ECL82 tube headphone amplifier: an owner’s review of an early Demograf Audio build

In October 2010 a forum member, andafan, received a headphone amplifier made to his order by Demograf Audio and designed by Dmitriy Gubchenko, on ECL82 triode-pentodes with output transformers, a tube rectifier and a front-panel control for the depth of negative feedback. Over the following year he described its sound, the effect of the feedback control, its run-in and a change of tubes, while other members questioned its layout and design. This article summarises that thread, from October 2010 to November 2011.

These impressions are summarised and translated from owners’ posts on an audiophile forum. They are the subjective views of their authors, not measurements or claims of Demograf Audio. The amplifier described is an earlier Demograf Audio build made for one owner; there is no current model on ECL82 tubes. Today’s models with headphone outputs are listed among our headphone amplifiers.

The amplifier

The ECL82 holds two tubes in one glass envelope: as a member, Alexander, pointed out, the triode section works as the input stage and the pentode section as the output stage. Here Tungsram ECL82s drive the headphones through output transformers, and the power supply uses a 5Ts4-series rectifier tube made in the 1950s. The volume control is an Alps potentiometer; a second knob on the front panel sets the feedback continuously over a small range, from none upwards. The chassis measures 170 × 270 × 70 mm and weighs 4 kg.

It was a version of the designer’s own amplifier, which the owner had heard in the designer’s system, with a modified Philips CD304, a TDA1541 DAC, full-range loudspeakers and Beyerdynamic DT911 headphones, and remembered for its emotion, energy and drive.

Asked whether the output stage was transformerless, the designer replied that he did not see how headphones could be driven from an output pentode without output transformers, and that he preferred classic circuits.

andafan listened mainly on Audio-Technica ATH-AD1000 and Fischer Audio FA-003W headphones, from a CD player, with the volume control at 20 to 25% of its travel.

How does the ECL82 amplifier sound?

His first impressions, a few days after delivery, describe a “light” sound, perhaps slightly dry, open, energetic and very transparent. He did not call it soft or warm: the emphasis, he wrote, was on energy and emotion rather than on comfort.

Treble and midrange

Supple, agile and engaging, which he heard most clearly on voices and violin, with “not even a hint of harshness”. Sibilants, where a recording has them, were slightly emphasised.

Bass

Deep and fast, but not boomy.

Dynamics and detail

He rated both micro- and macrodynamics highly: the smallest changes in level came through freely, and so did sudden bursts. On King Crimson’s Larks’ Tongues in Aspic, much of which sits near the threshold of hearing, he could tell exactly what the percussion, guitar and violin were doing. On Schubert’s Eighth Symphony and a Prokofiev piano concerto the instruments stayed distinct at low and high volume.

Emotion and listening fatigue

His main impression was vividness in conveying emotion: from 1970s rock to Purcell and Handel, lyricism, sarcasm, joy and despair came across in strong contrast. Yet the sound did not tire him; there was no harshness even on bright headphones. The ATH-AD1000 came to life: their tonal balance evened out and their sharpness disappeared, as another member, clubnewmen, had predicted with a good tube amplifier.

After run-in

After about 120 to 130 hours, during which one tube was occasionally noisy and the sound at one point leaned towards too much bass, the sound settled. The early dryness was gone: it was fuller, with richer timbres. The designer had told him that timbre was his amplifier’s strong point; at first the owner did not hear it, now he confirmed it, describing timbres as varied, alive and close to natural. The energetic character stayed, and he found himself listening to whole albums picked at random from his collection.

Less or more negative feedback?

• Minimal or no feedback: a more open sound with freer dynamics, most noticeable in the upper midrange, a lighter balance and a range that seemed extended at both ends, but less clean and refined. Microdynamics seemed slightly better, with more vocal nuance. On the other hand: more sibilance and grit on poor recordings, and boomier, less articulate bass.
• More feedback: a denser, “meatier” sound, with tighter, better-articulated bass shifted towards the mid-bass, a balance centred on the midrange and noticeably less sibilance and grit. At first he also found it less interesting.

The difference was not dramatic but clearly audible, and the amplifier kept its character. It also depended on the headphones: the looser bass bothered him less on the ATH-AD1000, while the FA-003W tolerated sibilants better. He concluded that the control lets an owner fine-tune the sound to the headphones and to taste.

The designer had recommended the middle of the knob’s travel, a little feedback. andafan settled on almost none: more atmosphere, breathing, quiet decays and detail. The price, he wrote, was slightly vaguer bass, more sensitivity to interference from the mains or mobile phones, and stronger microphonics. He thought it worth paying, and the feedback can always be turned up again.

