The best way to give your digitally recorded tracks an authentic analog tape vibe is by sending them through a reel-to-reel tape machine. For example, you can route a pair of tracks from your digital audio workstation to a stereo tape recorder while simultaneously sending the recorder's output back to your DAW.
Assuming that you are using a 3-head deck, the “analog processed” tracks will be delayed by the distance between the record and playback heads as determined by the tape speed. You can easily compensate for this delay by realigning the processed tracks in your DAW. (With a 2-head machine, you'll have to finish recording to tape, then rewind and play your tracks back into the workstation.)
Unfortunately, open-reel tape recorders are not being commercially produced these days, so you'll have to find one used. I recommend buying from a company that specializes in recorder restoration, rather than making a risky purchase on eBay: you'll pay more up front but be rewarded with a dependable machine.
Because buying a used recorder is a gamble, you'll have to invest some time to prove that the machine is worthy before playing an expensive test tape or a valuable master on it. What follows is a list of steps you can take to assess the operating condition of an open-reel machine and diagnose any problems along the way, as well as an overview of what's involved in setting up and maintaining a trustworthy analog tape recorder.
No Pain, No Gain
When EM's editors asked me to write about analog tape machines, I was in the midst of restoring a mint-condition Fostex G16S, a ½-inch 16-track recorder. You might be wondering, why is it necessary to restore a mint-condition machine? As with any vintage item, time takes its toll on parts, often in very subtle ways. And few other pieces of audio gear are as finicky as vintage analog tape machines.
FIG. 1: This figure represents a ½-inch cross section of tape. Wider tracks yield more signal, less noise, better low-frequency response at higher speeds, and more headroom across the frequency spectrum.
As you might expect, a 2-track deck will be somewhat easier — and consequently less expensive — to calibrate and maintain than a multitrack machine. It can be a challenge to get all 16 or 24 tracks working equally well at the same time. That's why I recommend buying a used tape deck from a company that specializes in machine restoration. No tape recorder that is 20 years old or more can be counted on to be fully functional all the time, no matter how nice it looks.
Of the original manufacturers that still exist, few can provide support and parts. However, a remarkable amount of support is available on the Web, including third-party vendors that are making parts for the most common machines (see the sidebar “Resources for Analog Recorders”). No matter which track format you choose, the goal is to be able to record with confidence and know that you are getting the best of what analog tape has to offer (unless, of course, you are looking for a “broken” sound).
On a 24-track pro machine that uses 2-inch tape, three tracks take up ¼ inch of space (see Fig. 1). On a semipro, narrow-format machine, you will have four or eight tracks for every ¼ inch of tape. The more tape real estate each track uses, the better the overall audio fidelity.
As an example of the kinds of problems you may find in a used recorder, let's look at a Fostex narrow-format multitrack recorder.
On the upside, a fully functional G16 or G24 has features like looping, built-in synchronization, and noise reduction. The transport is fast and responsive, and the front panel serves as the remote and offers metering. Squeezing up to 24 I/O cards into 19 inches was possible thanks to early surface-mount technology.
The downside is that surface-mount capacitors from that era are particularly prone to failure. So what may have started out as a $450 eBay deal could turn into a $2,000 project — either you're cool with that or you're not. But it's still a deal if you consider the original price of the recorder and the value of this machine in general.
Whether semipro or professional, nearly every multitrack is a similar investment. For instance, a 2-inch head assembly could easily run $2,500 per head, a true reality check if you paid as much for the recorder itself.
When service is required, narrow-format machines like those from Fostex, Otari, and Tascam can be shipped, though not necessarily to the manufacturer (with the exception of Tascam). On the other hand, a professional-grade 2-inch-tape machine by Ampex, Otari, Sony/MCI, or Studer requires that you either have it restored in advance, be willing to crate and ship it both ways to a repair shop, or be able to import a technician. These options depend, obviously, on your location and budget.
