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Author Topic: Beginners Guide to Tape Recorder Basics  (Read 48543 times)

Offline ironbut

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NAB vs IEC tape eq
« Reply #30 on: November 01, 2008, 11:16:07 pm »
Boy, was this ever a hot button topic at the beginning of the Tape Project. This is going to be just a basic overview of the subject since this is still a beginners guide.  Those of you who have phono systems will be familiar with RIAA eq which is used on modern vinyl. This is similar in that it is a pre emphasis and de emphasis system. Just like RIAA eq, this system is used to compensate for idiosyncrasies of the medium.  It would be a happy coincidence if the head/tape interface produced an extended flat frequency response with an inaudible noise floor and realistic dynamics without any help, but that just isn't the way things are. So when they record music onto a tape, one of the things that happens to the music is it is equalized. The inverse of this is done on playback to return it to it's original state. Bear in mind that this is done to the music that's imprinted on the tape so as long as it's played back on a similarly eq'ed playback machine, the eq should do it's job and the tape will sound the same as if it were played on the machine it was made on.
Please keep in mind that this post is still pertaining to playback only. We'll be jumping into the record side of things very soon.
NAB eq was developed in 1953. It has high and low frequency pre/de-emphasis. Also called IEC2.
IEC has been the European standard and only has high frequency pre/de-emphasis. Also called IEC1 or CCIR.
Well, it would be great if we could have our machines set up for IEC eq, put on a Tape Project tape and bam,.. perfect sound forever (gee, where have I heard that before?). Of course not,.. what were you thinking!
If you're a Charter subscriber you have or soon will have a Tape Project alignment tape. This is a calibration tape to do the adjustments to the heads that were outlined in the first few posts of this thread. These tapes were made on the same ATR's that our music tapes are made on  which eliminates one of those "If only they could have,.." wishes that keeps a playback media from being truly purist. With these alignment tapes we're able to align the heads and calibrate the eq to the machine that produced the TP tapes. I don't think that there's ever been any releases that can boast the same level of commitment to the purist ideal.
If you have the Alignment tape there are tutorials on the use of the test tones in the Tape Project Newsletter. If you haven't subscribed to it you should and copy them to a file on your computer to refer to as you use the tape. You'll also need a service manual for your machine to find out where to make adjustments. To subscribe to the Newsletter you have to take a trip over to the Tape Project home page;http://www.tapeproject.com/

So, what if you have a Technics or Otari with 1/4 track heads too. Can you use the TP alignment tape on that playback head too? Unfortunately no. For one thing these tapes are speed specific. You could use it for getting the adjustments close but then there's the tracks. Most alignment tape are done full track meaning the entire tape is recorded in one direction. But since these were recorded on 1/2 track machines with a 2mm guard band (space in between) and the tracks are offset on 1/4 track, the levels of the channels will be slightly different. Anyway, even if you could accurately do head adjustments on your 1/4 track head, this is an IEC tape and many of the adjustments are done with test tones that receive the correct de emphasis.
It's better to get the right alignment tape from MRL.http://home.flash.net/~mrltapes/
« Last Edit: November 02, 2008, 07:01:07 pm by ironbut »
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Offline ironbut

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Basic Recording 1
« Reply #31 on: November 02, 2008, 06:59:22 pm »

By ironbut at 2008-11-02


Ok, the previous post on eq was kind of a warm up lap for this one. And even if you don't have any aspirations to drag your machine into the confessional of your local cathedral to "ride" the faders, this post will help fill in the voids in understanding magnetic tape in general. If you happen to have an owners manual you can probably skip the last part of this post since it should be easier to follow (being specific to your particular machine) and I won't be going into much more detail in this post.
To begin, we'll have a look at the controls and components to get you started and pushing that record button.
Connections To begin with, we'll record something off of a CD or record from your system. Bear in mind that sometimes the back panel connection of your tape deck and/or preamp can be a little confusing (manufacturers idiosyncratic labeling). On my Technics it's pretty straightforward. There are a left/right line output that is your playback output. You can connect this to any line level input on your preamp. The left/right line in are for connections for the record section of your machine. If you have a tape loop on your preamp, you're in luck since this preamp connection bypasses the active gain sections, volume/balance pots of your preamp. It's essentially a stereo patch connection so you don't even need the preamp to be powered up to send the signal from your CD players (or other source) signal to be passed on to the recorder. Just remember to set the input selector to the source you wish to record (on my preamp, you also need to throw the record switch too. Don't forget to switch this off when you're done or you'll be pulling cables and hair out while you try and figure out why you're not getting any sound). If you don't have a tape loop, you can connect any line level source component directly into the line in on the tape machines back panel (this includes phono stages). From a purist point of view, this is preferable since you don't have to send your delicate signal through a couple of switches and an extra set of cables.
Now we get to use the pictures of the Pioneer 909 that I "borrowed" from an auction ad.
Components Most modern reel to reel decks have a couple of amplifiers built into them.
1. Input amp
2. Playback amp
and many times;
3. Microphone amp
4. Headphone amp (actually just a the playback amp with a headphone jack)

