Sennheiser HE 90 on an 811 tube amplifier: a listening session

In December 2024 one owner got his amplifier on G-811 triodes back from Dmitriy Gubchenko after an upgrade and organised a listening session around it. He brought his whole chain of cables, network switches and power supplies, and built it around a Demograf Audio Prometheus DSD converter and the 811 amplifier, with a Tantal alongside for guests who wanted to hear it. The headphones on the table included the Sennheiser HE 90 Orpheus, STAX SR-Omega and SR-007, several pairs of handmade electrostatic headphones, the HiFiMAN Susvara and the T+A Solitaire P. This article summarises what he heard from the 811 amplifier and how it compared with a solid-state headphone amplifier.

These impressions are summarised and translated from an owner’s posts on an audiophile forum. They are the subjective views of their author, not measurements or claims of Demograf Audio. The amplifier is an earlier build of the model now offered as Helios MkII. How this owner’s system came together, and how the 811 amplifier first compared with his Tantal, is told in CS4397 tube DAC and Tantal: one owner’s long-term review.

The amplifier and the brief behind it

The owner ordered the amplifier for heavy metal, classical music and everything except the folk and vocal music he plays on his Tantal. His brief asked for hard-hitting, firm and massive bass, wild dynamics, the highest possible resolution across the range, scale, and a light warmth in the midrange. Earlier in 2024 both of his amplifiers went back to Dmitriy for upgrades, and the session was the first time he could share the 811 amplifier with other listeners after its return.

The source was a Demograf Audio Prometheus DSD converter, slightly simpler than the one he has ordered for himself, with a solid-state output. Most of the listening was done on the 811 amplifier.

Electrostatic and planar headphones on the 811 amplifier

He describes the evening as a ladder, with each pair compared several times against the others.

HiFiMAN Susvara and T+A Solitaire P

Between the two planars he heard the Solitaire P as a step up from the Susvara: deeper and better-drawn bass, and resolution and micro-contrast that he rated very high for a planar. The Susvara kept the better stage and timbre, but for him the Solitaire P’s technical lead outweighed both.

Handmade electrostatic headphones

Straight after the Solitaire P he put on a pair of handmade electrostatic headphones on the same amplifier. He heard slightly higher resolution across the range together with a much fuller, warmer and more convincing tone, and in his view neither planar came close. Earlier that year he had received the latest revision of these headphones: more reliable, with stable bass at high volume and lighter on the head, combining the tonal balance of his favourite earlier pair, with its gentle dip around 3–4 kHz, with the newer technical level.

Sennheiser HE 90 Orpheus

Then came the HE 90 on the 811 amplifier, which he called the best sound he had ever heard. He had once heard a first-generation STAX SR-Omega on a STAX SRM-T2 amplifier at another collector’s home, which he found slightly more technical, but without this depth, punch and midrange: that sound was about realism, this one about realism and pleasure together. In his experience the HE 90 is one of only three headphones that resolve more than his handmade electrostatic pairs, and here it came close to their presentation as well.

Compared with the handmade headphones, the HE 90 reaches less deep into the sub-bass, has leaner bass overall, a less dark presentation and a slight lift in the upper treble. For heavy music he would still choose the weight and bass quality of the handmade pairs, but with the HE 90 he wanted to close his eyes and tap his foot.

STAX SR-Omega and SR-007

• First-generation SR-Omega: continues the trend from the handmade pairs to the HE 90, with less body, less sub-bass and a less musical presentation, but higher resolution. For daily listening to heavy metal he would choose the HE 90 or the handmade pairs.
• SR-007 (Mk1): nothing new compared with his earlier listening. If he wants bass-rich electrostatic headphones, he prefers the handmade pairs for their resolution in the mids and treble, deeper and firmer sub-bass, larger stage and timbre.

Compared with a solid-state headphone amplifier

At the same session he set the 811 amplifier against a DipAudio GSX Mk2, a solid-state headphone amplifier built by a small independent maker. He found the 811 amplifier more technical, deeper, richer, larger in scale and better at placing instruments and voices. But he stresses that the difference is heard after five seconds, not in the first one: the GSX Mk2 held up well, and he would not describe the two as a world apart.

Earlier: the 811 amplifier against the Feliks Audio Envy

When the amplifier was new, the owner compared it with a Feliks Audio Envy. On planar headphones the Envy was faster, and there he still preferred it, though his own amplifier was more melodic and emotional, with noticeably more bass. With electrostatic headphones the picture changed: the 811 amplifier matched the Envy driving fast Heddphone planars on detail, separation and speed, and pulled ahead on vocals, bass and midrange warmth. On a fast metal track by Archspire he heard for the first time that each note in a guitar run had its own pitch.

Tantal at the session

A Tantal very close to the owner’s own was set up beside the 811 amplifier, and several guests listened to it. He had described the difference between the two amplifiers before: Tantal is the more midrange-centred, massive and saturated of the two, richer in timbre and decay and darker, while the 811 amplifier is noticeably more detailed and dynamic across the whole range.

Summary

For this owner the 811 amplifier met a brief written for heavy music: weight, speed, resolution and scale with some warmth. At this session it let him rank top electrostatic and planar headphones against each other, and it gave him what he called his best listening experience with the Sennheiser HE 90. Against a solid-state headphone amplifier it kept a clear but not dramatic lead. These are one listener’s impressions in one carefully assembled chain, and other systems may hear the same headphones differently.

Which Demograf Audio piece fits

• An amplifier on G-811 triodes for demanding headphones and loudspeakers: Helios MkII, single-ended Class A, 15 W per channel, with 6.3 mm and 4-pin XLR headphone outputs and an electrostatic output as an option. A push-pull version doubles the power.
• Electrostatic headphones and vocal music: Tantal on 3C24 triodes, with a STAX-type output built in.
• A converter with native DSD: Prometheus, the programmable-logic DAC, with native DSD1024 and PCM up to 32-bit / 768 kHz.

Our guide to amplifiers for headphones and loudspeakers explains what an electrostatic output needs. Every unit is made by Dmitriy Gubchenko. Each is made to order with a one-year warranty (extra warranty available: +1 or +2 years), and the tubes and outputs are agreed before the build starts.