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Otari Mx-70 Alignment Problems
Old 15th December 2019
  #1
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Otari Mx-70 Alignment Problems

Hi, everyone!
Long time lurker, firs time poster here.
I'm trying to build a fully analog studio with an Orati Mx-70(16tk) as the centerpiece and it's been giving me a hard time so far..
The machine came with a 355nw/m NAB calibration tape which was working okay, but is not the correct tape to use with this machine so i got the correct 320(320G)nw/m IEC1(CCIR) tape that was specified in the manual.
The low end and the 1k portion plays stable and looks good, until you get to the 10k/16k portion that's where chaos begins. Once i try to set the repro eq, the meters go nuts, some channels start dropping out and the whole thing looks all over the place an it's impossible to align, as soon as you rewind and play it again everything gets out of whack.
Also ch1 seems to be low, and changes the response when you put slight pressure with a q-tip to the edge of the tape..
My question is: Could this all be caused by the transport tension that out of whack or could there be something else that's at play here?
I've never seen anything like this before, although I'm new to tape and sill have a lot to learn.

I have a few theories of what it could be:

1) Tape transport/tension/tape-head contact
2) Head needs to be demagnetized, but probably unlikely since the other tape plays fine and i recently demagged it..
3) Problem with cards, but it appears to be random regardless of the card
4) Bad MRL tape? -which is fresh out of the box, and no shed on the heads...
Old 15th December 2019
  #2
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Radardoug's Avatar
 

Firstly, you need to make sure tape tension is correct. Secondly, you need to make sure that the tape is passing correctly over the heads, and that all mechanical parts in the tape path are in good order. On an old machine, you may have to change bearings and pinch rollers.
Thirdly, the heads need to be in good condition and not worn.
Just because a tape is brand new out of the box does not mean it wont shed, Also your head could already be dirty. Some of the shedding tapes had a clear substance which shed on the heads, and is very hard to get off. I would clean and clean again.
The way you describe the symptoms sounds suspect. If you play the 1K tone, does it vary at all? Have you listened to it for wow and flutter? If the meters at 10K are going up and down, it points to poor tension or poor transport control or badly worn heads. If you are not experienced with tape recorders, I would strongly suggest you find someone in your area who knows tape recorders. As a novice you could get yourself into real trouble. It would also be worth sending your heads to John French at JRF for a head report. And understand, getting in to tape is a VERY expensive exercise.
Old 15th December 2019
  #3
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When i felt the tape tension at the takeup/supply reel it did feel very loose, definitely didn't feel like 2kg recommended in the manual.
I'm pretty new to tape, but the machine belongs to my studio partner who's had it for a while, just didn't use it that much.
I feel pretty confident with the audio alignment, haven't tried my hand at the transport yet and it's a pretty big pain from what it looks like in the manual.
I'm good with the soldering iron, we have a scope and a multimter so can troubleshoot basic stuff,nothing like complicated tracing or sniffing with logic analyzer of course but i can follow the manual steps .
Old 15th December 2019
  #4
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The heads look nice and shiny, can't see any flat spots or obvious wear on them, at least visible to the naked eye.
Old 15th December 2019
  #5
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BTW, thanks for such quick reply!
I'll go(with caution ) through the transport alignment routine and report back with the results..
Old 16th December 2019
  #6
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Maybe I'm missing something here......The older NAB MRL tape is stable at high frequencies but the new IEC1 tape has all sorts of HF wobble?

Bri
Old 16th December 2019
  #7
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GYMusic's Avatar
Flip your alignment tape over and see if the flaky track 1 is now track 16. If so, bad alignment tape. Also, rock the HF pots back and forth a few times - could be dirty pots. I know all the relays on my 8 track need contacts cleaned once in a while - they can become intermittent along with the rec/repro switches.
Old 16th December 2019
  #8
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Yeah, that's the weird part the NAB tape is more stable, not perfect but is somewhat usable it's also a hotter tape - 355nw/m. Maybe it's magnetized stronger and that's what makes it work somewhat better..?..no idea..