Controls I'll only cover the ones that most machines will have.
The photo on the left show the controls for these amps.
-There's a single output level knob which will also control the output of the headphone jack (headphones are almost essential if you do lot's of recording). Just above the output pot is a pushbutton labeled Monitor. This toggles the output, between the source (CD, Phono?) and the tape (playback head). This allow you to "monitor" between the source (CD player) and the sound from the tape (playback head).
-In the middle is the mic input level (there are left/right mic input jacks to the left).  The setting for this pot depends entirely on the mic amp circuit design, the sensitivity of the microphones used, and the level of the sounds that you're recording.
-The control on the left controls the level of the line level input you connected to on the back panel of your deck. Too little signal results in a poor noise level (signal to noise ratio). Tape hiss is your noise level and with modern tape formulations, you should be able to record at a level that this "hiss" is barely noticeable. To find the correct level to record your CD you'll use the VU meters on your machine (the one in the picture is a digital bar type meter and you can see just a bit of it (blue).
VU Meter A standard VU (volume unit) meter has an arc that the indicator swings across. Somewhere to the right of center is a zone which starts with a large Zero and is printed in red. When you record, you don't want the indicator to hang out in that red zone for more than an instant and depending on the tape/record circuit you may not even want it to go into the red at all. Zero VU indicates the level at which the recording could begin to distort. On the other hand, you want the peaks on your music to be at Zero VU since it lifts the sounds you want to hear as far above the noise floor (hiss) as possible. Some experimentation is needed to find out just how much headroom (level above Zero VU you can achieve without distortion) with your particular tape/head setup. To get the most headroom and take advantage of the high output of modern tape formulations, your machine need to be biased for the tape you've chosen to use.
Bias When we talked about output eq in the previous post, I had to let you guys know that magnetic tape recording isn't perfect. I know, I know,.. BooHoo!  A simplified explanation of bias is that it's a high frequency signal that's added to the signal which lowers distortion and improves frequency response. The  level of the bias is tape dependent and manufacturers provide tables for these levels. Record gap length, tape speed and tape type determine the bias level.
For most home users, it's probably best to choose a tape that you want to use and have your machine calibrated to use that tape. Most machines have a couple of different setting for bias and eq which means that you can have more than one type of tape to choose from. If you look above the mic input level pot, there's two buttons. One is bias (two settings-in or out) and the other is eq (two setting- in or out) so this machine has the potential for four different tapes.
Choosing a tapeTo a certain extent, the upper limit on which tape to have you machine biased for will be determined by the machine itself. Some of the highest output tapes can't be taken advantage of by consumer level machines. Some of these are also more abrasive so it will increase head wear too. There's a lot to say for biasing your machine for RMGI 468. It's currently available, it's not crazy money, and it's recommended by Paul Stubblebine. Paul has the opportunity to test the tapes that are available and he's a real perfectionist. So, as Doc would say, this one's a no brainer (IMHO).
So, now we're set to use the picture on the right and record that CD.
After threading a blank tape onto the machine (make sure it's not "Waltz for Debby"!) and setting the bias/eq switches we want to check the line input levels.
Set the record mode selectors (two buttons above the line input pot) left and right to on. Most machines have these and they're a great safeguard. These should always be off unless you're recording. On some machines there's red warning lights to let you know that you're in record mode. When I demo TP tapes I actually put tape over the switches to keep folks from recording over my tapes.
Start the CD and find an spot where you think that the level is about as high as it goes.
Set the Monitor button (over the output pot) to source. You'll see the VU meters deflecting with the music now. Adjust the line input pot so the musical peaks just hit Zero VU.
Once you find a level you like, press the play+record+pause buttons (picture on right) at the same time.
Start the CD again and hit the play button. A red record indicator light should be lit and the reels a turnin.
Your recording now!
If you want to hear what the tape will sound like, you can push the monitor buttons again setting it to tape and the output will be fed by the playback head. Keep in mind that there's a time delay from monitoring the source or the tape. That's the distance between your record and playback head.
When you're done hit pause again (you could use stop but pause can stop clicks that occur sometimes with a sudden stop) then stop.
Unless you want to do some more recording right now, turn off those record mode selectors!
That's it. Some folks prefer the sound that tape gives digital recording so give your "creation" a critical listen.
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Offline ironbut

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Re: Beginners Guide to Tape Recorder Basics
« Reply #32 on: January 07, 2009, 01:02:48 pm »
Thanks for tidying things up Doc. I'd like to ask that members refrain from general posting in this and other stickies. It's meant as more of a learning tool than an area for discussion. I would like to welcome posts that will add to the better understanding of all aspects of tape recorders and recording.
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Offline ironbut

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Further Reading
« Reply #33 on: January 10, 2009, 01:56:53 pm »
Here's a list of publications from Jay McKnight of MRL test tapes fame (along with a host of other accomplishments while working for Ampex during the golden years). Although I haven't exactly quoted his works, much of the knowledge that I have regarding magnetic tape has come from reading them and following his postings on various online lists (Ampex, Studer, ARSC).
All of these papers (excluding one) can be downloaded from his website;http://home.comcast.net/~mrltapes/
These are only suggestions and given enough time, reading everything there is certainly time well spent.

