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iFi-Pro iESL
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iFi Audio - Pro iESL - Electrostatic Headphone Amplifier Driver is available to buy in increments of 1

iFi Audio - Pro iESL - Electrostatic Headphone Amplifier Driver

iFi Audio - Pro iESL - Electrostatic Headphone Driver

iFi Audio - Pro iESL - Electrostatic Headphone Amplifier Driver

The Pro series iESL is the best way of driving electrostatic and dynamic headphones.

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.

Imagine that your electrostatic headphones are like the top of the range Porsche. A Porsche engine requires a lot more power than your standard car. So do electrostatic headphones! They need to be ‘charged’ or more accurately, ‘energized’.

Traditional amplifiers do not deliver the either the EHT (extra-high tension) voltage or the required audio voltage that electrostatic headphones need. A special ‘energizer’ is required to ‘energize’ the electrostatic plates in the headphones, typically a maximum output of 300V!

The Pro iESL makes use of 3 core components, all developed using the very best classic approaches combined with the latest in cutting-edge technology, to deliver the ‘perfectly matched’ headphone experience.

The Pinstripe Permalloy Core Transformer (PPCT) – Making a transformer with the wide bandwidth and low distortion needed in the iESL is very challenging. To attain this, the custom transformers use complicated hand-wound, multi-section windings with both vertical and horizontal sectioning. They exceed the standards set by Siemans (Germany) and Peerless (USA). With a bandwidth of < 5Hz to > 60kHz (-3dB), transformers in the iESL far exceed the requirements of even the JAS High-Res Logo.

The Capacitive Battery Power Supply. They are charged up to the required voltage and then the charger circuit is turned off completely, leaving the capacitor bank to ‘float’ at the required bias voltage. An essentially perfect bias voltage source with no electronic noise whatsoever at any frequency as the headphones are in essence, powered by the battery bank and not the mains!

Wima Capacitors – Another quality component and perfectly suited for the capacitive power supply. These 1,000Volt rated capacitors are from Germany. The key is the very high insulation resistance and minimal current leakage, as any such leakage causes self-discharge. The whole capacitor pack has around 35,000,000 kiloOhm insulation resistance, which means that self-discharge time (to 30%) is around 100,000 seconds or 27 hours. So one is always listening on battery (not mains) power.

Vishay MELF resistors – MELFs offer superior SMD resistor performance in terms of accuracy, stability, reliability, and pulse load capability. The cylindrical construction of MELF devices provides the optimal power rating and pulse load capability need for the iESL. MELF are more complex to make and so cost more. When assembling PCBs, MELF resistors require special machines and treatment but at iFi we do not shy away from such complexities if it means higher component quality and ultimately improved ultra-sonics.

Elevate flagship dynamic headphones – The unique transformer properties gives the iESL an ear-tingling transformer coupled-stage that is unsurpassed. So each and every flagship dynamic headphone, when used through the iESL, enjoys a whole new level of smoothness and airiness.


  • Ultra-wide bandwidth One-off Pinstripe Permalloy Core Transformer
  • Bias Voltage Generator
  • Capacitive Battery Power Supply


Maximum Output voltage
640V RMS (16Ω/20V in)
320V RMS (64Ω/20V in)

Frequency Response
5Hz – 50kHz (-3dB)

Input Voltage (Pro iESL)
5V – 9V/1A max

Input Voltage (iPower)
AC 85 – 265V, 50/60Hz

Power Consumption
< 1W

213(l) x 206(w) x 63.3(h) mm

2.5kg (5.5 lbs)

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