Nonetheless, the essential accessories for any tape machine include a service manual, a head demagnetizer, a dedicated set of nonmagnetic tools, and a test tape for playback calibration. A service manual will help you do the simple stuff, whether you're a geek or not. (Some manuals are actually a treasure trove of information.) At minimum, you'll need to know how to remove the head assembly so it can be shipped out for evaluation, restoration, and alignment.
Check Your Heads
Heads — electromagnetic devices that get signal to and from the tape — are the wear item on a tape machine. Like brake drums on your car, heads need to be resurfaced, contoured, and polished (the process is known as lapping) to maintain optimum performance. I can't emphasize enough that heads in good condition can minimize the more finicky aspects of tape head alignment.
To do any work in the head area, you will most likely need a hex key set. The recorder's country of origin will determine whether SAE (the United States) or metric (everywhere else) tools are used. You'll also want #1 and #2 Phillips screwdrivers, preferably in new condition, made from an extradurable alloy. Screws that are tight will require downward pressure so that the driver does not slip out and damage the screw head or the driver tip.
The capstan is the rotating shaft that maintains constant tape speed, and the pinch roller is the rubber tire that presses the tape up against the capstan. Know what a pinch roller costs and where to get one, and have a spare. Reel table clamps (for 10.5-inch reels) are becoming scarce, especially for machines like the Tascam MS-16. When the manufacturer cannot supply what you need, eBay (www.ebay.com) is a good place to search.
It's important to have a good visual view of the head area when doing maintenance. That is especially true considering the amount of oxide old tapes can shed. For best viewing, the deck should be horizontal. Place a piece of white paper in front of the head stack to reduce glare (see Fig. 2). Clean the heads with an alcohol-dampened cotton swab, using 99 percent (anhydrous) isopropyl or denatured alcohol. Do not use rubbing alcohol, which is 30 percent water.
FIG. 2: A Sony APR-5000-series head assembly showing the head and scrape flutter filter locations, as well as azimuth orientation. Notice how the white paper under the erase and record heads improves visibility. Above the playback head is a miniature view of a single track. See Fig. 4 for a larger look.
Note that pinch rollers can turn gummy due to many factors, not the least of which is age. Whether it is real rubber or synthetic, the pinch (and other rubber-clad rollers such as the tachometer) will react to chemicals in the tape as well as in various cleaning fluids. For this reason I recommend cleaning all “rubber” immediately after a recording project is completed — not when starting one — so that the tape chemicals will not have a chance to be absorbed by, and do damage to, the pinch roller material. This will make the cleaning process easier, require less chemicals, and minimize the aging process.
Because it is likely that you will be buying a new pinch roller, the manufacturer will recommend (and I suggest that you purchase) its product-specific cleaner. For example, Athan's pink cleaning solution is water based, while MDI PrecisionMotorWorks' Head, Red & Roll cleaner is a more volatile, quickly evaporating elixir. Both are equally effective at cleaning their respective rubber products and most likely will not do damage if applied to another manufacturer's products. That said, if there is any doubt, consult the manufacturer.
To clean original rubber parts, start with a cloth dampened (not soaked) with a water-based product such as Windex, Fantastik, or Formula 409 (which also works well on ceramic capstan shafts). Wipe a second or third time with a water-dampened cloth to remove any residual dirt and soap. Do not allow liquid to go down into the capstan shaft, or the bearing and motor will be damaged. Avoid using consumer-grade rubber cleaners.
There is only one head demagnetizer to own: the R.B. Annis Model 115-S Han-D-Mag (see Fig. 3). A demagnetizer with a switch is dangerous and should be discarded or repurposed to the school science lab. Note that powering a demagnetizer up or down in close proximity to recorders and tapes can do more damage than residual magnetism from the recording process ever could. If the following exercise does not yield results, do not demagnetize your recorder without help from someone experienced in tape machine maintenance.
FIG. 3: The R.B. Annis Model 115-S (Short) Han-D-Mag has a curved tip for getting into hard-to-reach places.
