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Author Topic: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?  (Read 6114 times)

Offline dbxdx5

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Hi,

Has anyone used one of the MRL Short Calibration Tapes from Audio Village http://www.audiovillage.org/gear.html and software like that from http://www.audiotester.de or http://www.sillanumsoft.org/ to adjust playback azimuth on their MX-5050 BII? If so, I could use some help, including with which settings in the software to use.

Thanks
Matt

Offline ironbut

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #1 on: July 01, 2012, 10:02:13 PM »
Hi Matt,

First off, I don't think that saving a few dollars on those short tapes is worth it. If you're new to alignment of your heads, you're bound to take a little time to do each adjustment. I know I needed as much or more time that's provided on the regular MRL test tapes the first few times I did it. Having more time will save you the trouble of rewinding over and over again and also reduce the wear on your test tape. Wear on them will eventually skew your results and require replacement.
Just my opinion of course.

Secondly, head alignment isn't something that you should have to do all the time. On a machine that's working properly, the main reason is head wear. You should read the "Beginners Guide" located above the General Forum for info regarding heads. If your heads are heavily worn, it may be better for you to get them lapped or replaced.
If your heads are in great shape, there's a good chance that they don't need alignment so it's a good idea to somehow mark the setting you currently have before you start to fiddle with the adjustment screws.

I took a quick look at the "Audiotester" site and found a screenshot of the oscilloscope function showing a lissajous figure. That is the setting you need to use to align your playback head. I don't know the exact settings you'll need to use but if Audiotester has an autozoom function, use that.
You input both channels of your machine and the "figure" shows the relationship between the two channels. When the head is aligned, the ellipse (the two channels) closes into a line.

Before you change the adjustments, take advantage of fact that you can take a screen shot of what the "figure" looks like before you change anything. It may come in handy later.

Start with 1kHz, then the higher frequencies, then the lower ones. 1kHz is where you'll get all your adjustments pretty close and 10kHz or above is good for small tweaks.
Don't worry if the very high frequency tones don't produce a perfectly stable line. Just get it as close as possible.
1kHz and below should be pretty solid and the differences in level represent how "flat" the frequency response of your machine/head/playback electronics are.
And don't forget that your soundcard and cables make a difference too. That's an advantage that measurement with a hardware scope makes a real difference (and one of the reasons that good oscilloscope probes aren't cheap).

Before you attempt to do your own alignment, I suggest reading the excellent tutorials on the MRL site. I realize that they are pretty technical and tough to understand the first time your read them but I believe it is well worth the time (I must've read some 20 times before I started to get it).
Just bear in mind that what you're trying to do is adjust for the maximum output with the two channels equal in volume and phase.
steve koto
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Offline dbxdx5

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #2 on: July 02, 2012, 10:35:04 AM »
Hi Steve,

Thanks for the great info. I really appreciate you taking the time.

Regarding the short tapes, in hindsight I agree that I probably would have been better off going with the regular tape for my Otari. Live and learn.

Let's see... I believe the heads are in good shape?this had been a maintained recording studio machine?and I really just wanted to confirm that the azimuth was correct. Of course, I already started fiddling with the 2-track playback head without marking the setting I started with.... So now I definitely need to check and adjust that one (I didn't touch the 4-track head).

I think I know how to get the lissajous figure in Audiotester's oscilloscope function. There's a settings screen that has an adjustment for "Timebase." I believe that should be "X-Y" for lissajous. Does that sound right? I'm unsure about a few of the other settings:

1. Any idea what dig. Level/ dB FS should be set at?

2. Should I choose Sine or Dual Sine for the sound output?

3. Under Timebase, there's another oscilloscope setting that lets me choose between Channel 1 and Channel 2. I would think I want both, but when I tried checking both boxes last night, it wouldn't let me.

In terms of my soundcard, I have an M-Audio 192 Audiophile with balanced inputs. My cables are balanced Mogamis from Redco Audio.

