Tascam 388 Ch. 8 playback muddy

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BennyS

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Hello,

I've been recording/mixing with my 388 and ch. 8 playback has become unbelievably muddy. Since I first noticed the problem a couple days ago the heads have been twice cleaned with 99% iso alcohol, demagged, I've tried FF and Rew a few times over with the tape lifters disengaged, and none of this has helped. A few months ago I was having a similar issue but it was intermittent at worst and a head cleaning seemed to take care of it.

I will say that since the last time I observed all channels playing back properly, I have replaced the pinch roller rubber, made a slight adjustment to the pinch roller pressure to get it within spec, and adjusted the reel table heights so that the tape no longer makes contact with the reel flange. This issue--as a persistent and not immediately fixable one--has only surfaced after those adjustments, though I do not know if they're related.

I'm using ATR Master Tape and have been for the whole project.

I'm posting a pic of the rec/playback head here in hopes that there may be a visible clue.

Thanks for your help.
 

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Ok, it's the tape making poor contact. I just pressed it against the head and ch. 8 played clear as a bell. Stays that way for about 10-20 seconds after I take my finger off in fact. I'm not sure what adjustment I need to make at this point so any advice would be very welcome. The manual says head height and tilt are factory fixed. Am I looking to adjust the tangency screw? I only have a 15 ips MRL tape for 1/4" and would love not to have to purchase a 7.5 ips if possible.
 
When you’ve tried fast wind with the lifters disengaged, are you doing that for the whole tape pack?
 
No, admittedly I only went for about half the reel each time. Can that technique correct for tape making poor contact on this outer channel? I was throwing things at the wall when I tried that, though now it seems like a mechanical adjustment is needed.
 
I’ve written about this a few times…if you have an issue where you have poor contact at one or both edge tracks, it’s usually because the wear path is too narrow for the tape you are using. Now I’m sure the first thing you’re thinking “it’s a 1/4” machine, I’m using 1/4” tape…”, but unfortunately not all 1/4” tape is created equal. Ampex/Quantegy tape slitting equipment was ever so slightly less precise than the rest of the world, so what they did was undersized their standard by about 0.002”~0.003” compared to everybody else. This allowed for their production variances and avoided the possibility of their tape being too *wide* and not fitting properly in the throat of fixed or rolling guides. But that means if you have a wear path on a machine like a 388 where the track width is really narrow, and then you load tape that is precisely slit to the international standard, it’ll ever so slightly lift or curl at one or both edges. You can’t adjust anything to make the wear path wider. The only proper solution is to relap the head and when you have it done have edge slots cut to avoid future reoccurrence. It takes very, very little deflection at the edge to diminish or completely lose signal continuity to/from tape to the edge head core. So if you can apply some pressure and get good signal my theory is possibly your plight. The other thing I’m curious about though is what looks like a glaze on the face of the head at the bottom tracks…like a varnish. Are you completely sure the head is clean? Forget dainty dabbing or wiping with a cotton swab…get a 100% cotton makeup remover pad and rub it to clean it thoroughly. Report back.
 
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Yea I did actually read another thread where you talk about the wear path issue. The only reason I'm dubious is because I've been using the same ATR master tape on this thing for a year and a half and it's only become a problem very recently. Can you tell me though if the curling would be visible if well lit?

I think what's showing in that picture is a reflection of the top panel. I saw that too and moving the light source moves the dark spots. Definitely cleaned the hell out of the heads but I suppose another go around isn't going to hurt. I already do clean them and demag more often than the every eight hours of use recommended.

I guess I'm curious if, to your knowledge, a new pinch roller rubber, change of reel table height, or adjustment of pinch roller pressure could cause what I'm experiencing as those were the only changes that I made before the problem began. Or if you would recommend trying to adjust the head tangency screw.
 
Thanks for the helpful response. Yeah if it’s the same tape and only now is different after a year and a half, then it’s NOT likely an Ampex/Quantegy narrow-wear-path issue…or at least not primarily. If it was working and now it’s not with the same tape after a year and a half, you should be able to make it work again with the same tape. Something else has changed, and yes changes in the height of tape path components can affect things like this…more below.

On the visibility of the lifting or curling, sure sometimes you can see it, but more importantly the amount of deflection needed to cause a substantial reduction in response/performance can be so small on a 1/4” 8-track machine it’s hard to, if not impossible, to see.