"Master Tape Equalization" There's an entire section on tape eq but I think this and the " Revisited" paper are the fillet.
"Tape Recorder Reproducer Response with a Reproducer Test Tape" Excellent info regarding the use of test tapes and getting the best alignment with them.
"Flux and Flux-Frequency Measurements and Standardization in Magnetic Recording" If you wish to understand more about what happens at the head/tape interface, this is it.
"Speed, Pitch and Timing Errors in Tape Recording and Reproducing" Great study of the sources, magnitude, and effect of temporal errors.
"Biasing In Magnetic Tape Recording" If your interested in the recording end of things.
"Permeability of Laminations" This is the one not on his website (I don't think) but is an AES publication. You can find it by googling the title. If you're an AES member, it's the usual $5 to download, if not,.. shame on you! ($20) Just joking, but if you've gotten far enough to want these relatively technical papers, you'd do well to join and have access to all the great stuff that AES does all year round.
« Last Edit: April 17, 2009, 10:48:37 am by ironbut »
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Offline steveidosound

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Re: Beginners Guide to Tape Recorder Basics
« Reply #34 on: January 24, 2009, 04:05:53 pm »
In an effort to supplement Steve K.s excellent discussion of head types, I would like to cover all the basic formats of 1/4" tape here and also give a bit of an explanation of what you might expect playing tapes of another format than the machine is configured for.
I will not cover speeds here as that is pretty evident if it is wrong, except to say that the two most common speeds in the consumer world are
7 1/2 inches per second and 3 3/4 ips. The pro world has 30 ips. which is not so common, 15 ips. (very common) and 7 1/2. Some consumer machines for voice also included 1 7/8 ips. and 15/16 ips. Note that these are all sub-multiples of one another and raise or lower the pitch by one octave... sorry... on to formats...

I am going to try to be consistant with a few definitions that get tossed about:

1. track: a single recorded length of information on a tape. It takes at least one of these for mono sound and it can cover the whole width of the tape or 1/2 the width or 1/4 the width. It takes 2 tracks to produce stereo (left and right) There are typically 2 or 4 tracks on a stereo tape. There are 4 tracks on a 4 channel or quadraphonic tape.

2. channel: a discrete information carrying section of electronics, whether for playback or recording. Thus a 2 channel machine would typically have 2 discrete inputs, 2 level controls, 2 outputs etc. capable of handling 2 streams of information from 2 sources. To store them on tape would require 2 tracks. These may be related as in the left and right channel of stereo or not. A 4 channel machine would need  4 tracks .
In the studio world, 24 channels on 24 tracks on 2" tape was common for a long time.

3. gap - relating to tape heads -  This was covered by ironbut, but I will say again that this has to do with what portion of the available 1/4" tape width is recorded with what number of tracks. There is not a one to one correspondence between gaps, tracks and channels because in most consumer format tapes you can flip the reels over at the end and record the other direction making what was the bottom of the tape now the top and record the other "side" by repositioning where the gap(s) align on the tape. The term "side" is interesting because it is the other "side" of the reels as in turning over a record (or tape cassette) but it is always the oxide "side" of the tape facing the heads.


Tracks on tape:

full - We started here, but only in the fairly early pro world. 1 gap - full 1/4" tape width. 1 track on the tape. I channel of information. (mono)

2 track  or 1/2 track or "half track" -  In the consumer world, a mono format using a 1 gap head to cover half the tape width to record 1 track of audio (1 channel  mono) in either direction on the tape. Very common from the early 50s through the end of portable battery reel recorders in the early 70s.
In the pro world, a stereo format (The Tape Project Format) for master tapes. A 2 gap head covering the whole tape width to record 2 channels of information on 2 tracks in one direction only. Could be used for 2 unrelated programs in one direction, but to my knowledge never was.

4 track or 1/4 track  or "quarter track" - consumer or semi-pro standard for either 2 channels of information in 2 directions of the tape in an interlaced (see below) format using a head with 2 gaps centered on the 1st and 3rd "quarters" of the tape width from top to bottom, recording 2 tracks in stereo per side as in:
Track 1 = Left Side 1
Track 2 = Right Side 2
Track 3 = Right Side 1
Track 4 = Left Side 2
or 4 dissimilar tracks by recording program on one track at a time in the so called "4 track mono" format.

-OR- a 4 gap head recording 4 channels in one direction on 4 tracks for either the quadraphonic surround format popular in the 1970s or with the ability to use the record head to play back in sync, for early project studio "4 track" multi track / multi instrument use.

I guess I do have to mention that there was a format using an 8 gap head recording 8 tracks for 8 channels on 1/4" tape made by Fostex and to my knowledge no one else for the same semi-pro multi track project studio use as the 4 track machines above.


From all of the above, hopefully it will be more clear what happens if you play a 1/4" wide tape on a machine of another format than the machine which recorded it.
The basic rule is the head gap reads whatever portion of the tape it covers. If there are more tracks than one covered by that gap you will hear all of them, though not perhaps perfectly. Similarly if there is a wider track on the tape than the gap you are reading it with, you will still hear that tape track - but not perfectly as the head gap is not aligned with the center of the track.
A full track head, for a silly example, would read all 4 tracks on a 4 track tape or both tracks on a 2 track tape.
One channel of a 4 channel 4 track machine with 4 head gaps will read whichever fourth of the tape it is covering. So, you would hear the same thing from all 4 (more or less) if you played a full track, full width mono tape on it.