EDIT: I forgot something, Steve. If there's software that you've used for azimuth adjustment, I'd be fine with trying that instead of Audiotester, especially if it meant you could tell me exactly which settings to use.

Thanks,

Matt
« Last Edit: July 02, 2012, 10:48:13 AM by dbxdx5 »

Offline ironbut

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #3 on: July 02, 2012, 01:35:22 PM »
Hi Matt,

Hopefully you just twiddled the azimuth adjustment screw.
If you did mess with the other adjustment screws, you'll need more than just the Lissajous to get the other adjustments correct.
In fact, when I do my adjustments, I keep a stereo level meter open at the same time (zoomed into the area of interest). If I see the levels dropping I know I'm going in the wrong direction.
So, the following is just for azimuth adjustments.

Just leave the input level to default (0dB) and if the scope has autozoom while using the Lissajous function (most do) the figure should be big enough to use.

Here's the wiki page for Lissajous and while the animation is kind of cool looking, the b&w chart below it is what you'll see when you get things hooked up right.

http://en.wikipedia.org/wiki/Lissajous_curve

So, just like that chart, you need to compare phase between channels 1&2. Make "X" the left channel and "Y" your right channel.
On most programs your screen should look like the view through a rifle scope.

Regarding the timebase, just leave it set to channel 1. I'm guessing that's where you would set any delay between channels but you don't need any delay for this measurement.

The display type should be stereo in most programs but you may have to try the different settings in Audiotest.
The choice between sine and dual sine for output sounds like settings for a generator function so you shouldn't have to worry about those.

Regarding the program I use, I'm a Mac guy and it looks like these are PC meters.
If you run into questions which are program specific, you should contact the guys who sell the software and tell them what you're trying to do and they'll be able to tell you exactly what settings to use.

Overall, think about what's happening when you make these adjustments. If you think of the test tone more like a click track and you're trying to line up the clicks between channels. In the center of the head face is the "gap" which runs across the width of the head in a fine line. The "click" runs across the width of the tape. If the click arrives at the gap of one channel ahead of the other, the phase between channels is skewed. The higher the frequency of the tone equals the more "clicks" per inch so the finer the adjustment has to be made. Eventually you get to a high enough frequency (15k clicks per second) that the precision of the gap, minute tape irregularities  and even environmental issues  come into play so some smearing between channels is unavoidable.
Well before that, most home measurement gear and the signal path between the heads and that gear will start to effect the measurements.
And remember how much the view on the "scope" is being zoomed.
It kind of reminds me of when I was fooling around with astronomy.
I could take a nice pair of binoculars and look at the moon or star fields with no problem. But once I wanted to get a good look at the planets it took a lot more "zoom" and I had to have a stable tripod and the images would jump around when a truck drove by.
It's the same thing with these signals you're looking at to do your adjustments. Don't assume that every irregularity is the fault of the head adjustment with tones above 1kHz. At those zoom levels, just about anything could be effecting what you're seeing. So just get it as close as you can while you still get a nice stable line at 1KHz.

If you have trouble getting the settings of the 'scope' on your 1/2 track head, try the 1/4 track head just to get the meter settings right. The MRL test tapes are all full track mono so the configuration of the 1/4" head won't matter.
steve koto
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Offline dbxdx5

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #4 on: July 02, 2012, 08:34:06 PM »
Hi Steve,

Thank you. This is invaluable information (at least for a azimuth-adjusting newbie like me). I'll be taking another stab at the adjustment sometime in the next few days. I'll report back on how it went.

Matt

Offline dbxdx5

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #5 on: July 10, 2012, 08:52:18 PM »
Success! Well, sort of. I was finally able to figure out what I was doing wrong with the AudioTester program. The good news is that I was able to adjust the azimuth at 1kHz to produce a pretty stable and solid 45-degree angle line. It was more difficult--make that impossible--to get the same kind of 45 degree line at 10kHz and 16kHz, but from what I read, that's normal and you're just shooting for the narrowest oval possible. My concern is that the image wasn't holding steady at those higher frequencies, which I also read could indicated problems with the tape path and/or head wear. Thoughts?

