voltage levels and may exceed the rated limit of the electrostatic headphones. Please con rm with your electrostatic headphone manufacturer what levels are allowed and, if in any doubt, only use the high impedance settings. When using the iESL with Pro iCAN, remember to keep the Gain, XBass and 3D Sound settings moderate.
Given the high voltages involved even trivial jobs like circuit board design become challenging as we must avoid any chance of these high voltages to get out of control. Therefore great amounts of spacing between voltage carrying traces and pins are needed, making a simple circuit board layout suddenly very challenging.
The Bias System - Capacitive Battery Power Supply Commonly the bias voltage is created using the 50/60Hz mains power and a so-called Villard or Greinacher cascade recti er (which is also sometimes called a Cockcroft-Walton voltage multiplier) is employed. This circuit can deliver very high voltages using rather generic and inexpensive components, but its operation is noisy.
completely separate and independent bias circuits are employed, one for the 230V “normal” bias and another adjustable, to cover a wide range of modern electrostatic headphones. The Signal Routing The entire signal switching for the input selection utilises gold-plated silver contact miniature relays lled with an inert gas. This makes sure the contacts will remain like new for a long time to come.
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May 2017 Pro iESL Tech Notes An Exacting Energiser Part one. A little background The Pro series iESL is the best way of driving electrostatic headphones. We are confident that the iESL Pro driven by either the iCAN Pro or your existing amplifier can go toe-to-toe with the best amplifiers out there for electrostatic headphones. Its defining characteristic is a transparency and an ultra-wide dynamic range that is totally natural.
Tech Notes Pro iESL ELECTROSTATIC DRIVERS CONSIST OF A THIN, ELECTRICALLY CHARGED DIAPHRAGM, TYPICALLY A COATED PET FILM MEMBRANE, SUSPENDED BETWEEN TWO PERFORATED METAL PLATES (ELECTRODES). THE ELECTRICAL SOUND SIGNAL IS APPLIED TO THE ELECTRODES CREATING AN ELECTRICAL FIELD; DEPENDING ON THE POLARITY OF THIS FIELD, THE DIAPHRAGM IS DRAWN TOWARDS ONE OF THE PLATES.
May 2017 Pro iESL Tech Notes To put this theory into perspective with some figures, Sennheiser HD800 dynamic headphones = 102dB/1V Typical pair of electrostatic headphones = 102dB/100V!!! Traditional headphone amplifiers do not deliver either the EHT voltage or the required audio voltage. So a special ‘Energiser’ is required to match the electrostatic headphones. Typically a maximum output of 300V is needed.
Tech Notes Pro iESL To give: The Transformer – the ‘sound’ of the Energiser Like a good chassis in a car, a transformer makes or breaks the Energiser. This is fundamental, simply because it is almost solely responsible for the ‘sound’ of an Energiser. Ideally a transformer would have no ‘sound’ signature of its own, but simply and transparently pass on the audio signal. In reality this is a challenging mandate.
May 2017 Pro iESL Tech Notes 1.1 The Core – the ‘tone’ The iESL transformer core uses a mix of Mu-Metal (aka Permalloy) lamination and Grain Oriented Silicone Steel (aka GOSS). Most audio transformers for such higher levels and power restrict themselves to using steel. https://en.wikipedia.org/wiki/Electrical_steel#Grain_orientation + GOSS handles high signal levels well, which is needed if we wish to produce 300V or even more.
Tech Notes Pro iESL Peerless Transformers featured in the legendary Western Electric and Altec (“All Technical Services”) recording equipment from the golden age of stereo. Getting identical laminations in GOSS and Mu-Metal/Permalloy is challenging, getting ultra-thin laminations such as we prefer to use, more so and then manually and individually assembling each core with different materials in a repeatable pattern has to be done by hand. Arduous? Yes, but worth it. 1.
May 2017 Pro iESL Tech Notes The Scheibenwicklung is also quite old, German patent DE861406 C issued to Siemens GMBH Jan 5, 1953 with a filing date of May 14, 1943. (http://google.com/patents/DE861406C?cl=ko) covers this. The much more common layered winding is not able to offer as wide bandwidth.
Tech Notes Pro iESL Transformer Illustration from here: http://elektronik-kurs.net/elektrotechnik/transformatoren/ Transformers in the iEnergiser are unique in combining Scheibenwicklung and layered winding in a complex interleaved pattern to achieve results that considerably exceed either technique. The design of such transformers is mostly an extinct art, with virtually no text remaining (never mind in print) and few people who still have the know-how.
May 2017 Pro iESL Tech Notes In terms of performance, only such an exceptional transformer can approach and even exceed the best transformer-less amplifiers. Part 2: Bias Voltage In addition to the actual music signal, a pair of electrostatic headphones requires the so-called “bias voltage.” Whereas so-called dynamic headphones have a static magnetic field which provides the ‘bias,’ in the case of electrostatic headphones, a static electricity field is needed.
Tech Notes Pro iESL • Cascade rectifier: achieves high voltages but is very noisy. The noise can be filtered but this is not preferred as some residual noise always ends up in the music path which is sub-optimal. Background to Biasing Voltages The Cascade rectifier circuit is perhaps the most common yet is also the most compromised.
May 2017 Pro iESL Tech Notes Option 3: The Capacitive Battery Power Supply Listening to a vintage battery-powered Energiser from our collection of eclectic and sui generis HiFi collection, we noticed that once the power was turned off, the electrostatic headphones kept playing for many minutes just on the retained charge in a small capacitor. More apparent was that sound quality was noticeably better as the primitive switched mode step-up circuit was off. This was a real "eureka!" moment.
Tech Notes Pro iESL (microseconds) as usually one or two switching cycles suffices to replenish the lost charge. Then the switching system is again off completely. Any noise that this system creates is confined to medium frequency radio bands for the infrequent short durations during which it is active. In practice, over 99.999% of the time the charging circuit is completely off. The practical outcome is in effect a perfect high-voltage battery to provide the bias for electrostatic headphones.
May 2017 Pro iESL Tech Notes While this is an uncommonly comprehensive wide range of adjustability, compared to other Energisers, the iESL approach to bias voltage is unique. Part 3: Audiophile parts, unparalleled signal performance In order to select input signals and to switch speaker connections, high-grade signal relays are used. WIMA capacitors These 1,000Volt rated capacitors are from Germany.
Tech Notes Pro iESL Gold-plated silver contact relays The entire signal switching for the input selection utilises gold-plated silver contact miniature relays, filled with an inert gas. This makes sure the contacts will be as new for many years to come. Sealed-silver alloy contact relays The speaker connections are switched using sealed silver alloy contact relays for minimum impact on the sound quality of the speaker path.
May 2017 Pro iESL Tech Notes Addendum notes on Pro iESL use with Pro iCAN Most ESHP are very inefficient. Due to the limited Voltage handling and the low sensitivity ESHP generally do not play very loud, especially compared to traditional dynamic headphones. So do not expect them to go as loud as dynamic headphones.
Tech Notes Pro iESL For further information, please contact: Victoria Pickles press@ifi-audio.com / +44(0) 1704 227 204 About iFi iFi Audio is headquartered in Southport, UK. It is the sister brand of Abbingdon Music Research (AMR). They respectively design and manufacture portable and desktop ‘ultra-fidelity’ audio products and high-end audio ‘home-based’ components. The combined in-house hardware and software development team enables iFi Audio and AMR to bring to market advanced audio products.
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