Balanced Direct Coupled Ultra Wide Bandwidth Phono PreamplifiersSeta phonograph preamplifiers provide the users of Channel D Pure Vinyl software with an end-to-end route to the superb performance obtainable from "flat" vinyl reproduction (linear amplification followed by software RIAA correction). Seta preamplifiers offer a fully balanced (from input to output), low-noise, direct coupled (DC) differential circuit design, with an unprecedented (5 MHz) signal bandwidth - even at high gain settings.
About SetaListening evaluations using a variety of reference systems and program material show that an important key to accurate reproduction of vinyl audio involves greatly increasing the signal bandwidth of the preamplifier front end (the first stage of amplification touching the signal from the phono cartridge).
Why? High quality phonograph cartridges are capable of reproducing signals well over an octave above the audio range.
While such signals are inaudible, the preamplifier also must work to amplify these signals, which also are boosted over 20 dB above midrange levels (because of the standard vinyl treble pre-emphasis curve used in the mastering process). A preamplifier unable to handle out of band signals will distort in the ultrasonic region. This distortion will carry over into the audio range, affecting the reproduction of the midrange and treble.
Futhermore, the audibility of one of the most maligned deficiencies of vinyl, those irritating "pops and clicks," is a function of and can be exacerbated by the design of the preamplifier. The reason is that the transient signals caused by the stylus striking a scratch or foreign object in the groove have, in addition to large amplitude, a very fast risetime, and are unlike any musical signal. The fast risetime can cause slewing distortion in traditional narrow bandwidth or inexpensive phono preamplifiers, magnifying the audibility of pops and clicks. It's quite possible that this nonlinear coloration from a less capable preamplifier is at least partially responsible for causing many music lovers to shun recordings in the vinyl medium! The Seta wide bandwidth design employs a fast-responding front end gain stage with a slew rate of over 500 volts per microsecond (Model L), making it immune to transient distortions induced by pops and clicks, minimizing their impact on the listening experience. (The slew rate of the Seta output is deliberately limited to avoid causing slew rate distortion in any following components.)
How much bandwidth is enough?The rule of thumb for linear signal reproduction is ten times (an order of magnitude) greater than the signal of interest. With that criterion, the amplifier is able to linearly reproduce out of band signals, while preserving the integrity of the midrange and treble without the "haze" caused by, and characteristic of, ultrasonic intermodulation distortion. Going still further, extending the bandwidth by two orders of magnitude, delivers a stunning improvement in three-dimensionality and imaging.
Noise LevelSeta preamplifiers, besides providing the widest bandwidth of any phono preamplifiers available (Seta Model L, -3 dB DC to 5 MHz), also feature low noise. Here is a comparison of measurements performed by Stereophile of the signal to noise ratio (SNR) of moving coil phono preamplifiers, including our Seta Model L. Higher numbers are better.
Circuit DesignThe Seta front end circuitry is tailored to preserve the strengths of the characteristics of different cartridge types. A low noise, high impedance FET front-end is used in the Seta Model H for moving-magnet and other high output cartridges, while an ultra-fast, ultra low noise bipolar transistor front end is used in the Seta Model L for low impedance, low output moving coil cartridges.
The circuit topology is fully differential, balanced direct-coupled circuitry from input to output. The front-end active circuitry is surrounded on five sides by a sub-enclosure machined from a solid block of copper. This provides electronic and acoustical noise isolation plus thermal stabilization. Bare copper metal surfaces are coated with a clear lacquer to prevent oxidation (and to maintain their beautiful color).
Unlike many other preamplifier designs: the rated (-3 dB) bandwidth is independent of gain.
