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Teac A-3340s problem

I thought you said playback is ok? If so, the playback head doesn't need to be lapped. Possibly the bias is off on tracks 1 and 4.
 
YOu should also try aligning the record head. You need an oscilloscope and a generator. You record a 15KHz tone and monitor the output with the scope on X-Y, monitor switch set to "Tape." Adjust the azimuth for a diagonal line from lower left to upper right on the scope.
 
The lapping job looks really good mechanically. Lapping takes care of physical tape to head contact problems, called "cupping".

There is a limit to what lapping can do. If the cuts are too deep into the material of the head, the the gaps can be worn wider. The gaps are formed where the head laminations converge to a point, but don't touch, at the apex of the head. These two laminated sides of the gap are very sharp and as the head material is worn away, the gap opens and becomes wider. The more narrow the gap, the higher the frequency the head can resolve.

If you have a playback tape, you can look at the play response. If it's good, that means great job on the head and that the head gaps are still sufficiently closed.

If playback response can't be made good, it means a new head is in order. .... which TEAC is pretty good about having one or a sub available.
 
Jon_Logan said:
The lapping job looks really good mechanically. Lapping takes care of physical tape to head contact problems, called "cupping".

There is a limit to what lapping can do. If the cuts are too deep into the material of the head, the the gaps can be worn wider. The gaps are formed where the head laminations converge to a point, but don't touch, at the apex of the head. These two laminated sides of the gap are very sharp and as the head material is worn away, the gap opens and becomes wider. The more narrow the gap, the higher the frequency the head can resolve.

If you have a playback tape, you can look at the play response. If it's good, that means great job on the head and that the head gaps are still sufficiently closed.

If playback response can't be made good, it means a new head is in order. .... which TEAC is pretty good about having one or a sub available.
Click to expand...

Jon, the one he lapped is the record head. So if the playback response is ok, the record head gap could still be too wide. However, he said it only took him a few minutes to lap the head, so the wear could not have been that deep. When I lap heads it usually takes me 15 minutes on each grade of sandpaper, then 15 minutes with felt and silver polish. So 45 minutes to an hour for most heads I have done. I think the bias could be off on 2 channels. Or record EQ could be off.
 
dr*audio said:
Jon, the one he lapped is the record head. So if the playback response is ok, the record head gap could still be too wide. However, he said it only took him a few minutes to lap the head, so the wear could not have been that deep. When I lap heads it usually takes me 15 minutes on each grade of sandpaper, then 15 minutes with felt and silver polish. So 45 minutes to an hour for most heads I have done. I think the bias could be off on 2 channels. Or record EQ could be off.
Click to expand...

Hi Warren, thanks. I missed what head it was. Yeah, the record head is more forgiving with gap width. At least that's what I've always been told.

I like your described technique on lapping. I agree, patience is a real key to successful lapping.
 
Bias and Record EQ

Dr.Audio - thanks for sharing your knowledge and experience. Can you explain how to diagnosis or set the Bias and Record EQ or summarize what's involved? Equipment required? Scope? Etc...

This thread is really providing some useful info that many of us can or will need down the road. Head wear, replacement, lapping and diagnosis are top issues with these RTR's!

Thanks again for everyone's feedback and contributions here. Especially our "patient" ... SoundBall's machine!
 
The procedure is in the service manual. Briefly, record a 1KHz tone at -20dB, while monitoring the output (on tape) with either a DMM that has flat AC voltage frequency response out to >30KHz, or a scope. Switch to 10KHz and adjust the bias for the same level. Go back to 1KHz and recheck, and compare with 10KHz adjusting until they are the same. Go to 15KHz and adjust EQ so the level is the same. You can then go up to 20KHz and tweak the EQ a Bit if it's rolling off.
 
Luckily enough this is a "Simul-Sync" machine. Since you can play through the record head, you can tell whether or not the playback head is now the weak link. The frequency response is nowhere near as good through the record head in playback mode as it is through the actual playback head but at least you should be able to verify similar performance on all tracks. I know, since the record head doesn't have the same frequency response in playback mode as the playback head itself does, you might still be testing in the dark but there's a good chance that if all tracks respond the same on it, the head is OK. You need a test tape of some sort to test the playback head.