Flipping the tape was the 1st thing i did..
..Filpped the spool upside down and played it though - same thing
Rocked the trimmers, sprayed some of them and even refreshed their solder joints.
Maybe this MRL is a little "grabby", and with a weak tension it jumps a bit or not making good contact with the head ..
Btw ch16 is shut right now(stuck in monitoring mode), so i didn't check it, was too lazy to swap the cards..
We're waiting for some relays to come in ...
So I guess i'll check the tension first..
Old 16th December 2019
  #9
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The reference levels of the tones will have no effect on the stability of the HF tones.

Do you see similar wobble when in "sync" playback?

A seat-of-the-pants check is to gently drag a fingertip on one of the flanges of the supply reel while watching the stability of the HF tones. This artificially increases the holdback tension for testing purposes.

Bri
Old 16th December 2019
  #10
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The sync head is a bit better but still no cigar..
I'll try the thumbing the reels later.
Old 17th December 2019
  #11
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Just got it going, it was the cards.
More specifically the connection between the pins on the cards and the card receptacles in the machine.
The high end is reasonably stable now.
I switched out the order of the cards to complete opposite of what it was, sprayed the connectors and the fluxivity switch .
Channel 1 HF loss was the tension problem, i put my finger on the reel and in came up..
BTW is there a way to re tension those card receptacles/female connectors or some place i can get replacements?
Old 17th December 2019
  #12
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How stable? You should still check the tensions though. Follow the manual carefully. And if it was me and the heads had any wear I would send them to JRF.
Old 17th December 2019
  #13
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Stable enough to go through the repro eq setup with occasional(once or twice) needle bounce but nothing like before.
Sure, i'll still have to go through the transport setup anyway...
I'll get to the heads at some point, JRF is within driving distance from us.. We also have an 8tk head stack that is being used more often and looks to be in a better condition.
The thing is that we have an MTR 10 with a busted capstan drive board and an Ampex 440 that won't align, both need to see the tech(in January, so the JRF would have to wait).
Does anyone know where to get the card connectors(female side)? Or is there a way to re tension them?
Old 18th December 2019
  #14
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To answer my own question on the card receptacles, they're called Euro Card connectors or Euro DIN 41612 Connectors.

Here are some links if anybody has the same problem:

[url]https://www.peconnectors.com/euro-din-41612-connectors/hws7743/
[url]https://www.te.com/usa-en/plp/eurocard-connectors/Y30n1.html

They come in many shapes and configurations, so it's a matter of figuring out which is gonna fit.
Old 22nd December 2019
  #15
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Update:
Did the tension, surprisingly the machine was able to get almost dead on the factory specs. The MRL sounds a lot more confident now and the transport is a lot snappier now. Some needle bounce from the worn pots(1 or 2 channels) but not from the tape anymore. Ch 1 is 1db below 0 now.
Btw i was able to use an Xacto blade to tension some of the pins on those receptacles, gonna try a dental pick on the rest.
Some of those repro eq trimmers are REALLY worn, or coming apart internally.
Does anybody know the value/mouser part #?
Old 22nd December 2019
  #16
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The value(s) will be in the manual. You may have to spend some time at Mouser looking at the variations.
Old 22nd December 2019
  #17
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Ok, I'll check the schematic..
Thanks for your help!
Old 30th December 2019
  #18
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Yesterday my new MRL started shedding.I had a sneaky feeling about that all along...
It gunked up ch 4 on the 8tk head so the 10k tone went completely flat lol.
Time to call MRL...
Old 8th January 2020
  #19
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crosscutred's Avatar
Quote:
Originally Posted by konstantingroove View Post
Yesterday my new MRL started shedding.I had a sneaky feeling about that all along...
It gunked up ch 4 on the 8tk head so the 10k tone went completely flat lol.
Time to call MRL...
Was it a brand new MRL tape?
Where did you get it?
Could it have been a bit of left over tape gunk from another reel?
Old 8th January 2020
  #20
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Scrubbed the tape path, and i scrubbed.. and scrubbed...
Even cleaned the heads after they gunked up the 1st time.
Played it the 2nd time, ch 4 area shed again, cleaned again - same thing .
Old MRL(NAB) plays fine, besides being old and chewed up..