A word about interlaced and/or 2 direction formats -
This is where you can start hearing material backwards. Because they chose to interlace the left and right tracks (as explained above) on the most common consumer stereo 4 track format, if you play them on a  2 track stereo machine you will hear material from the other side of the tape backwards as the top gap of the head is covering the first quarter of the tape - which is the left channel forward from side 1, AND the 2nd quarter of the tape which is the right channel from side 2  backwards!
The bottom head gap is covering the other 2 tracks (3rd and 4th quarters of the tape), and gives you the right channel from side one combined with the left channel from side 2 backwards.

The other common related issue is playing a 2 track mono tape recorded both sides on a 1/4 track stereo machine. The left gap positioned on the top 1/4th of the tape will read the information from the top half of the tape (side one) whereas the right head gap of this machine will be positioned over the 3rd. quarter of the tape from the top and will read side 2 from the bottom half of the tape -again backwards.
The left channel of a 2 track stereo machine will read these mono tapes with the gaps properly centered, though the right channel will again be the other side backwards.
A  2 track mono machine would play only the left channel of a 2 track stereo tape and it would play side one left channel and side 2 right channel backwards of a 1/4 track stereo tape.

A  4 gap head on a 4 track 4 channel machine will play anything to some degree, though again, if you play any 2 direction tape recorded on both sides, either mono 2 track or consumer 1/4 track stereo, some of the channel outputs will have backwards audio from the other side. And none of the gaps will be properly centered for either 2 track mono or 2 track stereo formats.
« Last Edit: January 24, 2009, 04:48:45 pm by steveidosound »
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Offline ironbut

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Print Through
« Reply #35 on: May 11, 2009, 03:06:40 pm »
This discussion pertains to the a tape phenomenon that applies primarily to prerecorded tapes. It appears as an echo of music that can be heard during silent or quiet passages during playback. This is most noticeable in classical music tapes where the dynamic swing can be large from moment to moment as opposed to popular or jazz which is fairly "steady state" in loudness and has fewer passages with very low amplitude. The source of this sound is from the adjacent tape wraps below and above the the one that is being played. It occurs while the tape is wound on a reel.

Before we get into it, there is also Crosstalk. For our purposes crosstalk can sound very similar to Print Through but is entirely different in origin. On 1/4 track tapes (like the 4 track tapes you buy on eBay) it shows up at about the same volume levels (relative to the levels of the recorded signal we want) as Print Through but is in reverse. The source of this crosstalk is mistracking of either the record head/tape interface during production of the tape or mistracking of your playback head/tape interface. It's quite often the former especially on tapes that were produced in a less than ideal way (high speed duplication, poorly adjusted duplication machines, poorly slit tape stock). One way or another, the space between the tracks (guard band) is being breached.

For the purposes of this discussion, we will use the way that one of the Tape Project tapes arrives which is tails out. Tails out just means that the tape is stored on the reel backwards. That is to say that if you were to load the tape like your typical 1/4 track tape that you bought on eBay on the left, supply side, and play it as is, the sound would be in reverse. With the TP tapes as well as most 1/2 track tapes, you would load the tape on the take-up reel side (right) and rewind it before playing. One of the reasons for storing tapes in this way is Print Through.

As the earlier statement would indicate, this echo is sourced from either the length of tape that is immediately above or below a given piece of tape (when wound on the reel).
Pre or Post-Echo implies the source of the unwanted signal that can now be heard on the tape. For "tails out" storage, pre-echo would come from the layer of tape just below the tape in question and post-echo would come from the layer on top of the section in question. The reason that tails out is preferred is Print Through is stronger in the direction that the oxide, relative to the substrate (backing) is facing. Because of this, when a tape is wound tails out the dominant Print Through is Post Echo which is less obvious than Pre Echo.

As you might guess, this unwanted printing of the tape happens when the tape is wound on the reel and is not an artifact of recording or duplication. It would seem to occur with all recorded magnetic tape to some degree but knowledge of print through by the recording engineer and duplication facility (as well as tape manufacturers) can minimize it.

I've been meaning to write this for quite a while but to really understand what's going on here you have to look at the entire process of what magnetic recording entails at the molecular level. It took a good 3 months to get this stuff through my thick skull before I felt confident enough to distill it down to something that most folks can understand (or want!).
That said, there is lots of disinformation out there on the web regarding Print Through but it's usually pertaining to it's sources and the mechanisms associated with it. I'll do my best not to add to it.

For us (the end users) we only need to know how to minimize the level and prevent any further Print Through from happening.
Here are the key elements that determine the level of print through.

Tape Thickness-
This includes the thickness of the substrate (backing), the thickness of the oxide and distribution of the oxide particles on the backing.
  The thicker the backing the better. This actually has nothing or little to do with the backing itself but rather the distance.
  The thicker the oxide layer the worse. This is more to do with it's tendency to accept a magnetic print.
  The even distribution of oxide particles within the binder (glue) makes them more stable and less likely to accept a magnetic print. Higher oxide thickness also makes practical distribution  of particles less precise.

