Tascam Porta-One head alignment help!

[Bucko]

I'm breathing new life into this old beast and I'm stuck. I had to remove the play and record heads in order to fix the transport spring issue. Now the play heads and record heads are out of alignment. There seems to be just one screw in each head to make adjustments and that's not working too well. Did I reinstall the heads wrong? There was a tiny copper shim or washer that fell out of the play head spring when I removed it and I guessed where that was supposed to go. Maybe I put it in the wrong place.

Any insights would be amazingly helpful.

[Gnobuddy]

Any insights would be amazingly helpful.

Do you have access to any tapes recorded on this machine before it died? Playing back one of them and tweaking playback head alignment by ear might at least get your playback head in the ballpark.

If a generic audio cassette will play back through the Porta-One, that might work too. Even if some tracks are playing backwards (I'm not familiar with the Porta One, assuming it takes the same 4 tracks that are standard on all cassettes, but plays them all four in the same direction, rather than two forwards and two reverse like normal cassette players), you can still tweak the playback head for maximum high trebles (sibilance, etc).

If you get the playback head aligned, you can then align the record head by playing back one track while recording another into the mix. This time, tweak the record head for maximum high trebles. If you have a signal generator, it works even better to use a high frequency test tone (sine wave) as the record signal, and maximise its playback volume by tweaking the record head alignment.

You probably know that head alignment is particularly critical for cassette players. Because of the very slow tape speed, recorded wavelengths on the tape are extremely short. If the head is even a tiny bit out of alignment, the shortest wavelengths (treble) won't line up with the head gap, and you get drastic treble loss.

-Gnobuddy

[olddawg]

Generally you would put a 10kh test tape in it, put a scope on the output, and adjust for the most amplitude. If you don't have a scope... yeah you can get close by ear. If you don't have at factory test tape, a known good previously recorded tape can be used as previously mentioned. Do the playback head first. It will take some trial and error to get the erase head correct since you are erasing individual tracks. The erase head is segmented. Make sure the heads aren't trenched, the tap path isn't worn, the pinch roller is good. The clutch is right. And demagnetize the whole mess before you start. All of that makes a difference. The copper piece may be a physical ground to the chassis.

[Gnobuddy]

If you don't have at factory test tape...

I made the assumption that the OP probably didn't have access to one (heck, I haven't seen one in decades!)

Make sure the heads aren't trenched, the tap path isn't worn, the pinch roller is good. The clutch is right. And demagnetize the whole mess before you start. All of that makes a difference.

All this is why I loved the CD when it first arrived (and still do). Even those MP3 files everybody loves to hate - at least you don't have to worry about trenched heads, head misalignment, demagnetizing, or any of the other ridiculousness we had to go through to keep our cassette players and turntables working.

In extremely humid weather, I remember that every cassette I listened to would gradually sound duller and duller as the minutes ticked by. Inspection would show a smear of brown oxide on the head, wiped off the tape as it rubbed itself over the playback head, because the humidity was weakening the binders and glues that held the oxide onto the plastic tape itself.

So the head would slowly scrape the oxide - and the music on it - off the tape as you played it. I was literally listening to my music destroying itself!

-Gnobuddy

[Enzo]

The four tracks are the same tracks as they alternate for two side stereo.

There are two things: the tracks need to align, then ther is azimuth. The vertical alignment you can do by ear. Play back something pre recorded, move the head up and down to peak the level and the high freq content. Azimuth is how close to vertical the head is across the tape. If it is off, one track is slightly ahead of the other, especially 1 versus 4. A test tape is full width recorded of a tone, but a music tape wil stil work.

If you put your scope in XY mode and monitor the end tracks with the same signal on them, you will get a 45 degree line on the scope it is is right. If they are out of phase from azimuth you will get a loop, an oval.

With music, use tracks 1 and 3 or 2 and 4. Less effective but you get close. Adjust for as close to a 45 degree straight line as you can.

Gross azimuth can be heard, but it is hard to hear small amounts of azimuth. You get a bit pf phasing sound.

[g1]

Is this machine new to you or do you have old tapes that were made on it?
If it's new to you, it's better to get it 'right'.
If you want to use old tapes that were made on it, it's better to get it like it was before, even if it wasn't 'right'.

