Pops & rocks on MRL test tape signals

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Mo-Tech
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Pops & rocks on MRL test tape signals

Post by Mo-Tech » Thu Mar 26, 2015 12:18 am

Found this wierd problem playing MRL alignment tape - I hear pops & rocks. Particulary 15 & 30 IPS tape, 7.5 IPS does them less.

Machine is properly cleaned and de-magnetized.
Azimuth calibrated.
Level & EQ calibrated.
Mechanics should be checked.
Re-capped audio boards electrolythics with Nichicon Muse series (+ complete new machine recalibration after that).

I can still hear them. They're apparently identical when I switch playback between REPRO & SEL-REP heads. When I record my own test tones on my tapes, it's less. As said, playback-wise MRL 15 & 30 IPS tape creates them artifacts a lot and it's annoying, 1Khz sine seems to be the most audible, but they're on all test signals nearly equal amount. MRL tapes I bought brand are new and did this on the first run.

I see many people have the same issue, including high-end tape machines like Studer A810s etc.

Looking around the net some say it's tape fault (uneven particles), bias bubbles, others say it's tape path mechanics that causes them. Some say worn heads, but other say it's not possible. Some say a bad capacitor or bad connection on boards - I've triple checked those, all contacts cleaned and re-capped. Some say it's track width issue tape vs head. Fringing, but MRL says it's fringing-compensating tape.

Damn, way too many theories and BS going on around this issue.

Want to know if there's a definite answer what causes them and what's the fix?

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Gregg Juke
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Post by Gregg Juke » Thu Mar 26, 2015 10:31 pm

Wow, wish I could help, but beyond all that you have noted, I have no idea.

I'm responding because I know what a "pop" is, but what does a "rock" sound like?

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Mo-Tech
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Post by Mo-Tech » Thu Mar 26, 2015 10:53 pm

Gregg Juke wrote: I'm responding because I know what a "pop" is, but what does a "rock" sound like?
Pop is similar to a regular vinyl crack, but less sharp.

Rock is like two smaller rocks hit each other, more midrangy klick.

They're all silent, but audible when listening the test signals loud.

Although they still seem to have life left, just in case I'll have the heads re-lapped - it's a 4-head machine, will be quite an investment :)

That's the last straw I know now. OR somehow all of my MRL tapes have been fecked - a bad batch or badly X-rayed in customs?

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Post by kslight » Fri Mar 27, 2015 5:30 am

If I had bought them new from MRL I probably would have contacted them and sent them back if there was a problem out of the box?

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Post by CustomRecordingCo. » Wed Apr 29, 2015 2:56 pm

How old is the MRL tape? This sounds an awful lot like sticky shed.

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Post by wkrbee » Wed Jul 01, 2015 11:47 am

Scope the signal and verify it's a click,or just the signal disappearing momentarily and reappearing.I went round and round with a Tascam MS-16 until I found out that it was there no matter what-especially if you recorded a 30-40HZ signal.
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Post by Mudfoot Marshall » Mon Jul 06, 2015 8:52 am

Have you put a scope on the bias oscillator? With out hearing the exact behavior of the noise and just going on what you describe, it sounds like bias distortion is your problem. Try scoping the output of the bias oscillator at different points of the circuit path to see if the signal stays clean.
I had random bias distortion problems on my Otari 8track, turned out to be a faulty cable coming off the bias oscillator.
If you could put up an audio sample too that might better describe the problem.

Cheers,
jake

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Mo-Tech
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Post by Mo-Tech » Wed Jul 15, 2015 12:46 am

Thanks for the input guys!

MRL Tapes supposed to be fresh, bought directly from manufacturer not dealer.

It does the same when recording my own test signals. It's very little audible at 7.5IPS, more on 15IPS and most audible at 30IPS speeds. Particulary audible on the bass signals such as 100Hz.

Here's a MP3 file from MRL tape 100hz & 10kHz at 15 ips, and the same at 30 IPS (after 13 seconds):

MTR-12 calibration tape noise MP3

Still not sure if it's transport- or bias electronics induced sound.

Let me know if anyone has had something similar.

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Post by klangtone » Thu Jul 16, 2015 2:22 pm

Having similar problems with my MCI JH16. Eventhough it was refurbed by Chris Mara it has this pop and rocks issue with the MRL tape (also bought new) and when recording a tone myself. My heads are like new too, btw...

I wish I could help, but thus far I'm still in your camp- confused and uncertain...
The good news is, I don't really hear any kind of sounds like this with music. Just those pesky sine tones...

