Revolutions Per Minute

    The Giants of Tape, Part Eight: The Telefunken M15A, Part Two

    Issue 141

    In the previous episode (Issue 140), the Telefunken M15 and M15A machines were introduced. Time to look at them under the microscope.

    The M15A transport was available in 1/4-inch, 1/2-inch, 1-inch and 2-inch tape widths, running at a choice of two speeds, which could be 7.5 and 15 ips (inches per second), 15 and 30 ips, or 3.75 and 15 ips. The 1/4-inch model was available in mono and stereo versions, with exchangeable head blocks to convert between mono and the many varieties of stereo configurations, including the standard DIN 0.75 mm track separation stereo, NAB 2 mm track separation stereo, 2 mm track separation stereo with time code, and so on. The standard machine only had CCIR (IEC) equalization, but amplifier boards were available with NAB equalization. There were special versions of the amplifier boards that featured switchable EQ, by means of a coin-operated switch on the head block. This would switch between IEC and NAB eq. The 30 ips versions had AES equalization, although they did not call it as such in their literature.

    The 1/2-inch version was available in stereo or 4-track configurations, the 1-inch version was available in an 8-track design and the 2-inch variant could be ordered in either 16-track, 24-track or 32-track configurations, for use as a multitrack studio recorder. A 32-track machine could also come with head blocks equipped with 24-track and 16-track heads (as previously discussed in Issue 135, where such a machine was shown in the control room of the Town House Studio in the UK), to allow the machine to be used in any of the common multitrack tape formats needed.

     

    A Telefunken M15A in use in the control room at Town House Studios, London, 1978. Photo courtesy of Philip Newell.

    A Telefunken M15A in use at Town House Studios, London, 1978. Photo courtesy of Philip Newell.

     

    More is not always better and especially in audio, less is usually more. Therefore, given the finite amount of real estate available on 2-inch tape, dividing it into fewer tracks makes each track wider, which translates to less noise and better overall sound quality. If a recording can be accomplished in 16 tracks, then it is better to use a multitrack tape machine configured for 16 tracks rather than 24 or 32. On the other hand, if 32 tracks are absolutely necessary because it is a big band and the members are no longer on speaking terms with each other, with a possible history of violence and pending lawsuits, but contractual obligations render it too costly to not record that one last album stipulated in that contract signed ten years earlier, then neither a 16 nor a 24 track tape machine would suffice.

    The M15A was one of the very few analog multitrack tape machines offered in a 32-track configuration. Most others stopped at 24 tracks. Up to the 1960s this was entirely unheard of and during the 1950s, a recording artist or group had to do whatever it was that they were meant to do in a single track, on a monophonic tape machine or disk recording lathe. A group would commonly gather around a single microphone in a room and perform their music in real time, just like they would at a concert. This was already seen as a huge technical leap from earlier decades, when musicians had to crowd together and scream down a horn loud enough to get any usable level on disk, and the studio had to be located at the top of a tall building to provide enough of a drop for the weight attached to a string, which would power the turntable for as long as it took for the weight to reach the bottom!

    But, in later decades, with the progressive collapse of social and moral standards, recording equipment manufacturers were called upon to provide technical solutions for modern realities in an ever faster-paced world. Therefore, the number of tracks available for multitrack recording has kept on increasing, with 32 channels being the practical upper limit of the analog world. The digital world then came to the rescue, increasing the number of channels at the same pace as the weakening of moral fibers...

     

    An M15A-Q configured for quadraphonic recording using 1/2-inch tape.

    An M15A-Q configured for quadraphonic recording using 1/2-inch tape.

     

    I still remember a brief discussion I had a few years ago with a group of musicians expressing interest in using a 24-track tape machine for their recording.

    When I asked them if their plan was to complete their recording entirely in the analog domain, they replied that it would not be possible due to the small number of tracks. Assuming that they must have misunderstood something, I informed them that a typical 2-inch machine offers 24 tracks, to which they replied "yes, that's only the drums..." It was a three-piece rock band, by the way, just in case you are wondering what kind of large percussion ensemble it would have taken to use up 24 tracks. I don't actually think I even own 24 microphones, and neither do I have the patience to sit through 24 takes of each song, recording one drum at a time, in case that was the idea. I did not inquire further; this was clearly a job best suited for a digital audio workstation (DAW) and an engineer who understands that sort of workflow. I certainly do not and cannot even imagine what kind of audience would care to listen to the result. I can understand using 24 tracks for the entire production of Queen's A Night at the Opera, but that is as far as my imagination goes.

    Returning to the stereophonic versions of the M15 and M15A and to the sanity of long-established audiophile practices that have passed the test of time, the M15 and M15A, continuing along the same lines as their predecessors, the M5 and M10, were offered in a preview configuration, to be used with disk mastering systems, with a preview head that was used to provide the signal level information needed by the disk mastering lathe's pitch and groove depth automation systems. Most tape machine manufacturers never made such machines and the few that did usually only introduced one such model, or at best two. Telefunken introduced at least four different preview head tape machine models, becoming a market leader in this sector.

