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Help With Learning Calibration Procedure For 1/2" 8 Tracks.

Discussion in 'Vintage Analog Gear' started by Jmoog, Oct 28, 2011.

  1. Jmoog

    Jmoog Active Member

    Hello, I recently acquired two 1/2", 8 track machines - a Tascam TSR-8 and a Tascam 38. Both are in very good condition.

    I own a de-magnetizer and I know the heads will have to be de-magnetized occasionally as well as cleaning of the metal and rubber moving parts in the tape path.

    However I know nothing about aligning and calibrating these machines as far as adjusting azimuth, running calibration tones, oiling motors, ect.

    Can anyone recommend a place where I can buy an alignment tape? Also could anyone point me in the direction where I could maybe find a good tutorial online that explains the steps in calibrating and aligning machines like these?

    Thanks everyone.
     
  2. RemyRAD

    RemyRAD Well-Known Member

    Well, since I too am originally from Detroit, I guess it's my job to help you out. I used to own a 38 in the early 1980s. I found it to be a very functional decent machine. I had one without the DBX noise reduction which meant it would be a little noisy. So, since it could handle Scotch 250/Agfa 468 effectively, I usually ran + 6 over 250 nano webers per meter. So this basically meant I was hitting the tape +9 DB over standard operating level of 185 nano webers per meter. That blah blah is based upon the use of MRL Laboratories, of California, calibration alignment tapes. And yes, you always demagnetize the heads and everything else in the tape path. Demagnetization is an art by itself and not necessarily straightforward in a manner of speaking. First, the device should never be switched on and off anywhere near the tape recorder. It should be switched on at least 2 m/6 feet away. With the device on, you first demagnetize the tape guides and the capstan. You never pull the demagnetizer in a perpendicular manner from the deck plate. But rather you keep them within the same plane and pull it away slowly, very slowly in the same horizontal plane as the deck plate. You then proceed to the erase head followed by the record head. These rarely become magnetized because of the substantial AC magnetic properties of the record and the erase circuitry. The last item is the playback head. This is the one that becomes most easily magnetized it also presents the most magnetized damage. So while you bring the insulated tip in close proximity to the playback head, you pause for a second or so. Then you begin the long slow retraction in a straight line parallel with the deck plate away from the head. Now you're ready for the alignment tape.

    Alignment tapes from MRL Laboratories are available in a variety of specifications. They make comprehensive calibration tapes and budget calibration tapes. There is no difference between the quality of these calibration tapes but merely the amount of recorded frequencies utilized. When aligning a tape recorder, the most important frequencies are your calibration reference at 1 kHz. High-frequency calibration at 10 kHz. The low-frequency calibration is something that should not be performed during playback calibration procedures. The playback calibration on the calibration tapes are merely there for a partial reference. This is because some tapes are not calibrated for multitrack reproduction and others can be made for multitrack reproduction. Generally, all these calibration tapes are singletrack regardless of width. But with a multitrack recorder, there is a electromagnetic phenomenon known as fringing effect. This means that the playback head can see low frequencies outside of the track. This gives erroneous low-frequency playback references. So the low-frequency playback equalizer is only adjusted during a full record calibration. The machine is placed into record/repro mode where you will record low frequency sine waves and then adjust the low-frequency playback equalizer, with reference to input monitor.

    Had alignment is a whole other issue. Most recorder heads utilize soft ferrous metals. This means that after a couple thousand of hours, the tape files grooves into the head. These grooves can cause grave tape damage. So you might think that if there are grooves in your head, the head is worn out and no longer usable? That's simply not true. Heads can be re-contoured or re-lapped. That's actually a process of utilizing different fine grades of Emory cloth on a precision flat surface such as a pane of glass. And you don't wipe the head back and forth but drag it in one direction only. You rotate the head and drag it in the same direction to complete the re-lapping. You start with the coarser grit and finish with the ultra fine grit. At this point, the head will be lacking polish. No, you don't polish the heads. The tape will polish the heads in just a few hours of use.

