The technician's path is one of evolution, from repair andinstallation to modifications, design and, for some, manufacturing.This month, in lieu of my regular column, I've invited several techs toshare their specialized perspective. After all, who better to designgear (or replacement parts) than those who have stared death in theface? Here, capacitor and power insights share the spotlight with themany disciplines embraced by tape recorders (and reproducers). So digin!
— Eddie Ciletti
IN SEARCH OF THE MAGNETIC HOLYGRAIL V-3A
By Michael Spitz
The process of converting an Ampex ATR-100 Series transport into a1-inch 2-track required a priority shift: In order to realize the fullpotential of the wider format, a greater emphasis was placed onmechanical stability because azimuth error tolerance is considerablynarrowed. (Azimuth is to high-frequency response as focus is tophotography; in this case, the depth of field becomes very shallow.)This heightened scrutiny can be applied to any tape machine, initiallyby simple visual inspection combined with the familiarity that comeswith the process of playing and recording test tones on a regularbasis.
When tape machines were the capture device, alignmentoccurred once or twice daily, not due to drifting issues but in orderto accommodate multiple sessions. Now, the process is foreign to manyend-users and with it, the experience to interpret a tape or machineidiosyncrasy. Awareness of the three pragmatic issues below willimprove your chances of capturing and reproducing every single breathand nuance in chilling detail.
Tape path is the composite of mechanical parameters that dictate howtape passes over the heads. All items must be “true andsquare” — that's azimuth and zenith — plus height.Tape thickness is approximately 1.5 mils (0.0015 inches) and tape pathcomponent tolerances are in the 0.0004-inch range.
The end-user should perform regular spot checks to keep the machineon track. Put soft, nonglaring light on the head assembly and closelyobserve 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? Isthere any curling at the guides? If stability is not quick andconsistent, then alignment will be a bear. Any misaligned or worncomponent in the path can be at fault.
An analog tape machine that is not frequently used may require morethan an alignment. Before applying a tweaker, apply a low-frequencytone (40 Hz to 100 Hz) while exercising all external pots and switches,as well as punching in and out of record several times, on noncriticaltape stock to exercise any relays and demons. If the machine is still acontender, then the easiest way to check azimuth is to play back the10kHz section of the test tape from two adjacent tracks, on two faders,panned to mono; each individual fader level should be 6 dB downfrom 0 VU (or nominal). The combined level should be 0 VU with nowavering; the record head is similarly calibrated. Consult themanual for machine-specific details. No magnetized tools near the headblock, please.
Once playback and record are aligned, create a “tonereel” using the same stock as the session tape. If possible,recording a slow bass sweep from 200 Hz to 20 kHz is useful foradjusting the low-frequency playback response and at the masteringstage.
TAPE SATURATION AND COMPRESSION TECHNIQUES
On a multitrack recorder, finding the “limitations” oftape 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 specificallydeveloped to provide improved definition at lower recording levels (andspeeds) without any noise reduction.
Mike Spitz is chief mechanical disciplinarian at ATR ServiceCompany in York, Pa. (www.atrservice.com). Alignment seminars areoffered 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 thebest and worst of analog. When people want to hot-rod an old Ampex 351that they purchased on eBay for a mere $55, my reply makes it hardlyseem like a bargain: “Thousands later, you will indeed own avery good Ampex 351, but it will forever be“dinosaur” technology. When you want a Ferrari, if at allpossible, buy the Ferrari!”
OLD ANALOG GOOD ANALOG
“But it has tubes!” Tubes in a tape recorder usuallycome attached to an old AC transport, and with that, plenty ofmechanical baggage. Wow, flutter and scrape flutter in a recordingsystem, in tiny percentages, can be your friend. The sum of these“undesirables” is randomly subtle and yet still a part ofthat obscure, undefinable analog “feature set” that folksseek from digital gear. Good luck trying to model this stuff; thenagain, 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 taperecorder is likely to be the capstan. The larger its diameter, thelower the negative mechanical contributions. The Ampex ATR-100 (mychoice for the “Ferrari”) has the single largest capstan inthe business. For every 30 inches of tape that zips by the heads in onesecond, the ATR capstan rotates just four times! Thus, the majorflutter component is f = 4 Hz. You might get an occasionalcomplaint 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 quicksurvey of major studios and mastering rooms will show a clearpreponderance of “Ferraris” parked in the controlrooms.
