The Geeks Speak

Oct 1, 2003 12:00 PM, By Eddie Ciletti and Friends

Polls


Mix Regional

The Mix Regional section for Mix's May 2014 issue focuses on Nashville. Send us your studio news: updates, sessions, new rooms, club performances and installations. Let the Mix audience know what is going on! Send photos and descriptions to mixeditorial@nbmedia.com.

The technician's path is one of evolution, from repair and installation to modifications, design and, for some, manufacturing. This month, in lieu of my regular column, I've invited several techs to share their specialized perspective. After all, who better to design gear (or replacement parts) than those who have stared death in the face? Here, capacitor and power insights share the spotlight with the many disciplines embraced by tape recorders (and reproducers). So dig in!
Eddie Ciletti

IN SEARCH OF THE MAGNETIC HOLY GRAIL V-3A


By Michael Spitz



The process of converting an Ampex ATR-100 Series transport into a 1-inch 2-track required a priority shift: In order to realize the full potential of the wider format, a greater emphasis was placed on mechanical stability because azimuth error tolerance is considerably narrowed. (Azimuth is to high-frequency response as focus is to photography; in this case, the depth of field becomes very shallow.) This heightened scrutiny can be applied to any tape machine, initially by simple visual inspection combined with the familiarity that comes with the process of playing and recording test tones on a regular basis.

When tape machines were the capture device, alignment occurred once or twice daily, not due to drifting issues but in order to accommodate multiple sessions. Now, the process is foreign to many end-users and with it, the experience to interpret a tape or machine idiosyncrasy. Awareness of the three pragmatic issues below will improve your chances of capturing and reproducing every single breath and nuance in chilling detail.

Tape path is the composite of mechanical parameters that dictate how tape passes over the heads. All items must be “true and square” — that's azimuth and zenith — plus height. Tape thickness is approximately 1.5 mils (0.0015 inches) and tape path component tolerances are in the 0.0004-inch range.

The end-user should perform regular spot checks to keep the machine on track. Put soft, nonglaring light on the head assembly and closely observe how the tape passes over the heads and through the guides. Watch what happens from stop to play. Does the tape ride up or down? Is there any curling at the guides? If stability is not quick and consistent, then alignment will be a bear. Any misaligned or worn component in the path can be at fault.

ALIGNMENT


An analog tape machine that is not frequently used may require more than an alignment. Before applying a tweaker, apply a low-frequency tone (40 Hz to 100 Hz) while exercising all external pots and switches, as well as punching in and out of record several times, on noncritical tape stock to exercise any relays and demons. If the machine is still a contender, then the easiest way to check azimuth is to play back the 10kHz section of the test tape from two adjacent tracks, on two faders, panned to mono; each individual fader level should be 6 dB down from 0 VU (or nominal). The combined level should be 0 VU with no wavering; the record head is similarly calibrated. Consult the manual for machine-specific details. No magnetized tools near the head block, please.

Once playback and record are aligned, create a “tone reel” using the same stock as the session tape. If possible, recording a slow bass sweep from 200 Hz to 20 kHz is useful for adjusting the low-frequency playback response and at the mastering stage.

TAPE SATURATION AND COMPRESSION TECHNIQUES


On a multitrack recorder, finding the “limitations” of tape and head performance (saturation) can be used as a form of “artistic expression” on a track-by-track basis. However, hot record levels on stereo tracks will kill definition, “air,” stereo separation and center-stage depth, undermining any noise-reduction system (if applicable) in the process. One-inch, 2-track recorders like the ATR-102 were specifically developed to provide improved definition at lower recording levels (and speeds) without any noise reduction.


Mike Spitz is chief mechanical disciplinarian at ATR Service Company in York, Pa. (www.atrservice.com). Alignment seminars are offered on a regular basis at a low cost.

THEORIES, MUSINGS AND UNDENIABLE TRUTHS


by Jeff Gilman



After 25-plus years of studio and technical endeavors, I've seen the best and worst of analog. When people want to hot-rod an old Ampex 351 that they purchased on eBay for a mere $55, my reply makes it hardly seem like a bargain: “Thousands later, you will indeed own a very good Ampex 351, but it will forever be “dinosaur” technology. When you want a Ferrari, if at all possible, buy the Ferrari!”

