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The Mobile Fidelity Mobile GAIN System

(But Mobile Fidelity is No More)

Francis Vale

 

A few years ago, Herb Belkin, the owner of Mobile Fidelity Sound Labs and maker of audiophile CDs and LPs, did something most people never do: He put his money where his mouth was. He opened up wide his checkbook, and called in Nelson Pass, the legendary amplifier designer, and Mike Moffat, equally legendary for his work in digital electronics, and told them both to make MoFi the best damn recording system in the world. Herb got his money's worth. The result was the GAIN system (Greater Ambient Information Network).

As the man said, there is nothing like the thought of being hanged in the morning to help clarify one's thoughts, so here a few things to keep in mind should you care to try this redesign at home: The prior system used for cutting MoFi's analog LPs was made by Ortofon, and used 17 op amps in series with the gain path. It was all 1960's grade stuff, even though it was extremely advanced at the time.

At the LP cutting head, there is a 100dB difference between the bottom and top frequencies Furthermore, the protection systems for the cutter head are extremely difficult to get right. You don't want to be too obtrusive in protection and overload the circuits; yet you don't want to be too loose, and blow out the heads. These cutter heads are no longer made, and hence, are extremely expensive to repair.

And also don't forget, the instantaneous energy required by the cutter head is about 1 billion times that of a phono cartridge. Finally, the heavy coils used in the cutter head produce an Everest-sized, fundamental resonance peak smack in the middle of the 2KHz audio band, creating a 50dB response variation.

Piece of cake, right?

The Pass redesign agenda first and foremost called for minimizing the circuit stages in the analog recording process. By significantly reducing the number of potentially grundge-producing stages, he sought to bring a purer signal to the cutter head; and hence, a less distorted recording, with more of the master tape's original ambient detail still intact.

This subtle ambient detail is usually lost in commercial recordings. However, it is vitally important to overall sonic quality, as it can give a recording that elusive, you-are-there experience. Ambiance can include the reverb tail of an instrument, the ambient decay of a note, the recording venue's 'spaciousness', the hall ambiance, and all the rest of the pycho-acoustic cues necessary for your brain to successfully produce a good facsimile of a live event, with real people playing actual instruments.

What Pass did was quite clever. He took a cutter head and made a computer model. Next, he reduced all of the existing Ortofon circuits to yet another model. And then he extensively modeled everything to figure out how to make the most simple, overall circuit.

His hard work and patience ultimately paid off. He got exquisite control over the cutter head protection circuits; easily adjustable feedback; and most critically, he achieved a circuit with minimal gain stages.

All recording EQ and RIAA pre-emphasis were reduced to a single summing junction, and the Pass-deigned, single ended, 250W/Ch amplifiers (loosely based on the audio-rave Aleph 0) sat in the same feedback loop. This single junction provides: 1) the equalization-reverse RIAA characteristic of the cutter head; 2) the equalization on the cutter head itself; and 3) the feedback needed to flatten that 50dB response variation.

Overall, everything is set up in such a way that the reproduction system mirrors the idiosyncrasies of the original recording equipment involved. Finally, XLR interfaces tie all the GAIN system components together.

The initial GAIN system was installed in 1993, and it took a year of tweaking to get the EQ right. Incredibly, not a single cutter head was blown during the development process. (The heads also now sit in a helium cooled bath for increased thermal protection.) For analog discs, the desired cutting curve is now accurate to .1dB.

About those GAIN System single ended amps, now that these atavistic devices are the new darlings of the high end crowd: Pass said it is true that the unique second harmonic signature common to most SE amps does find its way into the cutter head. However, he said there is also some second harmonic distortion cancellation at the cutter head.

Moreover, Pass has two amps running in balanced mode within the GAIN system. He says this setup provides a certain amount of a conventional amplifier's push-pull characteristics.

But most important, according to Pass, a single ended amp design yields circuit simplicity. Instead of the 4 to 7 gain stages usually found in amplifiers, the Pass SE units have only three gain stages in the signal path. This minimalist amp philosophy is in perfect keeping with the overall goals of the MoFi system redesign.

And so, MoFi got what it wanted: a minimal signal path via the GAIN system, with the result being a minimum of overall signal degradation. But garbage in, garbage out. Thus, MoFi almost always uses a non-Dolby, half-inch tape analog master, running at 30 IPS with no equalizer, no processing equipment, and no patch bay. (It should be noted that most artists consider analog tapes to be superior to digital.)