CARE AND FEEDING
Motors have two types of bearings. Ball bearings that make an awfulgrinding noise cannot be helped with oil! In low-speed applications(i.e., tape recorders), ball bearings are lubed with grease. Oildissolves grease, as well as some motor-winding insulation! What mightseem 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-80sand others — do require oil. Manufacturers don't alwaysmake this clear, unless you crack open the manual. Use the right stuff!Oils have very different chemistry. No oil, or the wrong oil, means nomotor.
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 aKirby vacuum side by side. Do they look at all similar? A word to thewise: 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 inthe undead: the afterlife for tape-based recorders.
TROUBLESHOOTING ELECTROLYTIC CAPACITORS
By Peter Florance
Electrolytic capacitors fail or gradually degrade in one of twoways: They either short or open. Checking a shorted part is easy: Justconnect an ohmmeter, and if it never charges up to an open circuit,then it's either leaky or shorted. Testing for open electrolyticcapacitors is a little different.
Real-world capacitors aren't perfect; it's better to think of themin complex terms as an amalgam of passive components (resistors andinductors). The internal resistance of the capacitor — calledEquivalent Series Resistance (ESR) — is due to design andconstruction limitation, as well as heat and aging effects. Anelectrolytic cap contains a wet chemical to increase its effectivevalue while decreasing the ESR — that is, until the chemicaldegrades by drying or oozing out.
THAT DRY, FLAKY FEELING
Heat dries the chemical, let me count the ways. Locating a capacitornear a hot transistor, resistor or IC will shorten its life span to acouple of years. In old equipment, it's the first place to look.Capacitors used in high-frequency power supplies (more and more commonin digital devices) must pass a lot more current than an audio pathcapacitor. 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. Thechemical ooze is corrosive and conductive enough to darkencopper-printed circuit board (PCB) traces to a black patina. It canalso destroy the plated-through holes on PCBs and even penetrate underthe green solder mask, damaging copper in a way that is a little harderto discern. It's a real mess that requires thorough cleaning withdetergent 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; manytesters work in-circuit by applying a high-frequency signal. If notsure whether the ESR is reasonable, then measure a new cap of similarvalue, beyond which the cap is dying fast. Note that high-voltage capstend to have much higher ESR values.
AN ELEMENTARY GUIDE TO CALIBRATIONTAPES
by Jay McKnight
First, locate the “Operation and Maintenance” manual.All tape recorders have the same basic adjustments, but their locationand procedures are usually machine-specific. Before tweaking, have thecorrect test tape on hand, know how to perform the adjustments (in thecorrect order) and know when to call a more experienced technician.
Second, understand the basic recording parameters. While tape widthmay seem obvious and easily measured, most recorders can be set up forany combination of widths, speeds, equalizations and levels. As such,the recorder's model number alone may not be of much help and willrequire 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. Forall other tape types, contact MRL for the equivalent part number.
The choice of internal (magnetic) operating level, referred to as“Reference Fluxivity,” may be based on severalconsiderations such as the type of program level meter — standardVU, peak program meter (PPM) — blank tape type, whether noisereduction is employed (e.g., Dolby, dbx) or for“tape-compression” purposes. Fluxivity is commonly statedin nanowebers per meter (whose international standard unit symbol is“nWb/m”): 200 nWb/m is typical for older and consumer-typetapes, 250 nWb/m for general studio usage, and 500 nWb/m for thehighest output mastering tapes and/or when tape compression is desired.If the calibration tape is not at the desired reference fluxivity, butis otherwise correct, you can easily set your reproducer for adifferent reference fluxivity.
TEST SIGNALS AND CALIBRATION TAPES
In addition to level, azimuth and preliminary frequency response, amultifrequency calibration tape will include 13 spot frequencies bestsuited for “first-time” calibration and reproducertroubleshooting.
While multifrequency tapes are only available in single-speedversions, 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 tapereproducer: 1 kHz to set “Reproducer Gain” (also called“Reproducer Level”) and 10 kHz (used first to adjust themechanical azimuth of the reproducing head, and then to set the“High-Frequency Reproducer Equalization” control). Anoptional 100Hz tone is really too high for accurately setting thelow-frequency reproducer equalizer response, but it does provide aquick test that the low-frequency response of the reproducer has notfailed. Some tape reproducers do not even have a low-frequencyadjustment control.