If you are confident in your cleaning don’t feel like you have to do it again on my account. It seems like you understand the importance of it. So, fair enough there.

Okay on the pic of the head…the reflection. Can you post another pic or two without that reflection? Better light? And defer to getting the head in focus rather than getting close? I don’t know what you’re using to take pics but my iPhone 14 won’t let me get close, but if I have good light and stay back so it can focus on the small subject I can just crop and have a good image.

Now, regarding if changes to the reel table height or pinch roller or pinch roller pressure could cause a change like you’re experiencing, which is maybe a deflection of the tape downward in the path across the R/P head…yes. Long answer: each point in the tape path that acts as an upper or lower boundary for the tape, like the guides, for instance, also create pivot points if the tape is pressured into them. I can’t really explain it well, but I’ve experienced this when setting up tape paths and finding the tape heading the wrong way at one point and identifying it’s because of something ill-adjusted at a completely different place in the path. The tape can end up in a gentle ‘Z’ pattern through the path. I think this is more true the more narrow the tape. There is great variation in tape paths and how they are setup and handle this. It’s very complex. The 388 tape path though is pretty simple, and the transport is pretty gentle on the tape. So reel table height I would not expect to influence behavior across the R/P head, okay? I’m not saying it’s not possible, and I don’t have a 388 anymore to test my theory, but my suspicion is that’s not the droid you’re looking for. Tell me about your pinch roller. Tell me you did not refurbish the roller by getting one of those replacement tires…no judgment if you did, but I most definitely have opinions about that solution for a pinch roller rebuild.
 
I'll get another pic of the head up here tonight.

I'm ashamed to say I did replace the rubber myself with a tire I purchased online. I'm going to try and see if the roller is making even contact against the capstan shaft when pressed lightly against it by shining a light behind where they meet. I also see a replacement 388 pinch roller wheel I can purchase for relatively little money so I can at least check that against the one I'm using to see if the problem remains.
 
Don’t be ashamed for purchasing the budget option for your pinch roller. I think the people selling them should be ashamed. Maybe they work in some cases, but I bet not to factory spec, and in every case so far of me working on a machine with one of those replacement tire pinch rollers there were issues requiring getting rid of it. 100% you get what you pay for when refurbishing/replacing your pinch roller, and in my book there are only three viable options:

1. New factory part from the manufacturer (and not new old stock but new stock…this is often not an option as the part is no longer available),

2. Sending it to Terry’s Rubber Rollers and having Terry remanufacture your original roller, or

3. Purchase a new roller from Athan Corp.

So do what you want, but I *highly* recommend you pony up and pay for a quality option. We’re all on a budget. I get it. But some things are just not worth cutting corners on.
 
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The pinch roller appears to be making good, even contact with the capstan shaft.

Here are a couple more pics of the head, really difficult to get and angle where it isn't reflecting the surrounding housing and light source but I think these at least offer some perspective
 
Thanks for the additional pics. At least by the pictures the R/P head looks fine to me. And clean :) I do see a wear pattern, so there is the potential for that lifting or curling if the tape is skewed across the R/P head.

So did the issue with the diminished performance on the edge track start in direct correlation to any of the service you performed (reel table height adjustment, pinch roller rubber replacement, pinch roller pressure adjustment)? Like, did you do any or all of those things and then the issue started?
 
sweetbeats said:
Thanks for the additional pics. At least by the pictures the R/P head looks fine to me. And clean :) I do see a wear pattern, so there is the potential for that lifting or curling if the tape is skewed across the R/P head.

So did the issue with the diminished performance on the edge track start in direct correlation to any of the service you performed (reel table height adjustment, pinch roller rubber replacement, pinch roller pressure adjustment)? Like, did you do any or all of those things and then the issue started?
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Those are excellent points. I learned a long time ago from an old guy who could repair anything to find out what happened BEFORE the problem that needs fixing manifested itself.
That universal truth has helped me out numerous times.
 
A few months ago I noticed that track 8 was intermittently playing back muddy just as it is now, although it seemed to correct itself without intervention, often during playback, and the next time I cleaned the heads it was gone, so I assumed it was just some build-up. I honestly can't recall if I've recorded onto track 8 since that happened, but I did put on the new roller rubber, adjust pinch roller pressure, and adjust the reel table height in the interim and just noticed the problem this week while attempting to begin mixing the project I've been working on. So short answer, yes, I did those things and the problem began, as far as I can tell.
 
