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Beginners Guide to Tape Recorder Basics

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To continue on with our discussion of heads, the picture below is of the heads on a 1/2 track stereo Sony APR 5000 series machine. It has a somewhat specialized head assembly. At first we'll focus on the three heads we already know. Once again, we find the same configuration of erase head>record head>playback head (following the direction the tape travels in play-left to right). Although it's a little harder to see the tracks on the record and playback heads you can see a lighter space in the very middle of the head. This is the border between the two tracks. This is the format that the Tape Project tapes are recorded in. Once again, the left channel is on top (track 1) and the right channel is below the border. So, as you can see, the two tracks take up the full width (except for the border between them).
Because the 2 tracks take up the entire width, the tape is unidirectional and unlike the 4 track stereo tapes that were mentioned in the first "heads" posting, if you were to flip the tape and play it, it would be in reverse (which is pretty fun about once). These tapes are best stored in what we call "tails out". All that means is that the tape is put away (without  rewinding it/flipping it or any other tom foolery), just the way it is after playing it till the end. It's actually the most convenient way to deal with these tapes and good for the tapes to boot. Of course this means that before playing a "tails out" tape, you need to rewind it onto an empty reel on the left reel turntable. We'll get into tape storage/handling and care in a later post.

By ironbut at 2008-08-25
 What's particularly cool about this photo is all the other parts in a head assembly are clearly labeled.
Starting on the far left is a metal guide. The guides do just what they say, but this is another case of less is better. The less guiding the guides have to do the better the sound. Any contact that the tape has with a guide creates friction and this friction creates noise. Minimizing this guiding is the result of proper adjustment done on the entire machine. This is a part of what Doc ( the wise guy dude ) does when he optimizes the tape path with his modifications.
After the guide is a "time code" head. It applies a track into that border between the 2 tracks to sync sound to film or whatever. For the purposes of this discussion that's all I'll say about it (pretty easy since that's about all I do know!).
After that comes the 2 track erase head and then the first in a pair of lifters. The lifters "lift" the tape above the heads during fast forward and rewind and retract during play. When the lifters are retracted the tape moves across the heads and through the guides to allow the heads to "read" the information on the tape. When engaged, the lifters prevent wear on the heads. All adjustments of the heads are done without the lifters engaged.
The idler is only present on some machines although one can be added if there's room. The idler on this machine is used for sonic improvement and the use of these devices will be discussed when we talk more about tape handling and the effects it has on sound.
The last device on this head assembly that we haven't addressed before is the tape sensor. There are several different types of sensors (this one appears to be opto-electric) but they all have the same basic function. They stop the machine at the end of a tape from fast forward, rewind or play when there is no tape breaking a light/sensor interaction (as in this one) or releasing a spring loaded arm (as most consumer/prosumer machines have). When you work on a machine you can "fool" any sensor into thinking there's tape present (and you'll be able to engage play, rewind, fast forward) with a piece of tape either blocking the light sensor or holding the mechanical arm up.
If you look at the top of the head assembly, you'll notice a series of labeled holes. These are for access to the head adjustments. One of the main adjustments for a playback head is to keep the vertical orientation as close to 90 degrees as possible or needed. Imagine a tape with a quick, regular pulse recorded on it. If you could see it on the tape, you'd have a pattern that would look a little like a bar code down the length of the tape with this recording on it. If the playback head was tilted , you could see that part of each track of the head, would be "reading" this pulse before it should, while other parts of the head will be "reading" the pulse after it should be. If the tilt was extreme enough you'd also get pre and post echoing from the other track as it read it's track before or after the other. As you might guess, very slight tilts would result in phase issues with transients and images smeared. Adjusting the heads to eliminate any "tilt" is obviously central to the qualities of the outputs sound. This adjustment is called azimuth.

