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Having satisfied myself that the speaker's low bass was excellent, in absolute terms, I felt the Parsec to have too much mid- and upper-bass energy. While this added a quite exciting degree of impact to typical rock recordings—the Stygian synth just purred in Simple Minds' "Let it all come down," from the band's The Amsterdam EP (Virgin SMXCD 6)—it was a little too good to be true. Not that I'm complaining, mind. But I should point it out, particularly as this midbass balance will make finding the optimum placement in rooms smaller than mine more difficult than usual.
Sidebar 1: Review context
Description: Three-way, reflex-loaded, floor-standing loudspeaker. Drive-units: 1" metal-dome tweeter, 6.5" polypropylene-cone midrange, 10" graphite-impregnated cone woofer. Crossover frequencies: 350Hz, 1500Hz. Crossover slopes: first-order, 6dB/octave, high-pass, second-order, 12dB/octave, bandpass and low-pass. Frequency response: 25Hz–22kHz, no limits given. Sensitivity: 87dB/W/m (2.83V). Nominal impedance: 8 ohms. Amplifier requirements: 50–300W (120W continuous).
Dimensions: 47" (1194mm) H by 12" (305mm) W by 16" (406mm) D. Weight: 92 lbs (42kg) each.…
Sidebar 2: Review context
Source components used in the preparation of this review consisted of a Revox PR99 to play 15ips master tapes, a Linn Sondek/Lingo/Ekos/Troika setup sitting on an ArchiDee table to play LPs, and the Meridian 208 (Bitstream) CD player. Amplification consisted of a Mod Squad Phono Drive EPS hooked into one of the line-level inputs of the Meridian 208 CD player, which in turn drove either an Audio Research Classic 60 or a pair of Mark Levinson No.20.5 monoblocks via 15' lengths of AudioQuest Lapis unbalanced or balanced interconnect, respectively. Speaker cable was…
Sidebar 3: Measurements
I use a mixture of nearfield, in-room, and quasi-anechoic FFT measurement techniques (using primarily DRA Labs' MLSSA system with a B&K (DPA) 4006 microphone, but also an Audio Control Industrial SA-3050A 1/3-octave spectrum analyzer with its calibrated microphone) to investigate objective factors that might explain the sound heard. The speaker's nearfield low-frequency responses and impedance phase and amplitude were measured using the magazine's Audio Precision System One.
The Parsec's plot of electrical impedance magnitude and phase is shown in fig.…
Neither its rather pedestrian name nor Manley Labs' own literature gives much of a clue as to the 175 monoblock's special pedigree. Where are the bands, the fanfare?! After all, the rolling-out of a 6L6–based high-power audiophile-grade tube amplifier definitely qualifies in my book as a momentous occasion. Deplorably, such happenings are rare indeed; the 6L6 has been unjustly neglected in high-end circles.
The 6L6 was the first-ever beam power tube to be designed, and a certifiable American classic. Thousands upon thousands of guitar amplifiers, from Fenders to Mesa Boogies,…
Then I sobered up enough to form a more objective picture of the 175's performance with the Audiostatics. Stage lighting was darker than with either the Music Reference RM-9 Mk.II or the Pass Labs Aleph Zero amplifiers. The presence and lower-treble regions were a bit subdued, such that violin overtones lacked a full measure of sweetness. Specifically, while the extreme treble sounded open and reasonably airy for a tube amp, the 5–10kHz octave seemed deficient in brilliance. Bass lines weren't fleshed out with convincing definition, sounding a bit full and bloated. More seriously, bass-line…
The existing N.O.S. inventory is undoubtedly polluted by such rogue tubes. And with the high prices commanded by the likes of M-O Gold Lions, the temptation to falsify a tube's true origins becomes great. The problem, however, extends to new production as well. Bad batches of new tubes are just as likely to be sold as is the plant's premium production. Prospective buyers may get hurt, not only because they got ripped-off in the first place, but also from subsequent physical damage to the amp—a tube arc could easily take out a whole circuit board, causing extensive damage.
Manley argues…
Sidebar 1: A Bit of History
In the July 1936 RCA Review, R.S. Burnap recounted the development of the 6L6 at RCA's Radiotron Division. The power triode operating in class-A was recognized as the ideal output configuration—at least where its low efficiency (about 25%) and moderate power output were not practical obstacles. The power pentode, already around for several years at this time, was capable of class-A operation with nearly twice the plate efficiency of a triode, while requiring less than a third of the drive signal. The pentode's inherent fly in the ointment was rather large…
Sidebar 2: Specifications
Description: All-tube amplifier with class-AB, push-pull output stage. Output transformer tap: 5 ohms (factory-set). Output power (at 1.5% THD): 145Wpc into 8 ohms (21.6dBW), 180Wpc into 5 ohms (20.5dBW), 169Wpc into 4 ohms (19.3dBW). Frequency response: 10Hz–40kHz ±0.5dB. Input sensitivity: 1.4V for full output. Input impedance: 100k ohms. S/N ratio: 80dB ref. 180W into 5 ohms. Power consumption: 240W quiescent, 480W full-power.
Dimensions: 19" W by 7" H by 13" D. Weight: 48 lbs.
Serial numbers of units tested: MANEM175007/08.
Price: $4800/pair (1995…
Sidebar 3: Measurements
Following its 1/3-power, one-hour preconditioning test, the Manley 175 was no warmer than normal for a tube amplifier. Its input impedance at 1kHz measured 146k ohms; its output impedance was 1.6–1.7 ohms at low and middle frequencies, decreasing slightly to just under 1.5 ohms at 20kHz into 4 ohms. These are middle-of-the-road values for a tube amplifier, in my experience. The Manley's performance—particularly its overall in-system frequency response—will be somewhat dependent on the partnering loudspeaker.
The 175's voltage gain into 8 ohms measured 28.…