Otari MTR90 record head 10k tone fluctuates back and forth.

[WarmJetGuitar]

Had my share of RTM with poor slitting including a 2" SM911 two years ago. Very wobbly edge tracks on an MTR90 MKII.

These machines are picky about mechanical alignment... I strongly suggest you get a tech to look at it and set up the transport according to the manual.

 

[SoundBlaster]

Can you look at the signal on an oscilloscope? Ever consider it's something subsonic? I've worked on machines that had a Hi Q subsonic hump in response.

 

[MicMan]

Misalignment. Tape guides or pinch roller

 

[RoadrunnerOZ]

Can be a build up of hardened deposits on the upper and lower edges of the tape guides or uneven wear causing tape path to drift. Or it could be a sticking bearing on the pinch roller, surface contamination on the roller or capstan or hardening of the roller rubber causing uneven grip - does the fluctuation repeat cyclically coinciding with each revolution of the pinch roller or is it random? Does the pinch roller run free when spun by hand, or does the roller have any play as in loose worn bearing?

 

[One F Sound]

FWIW The MRL tape is 1 track and therefore in general won't show a tracking issue except on the edge tracks.

This definitely looks like a tracking issue as you can see the tape riding up and down. what's slightly odd is that the meters aren't precisely in sync so there could be added problems in the transport like bent tension arms which is common on MTR90 Mk II's. Back in the day we had a fleet of rental MTR's and clients often would bend the tension arms. This can occur when lacing a machine and the tape pack is a bit loose. You hit the stop button to arm the transport and the reels motors violently take up the slack, the tension arms hit the end stops and get bent. Not great for the tape either!

The whole tape path top and bottom edges should be straight and smooth. If there's any slack on top or bottom edges from reel to tension are or from tension are to roller then the arms are bent. Of course the rollers can be a source for the problem too. How old are they and what colour? If they're dark brown and hard they could need replacing too.

So I'm pretty sure your transport needs a good service and there's no point in getting the heads lapped beforehand.

 

[CanuckProducer]

In my experience, I'd go to another tape to see if its a tape thing or a machine thing. I'd guess that the tape might also not be of consistent integrety. A quick check on the width of the tape in various obvious section might yield results.

 

[RoadrunnerOZ]

So this meter fluctuation is from record>repro but you don’t see it when using a pre-recorded test tape if I’m reading your earlier posts correctly - if the tape is passing the heads in a slightly different position then that could explain that. I noticed that in your video of the tape passing over the head that there is also some surface rippling (on top of the vertical movement) indicating either low roller pressure tension or irregularities in the grip of the roller to the capstan. I’d check the roller for hardening/cracking of the surface under a magnifier.

In my experience, I'd go to another tape to see if its a tape thing or a machine thing. I'd guess that the tape might also not be of consistent integrety. A quick check on the width of the tape in various obvious section might yield results.

OP indicated using several different tapes with same result. See post #10

 

[Brian Roth]

The MTR-90 machines don't have a pinch roller. The large rubber coated drum to the right of the head block is the capstan, but there is not a typical pinch roller.

Bri

 

[RoadrunnerOZ]

Ah - my mistake - now I recall - the pinch-roller-less drive - capstan and pinch roller all in one. They are sold named as pinch rollers. Tape tension sort of critical here.

 

[Brian Roth]

Ah - my mistake - now I recall - the pinch-roller-less drive - capstan and pinch roller all in one. They are sold named as pinch rollers. Tape tension sort of critical here.

Yep. The Ampex ATR-100 machines have a similar design as well.

Bri

 

[RoadrunnerOZ]

IIRC tape path alignment is critical on these machines including the reel table heights - also tension on the lifter arms, servo setup for correct tape tension etc.

 

[JohnRoberts]

At relatively high frequencies (short wavelengths) like that (10kHz), the alignment of tape to head gap can be critical. Mechanical instability in the tape handling is an obvious suspect.

JR

 

[RoadrunnerOZ]

Gets compounded when recording then playing back compared to using a test tape on repro only

 

[One F Sound]

As I mentioned, an MRL tape is one track. i.e. one large single track record head makes it so on a 24 track head all the heads in the head block are reading the same wave and you'll get a solid signal except on the edge tracks. And looking at the second video of the tape path you can see the tape is riding quite high by looking at the erase head and the sync head. Probably half a mil which is a lot. So with the MRL tape, is track 1 more stable than 24? My guess is it will be because the tape is riding high.

Also, as RoadrunnerOZ commented. unless it's the video quality, there does appear to be some slackness in the tape across the top of the head and this would explain why the meter fluctuations of 5/6 aren't exactly in sync with 13/14.

In short, I reckon your MTR needs a decent transport service and you may be looking at new tension arms and rollers. I used Nathan brand rollers as they used to track better but I don't know if they're still available. I recommend getting it done soon otherwise you'll get uneven wear on the heads and rollers.

 

[inkster]

In my personal experience with tape machines that have poor or inconsistent high response is that the heads are in need of attention...time and time and time again I have struggled to get a machine to behave only to eventually send the heads out to JRF (or one of the very few capable techs), only to have the machine align solidly usually beyond manufacturers spec with properly serviced headstack.

I could draw countless analogies but the heads need to be assessed before anything else, until then you are dealing with an unknown, and I highly recommend John French as he has always been a true professional and a great resource.

 

[RoadrunnerOZ]

if the heads are worn you’d get constant loss - this is fluctuating across the tracks

 

[Brian Roth]

if the heads are worn you’d get constant loss - this is fluctuating across the tracks

More than a few times I've had HF stability problems on our Ampex ATR-102 machines, often worse on one track than the other. After a full service from JRF, the HF response almost always stabilizes on both tracks. The outliers are a couple of assemblies with low amounts of head life left (as reported by JRF). FWIW, the all of our R and P heads are from Flux Magnetics.

Bri

 

[RoadrunnerOZ]

I guess also flattening of the head surface which leads to sharp leading and trailing edges causing air turbulence between tape and head resulting in lift of the tape from the surface as this seems to be across all 24 tracks.
Interesting read here:
https://www.precisionmotorworks.com/pdf/MTR90_Align.web.pdf

 

[Brian Roth]

It would be vaguely interesting to me if the OP posted a video of the machine playing the 10K tone from his MRL, with the video showing all 24 VU meters. Then, a video showing all 24 meters during a record/play pass. Sometimes, we all have an "AHA! moment with additional clues.....

Bri (the last 24 track I worked on was a Studer A-800 being used only for playback transfers to digital, circa 2019-2021)

 

[One F Sound]

Maybe the zenith of the record head is out? Unlikely but that could explain the sloppy tape at the top of the stack and why the tape is riding high.

A good photo of the heads might be useful too.

A guy I used to work with and I think may be back at 301 may know a tech in your part of the world. LMK if you'd like me to try and get a hold of him.