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Tube Headphone Amplifier and Docking Station The bad news: my old portable CD player died; the good news: I picked up a new Sony D-FJ401. This new player runs forever on two AA batteries and offers 45 seconds of shock protection (which must be disabled for serious listening) and, most importantly, a line-out (which is increasingly rare these days). The player shares a desirable feature with the best solid-state equipment: its sonic failings are only subtractive. Seven voices reduce to three, large resonant halls transform into anechoic chambers, fingers lose their fingerprints when running across strings. Of course, this holds true for only the line-out, as the headphone output’s failings are additive, sounding gritty and coarse. Why the difference? The problem lies with the amplifier used to drive the headphones. In order to extend battery life, a class-B amplifier is used — which in itself is bad enough — but this amplifier is also a member of the ultra-low current consumption group that sounds even worse. Furthermore the amplifier can only swing half a volt, which while adequate for 16-ohm headphones, proves inadequate when driving 300-ohm headphones, such as the Sennheiser HD580s or HD600s. One solution I can envisage is a small tube-based headphone amplifier large enough to house the CD player. Above is a side profile of such an amplifier. The CD player sits on top of half-inch thick foam or felt and four tubes protrude through the chassis. An eighth-of-an-inch thick sheet of anodized aluminum wraps across the top and front of chassis, hiding the plain Bud box underneath. Inside the chassis, the power supplies for both the amplifier and CD player are housed. On the front panel, two outputs are offered: 32-ohms and 300-ohms, the 32-ohm output having a much-larger-valued coupling capacitor but, by necessity, a poorer-quality coupling capacitor. The power switch sits exactly in the middle of the front panel. |
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April 3, 2003 |
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More š |
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TCJ horizontal headphone amplifier, capacitor coupled with DC servo loop |
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Here is one last variation on a theme (I can easily keep writing and drawing until this blog entry becomes a thick book that is never published). Unfortunately, there isn’t time to go into Pawel’s solid-state circuit; maybe next time. //JRB |