I’d ask if you’ve tried swapping amp cards, but you indicated you can mitigate the issue by manually manipulating the tape on the head…

Why did you adjust the pinch roller pressure, and is it safe to assume you did it using a spring scale and according to the instructions in the service manual?

What happens if you flip the pinch roller upside down? Remove the cap screw, flip it over, reinstall the cap screw. Any change?

The next step is to look closely and analyze where the tape is riding through each guide, rolling and fixed (including the tension arms) in the tape path. But start with the above.

I still think you have an issue where the tape is tending to ride low, and even though the wear looks pretty minimal on the head, maybe the path was established with Ampex/Quantegy tape, and you’re getting just a little edge shed, enough to cause the issue.

Can you post a pic of your lifters?
 
I measured the pinch roller pressure with a spring scale, yea, and adjusted within the range in the manual. Really just did it because I already had the top panel off to change the reel table height and had just put on the new pinch roller rubber so it was top of mind.

Flipping the pinch roller made no difference.

Looking as closely as I can I can see no curling or any other weirdness in the tape path.

Here's a pic of the lifters. Thanks again for the help.
 

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Should also mention that when I get track 8 to play properly it's most easily done by touching the bottom of the tape next to the head rather than just pressing it against the head. Doing this, it may play normally for up to a minute or so. So you may be right that it's riding low. I assume that would mean track 8 is at the top of the head?
 
Thanks for the follow up info about the pinch roller pressure adjustment and trailing flipping the roller over.

Also for the pic of the headblock assembly and lifters. The wear looks light to nominal overall assuming the lifters are original, so that’s good. The wear path across the erase head looks pretty centered…it looks like the tape is getting run into the bottom of the outgoing guide. I’m not sure about that, but if I’m right I think something is pulling the tape down on the takeup side. And I know what you mean about what you are doing to get track 8 to work. Like you’re applying just a little pressure upward on the bottom edge of the tape and then all tracks work, right? You won’t be able to see any lifting or curling…it’s too small to see probably.

What type of ATR tape are you using? Hopefully the MDS-36?

I’m hesitant to keep suggesting things because I could easily send you on a wild goose chase…not being able to see the machine close-up and in person is a crucial problem with this sort of thing. If I’m correct something is pulling the tape down, it could be any number of things…look at the takeup side tension arm roller…is the tape centered, riding at the top or riding at the bottom of that rolling guide?
 
Ok, I tried things all evening: adding a shim under the take up tension roller to raise it, messing with the reel table height again, closely inspecting every point of the tape path. Finally one thing I noticed is that when I pressed the supply tension roller down--since there's a little play there, I assume by design since both sides have that play--all tracks played back normally. It didn't help when I pressed down on the take-up tension roller, so I knew it wasn't that I was adding tension (many ways to check that of course). The real giveaway was that if I kept that supply tension roller pressed down I could stop and start the tape and track 8 would still back properly, whereas if I let go, press stop, then play again, the track was all low and muddy again.

So, I removed the one tiny shim washer from beneath the supply tension roller and so far, problem solved.
 
BennyS said:
Ok, I tried things all evening: adding a shim under the take up tension roller to raise it, messing with the reel table height again, closely inspecting every point of the tape path. Finally one thing I noticed is that when I pressed the supply tension roller down--since there's a little play there, I assume by design since both sides have that play--all tracks played back normally. It didn't help when I pressed down on the take-up tension roller, so I knew it wasn't that I was adding tension (many ways to check that of course). The real giveaway was that if I kept that supply tension roller pressed down I could stop and start the tape and track 8 would still back properly, whereas if I let go, press stop, then play again, the track was all low and muddy again.

So, I removed the one tiny shim washer from beneath the supply tension roller and so far, problem solved.
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Nothing like having a closeup view and hands on. :D
Hope it’s solved for good (y)
 
You can’t sustain having that “shim washer” removed…it’s not a shim. It’s a teflon thrust washer. Put it back. What happens if you lift up on the takeup tension arm roller? I have videos of having to straighten the tension arms on a Model 48 I used to have. Some of these machines…the architecture is not that robust. A good knock and something can be tweaked. I don’t remember what the construction of the tension arms on a 388 is like…it’s been too many years and I’m too lazy to go digging through pictures right now, but they are contemporaneous to the 48…nothing like any Ampex machines I’ve had or even my 58.
 
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