    Azimuth, height, Zenith, wrap have to be performed in the alignment of each head. Some of these adjustments have to be done by EYE. Such as the height. Azimuth is the vertical angle and is one of the most precise of adjustments needed. You have to get the angle on the dangle as near perfect as possible. This is both performed with the playback of alignment tape at 10 kHz and while recording on a blank piece of tape utilizing a sine wave oscillator at 10 kHz for the record head to match the playback head. The Zenith adjustment is a parallelism. When you look at the head path, the head must be completely parallel to the tape path. If the top of the head is pushing into the tape more than the bottom, the top tracks will wear out the head pastor at the top than at the bottom than the inverse is also true. That is a screw at the front and at the back of the head. The azimuth is generally an adjustment screw to the left or right of the head. A few are still experiencing a loss of high frequencies, it may mean that the wrap of the head is off. This frequently requires an electric tape protected pliers in order to rotate the head gap for best high-frequency response boat in playback calibration and with the record head. Poor erasure is usually a problem with wrap as the erase head is far less critical with azimuth since it relies on a wide, non-playback use gap. Frequently to verify head positioning alignment one can take a grease pencil/china marker and cover the face of the head. Then you run some tape for a couple of minutes. Remove the tape and observe the head. The tape will create wear marks. These wear marks should all be equal in width. If you notice a "V" wear mark or, an inverted version of that, you're zenith is off. Playback heads and record heads while they look similar to each other, in many instances they are not. In later multitrack machines design changes brought about improved sync response with a record had virtually identical to the play head. While the gaps may match, their inductance may not so they're not necessarily interchangeable with one another. Don't make that mistake.

    The playback calibration tapes in most use today are the 250 nano webers per meter +3 DB operating level reference. This simply means that the actual playback tone on the tape is recorded at a reduced level. This requires recording at a higher level and therefore, lower noise on playback. So make no mistake, a 250 nano weber per meter tape will playback 3 DB lower than a standard reference level tape of 185 nano webers per meter. I know this sounds goofy. Sine waves are usually utilized on calibration tapes although one can also obtain both pink noise tapes and high frequency sweep tapes. These types are used with different kinds of test equipment whereas the sine wave tapes require nothing more than an external full meter or the actual VU meter on the machine. No, tape recorder meters are not necessarily 100% accurate but they are good enough to generally get you through a 15 or 30 IPS alignment without the need for an external voltmeter. So for your purposes I would recommend the MRL sine wave tapes at 250 nano webers per meter and the budget calibration tapes. The budget tapes are restricted to 100-1000-10,000 cycles. But that's all that's really necessary.

    Okay so, let's assume that you want to record at +9 DB over standard reference levels. Your playback alignment tape at 250 nano webers per meter should indicate -6 on your VU meters. It should not indicate 0 as you will be robbing yourself of signal to noise ratio without any noise reduction such as DBX. If perchance you have DBX noise reduction I would recommend that your levels be set to 0 with a 1 kHz playback reference calibration tape. This will provide additional headroom while sacrificing signal-to-noise that the DBX noise reduction will take care of for you. You're tape machines conveniently operate at only 15 IPS which will make calibration and your decision-making much easier. For machines that operate at 7.5 IPS, excessive high frequency saturation occurs. Because of that, all 7.5 IPS frequency response measurements are done at -10 DB over whatever operating level the tape is ordered as, 185 versus 250. So calibration for 7.5 IPS really does require a voltmeter as the resolution of the VU meter at levels of -10 cannot be accurately judged. Typically at the factory or in the studio maintenance shop, Third harmonic distortion analyzers were utilized for all record adjustments. It was typical to adjust for 1% third harmonic distortion which typically related to your standard operating level or damn close. Not everybody used third harmonic distortion analyzers others used THD or total harmonic distortion analyzers of which similar but different results can result since THD looks at all distortion components which really isn't necessary. But hey, there were plenty of analyzers built for that purpose just like that. But distortion analyzer however is not something that most home studio users want to invest in so use the VU meter. Because close enough is good enough.