As you might guess there should be a "sweet spot" for the ratio of substrate to oxide thickness but this is hampered by the more practical matters of tape length (the thicker the backing/substrate the less tape you can get onto a reel) and what should be the primary aims of tape production- signal to noise, dynamic range and a relatively flat frequency response ( reducing oxide thickness increases high frequency output and lowers low frequency output).

Signal Applied to the tape-
The higher the amplitude of the signal printed onto the tape the more likely it is to be Printed Through. This is actually a combination of the physics involved and the biology of our perception of sound. There's no practical need to go into the details here. There are frequency dependent issues with Print Through ( related to tape thickness) but they are almost secondary to the frequencies that we are most sensitive to.

Practical Matters

Time-
A large amount of Print Through occurs within the first 48 hours of recording. Within this 48 hour period a level of Print Through is determined by the above factors . It could almost be entirely eliminated if tape duplication had some way of storing the tape for this period without intimate tape to tape contact. This time factor has a lot to do with the stabilization of the magnetic poles of each oxide particle and I won't bore you with the details (even though I have no problems with boring you with all this other stuff). Suffice it to say that reaching  equilibrium within the oxide particles is central to how all this works.

Temperature-
This is very closely related to the time factor. If you recall your high school physical science course, heat is just what we call the level of motion that particles are exhibiting. Or, at least this is what we're measuring (Larry and other scientists who are reading this may now cringe as one!). The magnetic equilibrium within the oxide particles is disturbed by the increase of heat (particle movement) making them more prone to any printing (change in orientation).

So,.. I did say something about Practical didn't I?

Rewinding-
It's been often said that rewinding tapes that exhibit print through several times can reduce the level . This is true and the amount of improvement depends a great deal on how stable the particles of oxide are on a particular tape. It's been theorized that this is due to the bending of the tape and the friction applied to the particles. I'm not inclined to believe the bit about bending but the friction part is somewhat believable. Tests have concluded however that the momentary loss of intimate contact with the adjacent tape layer(s) is responsible for most of this improvement.

It is suggested that all recorded tapes be "exercised" once a year by rewinding and playing them. Regarding the Tape Project tapes, I would certainly do this even if you don't have your "dream" rig completely assembled yet. I'm thinking about getting a pad to keep with my tapes to remind me to do this with the ones that don't get a lot of spin time.
With older tapes I've found that the ones that I listen to quite often have seen some improvement with "exercising". One of the reasons that this exercising works with Print Through and not on the "wanted signal" is that Print Through is applied without the benefit of bias. Bias leads to particle orientation that is more stable and orients particles that are more stable in the first place.

Proper Storage- Keeping tapes in a stable environment is huge. The best temperature to store them is around 68 degrees F (20 C). It's been found that with every increase in temp. of 1 degree C that print through can increase by 0.14dB. This figure is measured in the critical first 48 hours but as you can see, it is significant.

There have been efforts to reduce print through in the past. One of the main techniques has been to use purpose made "Low Print" tape. These tapes were formulated to take advantage of the types of oxides and the "thickness ratio" that leads to less Print Through. These tapes were made for spoken word since, as you might imagine, a lone voice in a hall would make Print Through a pervasive annoyance. They were however, not suitable for music production.

Another technique that never really took off, from what I can tell at least, is called skimming. This is the application of low level erasure to remove the print through. It surfaced during my research for this post in an AES paper or two in the late 50's on a product called the "Echoraser" but like I said, it doesn't seemed to have gotten wide acceptance. This could be partly due to some anecdotal findings that the application of small magnetic signals actually increased the level of Print Through particularly with tapes who had been incompletely erased with bulk demagnetizers.



« Last Edit: May 11, 2009, 04:32:11 pm by ironbut »
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Offline ironbut

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Preventative Maintenance
« Reply #36 on: May 24, 2009, 01:08:02 pm »
I did a little service visit to a Technics RS150x owner the other day and found that the tensioner bearings were in bad shape. One was grinding pretty badly and the other was all but seized up. This, combined with the effort of the tensioners to maintain the correct tensions was resulting in the tape speed being slowed down. Since I knew that the bearings had been in good shape not that long ago and the machine has been run regularly since then, the most likely problem was that the lubricant had been "flushed" out somehow.
 
Anyone who's read this Beginners Guide knows that keeping the tape path spic and span is critical for getting the most out of your tapes and preventing undue wear to them. I think that a little fine tuning of the cleaning process is in order.

I clean my tape path about every 10 tapes or so. My machine is currently located in a spot where I can get a really good look at all the guides and heads so it isn't that tough for me to see when I really need to do this. In between cleanings I can clearly see when there's a little oxide or dust building up and I just use a dry swab to get this stuff off. This keeps any loose particles of whatever off of the next tape(s) to be played and prevents dropouts.

When you do use a head cleaner, you need to respect it's ability to remove contaminants from whatever surfaces it comes in contact with. Some of them take a little while to completely dry and I can attest to this from a wonderful tape that I ruined by not letting the head cleaner completely dry before I played it.
After that bad experience, I always dip the Q-tip into the cleaner and then roll it on a paper towel or something so it's just damp. This minimized the drying time and prevents any possible run off that will end up where you don't want it (like in the bearings).

