Obvious Problem?

[sandman]

Hi,

I am trying to trouble shoot a possibly obvious problem with my Pioneer RT-701.  When playing a tape (the first side) the left channel VU meter always reads weaker than the right (also the image is off center to the right) When I flip the tape the left channel VU meter reads stronger than the right channel, and the image is shifted to the left.  I have thoroughly cleaned the tape path and heads, and am wondering, is this strictly an alignment problem?  I have had people say just keep cleaning the head because, once set the heads don't really drift over time(I guess that is assuming they were properly set up the first time) the head is still just dirty.  If this is strictly an alignment problem, does it require special screw drivers?  Is it even something that can be done with out taking it to a tech?  I am sure some machines are easier than others to align.  Thanks.

Kris

[ironbut]

It's true that alignment of your heads seldom drift for no good reason. Of course if the headblock gets bumped in the wrong way that would effect alignment. You didn't say when and how this problem happened. You should try several tapes since left channel weakness is very common (read the Beginners Guide about heads and tapes). Usually, there is left channel weakness on both sides of a 1/4 track tape but anything is possible.

Like I said, your alignment changing is unlikely but the actual fact is that it's always changing a tiny bit. This is because of head wear. It would be a rare consumer machine that is so perfectly adjusted that the wear on your heads is exactly even. So as the heads wear, there is an increasing loss of frequency and output balance. You didn't say how long you've had this machine so I won't guess much more about that. You do need to check your heads to see if there's any grooving (also in the Guide).

The other half of the equation is the tape guides. Even if your heads are perfect and in total alignment, if your guides aren't adjusted correctly than it doesn't matter.

Remember, all tapes are not created equal. When they're made they can be all over the place as far as channel balance, alignment, slitting and in the case of any 1/4 track tape with a right channel that is weaker than the left, just flat out poorly recorded or duplicated. And that's before 2-5 decades of poor storage, abuse and accidents.

You should fill us in with more details if you want a more detailed guess. If you've never done any alignment, it would be best to have it done for you. You really need a scope and alignment tape.

[steveidosound]

Hi,

I am trying to trouble shoot a possibly obvious problem with my Pioneer RT-701.  When playing a tape (the first side) the left channel VU meter always reads weaker than the right (also the image is off center to the right) When I flip the tape the left channel VU meter reads stronger than the right channel, and the image is shifted to the left.  I have thoroughly cleaned the tape path and heads, and am wondering, is this strictly an alignment problem?  I have had people say just keep cleaning the head because, once set the heads don't really drift over time(I guess that is assuming they were properly set up the first time) the head is still just dirty.  If this is strictly an alignment problem, does it require special screw drivers?  Is it even something that can be done with out taking it to a tech?  I am sure some machines are easier than others to align.  Thanks.

Kris

This is a bit odd from a logical point of view.It is not typical to have the "problem" channel switch when turning the tape over. I am making the assumption that we are talking about 1/4 track (4 track) stereo tapes here with a side one and side two.
You say that the left channel is lower when playing side one and then the right is lower when playing side two?
Is this consistent from tape to tape on known good stereo tapes? Pre-recorded ones from various commercial sources?
Because, for example, if all of the tapes were made on some other home machine it could have been the one out of alignment.
If they are tapes you are recording on this machine that might point to an issue between it's record vs play head alignment.
It would be more typical of dirty heads to always have one of the two channels lower no matter what.
Can you tell if the frequency response sounds the same in both channels or is the weaker channel also lacking high frequency response and sounds dull?

OK, I just checked, the RT-701 is auto reverse and so has a 4 track head, so you are not physically turning the tape over to play the other side. You are playing side one and side two with 4 different head gaps. So yes, this could be either a tape head alignment or a tape path alignment issue with the tape skewing across the heads slightly differently in forward vs reverse play. Possible issues with tape guides or pinch rollers could also cause this. There could also be switching contact issues with whatever (relay etc.) changes which head gaps are connected to the playback electronics.

[sandman]

Thanks for the replies.  I apologize for not giving more specifics.  The RT-701 is a NON reversing player so I do have to physically flip the tape.  That said, I am not the original owner of the machine, as it was given to me along with a huge collection of prerecorded tapes.  There is some head wear, but by looking at the example in the beginners guide it is minimal.  It is weak with almost all tapes, an when flipped it is almost always higher on the left.  All the tapes I listen to are prerecorded.  I have a seemingly very cheap Magnavox player that I got as well.  I have put the same tapes on that machine, and while the sonics are severely lacking in comparison, the channel weakness is basically gone and the channel balance was much more "locked" in.  Another thing which I have found peculiar is I have about 80 2 tracks, mostly(about sixty) are RCA "shaded dog" tapes, and though I have read that the left channel will be the strongest, most of the time the VU meter barely even registers when playing those tapes.  Many of you may be familiar with these recordings so you may know if that is normal for these to perform like this on a 4 track.  Thanks

Kris

[steveidosound]

  The RT-701 is a NON reversing player so I do have to physically flip the tape. 
Kris

Sorry, I just looked at a picture and was fooled by the symmetrical looking apparent "dual capstans and pinch rollers"
I see that the left one is not that, but a tape tensioner.
There was an auto reverse similar model though right?

