Pro iESL

Audio heaven.

iFi audio Pro iESL
Electrostatic headphones require the best ‘energisers’ to charge them which is the secret of their performance.

The Pro iESL energises your electrostatics. And then some.

Experience audio like never before.

Feel the energy.

Electrostatic headphones are the top of the range Porsches of the audio world, and the Pro iESL is the engine that drives them.

Unlike traditional amplifiers, the Pro iESL delivers the extra-high-tension voltage needed to energise the electrostatic plates in the headphones that produce ultimate musical nirvana.

Ifi Audio Pro iESL

Team iFi.

Coupled with the Pro iCAN, the Pro iESL lowers distortion, enhances and separates vocals, orchestras and instruments, opens the bass and leaves you with a wide, structured soundstage.

The ride of your life.

Paired with your beloved electrostatics, the Pro iESL amplifier takes you on a trip to audio heaven.

Unusually, flagship dynamic headphones can also be used with the iESL as the special transformer-coupled stage takes them to the max.

Ifi Audio Pro iESL

The tech spec.

The Pro iESL includes a:

  • Pinstripe Permalloy Core Transformer – To lower distortion,
  • Bias Voltage Generator – To charge electrostatics to the max before cutting them off to run on battery, not the mains so no electronic noise bleeds into the headset

The Pro iESL cuts out background noise and distortion. For ‘air’ and ‘smoothness’ to each note that takes listening enjoyment to the max.


Drive your electrostatics with one of the best energisers in the business. Compatible with all the great electrostatic headphone brands - including Orpheus and Koss.

The 'Perfectly Matched' headphone experience.

Both classic and cutting edge technology in 3 quality components delivers a perfectly matched listening experience - one-off Pinstripe Permalloy Core Transformer, a Bias Voltage Generator and the Capacitive Battery Power Supply.

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.

The battery is 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!

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 - complex, costly BUT superior. These resistors provide optimal power rating and pulse load capability. Nothing else comes close.

Good news for your flagship dynamic headphones.

The iESL has an ear-tingling transformer coupled-stage that is not found in other energisers. And its audio performance is unsurpassed. So each and every flagship dynamic headphone when used through the iESL enjoys a whole new level of smoothness and airiness.


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 (5.5 lbs)

We’re working on it — check back soon!


iFi Pro iCan and Pro iESL Reviews | Swiss Army Amps

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iFi Pro iESL Review

This costs a ton of money. But the build and options are why I know its going to work for me for … ever? I am currently pushing my L700 and 207’s with my Aune S7 pushed through the balanced input. Lots of options for those crazy Electrostats that exist. Really a special unit.

(Click name to read original review)
More reviews…
More reviews…

iFi audio Pro iESL + KingSound KS-H3

The iFi people walk their own walk; they think and act quite differently and after several years in the audio game that’s very clear to someone up to date with their moves.

(Click name to read original review)

Very impressed with the iESL

I was very impressed with the iESL. It benefitted dramatically from a lowering of noise which opens up the upper midrange frequencies to new and complex detail…the iESL is packed with value too. Any electrostatic headphone fan needs to grab one!

(Click name to read original review)

The iESL has a lot that separates it from the rest of the market

So much extra beauty breathed in the Pro iESL. Thanks to the Pro iESL, you can now enjoy equally superb sound quality through electrostatic headphones.

(Click name to read original review)

We can reach the new attraction of headphones that we have not noticed before

We can reach the new attraction of headphones that we have not noticed before!

Common trend with all of iFi’s products. They really hit the nail on the head with this product.

(Click name to read original review)

We can reach the new attraction of headphones that we have not noticed before

Pro iESL boasts contents that can be said to be the definite version of such a capacitor type headphone adapter. It is an item where you can enjoy the depths unique to condenser-type headphones.

(Click name to read original review)

There is a wonderful detail

With the recommended settings, everything is fine. There is a wonderful detail and distinct dynamics and most surprisingly, a comfortable musical balance.

What on earth is Tarasov from Salon AV on about?

The Pro iESL of course which also got the Expert’s Choice award!

(Click name to read original review)