Cleaners;
I always use the least powerful cleaner I can for the job. Following this thinking, I very seldom use head cleaner for rolling guides since they seldom warrant more than light cleaning. So I use alcohol for the tensioner bearings, the reversing roller and the capstan. It drys quicker than the head cleaner I use and is cheap-cheap-cheap. Of course the capstan is more likely to have some stubborn bits attached to it and you can feel these under the Q-tip as it rides the turning capstan.
Even though alcohol drys much more quickly, I still use a "just" damp swab for this cleaning.

The same thing goes for the pinch rollers. These do get dirty pretty fast and I use a swab dampened with just water and a swab damped with 409 cleaner alternately. There are rubber softening agents (Rubber ReNew) available that I use a couple of times a year. These products should be allowed to dry overnight.

Keep the areas around the tape path clear of oxide. You won't know if your tape is shedding excessively if there's always oxide there anyway.

Developing good habits for cleaning these machines is very important. You don't need to go overboard but it is important to look at what's going on.
Changes in the amount of oxide shed or parts wear are indications that something might be wrong with either the machine or the tapes you've been playing recently.
Bear in mind that excessive oxide shed may not be the result of your playing the tape. It could be the result of the previous playing, improper tape storage or the aging of the tape itself.

« Last Edit: May 25, 2009, 01:40:27 am by ironbut »
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Offline ironbut

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Annual Maintenance
« Reply #37 on: October 01, 2009, 02:21:09 pm »
It used to be that there were plenty of knowledgeable reel to reel techs in, at the very least, every major city. The shops where most folks bought their machines from would either have someone in house or someone that they used to service and maintain reel to reels. I used to have a buddy that used to have service contracts with several radio stations and sometimes I'd tag along as he serviced the tape machines, turntables and consoles around the area (very cool!). Some of you guys may have purchased ex-radio station machines that often have a sticker on it with the date of the last servicing, bias settings and the tape formula that the machine is biased for.
How often this regular maintenance was done depended on usage for the most part. But for the home user, it was usually an annual affair.

Well, here in the 21st century, you can still find those techs but you really have to do some searching. It's also important to use someone who's recommended by someone who knows. Many times a few calls to your local audio shops that were in existence in the 70-80's will result in someone who has the equipment and experience to do this kind of work will reveal their hiding places. Another good place to ask is pro audio shops.

To go back to our automobile analogy, many of the most important parts of your machine are mechanical. And anything on this planet that spins, slides or pushes against another object is subject to wear. Bear in mind, there's a big difference between something that has wear and something that's worn out.
The abrasive nature of the oxide side of a tape will grind down all fixed objects it comes in contact with. Of course the most common ones are the heads. But it also puts a flat spot on any fixed (non-rotating) guides or lifters. How long it takes for these worn objects to become a problem depends on the abrasiveness of the tape, the composition of the object in question and the mileage (we'll use this term since it takes tape speed into account as well as time).
As an example, the tape lifters are the arms that keep the tape from coming in contact with the heads during fast forward and rewind. This is meant to reduce head wear and prevent  playback of the tape during these functions. These can wear rather quickly since the contact area tends to be small and the tape speed across them tends to be high producing higher temperatures. Depending on how the machine was/is used will determine how much of a groove has been worn into the lifters. If, for instance, the machine has been used primarily for the playback of 1/4 track tapes, there may be very little wear since you don't really need to rewind these tapes very often (you just flip the full reel over or in the case of auto reverse, the machine just plays the B side automatically). But making sure that these lifters don't become too grooved is important since they contact the oxide side of your tapes and the groove edges can damage the tape edges and in some cases, if the tape "wanders", damage can take place further into the tape surface.
Some of these lifters can be rotated or a sleeve can be put over it since (in most cases) the diameter of the lifters can be increased with no ill effects (I put teflon tubing over mine and rotate and replace it when it becomes grooved).

The lifters are kind of a special case since they have no effect on the quality of playback.
The heads and guides are an entirely different story however.

As the heads or guides become worn, the way they contact the moving tape across them changes. For the most part, we just kind of live with the slow decrease in high frequency response until it's time to have the heads relapped. This change in frequency response is so gradual and slow, I seriously doubt that casual users will hear it's effects until it's pretty serious. Just like I said before, this all depends of usage so I can't tell you how often you might need to send your heads out but for most of us here, we're talking several years.
That is however, one of the things that a well equipped tech can do for you. He can use well calibrated equipment to measure record and playback response and let you know if it's time to have head work done.