Yeah, is was a new one. Got it from Analog Tapes/Duplication Specialists in New York.
The tape itself was shipped directly from MRL.
Looking at the tape stock itself felt like it was RMG from 2008 - dark brown oxide, pitch back coating.
When i checked their PDF( red dot on the box), low and behold red dots are for RMG 911 stock.
Old 8th January 2020
  #21
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12ax7's Avatar
 

Quote:
Originally Posted by konstantingroove View Post
Scrubbed the tape path, and i scrubbed.. and scrubbed...
Even cleaned the heads after they gunked up the 1st time.
Played it the 2nd time, ch 4 area shed again, cleaned again - same thing .
Old MRL(NAB) plays fine, besides being old and chewed up..

Yeah, is was a new one. Got it from Analog Tapes/Duplication Specialists in New York.
The tape itself was shipped directly from MRL.
Looking at the tape stock itself felt like it was RMG from 2008 - dark brown oxide, pitch back coating.
When i checked their PDF( red dot on the box), low and behold red dots are for RMG 911 stock.
Does this also happen with other reels of tape you put through the same examination?
Sometimes there are little microscopic "burrs" on these parts in the tape path, and they can cause this very problem...

...And sometimes it happens more on some tapes than others (to various degrees).
Old 8th January 2020
  #22
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RMG 911 does tend to drop a few flaky bits when it's new so it could be nothing to worry about.

I would look closely at the heads 12ax7 maybe right about a "burr" or something like that.

I've not come across any sticky shed on 911.
Old 8th January 2020
  #23
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Nope, i aligned the recording side with RTM 911 and ATR.
10k is rock solid, no shed, sweep is flat up to 21k
The 8tk head it happened on is in a better condition than the 16tk , better tape to head contact hence more sticky shedding..
I've had the burr problem on a bx5050, just needed to flip the guides and it went away.
Old 8th January 2020
  #24
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crosscutred, I have a reel of RMG 911 from 2008 that sheds like crazy and it does that in sections.
They had a bad batch right before they moved their production to France and became RTM.
I also have a reel of RTM 911 that is excellent and is even more stable in high end than ATR..
Sometimes tape manufactures have 'burps' in production, that 2008 batch is a good example.
Old 9th January 2020
  #25
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Quote:
Originally Posted by konstantingroove View Post
crosscutred, I have a reel of RMG 911 from 2008 that sheds like crazy and it does that in sections.
They had a bad batch right before they moved their production to France and became RTM.
I also have a reel of RTM 911 that is excellent and is even more stable in high end than ATR..
Sometimes tape manufactures have 'burps' in production, that 2008 batch is a good example.
Good to know, i'll watch out for that.
Old 10th January 2020
  #26
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MRL got the tape, i asked them "What's the verdict?".
They said "Tape's fine, your machine is scraping."
This is insane...
So it's only this tape is being "scraped".. All the other sticky tapes i have, i can see the same kind of striations on the surface.
The ones that do not shed the surface look smooth and they play fine .

They also claim to be using the current RTM stock, and all i saw is the stuff that looks like the stuff i have from 2008..Unless they tweaked their formula again. The new RTM(2012) looks a lot lighter on the oxide and the back coating as well.

This doesn't add up and smells funny..
Old 10th January 2020
  #27
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Not to be rude here, but I believe you are new to tape recorders. MRL have been around for a long time. Maybe they do know what they are talking about?
Old 11th January 2020
  #28
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How much ya wanna bet that if ya flip the tape over, it'll still shed at "the track 4 area"?

If it still sheds in the same place on the head, you can best bet that there is something different about that spot on the head.
Old 12th January 2020
  #29
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I'm sure they they know their stuff, but the facts are facts this is the only tape that has that problem. I have another mrl(NAB) that plays fine and other rolls that have no problems of that sort. I got sticky tape too, so it's easy to compare...
After i gave them the whole story and they agreed to send a replacement. If that doesn't work then the joke is on me
I've heard stories about people getting sticky tapes and read MRL talking about customer complaints in their PDFs, so it's not an unusual situation..
Old 19th January 2020
  #30
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Got the replacement.
Everything is smooth as butter.
My theory was right .
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