All tools should be tested and demagnetized before coming in contact with the heads. If a screwdriver can pick up a razor blade, one or the other is magnetized. (The residual magnetism on the heads is far less and can be measured only with a very sensitive magnetometer.) Plug in the demagnetizer at least 3 feet away from tools, tapes, and machines, then practice by slowly moving the demagnetizer toward the screwdriver and then slowly away. Do the same with the razor blade and then confirm that the screwdriver can no longer pick up the blade.
The tape machine must be powered down before demagnetizing the heads, or you'll risk damaging a preamp. Power up the demagnetizer away from the machine, then slowly position it toward the erase head, moving up and down to cover the top and bottom tracks. While maintaining the up-and-down motion, slowly move the demagnetizer away from one head and toward the next. Also demagnetize the surrounding components — guides and lifters — although these are not typically made of magnetic material.
Check Your Parts
Using a tape machine requires a certain amount of electromechanical awareness. Each component in the recording and playback process — from the iron particles in the tape to the preamp required by the playback head — contributes to noise. For that reason, all tape machines boost treble when recording and use an inverse equalization curve during playback. The standard curves are AES, NAB, and IEC (formerly CCIR).
While some machines have all of these options, others have none. You need to know which curve you're working with before buying a test tape. For example, semipro machines are typically fixed for IEC EQ. Pro machines running at 15 inches per second can be either NAB or IEC. At 30 ips, AES is the standard EQ curve. EQ adjustments compensate for tape, electronic, and mechanical variations.
In addition to optimizing the signal-to-noise ratio, EQ adjustments compensate for tape and day-to-day electromechanical variations. The most obvious compatibility issue is a tape recorded on one machine and played on another, but even when a tape “lives” on a single machine, the performance can vary with temperature throughout the day.
Considering the high cost of a test tape, do not attempt a playback calibration until you are sure the machine is operating properly. Here are a few DIY tips to determine whether a machine is in good working order.
Thread up a noncritical tape — but one that doesn't need to be baked — making sure the tape is wound snugly around the reel hub before pressing Play (see the sidebar “Baking”). Careless threading can stretch tape as well as bend or break guides, tension arms, and rollers.
Before it will do anything, the machine must recognize the tape's presence by using either a mechanical arm and a switch or an optical sensor. Some machines have mechanical brakes, while others use an electronic system. Once the tape is threaded, the brakes may release and the transport controls may be activated, or you may be required to press the Stop button. In the case of the Ampex ATR-100-series recorders, you will need to nudge the reels while pressing the Stop button.
Press Stop, then Play, then Stop: the tape should move forward and come to a gentle halt with no spillage or tension arm dropping. Next, fast wind to the middle of the reel from either end and press Stop. The tape should smoothly come to a halt in about the same amount of time in either direction. Any suspicious or dangerous behavior is reason to investigate or to consult a professional.
Now press Play and pay closer attention to how the tape passes through the guides, over the heads, and around the capstan on its way to the take-up reel. There should be minimal up-and-down tape movement and no tape-edge curling at the guides. (Use reels that are not bent or warped, so the tape edge doesn't scrape on the flange.) Some manufacturers, such as Otari, provided reel table shims to compensate for reel thickness or poorly adjusted reel table height.
Several mechanical issues can affect and exaggerate tape path problems: uneven tension on either side of the capstan, how “square” the capstan and other rollers are relative to the deck plate (the surface of the machine), or a pinch roller that has lost its shape. (Shimming the capstan or adjusting anything other than head azimuth is not for the squeamish or impatient.)
Any of these issues can cause the tape to skew up or down, and when things are really bad, the tape will curl and migrate out of the guides. Consult the manual for tension-measuring tools, techniques, and procedures. Fortunately, part of the head-lapping process includes a full mechanical alignment of the head assembly.
Quick Record Confirmation
All machines have midband, 1 kHz playback and record level adjustments. Typically, narrow-format machines offer a minimal adjustment range for high-frequency record EQ. Do not use bias to manipulate the record EQ because its purpose is to minimize distortion.
