BetterGrundigCut.JPG

Writing About Audio Gear

One of my hobbies is restoring old audio gear. Here are the stories of a few of the (mostly discarded) pieces of ancient junk…erm, I mean, precious artifacts I’ve patched up and sent on their way.

Tale of the Tannoy

FInishedTannoy1.JPG

Anyone who knows me (or reads this blog) knows that I’m a sucker for stray dogs, of a certain sort. Occasionally, that includes actual stray dogs (I live with one).

But in this case, it refers more to discarded or otherwise trashed audio gear. I just cannot leave an old, cool–well, come to think of it often completely UNCOOL–piece of gear to the trash heap. So when this old Tannoy ribbon mic came across my transom, I was even more excited than usual.

Background

These days, there aren’t a great deal of ribbon mic manufacturers (though anecdotally, that number is growing). But when this microphone–a Tannoy “Type 1”–was built, sometime in the mid-1940s I’m guessing, there were a large number of builders. There’s an analogy to be made with other industries at the time (I’m thinking of the automobile in particular). Eventually, the scores (or even hundreds) of producers were winnowed down to a handful; in the case of the ribbon mic, by the 1980s the type was essentially out of production save for a very few small manufacturers (the case may well be different in the former Eastern Bloc). In the past couple of decades, these mics have had a resurgence, fueled by their ability to capture “natural” sound and, one suspects, in part by their mystique.

To some degree, that’s due to their inherent simplicity: The microphone element itself is an absurdly thin strip of corrugated metal foil suspended in a magnetic field. Compared with the condenser mics of the day that typically required an internal vacuum tube and a bulky external power supply, ribbon mics could be made relatively cheaply. This should be a hint (to myself, mainly) that not everything “old” is “good.”

This could be said of the mic in question. By the time it was built, Tannoy had established itself as a large-scale producer of public address systems, to the extent that, as “Xerox” was to “photocopier” in this country, in the Commonwealth a PA was simply “a Tannoy.” This mic was likely intended for use with one of these setups; the “on-off” switch–damped with a pair of resistors when switched off–attests to a PA-grade unit.

That’s not an indictment in and of itself, but given the ribbon elements’ inherent fragility, it’s inevitable that compromises be made between fidelity and durability. But fortunately for us vintage freaks, the aesthetics of these “stage units” were still top-notch.

Restoration

Tragically, the “before” photos have gone missing. The mic arrived largely in pieces, with all the paint somehow stripped off. Some important bits–the original proprietary connector, for one–were missing, and the stand adapter was an odd (roughly 3/4″) size. Here’s a shot of the magnet assembly (aka “motor”) as I found it. The cloth mesh is an attempt to protect the ribbon inside, which in any event was shredded and largely MIA.

Tannoy.JPG

Disassembly was difficult, as this mic had clearly sat unused for many years in a damp environment, and most of the screws and bolts were stuck fast. Patience and WD-40 helped, but in the end many of the smaller connectors sheared off in the process of trying to remove them.

Eventually, I was able to remove the ribbon assembly. I appreciate the mic’s designers including this feature, as trying to install a new ribbon inside the field of the massive magnet seen above would have been ludicrous. Some steel wool and cleaning alcohol got the assembly serviceable; one of the (Bakelite?) mounts broke off but I was able to glue it back in place. Here’s the assembly below.

TannoyMount.JPG

Next I fabricated a new ribbon, using the little homebrew crimping rig seen below.

RibbonRig.JPG

This process is always a bit nerve-wracking; the ribbon material is a sheet of pure aluminum of a thickness of 1.8 – 2.5 microns (by comparison, an average human hair is roughly 100 microns thick). The merest of misplaced breaths will crumple or tear a ribbon beyond repair. After the ribbon is cut to the correct size and corrugated, it’s carefully placed between the clamps at either end of the assembly, tensioned to taste and fixed into place.

After the ribbon was satisfactorily installed, I tack-glued fine metal mesh on either side of the ribbon (where originally there was the cloth mesh seen above). This is to provide some shielding from breath, and also to form a electrical Faraday shield against electromagnetic interference (to which ribbon mics are particularly sensitive).

TannoyGuts2.JPG

Another slight modification was to rewire the top electrical connector in a hum-bucking arrangement (note two wires instead of one). This is shown by wiser heads than mine to reduce hum, though this particular mic is prone to it (more on this later). Though in normal use I would never employ the “on-off” switch, I felt it was better to keep the mic more or less original than to try to mod it into something–a modern microphone–it can never really be.

Finally, it was time to reassemble the mic body. Over the summer, I had painted the body in a Hammerite finish that roughly approximates one of the original finishes the mic was shipped in. Though it’s unoriginal, I mounted the same fine wire mesh to the inside of the mic housing as further protection from powerful gusts. I had considered beefier perforated brass plate as is often seen in older RCA and other microphones, but in researching these materials I was surprised to learn that they are far from a standard (or random) pattern.

Back in the middle of the last century, RCA’s engineers defined the leading edge of audio research in the United States, and–especially important in such a simple machine as a ribbon mic–these baffles were carefully calibrated to act as filters for specific frequencies, as well as providing blast protection. Some aficionados have remarked that modern, cheaper copies of old RCA designs feature such internal baffles, but they appear to be more cosmetic than functional, given their untuned, off-the-shelf construction.

Back to the mic: The yoke got a standard gloss black, and a new stand adapter courtesy of the excellent Dr. Stewart Tavener of Xaudia Elektrik. I need to remark that throughout this restoration, Stewart–a recognized authority on these and many other vintage mics–was incredibly generous with his skills and knowledge.

Lastly, the audio connection was jury-rigged with a borrowed Neutrik XLR jack, and I was in business!

Conclusions

Of course, the proof is in the pudding, so they say. How does the mic sound? As of this writing, I haven’t recorded anything with it, just tested it through a couple of utility mixers. Output is low, as is to be expected (the transformer ratio works out to be about 1:18). Testing this mic with my voice isn’t particularly demonstrative, other than establishing basic functionality. Most any ribbon mic will exhibit a soft, rounded-off top end and strong proximity effect. As I almost never use ribbons on vocalists, the real proof will come when its used with instrument recording.

Much like a single-coil guitar pickup, the mic is susceptible to hum depending on its placement and orientation. Thus far, the hum is noticeably reduced whenever the mic is oriented horizontally rather than vertically. The change doesn’t seem to be mechanical in nature (in other words, due to loose shielding or connections). The mic is just quieter on its side.

As I work it into the collection, I’ll update this post with findings. Till then, thanks for reading!