OLD ANALOG GOOD ANALOG


“But it has tubes!” Tubes in a tape recorder usually come attached to an old AC transport, and with that, plenty of mechanical baggage. Wow, flutter and scrape flutter in a recording system, in tiny percentages, can be your friend. The sum of these “undesirables” is randomly subtle and yet still a part of that obscure, undefinable analog “feature set” that folks seek from digital gear. Good luck trying to model this stuff; then again, if you can't get enough, then try using a cassette deck!

Any rolling part can do it, but the major flutter-maker in your tape recorder is likely to be the capstan. The larger its diameter, the lower the negative mechanical contributions. The Ampex ATR-100 (my choice for the “Ferrari”) has the single largest capstan in the business. For every 30 inches of tape that zips by the heads in one second, the ATR capstan rotates just four times! Thus, the major flutter component is f = 4 Hz. You might get an occasional complaint from a whale or an elephant, but not from a pianist.

For many, analog tape is still the preferred way to record music. How long that lasts is uncertain. One thing, however, is sure: A quick survey of major studios and mastering rooms will show a clear preponderance of “Ferraris” parked in the control rooms.

CARE AND FEEDING


Motors have two types of bearings. Ball bearings that make an awful grinding noise cannot be helped with oil! In low-speed applications (i.e., tape recorders), ball bearings are lubed with grease. Oil dissolves grease, as well as some motor-winding insulation! What might seem like a quick fix can actually ruin that very expensive, irreplaceable motor. Motors that use sleeve or sintered bearings — i.e., the Studer A-80/A-800, Otari MX-5050s, MTR-10s, MX-80s and others — do require oil. Manufacturers don't always make this clear, unless you crack open the manual. Use the right stuff! Oils have very different chemistry. No oil, or the wrong oil, means no motor.

Electric motors are not created equal. The “motor guy” up the street may tell you it's $70 to repair, and I'm telling you it's $370. Is it worth a shot? Try this simple test: Put a Studer 800 and a Kirby vacuum side by side. Do they look at all similar? A word to the wise: Do it on the cheap and the re-fix will be more costly.


Jeff Gilman, chief alchemist at Precision Motor, works in Hudson, Mass. (www.precisionmotorworks.com) and specializes in the undead: the afterlife for tape-based recorders.

TROUBLESHOOTING ELECTROLYTIC CAPACITORS


By Peter Florance



Electrolytic capacitors fail or gradually degrade in one of two ways: They either short or open. Checking a shorted part is easy: Just connect an ohmmeter, and if it never charges up to an open circuit, then it's either leaky or shorted. Testing for open electrolytic capacitors is a little different.

Real-world capacitors aren't perfect; it's better to think of them in complex terms as an amalgam of passive components (resistors and inductors). The internal resistance of the capacitor — called Equivalent Series Resistance (ESR) — is due to design and construction limitation, as well as heat and aging effects. An electrolytic cap contains a wet chemical to increase its effective value while decreasing the ESR — that is, until the chemical degrades by drying or oozing out.

THAT DRY, FLAKY FEELING


Heat dries the chemical, let me count the ways. Locating a capacitor near a hot transistor, resistor or IC will shorten its life span to a couple of years. In old equipment, it's the first place to look. Capacitors used in high-frequency power supplies (more and more common in digital devices) must pass a lot more current than an audio path capacitor. This current creates heat via the capacitor's “internal resistance,” its ESR.

Leakage is another issue that affects newer compact capacitors, causing some surface-mount types to fail at the rubber seals. The chemical ooze is corrosive and conductive enough to darken copper-printed circuit board (PCB) traces to a black patina. It can also destroy the plated-through holes on PCBs and even penetrate under the green solder mask, damaging copper in a way that is a little harder to discern. It's a real mess that requires thorough cleaning with detergent and distilled water before attempting repairs.

It turns out that high ESR is often the first sign of a dying cap. An ESR meter is particularly useful for checking open capacitors; many testers work in-circuit by applying a high-frequency signal. If not sure whether the ESR is reasonable, then measure a new cap of similar value, beyond which the cap is dying fast. Note that high-voltage caps tend to have much higher ESR values.


Peter Florance zooms in on microscopic parts at Audio Services (www.audio-services.com) in Virginia Beach, Va. He zooms out to apply his expertise at www.firstfives.org on vintage BMWs.