While the tape is stopped, set the machine to monitor input and apply a 1 kHz sine wave, either directly from an oscillator or through a mixer, preferably to all channels at once. (Be sure to disable any built-in or external noise reduction.) At some point, the oscillator's level must be precisely known and set, but don't strive for perfection yet. For the moment, make adjustments until the meters read roughly 0 VU.
Assuming that the deck has three heads, simultaneous playback during record is possible. Most narrow-format multitracks have only erase and record heads, and so monitoring from tape is not possible without first recording and then rewinding. This makes any part of the record alignment procedure a bit tedious and very time-consuming.
Put the machine into record and toggle between input and reproduction (playback mode) to confirm that all switches and relays are reliable. If the meters are not steady, the problem may be electronic (dirty switches and relays) or mechanical (funky tape, poor tape path). Continuing to toggle between modes is an exercise that may self-clean the switch or relay contacts in the short term. The alternative is to manually clean the contacts, if possible, or replace the parts.
Note that mechanical VU meters may also be part of the problem, especially if the previous owner loved to pin them in the red. There is a more transparent way to get additional saturation without slamming the meters: it's called elevated level, and it's achieved by calibrating with the playback tape to something less than 0 VU, then increasing the internal record level adjustment to compensate.
Switch the oscillator to 40 Hz while monitoring on headphones. A 40 Hz tone is great for finding funky pots, switches, and relays, as well as “tape rocks,” the latter being a sign of damaged or used tape, magnetized heads, or bias-oscillator distortion.
FIG. 4: Behind the polished head face is what determines head life. Performance and the amount of overbias for recording are determined by gap depth.
One other potential noise source is the scrape flutter filter (see Fig. 2), a roller located between the record and playback heads designed to support the tape so it behaves less like a resonating guitar string. You can easily test it by applying a little bit of finger pressure. If the noise stops, the roller should be removed, disassembled, and lubricated with analog watch oil.
Record 100 Hz, 1 kHz, and 10 kHz tones, flipping between input and repro (playback during record). The tones should be steady, even if not perfectly aligned at 0 VU. If they aren't, check the tape for up-and-down wandering or curling in the guides, then apply a little drag to the supply reel with a finger. If that helps, try to localize the problem by gently applying finger pressure to the tape on either side of the record head and then the playback head. If the signal level increases or becomes stabler, there may be tension or mechanical alignment issues. The heads may also be worn, in which case they can often be relapped.
Bias is a high-frequency signal that is applied to the erase head and mixed in with the audio signal on its way to the record head. Without bias, only the audio signal's peaks would magnetize and be captured by the magnetic tape particles, resulting in a very distorted recording. With bias, the particles are magnetized and oriented to capture the full dynamic range of the source material.
Bias optimizes the tape's sensitivity and minimizes distortion at mid frequencies and below. The optimum bias setting for minimum distortion reduces high-frequency sensitivity by a few dB, hence the term overbias. The recommended amount of overbias and the high frequency that is used for this adjustment is machine and speed specific and correlates to the size of the record head gap depth (see Fig. 4).
Bias is adjusted with a potentiometer, a variable capacitor, or digital controls. The adjustment location will depend on the make and model of the deck. The earliest tape machines had separate cards for repro/sync, record/input, and bias/erase adjustments. Later machines put all of the adjustments on one card. Access to the adjustments is through a pair of doors on pro machines and through removable panels on semipro machines. Consult the manual for more details.
Set the machine to input and apply a 10 kHz sine wave for 15 ips (or 20 kHz for 30 ips) so that the input level is 3 dB below 0 VU. Enter record and monitor repro while adjusting the bias control until the signal reaches the maximum level. If the meter pegs, then lower the audio oscillator's output level.
Once you find the maximum, further increase the bias by turning the bias level control clockwise until the signal is reduced by the specified amount as indicated in the manual. For example, if the recommended overbias at 15 ips is 3 dB, then continue to increase the bias past the peak until the 10 kHz level drops by 3 dB. If recording at 30 ips, you may use 20 kHz and the same amount of overbias, or use 10 kHz and overbias by half (1.5 dB). Consult a professional if the information on adjusting the bias on your machine is missing from the manual or out-of-date relative to current tape availability.