    On to bias and record calibration. Generally speaking you start at 1 kHz sine wave 0 DB operating level. So you have already calibrated playback and you're playback will allow you to calibrate your record. There are numerous ways to adjust bias. Different bias adjustments are required for each different tape formulation and dependent upon what you want your tape to do for you. In the old days, we strictly utilized 1 kHz ball for level setting of operating level and for bias adjustment. Later, it was determined that a more finer degree of adjustment could be had by utilizing 10 kHz at standard operating levels for bias adjustment. In this adjustment, tapes such as Scotch 206/226, Ampex 406/456 required an over bias condition at 10 kHz of 2 DB. This was only 1/2 DB when you tried to calibrate with 1 kHz. Sometimes, folks didn't want to over bias but wanted to peak bias. Peak bias allows the tape to retain more high-frequency information at the expense of distortion components and produces a completely different sound than over biasing. Both ways are correct depending upon your applications and the sound you're going after. For instance, saturation frequently sounds better with over biasing since you are purposely causing the tape to go nonlinear. And therefore unkind distortion artifacts are not accentuated as heavily. Conversely, John Stephens popularized another way of biasing. He used a sine wave function generator capable of outputting 10 Hz. Now there really is no analog recorder on the planet capable of actually recording 10 Hz. But there are plenty of guys that play bass guitar. And when biasing your machine, if you don't quite get the bias in the pocket, you are likely to hear what sounds like boots on gravel in the background of all bass instruments! Yeah, gravel which ain't nice to hear. So, you inject 10 Hz into your recorder. You roll tape in record and monitor playback. This should not be done to speakers and should only be done through headphones. You then start to adjust the bias. You will hear a harmonic distortion component of 10 Hz since you can't hear or record the 10 Hz. The 10 Hz will basically sound like "wampwampwamp". And you increase the bias as you listen to the gravel in the background. You increase the bias until the gravel is reduced. Of course, there is a point of diminishing return as the bias can be increased to the point of self erasure. But if you can perfect this technique, you'll find that it aligns quite nicely with the 10 kHz method in comparison. In fact every time I done the 10 Hz bias adjustment it's usually always on the money of +2 DB at 10 kHz. Other high-performance tapes such as Scotch 250/Agfa 468 and Ampex' equivalent frequently required +3 DB of over biasing for proper alignment at 10 kHz. And again remember low frequency adjustments are done during recording and the tones on the playback calibration tapes are merely for a ballpark reference. Calibration tapes can be obtained for 1/4, 1/2, 1 & 2 inch full track With or without multitrack reproduction of the fringing effect on low frequencies.

    So that in a vague way generally covers analog tape recorder alignment procedures. There is so much more that I could include that's beyond the scope of this posting please feel free to PM me with any further questions and you might want to include your phone number so we can technobabble.

    Former Ampex/3M/MCI/Scully authorized recorder technician.
    Mx. Remy Ann David
     
  3. TheJackAttack

    TheJackAttack Distinguished Member

    You're a gem as always, Remy.
     
  4. RemyRAD

    RemyRAD Well-Known Member

    I think I scared him??
     
  5. moonbaby

    moonbaby Mmmmmm Well-Known Member

    You're too good lookin', Princess!
    VERY good instructions!
     
  6. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    wicked enjoyable post. Looking forward to employing this stuff on a 34b machine. There's not as much stuff as i thought there would be on calibrating tape machines out there. Is (90%) rubbing alcohol acceptable to use when cleaning the tape heads? Soaking components in water (and air drying for at least a week) was recommended when i posted about making the accompanying crackly tascam mixer clean. Should a similar approach be taken for the recorders' components that hit tape? or no. I figure i should properly clean the recorder before attempting the calibration.
    Also, are there any uncommon tools i would need besides 'plastic straw-like thing' w/ a flat head type end (used to adjust the set screws) that would be necessary to clean/calibrate a 34b. Hoping to use the recorder to as a way for my signal to hit tape before the apogee A/D conversion, as well as possibly using it to sub mix to (mainly with the goal of experimentation w/ degrading digital signals). Our band's sound is of an early led zep/gritty howlin' wolf blues type. Guess i'm asking for a calibration prep method. I don't have the dbx noise reduction unit. I have no specific expectations of quality/characteristics, just had a hard time finding some reliable methods for getting these things up to par. i will surely mess around w/ the setting's for fun, but would love a nice base process, that gets the machine up to 'average'. Then i can mess with it from that point, and have some sort of a baseline to return to each time. Thanks!
     