[steveidosound]

when playing 2 track tapes with a 1/4 track head, the gaps are positioned on the "upper half" of each track
I will leave it to others to say exactly how this affects playback. I do know that some older decks had a  2 track/4 track (sometimes labeled "H"/"Q") switch which moved the head down to physically center the gaps on the tracks, but they were still not covering the full width of the track.

[ironbut]

I'm not that familiar with the RT-701 so I did a little search on this machine. The main thing I was looking for was the head layout. I'm not sure if you know it but a 1/4 track stereo machine has a playback head with two tracks (for stereo) but the tapes have 4 tracks. The two tracks on the head are offset with room enough for another track in between. So when you flip the tape, the same tracks on the head are playing the other two tracks on the tape ( but the outermost track of the head is always playing the left channel and the inner track on the head is playing the right channel no matter whether it's side a or b).

I'm sure this has got steveidosound scratching his head as much as I am. I could see an isolated case where the tape would have a low level on the left channel on side one and have a low level on the right channel on side two (I've never seen this in the hundreds of tapes I own). But you say it's happening with all your tapes.
The only answer that I can come up with is that a machine that these tapes were played on was damaging these tapes in this manner.

But then comes the question of why they would sound better on the Magnavox?

Discounting the VU meters (which can be totally misleading on playback and are really only there for recording) how much difference in volume are we talking about here? Is the right and left channel equally low on the respective sides?

If you look at the playback head (should be the last on the right after the erase and record heads) do the tracks on it look offset (one band closest to the outside, then a space, then another band a little past the center of the head).
Finally, is there a chance that this machine was altered or modified?

[ironbut]

OK,.. I think I've got it.

Take one of the tapes that seemed the most prone to this problem and look at the tape. Is it curled and wrinkled on one side. An easy way to see this is to take a length of this tape and lay it across a flat clean surface. It should lay down flat.
If one edge of the tape is curled enough it can prevent the left channel on side 1 and the right channel on side 2 from making proper contact with the head. The magnetic print on tape is very small and any magnetic field decreases rapidly with distance. If you've ever heard drop outs on a tape, that is the result of the increased distance that the tape is from the head surface by a piece of dust.
Tape curling on on side is almost always the result of improper storage. Usually it's from being stored in a rewound condition (rather than a played condition) which results in the layers of tape sticking out a little on one side or the other.

Oh,.. and the Magnavox has too high a tape tension so it flattens the tape out.

[sandman]

O.k. A little more about the player.  This player was modified(sort of).  It had direct outputs from the head for use with a repro amp.  I have since switched it back.  I will be switching it back again for a repro amp(the same one that went with it:)  Long story short, it is a custom David Berning design, and I am waiting for him to go through it as it is older, and probably not functioning.  Here are a couple pictures.  Sorry about the blurry head shot but took several and apparently my camera will not pull focus that close.  The second picture is of the typical difference in output.

http://s442.photobucket.com/albums/qq150/kriskosiba/?action=view&current=tapeplayer003.jpg&newest=1
http://s442.photobucket.com/albums/qq150/kriskosiba/?action=view&current=tapeplayer004.jpg&newest=1

[ironbut]

Nothing relevant to the problem at hand with the pictures of the head and like I said, the VU readings on playback are almost meaningless on consumer machines.
Since it does have 1/4 track heads it almost makes the above guess about the tapes being somewhat damaged is almost a certainty. One thing that could help is the tape tension on the Pioneer. Most consumer machines err on the side of too little tension. Most machines require a special meter to get an accurate tension measurement but even when it's set to factory spec's it still may have too little tension.

Older machines like I'm guessing your Magnavox is err on the side of too much tension. Those can stretch tapes even to the point of increased wow which effectively ruins the tape (Particularly "double play" tapes which were made on very thin backing).

Hopefully, it is more a matter of tension and not the tapes. It would be a crying shame if many of that huge collection has been curled (but it happens all the time). If you'd like to learn more about curling and tape damage,.. you guessed it, beginners guide.

[Studer Fool]

Kris,
You state:
"repro amp(the same one that went with it:)  ..., it is a custom David Berning design, and I am waiting for him to go through it as it is older, and probably not functioning."

If you are in communication with David Berning there is one big favor you could do for all of us dolby pre-recorded tape/tube heads, and that is to ask him about his tube-based dolby design for us!!!!!!!!  Any information would be great!!  But a schematic would be true gold!

Any Barclay/Crocker tape owner with a taste for tubes would stand in line for such a Dolby playback unit!  (well I know that I would!)

THANKS!
cdw