Watch Your Azimuth
Once the recorder is proven safe and functional, it is time to address the routine aspects of tape machine maintenance. The azimuth is perfect when the record and playback heads are perpendicular to the tape and parallel to each other. That's hard to see with the naked eye, but there are several ways to check it.
Send pink noise from your workstation's multifunction generator to all of your tape machine's channels. Put the machine into record and monitor playback while listening to all channels summed to mono. The noise should sound bright and clear with no swishing. However, if it sounds swishy, then the heads are not precisely lined up. By applying a bit of thumb pressure to the tape, on either side of the heads, you can nondestructively manipulate the azimuth enough to exaggerate this effect. (I will discuss adjusting the azimuth in a moment.)
Keep in mind that we have not yet calibrated the playback, but have been testing other aspects of the machine's performance in order to determine where the main problems are. If you've gotten this far without issues, then the machine is safe and ready for the alignment tape. You should now remove all tapes from the area, power down the machine, and demagnetize it.
The remaining task before calibrating the machine is to choose the playback reference level. As tape, heads, and electronics have evolved, so too has the ability to record at higher levels, lowering the noise floor in the process. You don't have to peg the meters to record loud — they're expensive to replace. Simply pick an operating level based on the capabilities of your machine and the brand of tape you plan to use on it.
The reference level is specified in nanowebers per meter — 185 nWb/m was an early popular standard. (A nanoweber is the quantity used to express the magnitude of magnetic flux.) The standard or reference level has changed over the years as tape formulations have improved by having greater headroom and lower noise. Just as 0 VU is a reference (and not the lack of signal), so too is 250 nWb/m.
FIG. 5: A typical head-block assembly that shows where you would make adjustments for each of the heads. Notice that each head has height, tilt, and azimuth screws.
Elevated levels generally increment in 3 dB steps. The level on tape will be referred to as “+x over y,” where “+x” refers to the number of dB over the reference level “y.” For example, +3 dB over 185 nWb/m is 250 nWb/m. To avoid confusion, always know and state the reference level; don't just say “+6.”
On narrow-format machines, level calibration should be done according to the manufacturer's specification (using the modern equivalent tape formulation). Internal noise reduction reduces the need to hit the tape harder.
Test tapes typically have a 1 kHz tone for checking playback level and a 10 kHz tone for checking high-frequency playback level. (A 1 kHz tone is in the middle of the audio spectrum and least affected by most anomalies.) Low-frequency response is typically adjusted after recording a tone sweep from 250 Hz down to 20 Hz. Because test tapes are recorded in full-track mono, do not adjust to the prerecorded low-frequency tones unless they have been “compensated for multitrack reproduction.” (Full-track tapes will show exaggerated low-frequency response when played on a multichannel machine.)
Tones at 8 and 16 kHz are provided on test tapes for coarse and fine adjustment of the azimuth. This adjustment optimizes the head's high-frequency response and compatibility with other machines. While adjusting azimuth, note any level discrepancies that may exist between 8 and 16 kHz. (A 10 kHz tone is used to set playback EQ, and the two frequencies on either side can be used to evaluate and get in the ballpark with the HF response.) Fig. 5 shows the typical locations where you would find adjustment screws.
Playback azimuth adjustment is tricky because the wavelengths of 8 and 16 kHz are so small. (The reason I suggested using pink noise during the record test is that any artifacts will be obvious to the ear.) The easiest, most accurate way to adjust record- and playback-head azimuth is by mixing all tracks from the test tape to mono (for the record and playback heads, respectively). The alternative is to route two neighboring tracks to either an oscilloscope or a mixer (summing to mono) while monitoring on a VU meter. (Each individual signal should read -6 VU and sum to exactly 0 VU.)