  7. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Never ever use isopropyl alcohol to clean anything on a tape deck!!!!! There is water in the solution and it will leave a film that WILL cause rust. ALL tape recorder manufacturers warned against this in their owners' manuals. That stuff will also harden and ruin the rubber components (rollers, belts, etc.) in a heartbeat...stay away from isopropyl alcohol! I have used DENATURED alcohol to clean tape heads (it evaporates quickly), and DeOxit (Caig Laboratories) is also recommended.
    BTW, that "plastic straw tool" (also called a "tweaker") is available from Parts Xpress, as well as many other electronic supply houses. And for the rubber components, check in your area for a rubber dealer that fabricates belts and seals and the like. My local dealer offers a small bottle ($25!!!!!!!) of rubber restoring fluid that works wonders, even on my Roland 555 Space Echo. And best of luck in your new venture, K!!!
     
  8. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Phew glad i asked!!!!!!!
     
  9. RemyRAD

    RemyRAD Well-Known Member

    Isopropyl 91% is acceptable for cleaning the tape path & heads but not good on the rubber compound pieces.

    Alcohol will not melt any headpieces. Some folks have utilized xylene but please please don't use that stuff. Unbelievably "Ampex Head Cleaner" used to be pretty heavy with XYLENE. But that's also because Ampex made their heads quite differently than most other manufacturers (and those companies that made heads for Ampex audio recorders such as IEM & Lipps). But if you use that stuff on Scully (NorTronics), Sony, TEAC, anything like those, it would melt the heads. Basically it would melt the epoxy between the pole pieces. LMAO I knew that happened to a lot of people. So no heavy industrial solvents like acetone or anything else like that should be used. Alcohol is the perfect compound since alcohol is actually an abrasive chemical. It also evaporates very quickly which is also desirable. This is where Freon was hands down the best head cleaner you could use. It cleaned everything without being abrasive. It was 100% inert. It Evaporated almost instantly. It would not short out any electronics even if the entire television set was dropped in a pool of it while plugged in and working. So it also wasn't conductive. But it killed ozone and so bye-bye. That's when we all went back to alcohol

    Now this word of advice should also be heeded. While isopropyl may not be considered ideal, its fumes are far less dangerous to breathe than that of denatured methyl alcohol. That stuff is deadly to breathe. Better you should use isopropyl 91% and then take a soft wet washcloth with or without a tiny tinge of soap to clean your rubber compound pieces & Pinch roller. Now many Pinch rollers also contain ball bearings. These should never be submerged in water with a grease cutting detergent. Avoid hassling any ball bearings mounted in some Pinch rollers. It is perfectly okay however to carefully remove the Pinch roller from most transports since there are devices that require periodic re-placement anyhow. In fact many folks running vintage machines such as Ampex 300/350/351/440's & Scully 280 & others have to get their Pinch rollers custom retreaded for around 100 bucks or so. Chemicals can sometimes help but any aberrations in the perfection of its original flatness & specifications will yield WOW & FLUTTER. It's no different than the tires on your car except that you won't lose your life even if they are screwed up. Enjoy.

    Old tape woman
    Mx. Remy Ann David
     
  10. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Cool stuff, i'm gonna check in a minute if there are any cracks on the pinch roller, while hoping it's not crisp (poke w/ guitar pic gently). Is general practice to remove them during a cleaning? Should i use a Q-tip to apply the alcohol (91%) to the tape path/heads? Ball bearings, remind me of that one skateboard wheel that always spun way longer than the others, and the... i left my board outside in the rain bearings, that i brought back into to action w/ oil. Here goes.
     
  11. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Well it fired up again, meters lit up when assigned button was cued. The left 'uh.?.' tape spinner thing, spun w/ play button, and right one registered a positive count on the digital playback meter when i flicked it clockwise. I noticed that the play/rec heads didn't move when the (transport) buttons were pressed, rather these 2 mini-metal spindles (outside of play/rec heads) seemed to set the distance of the tape from the fixed/or stuck heads. It's the opposite of the way my porta-424mk3's heads worked, where, the heads moved towards/away from the tape. <-Curiosity.
    I think the pinch rollers are missing the rubber part (on the left one), gonna try to see some stock pics of machine to make sure. Right side roller seems like it's as pliable as an average roller blade/car wheel. I also saw some 'spot rust' on the surrounding housing that the head mechanisms looked screwed to. The roughly ten spots look like rust applied w/ a ball point pen, or freckles. Think i gotta clean it up modestly, and get some tape moving to hear/see how this thing works. Used vs. New tape is in the searches. Haven't tried the i/o jacks on tape machine, because of i don't know how to test them w/out tape.
    This is for fun for me, no real specific expectations/hurry.
    Thanx.
     