Aside from doing measurements and adjusting for wear in the tape path, regular maintenance also includes cleaning of pots, switches, contacts and checking all the other adjustments. This includes your brakes, pinch rollers and tape tension.
These adjustments can be done in any order just as long as tape tension is last.
There are several different types of braking systems in reel to reels. The one that takes the most maintenance are the shoe and drum type (as on Technics). There are two small, felt brake shoes on an arm that rocks one way when braking clockwise, and the other way when braking counterclockwise. These shoes are raised to contact a drum which is an extension of the reel turntable to stop rotation.
The other type of brake which is common has the same type of drum but instead of having little felt shoes on a rocker, it has a metal band that's usually covered by a canvas like cotton material. The band is tightened to stop rotation.
Nice smooth braking is important since grabbing or chattering can ultimately stretch or even break delicate tapes such as acetate backed ones from the 50's-early 60's.
Brakes that are too loose or poorly adjusted can leave slack in the tape path which lower the tensioners and release the switches that allow you to engage the transport (you have to turn one of the reels to pick up the slack enough to engage the transport in this case).
Since the pads or bands are made of a material that wears, the brakes need to be adjusted to compensate for the loss of material. This can take years depending on use but depending on how exposed your brake drums are and other environmental elements (such as airborne contaminants), the drums may need occasional cleaning.

On my Technics, the drums are very exposed to dust and anything else that happens to be in the air. So, about once a year or so, I open up the back and top and clean them. I used to use alcohol but I find that something like window cleaner does just as well and I don't have to worry about it loosening the glue that holds the pads on or damaging the enamel coating on the drum surface (I think it's some sort of enamel?).
The procedure is very simple.
Take a piece of masking tape to hold down whatever tensioner/arm (in the case of optical switches tape over the light) to "fool" the machine into thinking there's tape present and the transport will work. Open the machine back or whatever it takes to access the back of the reel motors. On the parameter of the reel motor is a smooth surface (on a Technics, it's painted black). That's the drum. Take a q tip and lightly wet it with cleaner. Engage play and both reel motors should rotate with the brakes disengaged. Run the q tip on the surface for several rotations then dry the drum with the dry end of the q tip. You'll more than likely find that the q tip has collected some dark crap on it. Repeat this with fresh q tips till they come out clean.
Repeat this procedure on the other drum.
Allow the machine to play this way for about 5 minutes to assure that the drums are totally dry. Remove the tape and that's it.
Sometimes, right after cleaning the brakes might be a little tight or loose so take a junk reel of tape and work the brakes a few times. If it stays loose or tight, they need to be adjusted per your service manual. If they're still grabbing, the shoes/bands may be contaminated or loose and those will need cleaning or scuffing (depending on the material) which does require some disassembly.

The other major part of servicing is lubrication. For the most part, the bearings on your machine are sealed units and you should not attempt to lubricate them. Adding oil to a gunked up bearing will only loosen the hardened grease and you'll have to replace them anyway. But things like pinch rollers don't have ball bearings and can be removed and the surfaces cleaned and tiny amounts of oil can be applied. If you apply too much, the oil will run down the sides of the pinch roller and onto the tape contact surface (and you won't even see this if it's happening on the back of the roller!). The rollers are probably the only place I would recommend most home users to attempt lubrication. Just be sure and keep all those surfaces super clean and oil free. A tiny bit of oil on your capstan surface could ruin a tape fast!
There are adjustments that need to be made as your pinch rollers wear. Even contact and the correct pressure that the roller(s) exert on the tape/capstan interface prevents slippage or uneven wear on the capstan bearings.

Checking tape tension is important for both machine performance and the life of your tapes. It should be the last thing on the list of any adjustments are done that effects the tape transport (including head adjustments). You can do rough adjustments electrically but to take your tape path into account, you really need something like a Tentelometer which is properly calibrated to do it right. So, if you've done any tape path mods, had your heads relapped and/or adjusted, or made any changes to guides (rotating), your tension has changed. There is usually some wiggle room (+/- a given number of grams) so it doesn't mean that it's totally out of whack now, it's just changed.

Well, so that's an overview of some of the things that should be done on some sort of regular basis. I don't mean to scare you guys into thinking that you're ruining your TP tapes or that your playback is totally sub par, and for most of you, these things may not need to be done every year. But, it does need to be done sometime no matter which machine you own and since very few of us have all the equipment needed to do these things right, it pays to establish a relationship with a local tech who can get to know you and your machine.

As usual, if you wish to discuss the entries in this and other stickies, please do it in the regular forums so we can keep stickies free from discussion.
I welcome any criticism or reminders of stuff I just plain forgot. After all, these are meant to educate our members and not mislead them. Please PM me and I'll edit this and any other sticky if I find it necessary.




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Offline ironbut

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Sticky shed binder change
« Reply #38 on: April 04, 2010, 11:40:02 am »
This post is to supplement the previous post (#23) regarding sticky shed.
Over the years I've heard some explanations of why the tape manufacturers switched to the binders that resulted in Sticky Shed Syndrome and quite frankly, it all sounded like urban legends to me. Here's what sounds like the real deal from Dan Manquen who was working for 3M/Micom at the time;

"The main factor in new tape binders was to increase the ratio of
magnetic particles to "glue".  The stronger the binder, the less you
need.  High crosslink thermoset polymers offered significant advantages
in MPVC (Magnetic Particle Volumetric Concentration), yielding higher
outputs.  Old Scotch 111 type tape had about 40% MPVC, while later
high-output tapes got up to 60+%.  Some of the extra packing was also
due to the cleanness of the needle-shaped magnetic particles, referred
to as lack of dendrites (which are like branches on a tree.)  It is much
easier to orderly stack cord wood than tree trunks with branches still
attached.

