A familiar landscape under unexpected light conditions In the immortal words of Notting Hill's Rhys Ifans, only "a daft prick" would expect a high-powered push/pull amplifier to sound like a micro-powered SET. On occasion however, a leading man daft prick -- like Hugh Grant in the same movie -- does conquer the odds in the end to walk away with the coveted prize. In the real world of High-End audio, I got to wear Hugh's role for size. Little did I know that I'd enjoy equally smashing results (minus the movie star salary of course - writers live word to mouth). |
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The differences were not subtle. The new cap (since standard issue in all XL production models) was clearly more refined and smoother yet also offered more detail. This was my isolated brush against the dance of parts substitution which electronics designers undergo in their exhaustive voicing process of products. Now the real demonstration of the variable tuning could begin, centered around the predriver's idle current and output stage bias . The team unbolted the front grate and one of the sides and popped the cover and rear panel. Elliott then played math whiz on his calculator. He had decided to shift the tonal center of his amp subtly downwards. He would decrease the operating values of his eight emitter resistors in the Class A predriver stage to raise its quiescent current. He approximated a 20% offset to be a good starting point. He calculated the corresponding values for the piggybacked parallel resistors Dai would fish from the well-stocked traveling tool box to install momentarily. |
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With the nonchalant precision of a Black belt solder surgeon, Daii operated in what seemed rather crammed quarters of the tightly populated circuit board. He worked in record time and without missteps or "overdubs" on my kitchen's butcher block cart.
Michael then confirmed his handiwork under a magnifying glass. The patient was alive and kicking and close to ready for round II. |
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Before we could resume listening, a matching reduction to the bias current in the output stage had to be made. Out came the voltmeters and a Variac. After the requisite settling period of the heatsink temperature, the corrected value was affirmed and locked in via trim pots. The eagerly anticipated follow-up listening session could commence. I had no idea what to expect but remembered Rhys Ifans' scene-stealing character.
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At this juncture, it seems important to stress that these two adjustments were complementary to retain the circuit's innate balance. Elliott increased the idle current of the predriver stage and reduced the bias of the output stage. Apparently none of these changes result in any measurable frequency response variations. Audible changes would live in the realm of "you might hear it but you won't be able to prove it on paper".
Hot damn & vanilla ice-cream with tart cherries! The minor thickness and oversaturation had now evaporated. The aural landscape was recognizably the same, but the lighting had shifted. I could now clearly see between and around the performers to experience the space they were performing in. The subtle grit that hovered like dust motes between the artists and somewhat interfered with their outlines was gone. Put differently, the textural weave had expanded for more spaciousness. This released the concomitant aroma of musical relaxation coupled to keener resolution. Simultaneously, the sense of presence was strongly heightened. The drama of immediacy had been enhanced to accentuate what I call communicativeness - when the music reaches out across space to come to you. Though Elliott had indicated a small timbral downshift, I clearly heard added lucidity in the piano's decay trails even in the upper registers. What was going on? |
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Only after listening to the phenomenal French double bassist Renaud Garcia-Fons was I certain that Elliott had indeed shifted the timbral balance downwards - the Jacob's ladder of upper harmonics inside the blossoming bass notes didn't extend quite as high. Perplexingly though, rather than sounding darker, the amp clearly exhibited more openness. |
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While there probably was slightly reduced perceived HF energy, this apparent reduction acted as though a certain hash or high-frequency dither had been removed to deepen the blackness between and around the notes. Michael and I compared observations. Though we used different terminology to describe what we heard, it was clear that we not only both perceived the same phenomena but, in this particular system context, clearly preferred the post-op results.
Had I been a paying client -- or belligerent reviewer unawares of the travel fatigue both gents were exhibiting by now -- I would have pressed for additional adjustments. |
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Would a further movement in the same direction by, say another 10%, have elicited ongoing improvements? Or would it have worked backwards? And what, for curiosity's sake, would moving in the opposite direction past the starting point accomplish?
Mission accomplished, return to base
Say again?
Hugh Grant, disheveled, out of time and prepared to utterly humiliate himself in front of Britain's most distinguished press, finally utters the self-directed condemnation of his roommate-from-hell in public. Julia Roberts leans to her producer who asks one of the journalists to repeat his prior question. Post Script Both Aria and AUDIOPAX amplifiers accomplish their tunable voicing by altering their bias current. The former requires parts swapping by the designer, the latter is deliberately user-adjustable. Both designers confirm that these sonic changes do not affect measurable frequency response but operate in the timbral domain of harmonics. I recall a review of Herron Audio's solid state amplifiers who had been mistakenly delivered with miscalibrated bias current. Once rectified, the reviewer was shocked at the extent of the sonic improvements. Owners of tube amps with user-adjustable bias already know about these effects. Manufacturer's Reply Our deepest thanks to Srajan for taking the time to review the Aria WT100LSXL power amplifier. Ever since these amplifiers were introduced, we've received overwhelming response. Partially due to the excellent sound that listeners have enjoyed. Partially due to the great value that these amps represent. Partially due to the lifetime warranty . . . and I can't help but think that it is also somewhat due to the fact that the customer can deal directly with the designer (me). Each WT XL amplifier is built individually to the customer's requirements. As is illustrated by Srajan's experience where we were able to re-voice the amplifier to provide the SET sound he prefer, it is voiced to meet the sonic preferences of the listener. (Well, I better qualify that last statement: it's possible to get just about any sound quality you like as long as you like what tubes do. It's no more possible to get a WT amp to sound like a transistor amp than it is to get a transistor amp to sound like a tube amp. That said, within the palette achievable by a good tube amp, you can get what you want with the WT amps.) Reader Feedback (none yet) |
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