Please do make that video, by the way!
 
not much of an update, but i did try listening through the record head in Sync mode, i could still hear the difference between tracks 1 & 4, and 2 & 3, though not as much as when listening through the playback head (most likely due to the Sync mode's poor frequency response).

i will check alignment, and see what i can do about the bias adjustments
 
I would suggest your findings in Sync mode probably rule out the playback head (unless there is more than one problem but it's best to assume not until other possibilities are exhausted). If you are using tapes recorded on the same machine, the problem could now be in one of three areas: the record electronics, the record head or the playback electronics. I know I said test tape previously but you don't really need to go that far just for troubleshooting purposes. If you can get your hands on any recording made on another machine, there's a good chance of eliminating further possibilities.
 
I checked the azimuth on the record head, and made slight adjustments, but it was more or less aligned in the first place.

dr*audio said:
The procedure is in the service manual. Briefly, record a 1KHz tone at -20dB, while monitoring the output (on tape) with either a DMM that has flat AC voltage frequency response out to >30KHz, or a scope. Switch to 10KHz and adjust the bias for the same level. Go back to 1KHz and recheck, and compare with 10KHz adjusting until they are the same. Go to 15KHz and adjust EQ so the level is the same. You can then go up to 20KHz and tweak the EQ a Bit if it's rolling off.
Click to expand...

the biasing procedure you described is quite different than what is in the manual, where it says to record a 400Hz tone at -8db, and over-bias .5db(for scotch 203 or 150, neither of which I am using) the EQ procedure is also different in the manual

This is a bit confusing, I just read the sticky thread on tape biasing, and you're explanation is easier to follow along than that manual. So I think that's what I'm going to try
 
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There are 2 ways to adjust the bias. I find that mine gives better results most of the time. If the bias is off by a country mile, then it is best to record a 1KHz tone and crank the bias up for maximum output, then continue turning the control in the same direction until the output drops by about 1dB. Then do the 1KHz / 10KHz adjustment. The first part of this gets the bias close, the second part fine tunes it.
 
SoundBall - Have you tried testing playback quality with a tape made on another deck or a pre-recorded tape? Anyone local (AK'er) you can borrow a record tape from or we'll have to figure out how to get you something!
 
jmiles1960 said:
SoundBall - Have you tried testing playback quality with a tape made on another deck or a pre-recorded tape? Anyone local (AK'er) you can borrow a record tape from or we'll have to figure out how to get you something!
Click to expand...

hey Jim, I have tried playing back a pre-recorded tape, and I still get the same results.
 
dr*audio said:
I think the record head is shot.
Click to expand...

????? wait what? by "pre-recorded tape" I meant just another tape NOT recorded on my machine, that should have been recorded on a good machine. And by "same result," I meant that tracks 1 and 4 were still sounding muffled when listening to this tape.

I thinks there been some miscommunication here. because that should indicate that the problem lies somewhere other than the record head. That would mean too that it shouldn't be a bias problem(though maybe that could compensate for it, when recording on my machine?), but could still be a Playback EQ problem. This contradicts my earlier posting saying that tracks 1 & 4 did not have the problem when listening to other tapes. But this is what i just noticed.

I also made another recording and listened back on the sync heads again, and I'm not hearing a difference between any of the tracks. This too contradicts what I had written yesterday. Maybe it was because I was listening through crappy headphones(It was late and I didn't want too use the speakers).

sorry about the mis-information earlier

quick recap:

when playing back tracks 1&4 sound muffled
when playing back through "Sync" mode, things sound fine
when playing back a "good" tape (not recorded on my machine) tracks 1 & 4 sound muffled
Record head is in alignment (after having removed and lapped)

I think this rules out the Record head(or record bias) as the problem

Possible problems:

Playback head(groove maybe, or something else)
Playback EQ
 
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I just finished lapping, and installing the playback head...and IT WORKS!

all channels are playing back the same!

Thank you to everyone who helped me troubleshoot this machine, I know the mis-information that I posted earlier slowed process of finding what was wrong. But I guess that wasn't such a bad thing, because I did learn a alot about alignment, bias adjustments.
 
Yep. dr*audio made the same conclusion as me (although I would have added in the possiblity of playback electronics) but, since we now know you played a tape recorded on another machine through the playback head, it all makes sense. At least now you know how to trouble-shoot a tape deck :-)
 
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