     

    M15A, front view.

    M15A, front view.

     

    The M15 and later the M15A were sold by Neumann together with their disk mastering lathes to those who wanted a complete all-inclusive disk mastering package. They were installed in Neumann cabinets and sold as the MT-75, in playback-only configuration with the preview head block and a sliding bar between the reels, with a single roller, which could be moved up or down to derive the correct preview delay time for each combination of tape speed and disk RPM. This was accomplished by altering the length of the tape path between the two playback heads. The preview head block also offered thumbscrews to adjust head azimuth, a very useful feature which we had previously discussed as applied to the MCI JH-110M preview head tape machine (Issues 138 and 139), there in the form of levers. The purpose of this feature was to allow an engineer to quickly line up the heads to the recorded azimuth of each tape that was sent in for transfer to disk, without requiring any tools, thereby speeding up the setup, provided that the engineer was still young and excited about life (and therefore more likely to still be willing to grossly misalign their tape machine to match what was recorded on a tape sent in by someone who couldn't be bothered to even calibrate their tape machine).

    Unlike the MCI JH-110M, the equalization and level were still adjusted by means of trim pots requiring a screwdriver, as in the standard non-preview-model M15A. A very useful feature of the M15A was that the preview version kept the slots used for inserting the recording amplifier boards, so these could be installed and even permanently kept in the machines along with all four repro amplifier boards (two for normal stereo playback and two additional boards for the preview signal left and right channels). By exchanging head blocks, the same machine could be used as both a recording and reproduction (playback) studio machine, as well as a preview-head mastering deck.

     

    M15A capstan assembly.

    M15A capstan assembly.

     

    The 1/4-inch transport could in theory be converted to 1/2-inch in the field, by exchanging head blocks, rollers and guides. In practice, however, the tape tension would need to be readjusted, so while it was possible, it was a time-consuming process.

    The German engineering community was notorious at the time for their efforts to redefine standards, so that they ended up making things that were incompatible with what the rest of the world was doing. As such, their tape machines came with the heads the wrong way around (looking towards the reels rather than away from them) and the tape wound with the oxide facing outwards and threaded above the head block rather than below it. This was the standard used in German broadcasting for the entire duration of the tape era and as this must have been the biggest market for AEG/Telefunken tape machines – most surviving M15 and M15A machines are found in this configuration. The M15A was also available with the tape heads oriented in the usual manner; this model was referred to as the "international version" by Telefunken. The preview-head version could be found in both configurations, and despite the fact that Neumann was marketing this machine as part of their disk mastering lathe packages, there are very few M15 or M15A preview-head tape machines surviving today, even compared to the number of surviving Neumann lathes.

     

    M15A tape head made from Vacodur, an alloy with a 49 percent cobalt content. The cores are V-shaped for better crosstalk rejection.

    M15A tape head made from Vacodur, an alloy with a high cobalt content. The cores are V-shaped for better crosstalk rejection.

     

    A Telefunken catalog lists two separate part numbers for the preview-version sliding roller assembly, one that was compatible with the VMS-70 and earlier Neumann lathes, and one that was compatible with the VMS-80 and VMS-82/DMM (Direct Metal Mastering) lathes. No support was provided for Scully lathes and the several aftermarket pitch automation systems available for them, despite their popularity in many parts of the world, as these used a different standard of preview delay time.

    Sadly, even the big players at the time did not take much of an interest in what was happening across the Atlantic. Just as AEG/Telefunken did not care much about American disk mastering systems, MCI and Ampex did not lose much sleep over European disk mastering systems. Whether it was due to that particular market being deemed too small to be worth pursuing, or because of some form of national pride, this isolationist approach on both sides certainly hindered the development of audio technology on a global scale.

     

    M15A, bottom view.

    M15A, bottom view.

     

    In the next episode, we will look at the different options available for the M15A.

    Images in this article are from a Telefunken M15A product brochure, except where otherwise indicated.

    2 comments on “The Giants of Tape, Part Eight: The Telefunken M15A, Part Two”

    1. Good morning Mr. Agnew!
      Do you know if vacuum tube preamps are still being made for multitrack tape recorders like the ones you're talking about here?
      I'm still eye balling a vintage Magnicord 1024 open reel 4track tape recorder.
      But however, the preamp that comes with it, is full of transistors.
      I assume that these are early 1960's transistors.
      But I don't know if they will get me close to that warm tube sound that I love so much.
      It's gonna be connected to a vintage all tube stereo receiver.
      Sure you can record directly from the preamp tubes that are on the line out of the tape loop, but it's the quality of the sound that I'm concerned about.

      1. I am not aware of anyone currently making or selling tube preamps for both rec ad repro for multitrack tape recorders at present, although this would be exactly the type of project I would be taking on as an engineering consultant, as a custom design project. Unfortunately, a custom product is more time-intensive than a mass-produced product and cannot benefit from parts purchasing in large quantities, so it cannot compete in price. But the demand for this would be insufficient at present for a mass-produced solution. If your application justified the expense of a custom product, then your options are expanded to infinity.

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