AN ELEMENTARY GUIDE TO CALIBRATION TAPES


by Jay McKnight



First, locate the “Operation and Maintenance” manual. All tape recorders have the same basic adjustments, but their location and procedures are usually machine-specific. Before tweaking, have the correct test tape on hand, know how to perform the adjustments (in the correct order) and know when to call a more experienced technician.

Second, understand the basic recording parameters. While tape width may seem obvious and easily measured, most recorders can be set up for any combination of widths, speeds, equalizations and levels. As such, the recorder's model number alone may not be of much help and will require some investigation. If you're already using a calibration tape — from MRL, Ampex, BASF (Emtec), Standard Tape Lab, etc. — the label and the voice announcement will provide all of the details. If the tape has deteriorated, the MRL part numbers are still valid. For all other tape types, contact MRL for the equivalent part number.

RECORD LEVEL?


The choice of internal (magnetic) operating level, referred to as “Reference Fluxivity,” may be based on several considerations such as the type of program level meter — standard VU, peak program meter (PPM) — blank tape type, whether noise reduction is employed (e.g., Dolby, dbx) or for “tape-compression” purposes. Fluxivity is commonly stated in nanowebers per meter (whose international standard unit symbol is “nWb/m”): 200 nWb/m is typical for older and consumer-type tapes, 250 nWb/m for general studio usage, and 500 nWb/m for the highest output mastering tapes and/or when tape compression is desired. If the calibration tape is not at the desired reference fluxivity, but is otherwise correct, you can easily set your reproducer for a different reference fluxivity.

TEST SIGNALS AND CALIBRATION TAPES


In addition to level, azimuth and preliminary frequency response, a multifrequency calibration tape will include 13 spot frequencies best suited for “first-time” calibration and reproducer troubleshooting.

While multifrequency tapes are only available in single-speed versions, shorter tapes are less expensive to purchase, quicker to use (for touch-up purposes) and may be available as two-speed versions. Provided are the minimum two tones required to calibrate a tape reproducer: 1 kHz to set “Reproducer Gain” (also called “Reproducer Level”) and 10 kHz (used first to adjust the mechanical azimuth of the reproducing head, and then to set the “High-Frequency Reproducer Equalization” control). An optional 100Hz tone is really too high for accurately setting the low-frequency reproducer equalizer response, but it does provide a quick test that the low-frequency response of the reproducer has not failed. Some tape reproducers do not even have a low-frequency adjustment control.

EQUALIZATION AND SPEED


Equalizations, known by the standardizing organizations names, have changed during the years, resulting in some confusion. The names are: 3.75 in/s, the same equalization is used everywhere for new recordings and is standardized by both the NAB and the IEC so we call it “NAB and IEC”; 7.5- and 15-in/s, the equalizations used are commonly called NAB, which is mostly used in the U.S. and is now officially called IEC2, and IEC or CCIR or DIN Studio (all are the same), which is mostly used in Europe and now officially called IEC1; 15 in/s — narrow-format recorders, that's eight and 16 tracks on ¼-inch tape, 16 and 24-track recorders on 1-inch tape — the IEC1 (IEC and CCIR and DIN Studio) equalization is almost always used; and 30 in/s, the equalization used everywhere for new recordings is AES, also called IEC2.

Note: During the early years of tape recording (1948 through, roughly, 1968), some of the equalizations were changed several times, especially at the slower speeds, as new-and-improved tapes were developed.


In addition to standard and custom calibration tapes, Jay McKnight's MRL Website, http://home.flash.net/~mrltapes, is truly a source of reference material on the subject. If you don't see it, just ask.

LAYING THE GROUND WORK FOR POWER DISTRIBUTION


by John Klett



You can build a great-sounding room with the best gear, superb audio wiring and a fabulous grounding scheme, but if the power is not solid, your dream castle is built on shifting sands. Incoming power often has problems, from voltage fluctuations to noise issues and, worse, blackouts and spikes. Each in its own way can slow down or kill a session by corrupting digital data and damaging equipment.

In case of a blackout, an uninterruptable power supply (UPS) can keep a computer up long enough to save data. If the UPS is larger and “always online,” it can also provide continuous, solid and stable power to your whole studio. There are different kinds of UPS. True “double-conversion” units are always “online” and running “off the batteries.” These units fully condition and regulate at all times. Double-conversion online UPS units cost more than “standby and switch-over” types, but when you consider the advantages of having continuously regulated and conditioned power for your studio, the added cost may be justifiable.

