Fostex TH610 headphones and HPA4BL DAC/Headphone amplifier

Headphone amps and amp/DACs
Fostex HPA4BL,
Fostex TH610

So moving away from the Astell & Kern AK300 as a digital transport and a headphone amplifier, where the alchemy and synergy was wanting, I turn to the provided accompanying Fostex HP-A4BL, a headphone amplifier and DAC, which is based on the current Fostex HP-A4, and is a competitively priced unit offering balanced connections for headphone via a four-pin output. This of course necessitates a special cable, and I appreciate having what looks like a DIN connector to fulfil this function, as one of the widely used alternatives is to use a mini headphone jack with an extra ring. This means that a high-quality cable will struggle to fit into the jack, and its life expectancy is measured in minutes! For review purposes, a Fostex cable was supplied. 

The recent development over the previous model HPA4 is an external power supply via a wall wart, rather than being bus powered, and consequently the power output has tripled. There is a switch on the front panel which adds 10db of extra gain for harder-to-drive headphones.

The chipset employed is a Burr-Brown PCM1792A, capable of 192/24-bit PCM and DSD 11.2Mhz (DSD256/Quad). It is designed to be used with the Fostex Audio player to decode FLAC, ALAC, DSD, WAV, AIFF, and most other popular audio formats, and there is a choice of two different digital filters to suit taste.

The unit is diminutive in size, and its front panel includes an unbalanced headphone output, volume on/off switch, and input selection to add to the previously recounted features. Rather surprisingly, there is no S/PDIF input at the rear: There is USB, Optical in and out, and RCA output. I can see that in a unit of this size, space is limited, and I’m sure Fostex have their reasons, but from my point-of-view this is an oversight. A curious micro SD slot is for firmware updates.

Listening to the unit as a stand-alone DAC, optically fed with a glass cable, and an Esoteric K-05 transport, with Dvorak’s New World Symphony, by Solti [Decca], the DAC acquits itself remarkably well. Against the mighty Chord DAVE, its space is contracted, it lacks some of the low-end grunt, but tonally the two are surprisingly similar. Of course the Chord DAVE is a shade under twenty times the price, so I think the Fostex is really excelling in the value-for money department.

There is a real coherence to its presentation, and possibly a little lightness in the bass, with a sweet midrange, that makes for a good listen all things considered.

So how do the two products work together? Are the synergy levels better than with the Astell & Kern?

If you will permit me, I will use a piece of Operetta as a musical illustration; namely, Lehar’s ‘Merry Widow’, John-Elliot Gardener conducting the Vienna Philharmonic Orchestra [DG]. In the hustle and bustle of the Overture, listening through the balanced headphone connection, there is real energy and punch to this manic beginning. The bass interestingly no longer dominates. The tightness of the bass of the headphones which is overstated, and the quiet but accurate contribution of the Headphone/DAC seem to compliment each other really surprisingly well. This Deus ex machina is welcome, as it shows some method in Fostex’s thought processes. The sound errs on the close, but without a doubt, the two products help to potentiate each other. Mutually dependent dysfunctionality, I think a shrink would say!

Swapping over to the unbalanced (standard) connection yields some distinctly less engaging results. The bass is much less purposeful, even rather saggy. Some of the enthusiastic sparkle of the opening scene is obfuscated, and separation is diminished. This comes as a surprise to me, as I’ve not had the opportunity to investigate balanced headphones, and the differences are certainly an avenue worth pursuing.

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