Can you post some high res. close up pictures of how you ended up mounting the head and the shim you mentioned?
Also, refer to pg.40 of service manual attached.

[g1]

And if I'd have to guess, I'd think if any spot needed a shim, it would likely be under the right side of the rec/play head.

[Enzo]

Is this machine new to you or do you have old tapes that were made on it?
If it's new to you, it's better to get it 'right'.
If you want to use old tapes that were made on it, it's better to get it like it was before, even if it wasn't 'right'.

This is something you run into in a shop. If I have to work on the heads, I will adjust them to spec and proper alignment. However, if the machine was mis-aligned before., then all the previously recorded material will no longer play back properly in the machine.

If you align a head randomly, it will record and playback just fine, but the tracks from any other machine may or may not line up.


So in fact I usually ask the customer if he wants the heads aligned to spec or to retain the previous alignment to keep previous recordings useful.

[Bucko]

Thanks for the infor Enzo. When you say alignment, are you referring to azimuth adjustments? I don't have any previous tapes, unfortunately, nor a convenient way to make a 10k test tape! I put in an old White Lion tape, yes that White Lion, and adjusted the azimuth while listening on headphones. I can her terrible phasing and the left side is probably 6-8db louder. I'll look thru the manual, thanks to g1. Do you have some pointers that might help?

[Enzo]

No. I meant alignment to refer to the vertical of the head across the tape. SO the individual little head gaps are aligned with the stripes of signal on the tape. In other words if the head ga is aligned right to the edge of the tape, but the signal stripe down the tape is more like a half millimeter in from the edge, that is poor alignment.

Azimuth is whether the tape head is perfectly perpendicular to the tap or if it is tilted.

Endino's Cassette Transfer How-To

[olddawg]

Enzo... maybe my memory isn't serving me well, but I don't remember doing to many azimuth adjustments on cassette decks. Most were a single screw adjustment. 1/4" tape width and up, even 8 tracks (which is just 1/4" tape) had azimuth adjustments. Maybe a few super high end cassette decks, but the tape is so thin I seem to remember most with an adjustment on one axis.

[Enzo]

I guess it is one adjustment that covers both. I was speaking to the general case of tape decks moreso than this model specifically. I haven;t had a cassette deck in for anything serious in YEARS.


I guess what I was talking about applies more to reel to reel decks, I have done my share of those.

[Gnobuddy]

Most were a single screw adjustment.

That's what I remember also. I never saw an adjustment to traverse the head across the tape width on a cassette player. In many cases, when moved into playback position, the playback head occupied virtually the entire available thickness of the opening in the cassette. No (or hardly any) vertical adjustment would have been possible.

The problem of azimuth adjustment was a major source of frustration to me. Many of the pre-recorded music cassettes I bought had incorrect azimuth. I used to have to tweak the azimuth setting every time I played some cassettes, then tweak it back for the next. Trying to maintain any sort of decent treble response was an ongoing struggle with the cassette medium - there were half a dozen different ways in which you could lose treble, including having the misfortune to by an expensive pre-recorded cassette that had been recorded too "hot", at such a high recording level that the tape saturated at the treble frequencies, smearing and dulling the sound.

One of the weirder things about cassettes is that the recorded wavelengths (and head gap) were so small that recordings did not go all the way through the entire thickness of the oxide layer. All the high treble content essentially lived only on the surface of the tape. So there was less magnetic material to store treble information than bass information. This is one of the reasons why it was so easy to suffer from saturation at high frequencies, which gave you smeared sibilants and cymbals that sounded as though you were listening to them through a pillow.

-Gnobuddy

[g1]

Azimuth is covered on pg.29. Some of that may help you but you won't have the test tape so you'll have to improvise.
You want to set it using track 1 & 4. So with your standard stereo pre-recorded tape you'll hear a track running backwards on track 4.
Just the single screw for adjustment. Try to get them roughly equal level first, then fine tune the high freq. later.
It's best if you can monitor direct from the 'tape out 1' and 'tape out 4' jacks.

[Bucko]

Thanks for all the insights and help folks. Much appreciated.