Nagra Wear

People in business have to be conscious of changing trends and adapt to them. Location sound mixers are certainly no exception, and in this case we have to be aware of the effects trends have on our equipment.

While Music Videos can no longer be considered a new trend, it hasn’t been until recently that we’ve seen a pattern of wear on portable Nagra machines that is associated specifically with music video production.

Years of being a mixer based in Nashville means hundreds and hundreds of music videos under my belt (1,738 to date, since 1979). Because of this shameful fact, I have subjected Nagras to possibly record numbers of playback hours. All along I had the gut feeling that the constant repetitive playback, rewinding and cueing done for music videos would accelerate normal wear, but Nagras are so tenacious that wear is seldom quickly apparent.

However, with several years now past since the establishment of Trew Audio’s Service Department and Nagra service authorization, we have seen a pattern in the toll that years of daily music video playback place on Nagra machines.

There are a few things that can be done to prolong the life and minimize the wear or the Nagras that are still the most widely used format for this type of work.

Repetitive "rewind cueing" is the largest difference in operation demanded by music videos. That is, forcing the tape against the playback head while rewinding in order to quickly cue the start point while the director, artist and everyone else impatiently waits. This is also the most significant cause of accelerated wear to the heads.

The worst way to "rewind cue" is to close the head shield so that the tape is held in constant contact with the playback head. We were seeing a lot of machines whose playback and timecode heads had a very tiny but peculiar "mystery notch" on the playback head and (to a lessor degree) on the timecode head. It was baffling at first. The notch was somewhat different on the different machines, but it was definitely the same type of notch. Then we noticed that if the head shield was closed during rewind, the lower edge of the tape fell always into this mystery grove, cutting it deeper each time. All of the machines that had this notch also showed signs of "polishing" on the rivets on the underside of the head shield, indicating how this notch no doubt developed. This notch can eventually have an adverse effect on the performance of the heads and can definitely shorten their life span.

The way to avoid this wear pattern is simple: Do not rewind with the playback shield closed. Using your index finger to push the tape onto the head is not nearly as detrimental because the tape will usually be at a slightly different place on the heads each time. However, it is best to bring the tape just close enough to the head to hear the track without actually touching it.

The second place of wear caused by music video style playback operation is in the linkage connected to the rewind lever. Recording on feature style production, opening and closing the rewind lever usually happens only a few times per day; each time there is a reel change and a few times to check playback. On a music video however, it is not uncommon for the rewind lever to be quickly slammed open and shut over one hundred times in a typical 18+ hour day. Each time the linkage is opened and closed, there are five pivot points that are subjected to friction, and thus wear. The problem with this wear is in the stroboscopic roller that is held in place by this linkage. One reason for this roller’s existence is to position the tape across the record head with the correct "wrap". If the linkage is worn, the roller will not be pushed far enough forward and then the tape will contact less of the record head and record level is decreased. There is an internal cam type adjustment to correct a certain amount of this wear, but many of the machines we see are worn beyond the limits of this adjustment. The only fix is to replace the link assembly — an expensive but sometimes necessary repair.

To tell if this linkage has loosened on your machine, try this: Close the rewind lever then gently push the stroboscopic roller toward the back of the deck (toward the heads). If there is any play at all towards the back of the deck, then your tape is not correctly contacting the record head. A very small amount of play will still produce acceptable specs, but you should always be aware of the progression of this wear and its affect on the recording performance.

There are two ways to minimize the wear on this linkage assembly. First, go easy! Slamming the lever open and shut is often a temptation under pressure, but it increases wear and decreases the value of your machine. Second, have your machine cleaned, inspected and lubricated regularly. For machines used weekly on music videos, every six months is not too often and less than once per year is not often enough.
— Glen Trew