Pro iESL
Pro iESL
iFi audio Pro iESL
Love your electrostatic headphones but need more drive?

Look no further than the iFi audio Pro iESL – this flagship energiser will have them singing in no time.

The Porsche and the Pro

Imagine the audio equivalent of a Porsche engine of the flagship headphone world and you have the Pro iESL.

Electrostatics need high voltages to energise them to make sound. The Pro iESL is one such energiser and delivers the extra-high-tension voltage needed. The capacitor pack has around 35,000,000 kOhm insulation resistance, which means that self-discharge time (to 30%) is around 100,000 seconds or 27 hours.

It is one of the best energisers in the business (even if we do say so ourselves) and is compatible with all the great electrostatic brands – including Orpheus and Koss.

ifi audio Pro iESL

Big sound

If you like electrostatics, then you like ‘big’ sound.

The Pro iESL won’t disappoint. Coupled with our more traditional flagship amplifier, the Pro iCAN (or any other, but we like ours), the Pro iESL lowers distortion, separates vocals, orchestras and instruments.

It opens up the bass and leaves you with a wide, structured soundstage.

Dynamic duo

And, we’ve got good news.

The Pro iESL can also be used with your flagship dynamic headphones thanks to a unique transformer-coupled-stage that can take them to the max.

Ifi Audio Pro iESL

Just go Pro

Enjoy the pure luxurious, pleasure of flying high with your headphones – electrostatics or dynamics – with the iFi Pro iESL.

No more background noise, no more distortion. Just smooth, sexy, open audio.

Forget the Porsche – just go Pro.

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 Siemens (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.

So, what’s a capacitive battery power supply?

This means 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. You are always listening on battery (not mains) power.

Good news for your flagship dynamic headphones.

The iESL has an ear-tingling transformer coupled-stage that is not found in other energisers.

We reckon its audio performance is unsurpassed. Each and every flagship dynamic headphone, when used through the iESL, enjoys a whole new level of smoothness and airiness.

Vishay MELF resistors – complex, costly but superior.

These metal electrode leadless face resistors have excellent accuracy, stability, reliability, and pulse load capability. They provide optimal power rating and pulse load capability. They show some of the lowest noise and distortion of any resistor available in the market, period.


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: 220 (w) x 213 (d) x 63(h) mm

8.7″ x 8.4″ x 2.5″

Weight: 2.5kg (5.5 lbs)


iFi Pro iCan and Pro iESL Reviews | Swiss Army Amps

(Click name to read original review)

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)

The Sennheiser Orpheus HE90 are legendary headphones created in 1991 and limited to 300 pairs. They came with their very own valve amp and cost $16,000. Phew!


Founded way back in 1958, Koss now produce a wide range of headphones to cater for varying tastes. One of their most acclaimed creations is the ESP950, over electrostatic ear headphones which retailed at about $999.

JAS Hi-Res logo

When you see the Japan Audio Society (JAS) Hi-Res logo on a product it means that has this certification and conforms to the high standards for high resolution music put in place by the JAS consortium – to which the largest global electronics manufacturers and the biggest music labels have all subscribed.