What other forum members said

• VVK asked why the RCA input jacks sat between the hot tubes: a bulky interconnect could lever a tube out or get in the way when tubes are changed, and a hand could be burnt. He would have put them on the side.
• RomanSt agreed that jacks between tubes are not always practical, while noting that many amplifiers are built this way and it is a matter of taste. AlAnBek thought the worries exaggerated and pointed out that the layout can be agreed before the build.
• AlAnBek suggested that the limits in treble cleanliness probably came from the source, and that some vagueness in the low end is typical of Tungsram miniature tubes. He advised running the amplifier in fully before changing tubes, then trying older European and American ECL82s.
• One sceptical member pressed for technical data that the thread never received: output-transformer bandwidth, the feedback range and the power-supply filter. He suggested replacing the feedback potentiometer with a fixed resistor once a setting is chosen, adding a polypropylene capacitor to the anode supply and, more radically, fixed bias. Other members objected to his tone, and the exchange became heated.
• The designer wrote that he would not discuss the power supply and other details on the forum, as writing out his solutions would take time from his work, and offered to explain them by phone.

The owner declined the modifications: he liked the designer’s approach to sound and saw the amplifier as a coherent whole that he did not want to change blindly.

Practical notes and reported problems

RCA jacks between hot tubes

andafan chose this layout himself from the options the designer offered, to keep the signal path to the volume control short. The designer explained that the position was agreed with the owner for the shortest distance to the volume control and the tubes, that tubes running at 60 to 70 °C do not damage cables, and that the jacks could equally have gone on the side. The owner found that the cable did not overheat, though the output tubes “heat up like irons”. His remedies: moving the jacks, or fitting the supplied aluminium tube covers, drilled for ventilation.

Sibilance

A mild emphasis, larger with minimal feedback and on poor recordings, smaller with more feedback.

Mains polarity and interference

The amplifier was sensitive to mains polarity: with the plug the “wrong” way round, the sound became boomier and looser, the stage wider but shallower. With little feedback it picked up interference more easily.

Hum after a tube change

In October 2011 andafan replaced the Tungsram ECL82s with Svetlana 6F3P triode-pentodes made in 1964, a close relative of the ECL82. The sound became darker, fuller in the bass and denser, yet dynamics and scale grew, transparency stayed and the quietest details became clearer; the stage narrowed. With the ATH-AD1000 the excess brightness went and the lower midrange filled out.

The drawbacks were strong microphonics, the tubes responding to the slightest touch on the chassis, and loud hum, which he attributed to tubes that had lain unused for decades. AlAnBek’s pair showed no microphonics. The designer noted that only about half of these tubes had proved hum-free for him, and that a DC heater supply cures the hum but does not sound as good to him. A little over two weeks later andafan reported that the hum faded with warm-up: it lasted 10 to 15 minutes after switch-on, then the amplifier was quiet.

With loudspeakers

On his own 89 dB loudspeakers there was ample volume, clear bass and a transparent sound, but little dynamics compared with his integrated amplifier. The designer advised loudspeakers of at least 95 dB sensitivity; our guide to loudspeakers for single-ended amplifiers explains why.

Summary

The owner describes an energetic, transparent headphone amplifier that conveys emotion vividly: deep, fast bass, strong micro- and macrodynamics, voices and violin without harshness, and no fatigue. After run-in it grew fuller and richer in timbre, and the feedback control let him trade openness for density and less sibilance. The problems reported are practical: slight sibilance, RCA jacks between hot tubes, sensitivity to mains polarity and interference, and hum and microphonics with replacement tubes, the hum fading after warm-up.

In 2011 the same owner added a Demograf Audio DAC on the TDA1541; owners’ impressions of that converter are in our Persephone (TDA1541) review.

Which Demograf Audio piece fits

No current model uses ECL82 tubes. Every amplifier in today’s catalogue with headphone outputs drives loudspeakers too, with a 6.3 mm and a 4-pin XLR headphone output.

• A low-power triode amplifier for headphones and sensitive loudspeakers: Solaria on 45 triodes or Eurybia on 2A3 triodes, single-ended in pure Class A, 2 W per channel.
• Every type of headphone, including electrostatic: Tantal, two 3C24 tantalum-anode triodes in pure Class A, 3 W per channel, with a STAX-type output built in; see owners’ impressions.
• More power for loudspeakers: Atlas on 300B triodes, 5 W per channel.

Points raised in this thread can be settled at order time: the input tube (EL8, AL4, EF14 or ML6) shapes the voicing, a tone control / filter module is available, and a protective tube cage can be fitted. Our guide to amplifiers for headphones and loudspeakers explains what each headphone type needs. Every amplifier is made by Dmitriy Gubchenko. Each is made to order with a one-year warranty (extra warranty available: +1 or +2 years), so the input layout and tube types are agreed before the build starts.