Rechargeable Battery Power SupplyThe low-impedance, internally located AGM rechargeable battery is capable of supplying 50 amperes of current, outperforming other types of batteries used in audio applications. The battery is conditioned and kept float-charged by a proprietary, uniquely designed rail balancing circuit, rather than use an "off the shelf" microprocessor based conditioning and monitoring circuit, which would introduce unwanted noise. Locating the battery inside the preamplifier chassis also insures that the battery is in the same electrical environment as the sensitive front-end circuitry, eliminating potential sources of noise pickup. The external charging supply is automatically disconnected when an input signal is detected.
MechanicalAll connectors are the best available, professional quality Neutrik gold contact XLR, premium Switchcraft TRS and WBT gold contact helical conductor wide bandwidth RCA. Pushbutton actuated, sealed gold contact small signal relays are used to change gain settings (four different gain settings). A unique rear-panel (optionally on front panel) rotary balance trim control with a precision 2 dB range provides for fine cartridge channel balancing (the trim setting is not affected by the overall gain).
Seta Wide Bandwidth Direct Coupled Balanced Preamplifier Product Line
Seta Model L and Seta Model HModel L - Fully Balanced, Wide Bandwidth 5 MHz "Flat" Phono Preamplifier for Low Output / Low Impedance Moving Coil Cartridges; Low Impedance, Low Current-Noise Hybrid Bipolar Input; High Performance, Low Noise Internal AGM Battery Power Supply.
Model H - Fully Balanced, Wide Bandwidth 1 MHz "Flat" Phono Preamplifier for High Output / High Impedance Cartridges; High Impedance, Low Voltage-Noise Hybrid FET Input; High Performance, Low Noise Internal AGM Battery Power Supply Specifications
Of course, the "last word" in the evaluation of audio products should be done by using the best "measurement:" real-world, listening-based evaluation. However, we believe that careful measurements also are essential, if only to insure that the product you receive actually conforms to the designer's original vision and intent.
*Note: If you're accustomed to using conventional phonograph preamplifiers, the available Seta gain settings may seem somewhat lower than usual. However, they are tailored to using the Seta with Channel D Pure Vinyl's digital vinyl compensation curve. The required gain is about 10 to 12 dB less than needed in a conventional phono preamplifier, because the signal is provided to Pure Vinyl with treble emphasis (boost) intact. (For the technically knowledgeable: this turns out to be somewhat less than the maximum 20 dB correction of the RIAA compensation curve at 20 kHz, due to the frequency balance of most music.) For example, if you would normally use a preamplifier gain of 40 dB for a moving-magnet cartridge, then the proper setting on the Seta would be 29 dB (or perhaps 35 dB). Likewise, the optional RIAA hardware compensation module provides an additional 12 dB of gain (at 1 kHz).
Seta RCM - RIAA Compensation Module (Optional Hardware)Seta RIAA Internal Correction Option: Optional Internal Hardware RIAA Correction for Seta Model L or Model H. Includes Balanced (Neutrik Gold Pin XLR) and Single Ended (WBT Nexgen Helical Contact RCA) RIAA Phono Outputs. Can be used simultaneously with the Seta Flat outputs, for independent all-analog monitoring/listening plus Flat output to external digital converter. Specifications
Seta NanoFully Balanced, Wide Bandwidth 3 MHz "Flat" + RIAA Phono Preamplifier with Monolithic, Low Noise Front-End; for Low Output Moving Coil Cartridges; Low Noise DC Power Supply Specifications
"CLASS A" RECOMMENDED COMPONENT (Editors' Top Picks - Phono Preamplifiers,
Seta Model L) Stereophile -
"[The Seta Model L] is a quiet, remarkably neutral-sounding, extremely well-built phono preamplifier...
[the Seta with Pure Vinyl's digital RIAA] was fundamentally accurate in terms of tonality and space, and its low- level resolution was remarkable."
"A very linear circuit? [no intermodulation products in] the spectrum of the [Seta Model L's] flat output...
no distortion harmonics can be seen above the noise floor, even when the load impedance is reduced to a punishing 600 ohms!"
Experienced in developing commercial application software
for the Apple Macintosh platform since 1985.
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