Authorized re-publication of review from:
The Inner Ear Report,
Volume 15, #3 2003, pp. 17-20
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This preamplifier is Wyetech Labs brand new entry into the world of lower priced components. Regular readers may have noticed that we often refer to an in-house preamplifier-the Opal-which was introduced in 1998, shortly after Roger Hebert, founder and designer, launched his original design, the Topaz amplifier. Hebert is an idiosyncratic man whose designs are centered around vacuum tube electronics and the parts used in them. He is known for his attention to detail, his craftsmanship, his rationale for circuitry pureness and simplicity and his dislike for all commerce-related activities.
Most of Wyetech Labs' designs are expensive and all are what we consider high-end. Except for the Onyx monoblocks (single-ended vacuum tube amps often used for our auditioning sessions and reviewed in Vol. 13 #4) Hebert has simply ignored lower priced components and, until now, has not produced anything else in this price range, reasoning that too many short-cuts dilute performance. We were told that the preamplifier under review was a challenge to prove that cost efficient circuits can harmonize with other high-end components and please seasoned listeners. Be this as it may, the Coral is a cost efficient design and we begin with its...
The chassis and faceplate are made of dark lavender machined 1/4" and 1/8" inch aluminium plates which are bolted together with stainless steel screws. The front plate accommodates (from left to right) selector switch, tape monitor toggle, balance control, mute toggle, volume control and on off switch. A set of red and green lights serve as operational indicators. A pair of brass handles complete the preamplifier's front which results in a retro (circa 50's) look some folks will love and others will not.
The unit is 15 inches wide, 10.875 inches deep, 3.75 inches high and weighs 12 pounds (5Kg).
A line-stage preamplifier such as the one under review serves both to amplify the signal for the power amplifier and as a switching system for source components. -It's as simple as that, or is it? Well not quite! This preamp employs a grounded grid configuration which is separated before and after by a cathode follower stage. All stages are non-inverting, consequently retaining absolute phase. The grounded grid configuration is known for its extremely wide bandwidth and speed! The cathode follower output has a very low output impedance and can drive two pairs of RCA output jacks to accommodate bi-amping. All stages are DC coupled and only one capacitor is used in the output stage for DC blocking. The unit employs no feedback at all and its circuitry is designed in a mirror-imaged configuration on the printed circuit board for the audio section. Overall amplifier gain is selectable via internal jumpers for 4.5dB or 12.5dB.
A toroidal transformer is used in the power supply to assure low noise and decrease magnetic field radiation to surrounding areas. A Pi RC filter is used for the 250-volt plate supply and a dual Pi RC filter is used for the 12-volt filament supply. As in the more expensive OPAL and JADE preamplifiers, these filters employ only passive components that allow the speed of the power supply to keep up with the analogue circuitry. All components are hand-soldered on a dual layer printed circuit board that is masked on both sides to protect and insulate the circuit paths. In addition, a silk screened top layer identifies the components and their position on the board. All analogue wiring to and from the circuit board is accomplished by screw-down terminal connections.
Hebert imports the volume control from Denmark. It's an ELMA control that employs 0.1 % precision metal film surface mount resistors with a life expectancy second only to the Shallco military switches used in the Opal preamplifier. As in all Wyetech Labs components, workmanship, layout and parts quality are first-rate.
Have a look at these impressive specifications: frequency response (reference to a sine wave at 3.5Vrms output) is from 20Hz to 120KHz (+/- 0dB), from 9Hz to 425kHz (+OdB/-1dB), from 4Hz to 825kHz (+0dB/-3dB); [try that SACD player with this unit]. Input impedance is 50k ohms; output impedance is 150 ohms; rated output is 3.5V rms (maximum 7.5V rms); channel balance is an 11 position control offering +/- 5dB adjustments in 1dB steps; the gain control is a 24 step attenuator ranging from -60dB to 0dB. Though the specs are impressive, the proof of the puddin' is in.
As we have had the top of the line Wyetech Labs Opal in-house for some years and our listening panelists are intimately familiar with its sonic attributes, we undertook an A/B comparison. Although we don't believe in comparing different brands, we do believe in examining sonic resemblance in components from the same manufacturer. Thus, we began our test connecting the Coral to our in-house Onyx, Bryston (reviewed in Vol. 15 #1) and Croft amplifiers (reviewed in this issue). Auditioning speakers included the Gershman Acoustics model GAP and the PMCs (both reviewed in this issue).
Upon inserting the Coral into the existing system, our first impressions included a little surprise and a lot of disbelief. Surprise that the Coral's elementary sonic character was almost identical to the Opal?s; and disbelief that Hebert had come up with great sound at less than one third the price of the Opal. Armed with some CDs that include musically complex material, we settled down for some no-nonsense fault-finding sessions. Well, it took a little time but we found what we were looking for: a little less imaging proficiency than with the Opal, a little more energetic at top and midrange frequencies and a little less determination in the extreme bass range, though still quite satisfactory. Although the Coral doesn't sound as "open and graceful? as its larger sibling, it does preserve the tonal attributes.
Highs are sweet, transparent and unimpeded. As with the Opal, it is difficult to judge what technical system is at work, for the preamplifier doesn't sound like a typical vacuum tube device-nor does it sound like a characteristic solid state design. No distinguishing traits are evident except the ones picked up from the amplifier or source components.
Midrange information is clear of sonic impurities and allows listeners to hear musical subtleties, delicate inner detail and resolution. Extremely polished, complex harmonics-difficult stuff to reproduce-fall short of being complete but not by much, we may add!
The Coral offers tight, fast and resolute bass. It's powerful, full-bodied and only when compared to much higher priced components, including the Opal, does one get the sense of something missing-warmth and some harmonics.
During our listening tests, we switched between the two Wyetech Labs preamps and the various power amplifiers, which confounded our panelists again and again, making this evaluation a bit of a chore. The reason for this rather prolonged confusion was the Coral's sonic similarity to the Opal. Casual listening doesn't reveal the slight, difficult to notice and appreciate differences, as the underlying sonic attributes are simply too close to those of the Opal. Even experienced listeners will have some difficulty finding discrepancies which are limited to more intricate elements such as space-time, imaging, harmonic gradation, etc. This said, we feel that the Coral will function quite satisfactorily with high-end systems, allowing amplifiers to work freely-without imposing its own signature or altering the amplifiers' sonic attributes. Those who are acquainted with high-end will appreciate this preamplifier, as the price/performance ratio is exceptionally high; and those who are looking for a bargain to improve a system's performance will find that the Coral is a few steps above similarly priced preamplifiers. It can be regarded as the first move into the high-end market where function must coincide with enjoyment and convert technology to music.
© 2003 The Inner Ear Report