iFi adds to its flagship ‘Pro’ range of compact audio components with the Pro iESL headphone energiser a device designed to “make the most of electrostatic headphones”.

Electrostatic headphones, such as those made by Stax, are notoriously tricky to drive. They need more power than regular dynamic headphones, delivered in the right way to ensure their electrostatic plates are properly ‘energised’. Most amps deliver neither the EHT (Extra High Tension) voltage nor the required audio voltage to enable electrostatic headphones to perform at their best.

The iFi Pro iESL can be driven by any high-quality integrated amp or power amp, or paired with iFi’s Pro iCAN headphone amp, to deliver audio signals that are fully optimised for electrostatic headphones such as those from Stax or KingSound, or Sennheiser’s Orpheus. It can also be used to ‘transformer-couple’ high-end dynamic headphones – Focal Utopias, for example – to enhance sound quality.

Key features

  • Hand-wound permalloy core transformers
  • Bias voltage generator delivers fully optimised output signal
  • Capacitive battery power supply ensures a perfect bias voltage source
  • Qquality circuit components throughout, including WIMA capacitors and Vishay MELF resistors, plus gold-plated silver and sealed-silver contact relays
  • Impedance, bias and termination matched to the connected headphones


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

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

Weight: 2.5kg (5.5lbs)

The retail price of the Pro iESL is US$1,399 (ex-tax) or €1,575/£1,395 (incl VAT).





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