Matt

Offline ironbut

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #6 on: July 11, 2012, 02:36:01 AM »
Hey Matt,

Glad to hear you made some progress.
If you re-read the next to last paragraph of my last post (starts with "Overall"), the stability of the figures at the higher frequencies is what I was trying to keep you from getting too worried about.
Of course, getting them to be as stable as possible is the reason they're on the test tape.
Be sure that your tape path/heads (anything that the tape touches) is totally clean.
Getting the tape to move across the heads with no variation in speed or tension is the "ideal" we're shooting at here and is really the "name of the game".
Microscopic irregularities on the surfaces of each element of the tape path (starting at the supply reel and ending with the take up reel) are what keeps even the perfectly aligned great machines from reaching this ideal.
There is a great deal of info in the "Beginners Guide" on the tape/head interface but if you really want to get into it, check out the article on "scrape flutter" on Dan Manquen's site.

http://www.manquen.net/audio/index.php?page=17

Something a little more practical,.. I always advise beginners to find a good, local tech who can go over a machine that's new to you.
It isn't cheap but considering the bargain prices these machines often go for, budgeting it shouldn't create a hardship.

What you gain from having the machine lubricated, adjusted and perhaps, set up for recording on a current production tape, is a baseline.
It's hard for most folks to know if a machine is running at optimum performance, in need of a few simple adjustments/ repairs or in serious need of repairs.
A good tech will have the "proper" gear to do all the measurements needed and will know what to look for.
Many will even provide you with frequency plots at different speeds. They can also help you to interpret the meaning of those plots.
steve koto
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Offline dbxdx5

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #7 on: July 11, 2012, 10:48:17 AM »
Hi Steve,

As usual, lots of good info in your email. I had cleaned the tape path pretty well prior to checking and adjusting the azimuth, but I have to admit that I probably could have been spent just a little bit more time to make sure everything was pristine. Now that I have the software issue solved and know what to do in terms of adjusting the heads, I may try again in a few days after doing a more thorough cleaning.

I had thought about bringing my MX-5050 BII to a tech for a once-over, but I'm hesitating because it seems to operate fine and sound great. I also took care of lubricating the capstan motor using the correct Otari oil, so I know that's ok. Still, I am tempted to have it checked and serviced. I live in New Jersey, and JRF Magnetics isn't that far of a drive. I don't know anyone else in my area I would bring it to. What should I expect something like this to cost, ballpark?

Matt

Offline ironbut

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #8 on: July 11, 2012, 12:57:19 PM »
Matt,

When I had it done to my RS1500 (I had the record electronics biased for some RMGI tape too) it was about $275 IIRC.
JFR would be my first choice even if it was a long ass drive!
steve koto
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Offline Listens2tubes

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #9 on: July 11, 2012, 06:42:53 PM »
Yah JFR is the place! I will be bringing my BII-2 for setup and alignment. Though my recording Maxell 35/180 sounds excellent.
« Last Edit: July 11, 2012, 06:44:36 PM by Listens2tubes »
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Offline Waltzingbear

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Re: Otari MX-5050 BII Azimuth Adjst. Using MRL Short Cal. Tape?
« Reply #10 on: July 17, 2012, 11:41:27 AM »
Be aware John (RF) is on vacation til next week and out of town.

instability in the high frequency area is what separates the men from the boys. In order to get really good hf phase stability, you're talking about professional/mastering type decks, most consumer decks are made with stamped parts that are not stiff enough, allowing the tape to skew during its travels. This includes the deck top plate.  Decks made with cast parts and precision aligned give you the phase stability we have all become accustomed to from digital land.

Can't agree more about visiting Dale Manquen's site to get great background material on understanding tape recorder mechanics. And don't forget Jay McKnights site at MRL, technical reading material. Those are two of the people who helped design and build these decks in the first place. http://home.comcast.net/~mrltapes/#TechPapers

Alan Garren