Sonicraft A2DX Lab: Ampex MM1200 Tech Notes

AMPEX MM1200

One of the most remarkable achievements of the team that put together Sonicraft's A2DX Lab is our fleet of fully-restored and extensively modified Ampex MM1200 multitrack machines.

Why this particular make and model? We chose the Ampex MM1200 over any other multitrack platform for a number of reasons:

(1) Quality of Sound: What could be more important? The playback amplifiers in the MM1200 are discrete, class-A and single-ended -- the kind of design audiophiles dream about.

(2) Capstan/ Pinch Roller Design: The Ampex MM1200 uses a capstan and pinch roller for rock-solid control of tape motion and speed.

(3) Simplicity of Design and Availability of Parts: The Ampex MM1200 has a simple straightforward design that makes it reliable and lends itself well to modification and enhancement. Most of its components are discrete which means that many of its off-the-shelf parts can still be rebuilt, purchased new or upgraded with newer and better substitutions.

(4) Compatibility with Technical Advances: There is an underground of Ampex diehards that have produced a number of advances in analog tape playback componentry in general and head design in particular.

Before we tackled the first A2DX Ampex MM1200 restoration project, we did countless hours of research, testing, prototyping, and comparisons. We wanted to determine what kind of improvements over stock performance we could achieve. We investigated changes in heads, components, and signal paths, as well as other modifications. And, we discovered a wealth of innovations, products and strategies that would allow us to achieve significantly better multitrack analog playback.

Our expectations for the outcome of the restoration project were high. But, when we finally brought our newly renovated A2DX Ampex MM1200 on line, it yielded detail and sound quality well beyond what we hoped for.

The A2DX MM1200 Restoration Project

Gutted MM1200

The multichannel platform:

We began our MM1200 restorations by disassembling the entire machine and evaluating it part-by-part. While out of the machine, all individual parts were either fully reconditioned or, in some cases, replaced with new or newer versions.

Everything was thoroughly cleaned. Electrical contacts were individually restored and treated. Cosmetic restoration was also done at this point.

Electronics chassis (bays), and all printed circuit boards have been recapped and the power supplies and audio path have been enhanced and modified to provide a purer, more transparent rendering of the sound on tape.

Finally, the machines were reassembled, adjusted, aligned, tested and their operation evaluated.

RTZ Repro Amplifier - Class A, Single-ended, discrete Transistor design

The signal path:

The RTZ playback amplifiers retain the wonderful class-A single-ended discrete transistor characteristics of the original Ampex design, but also take advantage of 20+ years of progress in transformer, component and circuit-board design and layout. No corners have been cut in these audiophile-grade amplifiers from their Lundahl input transformers to their precision Roederstien metal film resistors and capacitors by Wima and Panasonic. Most importantly, they have the lower distortion and additional headroom necessary to handle the extended response of the amazing Flux Magnetics ME heads, discussed below.

The tape path:

MM1200 Transport - all static guides replaced with precision roller guides

We upgraded our A2DX Ampex MM1200s with the ATR Services roller guide modification. This mod replaces three static guides in the tape path with precision rolling guides. Why is this important? Two reasons:

Reason #1: sound quality. When tape passes over static surfaces, the friction between the tape and the surface sets up a resonant vibration of the tape (much like a violin bow being drawn across a string). This sound-clouding vibration is called "scrape flutter". The roller modification significantly reduces scrape flutter in the tape path resulting in a marked improvement in signal clarity.

Reason #2: Gentler tape handling. Reducing the static surfaces that the tape passes over reduces stress on the tape. This is particularly important with older tapes, especially if they have been spliced.

Having gone far beyond bringing the Ampex MM1200 back up to spec, we realized that we had a platform that was capable of extremely high accuracy, transparency and purity in reproduction. So, we set about getting the most mileage possible from this platform. To do this, we enlisted John French of JRF Magnetic Sciences to build head assemblies that would give us the ultimate in sound quality as well as support for all of the professional multichannel analog tape formats. John brought meticulous workmanship, decades of practical experience and amazing creativity to every project he undertook for us.

Custom head assembly with the incomparable Flux Magnetics ME play head (far right)

The first JRF custom head assembly was for 2" 24-track. The custom designed and hand-built Flux Magnetics ME playback head John chose for this assembly brought a whole new level of quality to the sound of our transfers.

Compared to a stock playback head, the Flux Magnetics ME head provides a full extra bottom octave and ultra-flat low-frequency response at 30 ips. We also found that, at any speed, low and high frequency response is flattened and extended, bottom end is tightened, undesirable coloration is reduced to the minimum and clarity is greatly improved.

One-inch 8-track and 2" 16-track head assemblies followed and both were outfitted with Flux Magnetics ME playback heads and precision rolling tape guides.

Additionally, John French hand-built two more 1" head assemblies for us. The first is a 1" 16T head assembly with a custom PLX playback head designed and developed for Disney Studios by JRF . The second was hand-fabricated at JRF specifically for Sonicraft A2DX Lab as an Ampex MM1200 1" 12-track head assembly. We are especially excited about these assemblies because they allow us to transfer 1" 12 and 16-track tapes with the unprecedented clarity, accuracy and warmth of our A2DX Ampex MM1200 platform.

A2DX MM1200 #2

Machine #2 features the same meticulous restoration work of the original A2DX MM1200. And, A2DX MM1200 #3 is almost ready.

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