MoFi also won't use copy tape; only first generation, two track tape. MoFi says the ordinary commercial version is 'dry' because ambient information is lost. And watching over everything to make sure that what comes out of your audio system is Sebastapol spring pure, is Joe Bermudez, the Vice President of MoFi Product development.

The first Mobile Fidelity ANADISQ 200 (gram) LP to be produced by the new analog GAIN System was Muddy Waters, 'Folk Singer'. After MoFi brought its big Muddy to gleaming Vegas for the 1994 winter Consumer Electronics Show, Belkin suddenly found himself deep in fresh invoice Waters.

For MoFi LP recordings, the GAIN system is all analog. But obviously, the CD reproduction system has digital stages. The key to the digital GAIN system is the a/d converter designed by Mike Moffat. But the real secret to MoFi's producing audiophile grade CDs lies in Moffat's super accurate sample clock within the a/d converter.

It is increasingly coming to light within the CD recording industry that timing errors can creep into the tape master to glass master disc recording process. And when they do, these time-shifted errors can cause significant playback problems. (The glass master contains the inverse of the land/pit information stamped into the production CD copies). These timing-induced errors are in the domain of jitter -- For more about jitter, see Impact article, this issue, 'Why DVD's Backers Won the Battle, but Lost the Consumer War.'

Rock bottom, the digital domain is all about time. E.g., the faster the CPU clock, the faster your computer. The faster the system clock of the main or local bus, the faster the data moves around inside the computer. And the poorer the data is timed in and out anywhere in this digital food chain, whether it be in your computer -- or in your CD player -- the more system errors you are going to have.

In the digital universe, the Clock is God. And if the Great Digital Clock God is having a bad hair day, then everyone suffers. Galaxies of bits collide, software universes collapse, and the digital music of the spheres gets corrupted.

Which is why Moffat's a/d converter super-clock is so critical to the success of the MoFi recording process. Anecdotal evidence now abounds that CDs made from the same master tape, but at different CD plants, still manage to sound different.

This phenomenon, if nothing else, finally puts the lie to "Perfect Sound Forever" and "Digital means perfect copies." This is simply not true, and explains why Moffat's highly accurate clock provides MoFi's UltraDiscs their decided purity of sound when compared to many other company's CDs.

It should also be noted that MoFi has succeeded in getting the full 16 bits of data as the CD spec mandates down on its UltraDisc recordings -- which full 16 bits very few commercial CDs possess; and even if all 16 bits are there, few CD players can process. (This great 'bit-rip-off' is another story unto itself.) But this full16 bit recording feat still pales in comparison to getting the bits accurately laid down in the first place. I.e., jitter free UltraDisc mastering.

Finally, there are the innovative, Thomas Tan-designed, interface modules. These proprietary modules couple the MoFi engineering consoles into both the analog and digital Gain systems. These interfaces maintain signal neutrality throughout the recording process. This highly neutral interaction is consistent with the Nelson Pass design goals for the GAIN System.

But somewhat remarkably, given the high purity of recording signal achieved by the GAIN system (or perhaps because of it), you will occasionally hear background hiss on some MoFi CDs. In the digital age, this hiss can initially be something of a shock.

Why isn't the CD hiss just processed out by MoFi? Because, according to Kreig Wunderlich, Chief Engineer at MoFi, such processing also takes out part of the music. Moreover, Kreig says hiss enters the recording process in many ways. For example, guitar amps produce hiss, microphones produce hiss, etc.

Kreig flatly states that analog tape is often unnecessarily blamed; its hiss contribution being far less than what most people say. Moreover, the human brain eliminates hiss as long as it remains constant.

So, which do you prefer; your Bach Bourbon straight, or some cockeyed digi-synth-blend?

One question that probably needs to be asked is, can the GAIN system be duplicated by another recording company? Perhaps, although the resulting setup will likely be quite different from the Pass/Moffat/Tan array. Successful design synergy is a rare event.

But most fundamentally, Belkin made the big commitment. He put up the dough necessary to do something unique and good. This stellar conjugation of cash + commitment is a rare cosmic event in the high end audiophile universe, which so often seems to rely on just big bang hyperbole. And which also helps explain why Mobile Fidelity did $12 million in sales last year.

In the next issue of 21st, we see how all this effort paid off, as we review several MoFi recordings made with the innovative GAIN system

Copyright 1996, Francis Vale All Rights Reserved

21st, The VXM Network, http://www.vxm.com

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