「DT HWT」Push-pull circuit, biasing A class-AB, electrostatic Head Amp

We heard lots of electrostatic head amps but keep tossing about a single tube amplifier that could get the most tonal richness and depth out of Stax's 009/007 as well as high-end dynamic headphones such as Focal's Utopia, Kennerton's Odin; and other electrostatic ear-speakers with various bias voltage. After months of prototyping, we have finally reached to the version that fulfills those expectations, called DT-HWT

It delivers a feeling of musical harmony that we never got close to before. The mid-range is gloriously rich, with more timbre on vocals. The bass is much fuller with far more weight. The soundstage is also expansive and the separation is much clearer.

With a separated and dedicated power supply unit, the noise floor dropped noticeably that you become very aware of the singer's breathing and physicality.
The highly reserved power supply circuit is constructed with choke coils and large capacitor group; achieving high headroom and wide bandwidth sound possible.

Two clips below demonstrate the DT-HWT performs as a preamplifier out to the Rotel RB-1552 mk1 power amp, driving a pair of DYN Contour 30 floor-standing loudspeakers, which gave just a glimpse of its natural and purest bliss of the sweetest sound signature. Music was flowing through your body with a level details that second to none. 

DT-HWT Headphone Amplifier features:
  • Inputs – it has two sets of RCA inputs. 
  • Outputs – it has different outputs, provided on a number of different connectors. On the amp front is a TRS ¼” unbalanced jack, and balanced headphone outputs on a single 4-pin XLR and a pro bias 5-pin Stax headphone jack. On the amp rear, there are two sets of 3-pin XLR and RCA preamp outputs. Both sets can be used at the same time if desired – for example, you could feed a power amplifier from the XLR connectors, and a subwoofer amp from the RCA connectors.
  • The bias voltage settings on the separate power supply unit are used only with electrostatic ear speakers (> 100K Ω impedance). You can select whichever bias level sounds better to your STAX/HE90 models from 230-500-580 up to 620 V DC bias.
  • Tube complement for the amp unit is: two EF86/E80F/6D8 & two 12AU7/5814A/E80CC/E82CC & four EL95/6AQ5
  • Tube complement for the power supply unit is: two KT66/KT77/KT88/6550/6L6/EL34/350B/350A & one 6080/5998/6AS7/6H13C/2399

a few measurements at R = 6Ω

This baby is neutral and unstressed for long listening sessions and linear and damn quiet, it has a very wide bandwidth/soundstage, high resolution and very high definition in spades. Happy tubes rolling...



Output Power

2.25Wrms x 2 into 16Ω Unbal. or into 64Ω Bal. w/ < 1% total harmonic distortion


< 1%, 20Hz ÷ 20KHz, full output

Freqency Response

12Hz ÷100KHz, -0.2dB @ 32Ω


82 dB, A-weighted

Phone Output impedance

16Ω : 300Ω @ 2.25Wrms Unbal. | 64Ω : 600Ω @ 2.25Wrms  Bal.

Power consumption

100W maximum


2x RCA @100KΩ

Max Analog input level


Separate Power Supply

support dynamic bias voltages

price: US$8,199 ― US$10,999 plus shipping

Estimated lead time in 12 to 16 weeks
Three years factory warranty (parts and labor)
The DT-HWT headphone amplifier is sold factory direct. Contact us for information how to purchase: sales @ leptoni.com