My latest aquisition ... custom 6EM7 SET amp

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by Scubadude, Jun 23, 2016.

  1. Scubadude

    Scubadude Almost "Made"

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    About two weeks ago I saw a custom valve headphone amp / linestage preamp being advertised on a local forum. Thought nothing of it until a fellow headphone fanatic asked if I would be interested to do a joint buy …. An opportunity to delve deeper into valve amps than previous experience with relatively mundane pieces like Schiit Lyr, LD Mk III and Pathos Aurium allowed. And to put a fine point on it ... two of these are hybrids, so they hardly qualify as valve amps at all!

    So I start to research this potential purchase and trace back it’s history to the late 90’s, when Wim Bouwman (Mr Valve to South African aficionados ... sadly killed in an all-too-typically South African botched hijacking some years later) was commissioned to do a cost-no-object custom build to a design by Alan Hobkirk (another highly-regarded local valve guru). The brief was to produce the “ultimate headphone amp for HD650’s” that could also be used as a line stage for his Mark Levinson amps feeding ProAc 3.8s. As it turns out the original owner is the same man I bought my beloved (and much hated around here) SPL Phonitor last year.

    So I got in contact with Gerald and from memory he gave me a rundown on some of the aspects of the design and construction of this decadent amp:

    • Dual power supply, dual mono valve amp

    • No feedback design, with three discrete cascaded power supply filter stages; all transformers and chokes custom wound using best materials available

    • Choice of 4-pin or 8-pin rectifier tube sockets (5U4G mercury vapor rectifier tube currently fitted)

    • 6EM7's as the audio stage (the 1st half of the 6EM7 is high gain-low current and acts as preamplifier while the second stage which is low gain-high current to drive the headphones)

    • All resistors are Mills non induction wire wound, and all non-critical resistors are Allen Bradley (all resistors are 12W+)

    • Input caps are Cerafin, others are MIT, Infincap and Solen Polyprops. Apparantly there were some Rubycon Black Gates installed at some stage but they have since been replaced.

    • The volume control is a stepped attenuator courtesy of Danish Audio (basically a stepped switch using an Elnaswitch + surface mounted 1% resistors)

    • RCA's are WBT

    • Brushed aluminum chassis
    I could go on … but you get the idea. Parts cost at the time was around $1800 ... so truly not a cheap build! Extreme care in the design, layout and construction resulted in an absolute gem of an amp. It weighs in at around 50 lbs – more than many power amps.

    Sound-wise it on the opposite end of the sonic spectrum than the SPL Phonitor I mentioned earlier. If you want deadly accuracy, razor sharp dynamics and pin-point imaging look elsewhere. Frequency response is not terribly extended up or down. Overall the sounds is a little mid-centric with a bit of upper bass bloom. Macro dynamics feel a little soft and micro dynamics is substantially diminished. And there is a bit of hum which a previous owner tried to fix by playing around with ground connections and slight channel imbalance at low volumes.

    So it is far from perfect, but if is real music you crave this is simply superb. I read somewhere that the more our lives become technology-driven we have an innate need to come home to a house full of furniture made of wood and leather. And that is the primeval nerve that this amp stirs for me, immersing me in a deep emotional experience of the music rather than begging analytical listening. If gives the HD800 an effortlessness reminiscent of the Woo WES / Stax SR-009 combination. Acoustic instruments and vocals sound full and rich … real … like it is made of wood and leather.

    A previous owner of this amp remarked “this is the best headphone amp I have owned, and I’ve had quite a few. Not the most accurate amp but by far the most satisfying.” I think I agree … this is a keeper!
     
    Last edited: Jun 24, 2016
  2. Scubadude

    Scubadude Almost "Made"

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