HOW MUCH POWER?


Choosing a UPS to condition power for all studio equipment requires knowledge of total current consumption and some idea of how your needs may grow. Uninterruptible power supplies are rated in terms of VA or kVA. VA is a measurement unit equal to the line voltage multiplied by the current draw in amps. One thousand VA is expressed as kVA. In an ideal world, 1 VA would be equal to 1 watt. In practice, you need to add padding onto a wattage figure when converting to VA.

Large commercial facilities with large SSL or Neve consoles (plus associated gear) require between 15 kVA and 20 kVA. At the other end of the spectrum, there are many small workstation-based studios that can be powered from one 20-amp (120-volt) breaker. This is something less than 2.5 kVA (120V × 20A = 2.4 kVA). Exceptionally large power amplifiers and/or multitrack tape machines will significantly increase the power requirements, especially if everything is powered up at once. Typically, two 20-amp breakers are required — just under 5 kVA — which I generally consider the minimum for a small studio.

Many recording studios have large breaker panels with a dozen or more 15- or 20-amp (120-volt) breakers for “just” the audio equipment. The majority of these circuits are running far below the breaker rating, so measure actual consumption rather than attempt to count the breakers. The easiest way to measure the load is with a clamp-on current meter that is accurate over a 2- to 60-amp range. Simply clamp the meter around the wire coming off of each circuit breaker and read the current draw. If more than one circuit is involved, then make note of each circuit, adding up the current draws for the total. This assumes dedicated circuit(s) are feeding only audio gear. If lights, air conditioning and any other appliances are sharing the same power circuits, power down and unplug everything that is not audio-related. (These should ultimately have their own breaker box.) Workstation consumption should be measured while playing back the fattest session, because increased disc access consumes more power than discs simply spinning.

CYPHERING


To calculate the kVA number, multiply the measured current by the measured line voltage. Then, add 30% to 50% to the total kVA to provide headroom for power-up surges. If you plan to add equipment, then allow some room for growth.

Note: Using a clamp-on meter is a relatively safe procedure — one hand in pocket, shoes and socks (no sandals) on, please — but if you are the least bit intimidated by poking around inside of an electrical panel, seek help from a qualified electrician. You can get killed by carelessly putting one or more of your appendages in the wrong place at the wrong time. Safety first!

If all of the gear is not present, create an estimate by starting with the published wattage specification and then add 50% to arrive at a kVA number. If only a fuse rating is available, then assume the actual current draw is quite a bit less; otherwise, the fuse would burn out every week or so. Two-thirds of the fuse rating in amps multiplied by the line voltage will provide a reasonable kVA estimate for that piece. As with measuring, after calculating the total kVA estimate, adding 20% to the total is a good “minimum” rating — consider it “headroom” for UPS.


John Klett (www.technicalaudio.com) is based in Carmel, N.Y., and chases electrons around the world.






Acceptable Use Policy
blog comments powered by Disqus

Mix Books

Modern Recording and Mixing

This 2-DVD set will show you how the best in the music industry set up a studio to make world-class records. Regardless of what gear you are using, the information you'll find here will allow you to take advantage of decades of expert knowledge. Order now $39.95

Mastering Cubase 4

Electronic Musician magazine and Thomson Course Technology PTR have joined forces again to create the second volume in their Personal Studio Series, Mastering Steinberg's Cubase(tm). Edited and produced by the staff of Electronic Musician, this special issue is not only a must-read for users of Cubase(tm) software, but it also delivers essential information for anyone recording/producing music in a personal-studio. Order now $12.95

Newsletters

MixLine

Delivered straight to your inbox every other week, MixLine takes you straight into the studio, with new product announcements, industry news, upcoming events, recent recording/post projects and much more. Click here to read the latest edition; sign up here.

MixLine Live

Delivered straight to your inbox every other week, MixLine Live takes you on the road with today's hottest tours, new sound reinforcement professional products, recent installs, industry news and much more. Click here to read the latest edition; sign up here.

[an error occurred while processing this directive]

The Wire, a virtual press conference offering postings of the latest gear and music news, direct from the source. Visit the The Wire for the latest press postings.