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Reviewer: Jeff Day
Vinyl: Garrard 301, Cain & Cain plinth, Denon 103 MC cartridge, Pete Riggle Audio VTAF, Fi Yph phono stage, Auditorium 23 moving coil step-up transformer, Origin Live Silver Mk 1; Miyabi 47 MC cartridge, Miyabi Standard MC cartridge, & Mk 2 tonearm, SME 3012 tonearm, Tom Evans Audio Design Groove+ phono stage, The Cartridge Man Isolator [in for review]
FM source: Vintage early 1960s Scott 370 FM vacuum tube tuner, Magnum Dynalab ST-2 vertical omnidirectional FM antenna
Digital sources: Meridian 508.20 CD player, Audio Logic 2400 DAC, Superscope PSD340 Music Practice Tool & CD recording system
Preamplifiers: Tom Evans Audio Design Lithos 7 Vibe with optional Pulse power supply
Integrated amplifiers: Almarro A205A Mk1 & Mk2, Sonic Impact Class T, Sonic Impact Super T
Amplifiers: Fi 2A3 monoblocks; Tom Evans Audio Design Linear A
Speakers: Avantgarde Duo 2.1, Omega Super 3 (Skylan Stands); Omega Super 3 XRS [in for review]
Cables: 47 Laboratory OTA cable kit; Nirvana S-L & S-X interconnects, S-L speaker cables, Duo wiring harness, and Transmission Digital Interface; Cardas Neutral Reference digital cable, Auditorium 23 speaker cable; Tom Evans Audio Design interconnects [in for review]
Stands: McKinnon Bellevue Symphony media cabinet, Atlantis Video Reference equipment rack, Billy Bags 2-shelf rack
Room size: 20' L x 17' W x 17' H
Review component retail: $7,000
The enthusiasm I had for the Tom Evans Audio Design components' high level of performance in my HiFi rig is quite evident in my reviews of the 25wpc Linear A stereo amplifier and the Vibe Lithos 7 preamplifier with optional Pulse power supply. I was really blown away by the transformation they made to my system. My Duos never sounded better. And I ended up buying the review samples, something I'm almost never tempted to do. I tend to be one of those guys who hang onto gear for a long time without being overly concerned about switching it out for the latest marvel. Yet the TEAD gear up-ended my apple cart and I parted with the long green.
Most of the top tier gear doesn't vary all that much in ultimate performance. Rather, it just brings something a little different to the sonic and musical sensibilities of my review system - a different flavor rather than a different world. Do you prefer strawberry, chocolate or vanilla? Or at least that was my flat-earth view of the audio world until I got my mitts on Tom's gear. That pretty much humiliated everything that went up against it and exploded my perspective on ultimate performance. How much better is Tom's gear than most top tier gear you ask? I think it's as much better as the best SET amps are better than a $100 integrated amp from Circuit City. I was flabbergasted!
There's a down side to nearly everything of course. The TEAD gear is no exception. It's relatively expensive, albeit fairly priced for its level of performance I suppose. Yet it's not going to win any realsization awards for pricing from Srajan. It did win a Blue Moon Award from me (as in something this good only comes around once in a blue moon). The Vibe preamplifier doesn't have any kind of a balance control. Two mono volume controls or a stereo balance control would be nice. A mute switch on the Vibe would be a nice touch, too. Then there's the 25-watt power output of the Linear A. While a powerhouse compared to most SET amps, in reality it is still limited to powering reasonably sensitive loudspeakers.
I've now had more saddle time with the TEAD electronics. Plus, I've received feedback from the field from a number of TEAD owners with different system contexts. I'll report on my further observations about this gear that have developed over time and talk about synergy effects that readers have shared towards the end of this article. You might be wondering if I'm still as enthusiastic as I was originally was about the TEAD gear? Read on.
Tom's Groove+ (pronounced Groove Plus) phonostage is the ultimate version of his already highly esteemed standard Groove. The Groove+ was created by adding the supercharged capabilities of the Pulse power supply to the standard Groove. This raised the Groove+ to a whole new level of sonic and musical performance just as it does for the Vibe preamplifier. On the Groove+, there's not a lot to see on the outside. The magic is hidden within the Perspex chassis. The only evidence of the life within is the softly glowing blue light indicating a powered-up condition. The back panel connections on the Groove+ main chassis are pretty straightforward. On the far left is a grounding point for your favorite tonearm, with one pair of RCA inputs & outputs right next to it. On the far right side is the connector for the power supply. That's it, tour over. The power supply is similarly Spartan: A blue indicator light on the front and a power cord receptacle and on/off switch on the back.