Once again, the photo is courtesy of Richard Hess 2001


By ironbut at 2008-08-26
OK, so you guys have seen pictures of the most often seen formats (1/4 track stereo and 1/2 track stereo). If you've studied the text, here's a little quiz. What is the format of the the machine whose heads are shown above? Well, here's some hints. The tracks are the orange colored slots and since there are two on each head, it's stereo. Another clue is that there's plenty of room between these tracks to put another track in between. From those two observations we can figure that this is probably a 1/4 track stereo machine. The main difference between this set up and what is usually seen on most 1/4 track stereo machines is the fourth head. One thing I haven't mentioned that would help, is that playback heads usually have a "shield" around them to reduce picking up hum from the rest of the machine (the record and erase heads are putting out a signal so they don't need shields). So the first and last heads are both playback. There are two main types of machines that have more than one playback head, a multi format machine such as the Technics RS1500 series and the Otari 5050 mk1 and 2 and auto reverse decks. This is one of the latter since as you can see, both of the playback heads have the same track width. The shields make it difficult to see the offset of the tracks but as I keep saying, the second head must be the erase head, the third is the record head and the fourth is the playback head. With an auto reverse deck, rather than having to flip the tape to play the "B" side, the machine plays backwards and switches which head is being accessed.  Even though we can't really see the opposite offset of the two playback heads, it must be there.
On one of the Technics machines (which playback in 1/2 and 1/4 track stereo) it depends on which model (1500 or 1506) on which head playback is first and which is last. A 1500 records in 1/2 track stereo and plays back in 1/2 and 1/4 track stereo. Once again the old rule applies. Erase>Record>Playback. If it records in 1/2 track stereo than the 4th head "must" be the 1/2 track playback head. If it's a 1506 which records in 1/4 track stereo, than the 4th head "must" be a 1/4 track playback head.
There are machines that were pretty popular in the 1970-80's that throw a monkey wrench in this. Teac created quite a stir when they released a machine called the 3340s. The "S" stands for sync and the 3340s was a 4 channel machine (that's 4 channels in one direction like the head assembly shown in the first picture in the heads posts). Four channels was nothing new but this machine allowed each channel to be recorded at a time and the remaining channels could be added (overdubed) one at a time later. This doesn't seem too revolutionary since it would seem that it would only require switching of each record channel as you overdub each channel. If you look at the picture above and look at heads 3 and 4 (record and playback) you will see that there's a space between the two. Depending on how fast the tape is moving, there is a significant delay between the moment the the sound is recorded onto the tape and when you could hear it. Not only that, but if you're trying to play in time with the other channel/s which have already been recorded, you'd need to anticipate this delay and "hit" the beat before you could hear it. What Teac did was enable the record head to also act as a playback head too. So if drums was recorded on channel 1 you could switch channel 1 on the record head to playback and add a guitar track on channel 2 in perfect sync. Of course studios machines had been doing this ever since Les Paul introduced overdubbing decades earlier but this was the first affordable machine that could do this. The home studio was born and Otari and Teac's own Tascam dominated this market right up to today. We can be mighty thankful for this home studio market since lots of the Pro-sumer stereo machines were designed and bought to mix down these multi track recordings. Some of the members here probably own ex- home studio mastering machines.
Another significant tape/tape deck format was mono. If you collect records, I'm sure you have at least a few mono recordings (enough are being currently produced to prompt cartridge builders to introduce mono versions of some of their stereo models). And if your into jazz, lots of Blue Notes (all the 1500 series ) were originally recorded in mono (can you imagine getting your hands on one of those!). There are actually two pretty popular mono formats. One was a full track (full tape width) and 2 track mono (I can't believe that no members jumped on me for forgetting this is the 2 track discussion). The 2 track mono is like a 1/4 track stereo and requires a tape flip to listen to the second side.
There are, of course, lots of other formats such as 24, 16, and 8 channel and some early consumer machines had combination record/playback heads, heads that rotated or raised to have a 3 head 1/4 and 1/2 track playback machine. If anyone has questions regarding these, feel free to ask.

Great stuff, Steve.  Thanks for the time you're putting into this.

Not to devolve too far into head trivia, but there is a class of consumer machine that people may frequently encounter that is NOT compatible with TP tapes. This is the 2 head 1/4 track format where the record and play functions are in one head as you described in "sync" playback using the record head in the last post. In fact some Tascam multitrack (8, 16) use this design too so the signal is always  in sync. It's just harder to optimize record play frequency response and impossible to monitor what you have just recorded on the fly without rewinding with a 2 head (erase, record/playback) system.

As an aside,
yes trivia buffs, that is what the "tape monitor" button is for on many many pieces of audio equipment. It continues to send the program signal to the tape output jacks while allowing you to hear the tape recorder output that can then be switched between tape and input to compare recorded quality.  Some may have forgotten or be too young...

But I digress.

I have also seen auto reverse 2 head designs that play and record both directions. These would have (from left to right) reverse record/play, reverse erase (remember, the tape would be moving the other direction), forward  erase, forward record/play.

And I own a semi pro 2 head design  2 track 15 ips. (inches per second since we are explaining things here) old tube Crown recorder. So at least one 2 track stereo machine is not 3 head !


--- Quote from: ironbut on August 27, 2008, 11:09:20 PM ---On one of the Technics machines (which playback in 1/2 and 1/4 track stereo) it depends on which model (1500 or 1506) on which head playback is first and which is last. A 1500 records in 1/2 track stereo and plays back in 1/2 and 1/4 track stereo. Once again the old rule applies. Erase>Record>Playback. If it records in 1/2 track stereo than the 4th head "must" be the 1/2 track playback head. If it's a 1506 which records in 1/4 track stereo, than the 4th head "must" be a 1/4 track playback head.

--- End quote ---

This feature of the Technics is atypical of multi format decks, in that the 4th head is in the main format of the machine and the opposite format head precedes all the others. As in 1/4 track play then 1/2 track erase, record, play. In most other dual format designs the opposite format additional playback head is after the primary format playback head.
 As in 1. 1/2 track erase, 2.  1/2 half track record, 3. 1/2 half track play, 4. 1/4 track play.


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