If you correctly set the bias as described earlier in this article, you can now adjust the record level. Set the machine to monitor input, then apply a 1 kHz tone at the machine's reference level: +4 dBu or -10 dBV as required by either XLR or RCA connectors, respectively. (This translates to -18 dB Full Scale in the digital domain.)
Some machines have an Input Calibrate adjustment that may interact with the record level calibration. Enter record, switch to repro, and adjust the record level for 0 VU. Check input and tweak the Input Calibrate control if necessary. Once satisfied, set the oscillator for 10 kHz, confirm the input is still 0 VU, then monitor the repro head while tweaking the record EQ adjustment.
Next, on a 3-head deck, record a bass sweep from 250 Hz down to 20 Hz while monitoring the playback head. Align the low-frequency EQ until peaks and dips fall on equal sides of 0 VU, then select a low frequency that falls on 0 VU. Print that tone to tape and note it on the tape box. Include the bass sweep at the beginning of the tape if it will be used for a mix master.
On a 2-head deck, record the bass sweep, then rewind and check playback. Because many narrow-format machines have neither a bass EQ adjustment nor VU meters, all you can do is note the frequencies at which there are peaks and dips. Select a low frequency that falls on 0 VU, print that tone to tape, and note it on the tape box.
Extreme bumps above 0 VU can cause noise-reduction mistracking, which results in artifacts such as pumping. Having the heads lapped can cure exaggerated bass bumps on all machines.
Tape Storage: Tail Out
Tapes should be stored after being played to the end, which is known as tail out. This serves two purposes. As it plays, the tape is packed evenly and smooth so that dust and humidity won't damage the exposed edges.
In addition, louder audio signals will saturate the magnetic particles on the tape, making it easy to magnetize the surrounding layers, causing pre- and postecho. Postecho is more acceptable and is often masked by the original sound.
Once you've done all the dirty work, it's time to play. Get to know the sonic characteristics of your machine. For example, record a kick drum while monitoring the playback head, slowly increasing the record level until you notice saturation. Then compare the input level — what's being sent to tape — with what's coming back. Saturation will affect the observed and perceived levels, and how much of it you want is your call. Don't forget that you can also send an entire mix to your “new” analog recorder.
Owning and maintaining a tape machine is a labor of love. The reward is knowing what your machine can do.
Eddie Ciletti has several tape machines in his audio cave, known as the Prototype, and he's secretly looking for a disc-cutting lathe.
RESOURCES FOR ANALOG RECORDERS
This list of third-party vendors should be helpful if you own an analog reel-to-reel deck.
Athan Online (www.athan.com) rebuilds motors and sells replacement pinch rollers.
ATR Services, Inc. (www.atrservice.com) offers Ampex machine restoration, recording tape, test tapes, parts, and classes.
JRF Magnetic Sciences (www.jrfmagnetics.com) offers head restoration, heads, and test tapes and does custom work.
Magnetic Reference Laboratory, Inc. (http://home.flash.net/~mrltapes) makes and sells calibration tapes.
MDI PrecisionMotorWorks (www.precisionmotorworks.com) offers machine restoration, rubber parts, and rollers and rebuilds motors.
Terry's Rubber Rollers and Wheels (www.terrysrubberrollers.com) sells pinch rollers for professional, consumer, and specialty machines (such as the Maestro Echoplex and the Roland RE-201 Space Echo).
BAKING The sad reality is that the glue, also known as the binder, that secures the iron particles to the plastic tape absorbs moisture over time and eventually becomes more like rubber cement. Tapes with degraded binder will shed their oxide onto stationary surfaces such as heads, guides, and lifters.
The good news is that baking the tape at a low temperature (130 to 140 degrees Fahrenheit) eliminates the moisture and reactivates the binder. The length of time required to bake the tape depends on the tape width, type, brand, and condition and the number of reels being baked.
Tape baking is typically done before archiving previously recorded material. It is not recommended for recycling old tape for new projects. For more information, visit www.tangible-technology.com/tape/baking1.html.