EQUALIZATION AND SPEED
Equalizations, known by the standardizing organizations names, havechanged during the years, resulting in some confusion. The names are:3.75 in/s, the same equalization is used everywhere for new recordingsand 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 arecommonly called NAB, which is mostly used in the U.S. and is nowofficially called IEC2, and IEC or CCIR or DIN Studio (all are thesame), which is mostly used in Europe and now officially called IEC1;15 in/s — narrow-format recorders, that's eight and 16 tracks on¼-inch tape, 16 and 24-track recorders on 1-inch tape — theIEC1 (IEC and CCIR and DIN Studio) equalization is almost always used;and 30 in/s, the equalization used everywhere for new recordings isAES, 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 weredeveloped.
In addition to standard and custom calibration tapes, JayMcKnight's MRL Website,http://home.flash.net/~mrltapes, is truly asource of reference material on the subject. If you don't see it, justask.
LAYING THE GROUND WORK FOR POWER DISTRIBUTION
by John Klett
You can build a great-sounding room with the best gear, superb audiowiring and a fabulous grounding scheme, but if the power is not solid,your dream castle is built on shifting sands. Incoming power often hasproblems, from voltage fluctuations to noise issues and, worse,blackouts and spikes. Each in its own way can slow down or kill asession by corrupting digital data and damaging equipment.
In case of a blackout, an uninterruptable power supply (UPS) cankeep a computer up long enough to save data. If the UPS is larger and“always online,” it can also provide continuous, solid andstable power to your whole studio. There are different kinds of UPS.True “double-conversion” units are always“online” and running “off the batteries.” Theseunits fully condition and regulate at all times. Double-conversiononline UPS units cost more than “standby and switch-over”types, but when you consider the advantages of having continuouslyregulated and conditioned power for your studio, the added cost may bejustifiable.
HOW MUCH POWER?
Choosing a UPS to condition power for all studio equipment requiresknowledge of total current consumption and some idea of how your needsmay grow. Uninterruptible power supplies are rated in terms of VA orkVA. VA is a measurement unit equal to the line voltage multiplied bythe current draw in amps. One thousand VA is expressed as kVA. In anideal world, 1 VA would be equal to 1 watt. In practice, you need toadd padding onto a wattage figure when converting to VA.
Large commercial facilities with large SSL or Neve consoles (plusassociated gear) require between 15 kVA and 20 kVA. At the other end ofthe spectrum, there are many small workstation-based studios that canbe powered from one 20-amp (120-volt) breaker. This is something lessthan 2.5 kVA (120V × 20A = 2.4 kVA). Exceptionally large poweramplifiers and/or multitrack tape machines will significantly increasethe 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 ormore 15- or 20-amp (120-volt) breakers for “just” the audioequipment. The majority of these circuits are running far below thebreaker rating, so measure actual consumption rather than attempt tocount the breakers. The easiest way to measure the load is with aclamp-on current meter that is accurate over a 2- to 60-amp range.Simply clamp the meter around the wire coming off of each circuitbreaker and read the current draw. If more than one circuit isinvolved, then make note of each circuit, adding up the current drawsfor the total. This assumes dedicated circuit(s) are feedingonly audio gear. If lights, air conditioning and any otherappliances are sharing the same power circuits, power down and unplugeverything that is not audio-related. (These should ultimatelyhave their own breaker box.) Workstation consumption should be measuredwhile playing back the fattest session, because increased disc accessconsumes more power than discs simply spinning.
To calculate the kVA number, multiply the measured current by themeasured line voltage. Then, add 30% to 50% to the total kVA to provideheadroom for power-up surges. If you plan to add equipment, then allowsome 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 — butif you are the least bit intimidated by poking around inside of anelectrical panel, seek help from a qualified electrician. Youcan get killed by carelessly putting one or more of yourappendages in the wrong place at the wrong time. Safety first!
If all of the gear is not present, create an estimate by startingwith the published wattage specification and then add 50% to arrive ata kVA number. If only a fuse rating is available, then assume theactual current draw is quite a bit less; otherwise, the fuse would burnout every week or so. Two-thirds of the fuse rating in amps multipliedby the line voltage will provide a reasonable kVA estimate for thatpiece. 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.