Urethane glues are also tougher, providing longer life under high-wear
conditions.

The use of the Phizer particle that gave an output boost for 456
required changes to the binder due to the chemistry.

The Achilles heel of the Urethane binders was that the long polymer
chains can break down in the presence of moisture, weakening the bond.

Dale Manquen at MANCO"
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Tape Mold/Milldew
« Reply #39 on: October 22, 2010, 01:44:04 pm »
I received an email regarding the question of tape mold and upon searching our discussion of tape care here, I realized that I hadn't recommended anything but "toss it!" to the readers.
In most instances, I still recommend getting rid of any moldy tape, the storage box and the box it was shipped in too.
Of course, some tapes are worth the trouble it takes to clean them so here's some info on how to do this.

First, how can you tell if it's mold?

Mold appears on the outside edges of a tape which is visible through the windage holes on the side of the reel. It's a light colored dusty blotching that looks as if someone with flour on their hands handled the tape. There's an excellent photo included on pages 3&4 in the research paper who's link is below.


The major issue with mold is the spores. The spores are used by the mold to migrate and are carried by the air. Playing or worse, rewinding or any fast winding of a moldy tape will spew these spores everywhere and contaminate the room, it's contents and particularly, the machine it's played on. Every tape that's played on this machine is potentially contaminated until it can be thoroughly cleaned. The room should also be vacuumed a couple of times.
Always wear a particle mask when dealing with mold. We may not be dealing with much, but it doesn't hurt.

As far as cleaning the tape, I've taken the liberty to cut an paste the recommendations of Marie O'Connell who posted here a while back.

1) Keep these tapes away from any other tapes.
2) Don't play them on any machine that non-moldy tapes will be played on.
3) Remove the metal flange and carefully soak in some Hydrogen Peroxide (the flange, that is!)
4) Lightly vaccum with a Hepa cleaner the first side of the pancake.
5) Lightly soak a cotton ball with Hydrogen Peroxide or Isopropyl Alcohol (more than 91% pure) and lightly wipe the tape edges in a circular motion.
6) Repeat this on the other side.  You will have to use a spare reel whilst the moldy one is being treated.
7) Using a dedicated machine, cover the heads with pellon and run the tape through this, fixing any splices as you go. (... take the machine out and away from other equipment, like in the garage).

This post was regarding a tape with sticky shed to complicate matters so you could use a cleaning tissue (pelon) before the tape enters the head nest.

Here's the best research I've found regarding the issue of tape mold. It was conducted using acetate tapes so bear that in mind. If you choose not to read the entire pdf at least look at the photos of molded tape on pages 3 and 4.
The pdf is at the bottom written by Jim Thurn.

http://www.ischool.utexas.edu/~anagpic/studentpapers2006.htm


« Last Edit: October 24, 2010, 02:55:49 pm by ironbut »
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Measuring Head Impedence
« Reply #40 on: July 21, 2013, 02:50:52 pm »
I had done some searching for how to do this measurement in the past and always given up.
Thanks to Rick Chinn on the Ampex list, finally have the procedure.
Haven't tried it yet but here it is.
Thanks Rick!

The head is an inductor, so the impedance varies with frequency. I think 1k is the usual frequency for a head. If you can find some old Nortronics lit, you'll see what they used.
You can measure impedance using a signal generator and an ac vtvm, like an HP 400EL/FL or one of the older models.
The generator needs to have a known output impedance. 600R works well.
you connect the generator to the ac vtvm, and you adjust the output for a known reading on the vtvm, say like -10dBu. (I wouldn't drive the head too hard, and you definitely don't want to saturate the core).
Then you connect the head across the input of the VTVM and note how much the output drops by. From this, you can calculate the impedance.
Assume 600R generator impedance. If you're working in dB: then Z = Zs * ((10^dB)-1) If you're working in volts,
then Z = Zs * ((Vunloaded/Vloaded)-1) Example:
you set the meter so it reads -10dBu, with the generator at 1khz. then you connect the head, and the meter reading drops 1dB
then, with your handy dandy calculator (or spreadsheet), you find 10 to the 1th power, which is 10, and then subtract 1, leaving 9.
Then you multiply the source impedance of the generator by 9, giving 5k4-ohms.
If you work in volts, then set the meter so it reads 100mv, with the generator at 1khz. then connect the head, and the meter reading drops to 90mv.
then, 100mv/90mv = 9, subtract 1, and get 8. then multiply the source impedance of the generator by this, 600R * 8 = 4k8-ohms. The head impedance is 4800R at 1khz. (I picked numbers out of the air, so I didn't think that the answers from the two examples would agree, and they don't)
Of course, you can sweep the generator frequency to see the change in impedance with frequency. If you can sweep over a far enough range, you'll see the head's self-resonance, although this is influenced by the source impedance of the generator and the capacitance of the connecting cables. To really see this, you need to raise the source impedance of the generator considerably, so the generator impedance has less influence on the resonant circuit formed by the head, the cable capacitance, and the head's stray capacitance.
This method works with other things than heads.
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