A walkthrough of the Groove+ power supply
To deal with the ultra-low output of a moving coil cartridge, the Groove+ employs more amplification of that delicate and fragile MC output signal than the amplification factor of Vibe preamplifier & Linear A amplifier combined (about 35 times the signal in their case). The Groove+'s first gain stage is 500 times the signal, which then goes through passive RIAA equalization and is further amplified by the next gain stage over 100 times, giving a whopping total voltage gain of over 5000!
Preserving all of the data contained in the tiny millivolts-sized output signal of a moving coil cartridge (my Denon DL-103 has 0.3 mV of output, for example) through all that amplification means that the power supply must provide vanishingly low-noise voltage to the critical amplification stages and enable maximum dynamic range. To accomplish this, we need more than just a big transformer. We need to also supply ultra low-noise voltage to the circuit, be able to support blindingly quick transient response times and provide instantaneous recovery times - a tall order. To accomplish these goals, there must be incredibly sophisticated regulation and filtering circuitry in the power supply as well as a big transformer.
Tom holds that commercially available voltage regulators have voltage noise equivalent to the output of a moving coil cartridge itself (off-the-shelf regulators produce internal voltage noise of 0.15 to 0.4 millivolts). It would be a sonic and musical disaster to implement a commercial regulator into a phonostage power supply if the noise was similar in magnitude to the signal. An alarming amount of signal data would be irretrievably lost to the masking of noise. According to Tom, all amps have an ability to reject some of this noise, but the ability reduces as the frequency goes up. Off-the-shelf regulators also exhibit very slow transient response and recovery times, compounding the signal degradation begun with the high noise floor.
Tom has developed his own high-performance high-speed line of regulators dubbed Lithos that resolve all issues of noise, slow transient response times and slow recovery rates. Tom's Lithos regulators provide a huge advancement in speed and resolution that makes for a much better sounding, more detailed and life-like musical experience. Tom develops his Lithos regulators to excel at specific tasks. The Lithos 7 was designed for local regulation, the Lithos 6 for pre-regulating multiple Lithos 7s for deeper regulation. Hence the blacker-than-black backgrounds with serious dynamic range and resolution. Tom's regulators are claimed to be a staggering 1000 times quieter, 53 times faster and 100,000 times more accurate than the best commercially available regulators commonly used in audio applications.
The main difference in the implementation of the power supply between the Vibe/Pulse and Groove+ is that the Lithos 6 used to pre-regulate the Lithos 7s located on the mono circuit boards would normally reside within the second chassis of the Pulse but is now placed inside the chassis where the standard Groove's power supply would normally reside which now has been relocated to the Groove+'s outboard power supply. The benefits are a shorter path for the Groove+ with the same deep depth of regulation as the Pulse.
Starting at the beginning of the Groove+, the AC mains supply goes through a TEAD- designed and manufactured 70-watt transformer with an electrostatic screen to remove RF contamination, then through ultra-fast soft-recovery rectifier diodes and 18,800µF of smoothing caps, then through more regulation located in the outboard power supply. The power is then regulated again and smoothed by 9400µF caps, then regulated again by Tom's +/- Class-A Lithos 6 regulators. Now that the AC voltage has had its pimply face scrubbed to super-model standards, the Lithos 6 regulators supply the ultra-scrubbed voltage to the Lithos 7 regulators located on each of the carefully matched mono phono amplification boards in the Groove+. This treatment of the AC power lowers the noise floor to a theoretical -186dB.
You might be wondering why Tom doesn't use a battery power supply for the Vibe and/or Groove+ given how much is involved in getting the AC cleaned up to the extremes Tom demands. I did. Tom's reply: "To get a battery to consistently outperform the L6 and L7, it would have to be the size of a walk-in freezer." Okay, that's a pretty compelling argument. Next topic.
The analog signal chain
To really understand the analog signal chain, you have to start a little earlier than the output of the moving coil cartridge seen by the Groove+. Let's take a quick moment to look at the vinyl recording and playback process to pick up some useful information. To generalize and simplify, let's start with the musicians being recorded onto audio session tapes at a live performance or in a recording studio. Those session tapes are tweaked by a mastering engineers to get the sonics optimized to their preference and produce what is called the master tape.
The signal from that master tape is then passed through electronics that apply an RIAA equalization curve on the signal's way to the lathe cutting heads. Almost all phono phreaks have heard of the Recording Industry Association of America's (RIAA) equalization curve applied to the signal upon disk cutting and record playback but don't know much about it other than that it's an equalization curve. The RIAA equalization curve has been around for quite a while - say 1954 or so. Before 1954, every record company applied their own equalization curves -- there were over a 100 different curves in use at one time -- so you can imagine the kind of pandemonium that resulted. In 1954 the RIAA equalization curve was informally adopted by record producers and by default became the global standard. [Yamada-San of Zanden Audio spent years cataloguing the diverse curves and then outfitted his phonostage with the three most important ones, providing a list of the most popular record labels and which equalization curve to use for their albums - Ed.]