Roy
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and our religious and charitable institutions may become, the music will still be wonderful." -Kurt Vonnegut

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Mo-Tech
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Post by Mo-Tech » Fri Jul 17, 2015 4:28 am

Cheers Roy,

It's EXACLY the same problem I have. Don't hear anything like this in music, just just those damn test signals. Does yours also do more on higher speeds? Mine's most noticable at 30 IPS while almost nothing at 7.5 IPS.

Some say it can be a permanent magnetization of certain parts on tape path, but I bought this Teac E-3 demagnetizer which supposed to be quite powerful and have done careful de-mag multiple times w/o any noticable change.

I'm thinking about doing a complete overhaul on transport path - all new bearings, brand new rollers when I get the time. Maybe this will help?

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Post by Injured Ear » Fri Jul 17, 2015 6:10 am

I remember (back in the day) talk of bias rocks, and that was a function of the record side of things. None of that should affect what's happening to you on playback.

Do you have MRLs for all 3 speeds or are you just playing the same one at different speeds?
When you play the MRL at 30 ips and the noises happen, are they in the same spot every time? If they are not, then the tape is not to blame. If they are... then the noise may well be on the tape.

MRLs are generally recorded as full track (imagine a giant mono head recording the tone in the first place) which would be why there's no fringing.

How old are your heads, how many hours are on them? Is it possible that they are nearing the end of their life and/or need a relapping? I'm leaning towards this.

When you do 30 ips playback, does it track smoothly across the heads when you're hearing these noises?

Are you demagnetizing every day? What model demagnetizer are you using? Can you describe the process how you do it? How far from the machine are you getting before you turn the demagger on/off?

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Mo-Tech
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Post by Mo-Tech » Fri Jul 17, 2015 7:26 am

I have different MRLs for different speeds - MRL for all 7.5/15/30 IPS speeds. The same phenomena is when I record my own test signals as well, on all tapes (Ampex 478, SM900/911, PER528, ATR Master), some little stronger than others, but not so much difference between different emulsions.

It seems to me the pops and rocks locations change every time I play, i.e. one louder pop is not at the same spot the next time I play. Hence I don't think it's MRL related issue, ditto when recording my own test signals.

Mahine is fully calibrated and cleaned.

As said, I'm using Teac E-3 demagnetizer.

I magnetize propery, machine off - turn on the demagnetizer 2 meters away, slowly come towards the deck, extra slow for the last 15 centimeters or so, make couple of slow sweeps on one detail just few millimeters away without touching anything, slowly go away again - repeat for absolutely ALL metallic bits and bobs on the tape path, I also ocasionally de-mag reel holders on the deck etc, turn off de-magger at least 2 meters away again.

I did a curiosity test when I intentionally blocked impendance roller with my finger while playing the test signal - it sounded pops and rocks changed a little as well, hence I'm starting to figure this can be (at least partly-) a transport issue?

I'll probably contact John French at JRF Magnetics, just in case I'll do a proper head relap too when I can leave my Otari standing for a couple of weeks useless.

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Post by klangtone » Fri Jul 17, 2015 11:01 am

Mo-Tech,

Yep, sounds like we have the same problems. I have also de-magged without any difference.

Chris Mara seems to think it could be related to the tape not making perfect contact to the heads. Your experiment with the impedance roller may speak to that since you did notice a change in the pops and rocks at least. He also said that he had this issue with my same model MCI JH16 machine in the past and noticed that 499 tape worked better (but still not perfect). He was thinking it was something about the thickness of the backing making for better/smoother contact with the heads.

I did do a tension adjust with Mara's team via Skype and it didn't help. So, it's still baffling to me why this is happening.

I'm glad we both find that music is ok, but it still feels concerning that perhaps there is some low level noise being added even with music. Maybe it's just generally masked by the music itself. I don't know. Keep updating us if you find a solution!

Thanks,

Roy
www.rarefiedrecording.com
"No matter how corrupt, greedy, and heartless our government, our corporations, our media,
and our religious and charitable institutions may become, the music will still be wonderful." -Kurt Vonnegut

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Post by klangtone » Fri Jul 17, 2015 11:03 am

Forgot to say that I haven't necessarily noticed it changing with tape speed, but I also haven't paid close attention to that. My machine only has 15 and 30 IPS.

Roy
www.rarefiedrecording.com
"No matter how corrupt, greedy, and heartless our government, our corporations, our media,
and our religious and charitable institutions may become, the music will still be wonderful." -Kurt Vonnegut

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tonejunkee
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Post by tonejunkee » Sat Jul 18, 2015 3:36 pm

Gotta love tape :D
Enjoy my web based guitar tuner and interactive tuning fork.

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