CD players modified by Demograf Audio: owners’ reviews of the Marantz CD-15 and Philips CD304

Alongside his own DACs and amplifiers, Dmitriy Gubchenko modified classic CD players for forum members: he replaced op-amp output stages with transformers or tubes, added tube clocks and external clock inputs, and in one case fitted a second DAC. Four owners wrote about these players between 2010 and 2013. Below we summarise what they heard from a Marantz CD-15 and two Philips CD304s, and what one owner’s system of modified players looked like.

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.

What was reviewed

These are one-off modifications of other makers’ players, made for their owners. Demograf Audio does not offer CD-player modifications as a catalogue service today; the current instruments closest to this work are listed at the end of this article.

Marantz CD-15 with two DACs

The player

The first owner’s player is a Marantz CD-15 from 1994. He describes its CDM-4/36 drive as a metal, industrial version of the familiar CDM-4, which he believes benefits the sound. The player carries two selected TDA1547 chips, a vintage DAC chip from Philips.

The modification

• Part of the circuit after the DAC chips was disconnected, and the op-amps were replaced with balanced output transformers that Dmitriy wound himself.
• A second DAC on the AKM AK4399 chip was added inside the player. Its op-amp stage is also bypassed, and the signal goes to balanced Sowter transformers.
• Each DAC has its own output.
• An input for an external clock was added on the rear panel.

A tube clock as a test bench

Wanting to experiment with tubes, the owner also has a large tube clock. Its power supply accepts a wide range of English and German rectifier tubes of the U, UU and RGN series, and English octal types; he had tried about twenty of them, with more on the way, as well as four tube types in the oscillator. He stresses that it is not a finished product but a prototype for auditioning tubes and their combinations, to be put in a proper, somewhat smaller case once the listening is done.

System and music

He listened through an amplifier that Dmitriy lent him for the purpose, with the Japanese and Chinese versions of the Sony MDR-CD3000 headphones; he prefers the Chinese version. He chose his test discs for recording and mastering that aim at a live, analogue sound, and mostly listens to classical music, especially a Philips series transferred from the master tapes at 24/96, on which faint tape hiss can still be heard, and FIM releases, also transferred from master tapes. He describes the sound of these discs as dense and full-bodied.

TDA1547 vs AK4399

With both DACs in one player, he could compare them directly. The TDA1547 sounded more natural and more analogue to him, and it was the one he wanted to keep listening to, especially on vocals. The AK4399 had higher resolution but less body and life. He did not write the AK4399 off: he expected its output transformers and the choice of cables to decide the matter.

From memory, he felt that the CD-15 in stock form, a stock Philips CD304 and a Naim DAC had all played much more simply.

Philips CD304 with a tube clock and an EL8 buffer

A second owner listened for a week to a Philips CD304 MkII that Dmitriy had modified with a clock on an EF180 tube and an output buffer on a Valvo EL8, both in the player’s own case. He had been using a Marantz CD player before, and listened through a Woo Audio WA3 amplifier with Beyerdynamic T1 and Koss Pro4AA headphones.

First days

His first impression was of too much brightness, together with remarkable detail. By the second or third day the brightness was gone. He was not sure whether the cables and tubes had run in or his ears had adjusted.

Music

Classical music pleased him most: Beethoven’s and Rachmaninoff’s piano concertos and opera with Pavarotti. Rock did not grip him at first and seemed to lack energy through the Beyerdynamic headphones, but with the Koss it improved. Blues and jazz went down well, and he found his tastes moving towards chamber music and small ensembles. Everything could be heard, the detail seemed unreal to him and voices were alive; he forgot about the equipment and simply listened.

Compared with the stock player

He had heard the same player in stock form. Apart from a more analogue presentation than his Marantz, he heard no advantages: the stage was flat and the sound cloudy. He recommends the modified player, built on the TDA1541, especially for classical music.

Philips CD304 with a Demograf Audio tweak

A third owner bought a modified Philips CD304 second-hand from another forum member, and it displaced his Asus Essence One. The main differences he heard were a rich range of timbres and depth: layering and long, natural decays. Detail was on another level, and the player had a singing, untiring quality; he spent the first night with his headphones on. He found its sound close to analogue in its flow, breadth and density. The player has a digital input, so he also uses it as a DAC for his computer.

A system of modified players

The fourth owner, who listens mostly to classical music, described in 2010 a whole system made by Dmitriy Gubchenko. His post lists the equipment rather than its sound:

• a Philips CD960 (CDM1 drive, TDA1541A) with a digital input for a tube clock, its digital filter disabled and its stock analogue output bypassed, with a Furutech mains inlet and Canare outputs;
• a Philips CD650 (CDM4 drive, TDA1541) with a crystal clock, an input for an external clock and two analogue outputs, one through an output transformer and one straight from the DAC chip;
• a Grundig CD 7550 (CDM1 drive) with its TDA1540P replaced by a TDA1540D, a digital input for a tube clock and its stock analogue output bypassed;
• an external DAC on the TDA1547, with its own EL8 output stage or a tube buffer on 6N9S triodes;
• a tube clock on a Telefunken EF13;
• a tube buffer with a transformer headphone output and a 5Y3GT rectifier;
• a two-box headphone amplifier with a 5Z4GT rectifier supply and stages on ECL82 and EDD11 tubes;
• alloy interconnects and an alloy coaxial digital cable.

What owners report

• More natural timbres, more depth and longer decays than the same players in stock form.
• High detail without fatigue, after a few days of running in.
• A bright first impression in one player, which faded within days.
• In a direct comparison, the TDA1547 more natural and the AK4399 higher in resolution.
• Classical music, voices and small ensembles named most often as what the players do well.

Summary

The owners of these players describe the same direction of change: away from a flat, cloudy stock sound towards a more natural, more detailed and more spacious one, with the most praise for classical music and voices. The modifications differ from player to player, but they share the ideas behind them: removing op-amp stages, adding transformer or tube outputs, and taking the clock seriously. These are reports on one-off modifications, not on a product you can order today.

Which Demograf Audio piece fits

The ideas behind these players continue in the current catalogue. The Reference Tube DAC is a DAC with a solid-state output stage and an optional tube stage, built on the multibit TDA1540, TDA1541, PCM63 or PCM1704, or the vintage TDA1547; owners’ reviews of its TDA1541 and TDA1547 versions are collected in Persephone (TDA1541) NOS DAC: owners’ reviews and Aphrodite (TDA1547) DAC: owners’ reviews. Charon is an external master clock with a solid-state or tube buffer, galvanically isolated, with BNC outputs. Our guide to NOS multibit DACs compares the classic Philips and Burr-Brown chips.

Every instrument is made to order by Dmitriy Gubchenko and covered by a one-year warranty (extra warranty available: +1 or +2 years).