Now back to the signal from the master tape. The signal goes through RIAA equalization electronics like in a phonostage but in reverse. This deemphasizes low and emphasizes high frequencies. The RIAA curves have transition points at 2,122Hz, 500Hz and 50Hz. Simplistically speaking, the RIAA curve cuts the lower frequencies at -6dB an octave below 1000Hz (the 0dB point) for a total of -20dB of attenuation and boosts the higher frequencies at +6dB an octave above 1000Hz for a total of +20dB of gain, giving a total of 40dB of equalization over the entire frequency range. That's a lot.
The low frequency attenuation is necessary when producing records to limit cutter head excursions such that a reasonable amount of playback time results. Smaller grooves means you can fit more grooves of music on each side of a record. If the recorded bass wasn't attenuated, you'd only get about 5 minutes of music per record side, a major pain from both a convenience and cost standpoint. Then there's the added sonic benefit of reducing stylus forces during playback to minimize distortion. High frequency amplification is necessary to insure that high frequencies are louder than the noise inherent in the vinyl media. When equalizing back to flat, this also reduces noise and high frequencies can be clearly heard above the noise threshold of the vinyl .
The signal from the master tape goes through the electronics that apply the RIAA equalization curve and on to the cutter head, which cuts a mechanical analog of the electrical signal into a lacquer disk as a modulated groove where the left and right sides of the groove represent the left and right channel signals. The lacquer master is then electroplated with metal to produce a negative and after a number of intermediate steps, becomes a metal stamper that is used in hydraulic presses to make LPs. It's really amazing that anything of the original signal survives at all after all those steps.
The cartridge stylus riding the record grooves converts the mechanical analog of the original electrical signal back into an electrical signal that is transmitted to the phonostage as a very small voltage. A moving coil's ultra-low output resides in the millivolts range - thousandths of a volt. There isn't a lot to work with. For example, my Denon DL-103 cartridge puts out 0.3 millivolts. That's a mere sneeze in the gale force winds of audio voltages.
A walkthrough of the Groove+ signal path
Now that we've got the power supply of the Groove+ sorted out and a decent description of how an analog of the original electrical signal coming off the microphones makes it onto an LP, let's return to the signal exiting the MC cartridge. With my Denon DL-103, 300 microvolts enter the Groove+ through hardwired silver/Teflon cables to the double-sided and through-hole plated mono printed circuit boards. These critical PCBs have been designed with both top and bottom ground planes tri-split to control earth current paths. The Groove+'s gain stage is a DC-coupled design with no capacitors in the signal path so that it will accurately reproduce the wide bandwidth analog is capable of. The output signal passes through the gain stage op-amps and is amplified by a factor of 500, then goes through a very accurate passive RIAA equalization stage.
"I found while designing the Finestra preamp in 86/87 that the common way in the industry of placing RIAA equalization inside the feedback of a device (valve, chip or tranny) was a bloody sonic disaster." Accordingly, Tom has been careful to avoid that performance-degrading mistake in his designs. The output of the RIAA stage is then further amplified by a >100 voltage gain for an overall gain of 500 x 100. The Groove+'s output stage uses current rather than voltage feedback to ensure faster rise and recovery times (less than 10 nanoseconds), made possible by the ultra-high performance Lithos regulators. With conventional voltage regulators, noise is too high to allow for this approach. Power supply noise would cause a significant reduction in resolution and dynamic range. However, "the intelligent use of current feedback enabled by Lithos regulation is a key feature in producing a more lifelike presentation because it greatly improves linearity and bandwidth.
"Within the second gain stage, there is also an active DC filter that allows the Groove+ to reproduce the fast rising and falling edges of music while maintaining a low output impedance to easily drive any length of cables. Like the Vibe, the Groove+ also utilizes error-correction circuitry and the application of psycho-acoustic principles in its design. It is a well known fact that the ear/brain is sensitive to changes in phase (time) versus frequency. It is in the ear/brain domain that the spatial cues are contained, which is one of the foundations for making some kind sense of what's being fed to your ears. To eliminate phase errors from my amplifiers; the Micro, Micro+, Groove, Groove+ phonostages; and the Vibe line stage; all incorporate 'active phase error cancellation' circuitry. This is why you now have access to so much more musical information and why it's become so easy to absorb what you are hearing."