  12. RemyRAD

    RemyRAD Well-Known Member

    Yeah, no professional machine ever manufactured had heads on a moving mechanism. Cassettes were never considered to be professional devices. Those little metal thingies are called tape lifters. They basically ensure that you don't blow out your tweeters in fast-forward or rewind unless you want to. But it also makes for faster queueing when you can take your cue. You indicated pinch rollers. There is only one pinch roller on a 38. And that's that large brown rubber tire. Well, dark brown, charcoal. You can get some in pale yellow, bright blue but generally not for the 38. Only offered in one drab color. Yeah I've seen some spot rusting on that otherwise mostly aluminum & steel chassis. It's been in some very humid places obviously. Oiling anything too much around a recorder transport can do more harm than good. Less is more everywhere. That means like 1 drop. One tiny drop. And no oil goes anywhere near the heads or adjustment screws. You can lubricate the brake mechanisms, tape break arm, spring-loaded tensioners, solenoids, motors. But everything else must be clean and free of excess lubricants of any kind. Remember to demagnetize the heads when you are finished cleaning and lubricating everything. Make sure you demagnetize your screwdriver before adjusting anything on the heads. And if you need a tone oscillator for alignment purposes, use your software on your computer to generate it. Most any audio program has the ability to generate clean sine waves over the necessary 20-20,000 Hz. And with proper use of your computer, you can use it for all your alignment needs. It has accurate metering. So getting into the ballpark these days is all that is necessary for the home recording enthusiast.

    And on this subject, I was recently giving thought to making available "EL cheapo Alignment tapes"? After all, I still have a perfectly new Scully 280 B 1/4 inch full track mono machine. It's quasi-modified since I know how to make them work right. Unfortunately I don't have any full width 1/2 inch nor 2 track heads in 1/2 inch. So I couldn't make anything for your 38. Calibration alignment tapes can be quite costly. Homebrew alignment tapes done on quality gear, tweaked by a quality tweaker, can still provide a reasonable close enough reference. That same scenario is what we used at the big-time studios. That's because multitrack tapes would come in from all sorts of studios all over the world. You have to align the machine that you were going to use these tapes on, to these tapes. So they always included sine wave frequencies of 50-100-1000-10,000-15,000. When multitrack tapes came in where the originating studio didn't include any reference calibration tones, we would still tweak our machines to the MRL reference calibration tape. We would then align the recorder to the clients tape formula be it Ampex, 3M, Agfa which were the bulk of the 2 inch suppliers. But you have to tweak the recorder, record section to each different brand and formula of tape for the utmost accuracy the machine is capable of delivering. You don't need to calibrate playback on any machine regularly except when the tape path has been disturbed in any way i.e. replacement or repositioning of tape drive motor, pinch roller replacement or adjustment, spooling motors replacement, tape guide replacements. Heads can become magnetized just transporting a machine anywhere on the planet north or south. They don't get magnetized when you travel east or west. Put that on your Q-tip and smoke it. No don't do that. But yes use Q-tips. The industrial ones with a long wooden stick are fine as well.

    I haven't looked for any new recording tape, on reels in many many years now. I know 1/4 inch stuff is still fairly readily available from the Asian suppliers. Many of those consumer recording tapes are quite fine. They differ more in the fact that most don't have a back coating. Back coated tape had a benefit in providing for a little better stiffness which promoted better tape to head contact and high speed shuttle packing. But everyone can and has lived without it. 1/2 inch tape may not be too difficult to find either? But that 1 inch & 2 inch has virtually disappeared. Two years ago there were still a couple of independent companies of guys who were manufacturing some of the stuff. Didn't see them at the AES this year at all. That doesn't mean they don't still exist. Maybe some folks will chime in here?

    Is it live? Or is it MammoRex?
    No it's... RemyRAD X.
     
  13. Jmoog

    Jmoog Active Member

    No you haven't scared me lol. I'm just trying to process all the info. Unfortunately it will be a while before I'm ready to do anything with the machines. I'm in the process of moving and it will be a bit before I get the home studio up and running. When I do I will most definately be in contact Remy and I really appreciate the time you took to answer my post.
     

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