DIY Alignment and Calibration

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lo.fi.love

lo.fi.love

Functionally obsessed.
I'm interested in aligning and calibrating my machines, and I'd like to know where to start on this. I've read the calibration article in the second Tape Op book and it gives what seems to be a good overview, but I'd like to have the opinions of people here.

So from what I understand, the following items are necessary:

1. MRL test tape
2. The manual for the tape machine being calibrated
3. Oscilloscope for doing azimuth adjustment
4. An oscillator

What else? Is this a difficult procedure for someone who is technically apt?
 
Hands On!

lo.fi.love said:
I'm interested in aligning and calibrating my machines, and I'd like to know where to start on this. I've read the calibration article in the second Tape Op book and it gives what seems to be a good overview, but I'd like to have the opinions of people here.

So from what I understand, the following items are necessary:

1. MRL test tape
2. The manual for the tape machine being calibrated
3. Oscilloscope for doing azimuth adjustment
4. An oscillator

What else? Is this a difficult procedure for someone who is technically apt?
Click to expand...

A good AC voltmeter that can read down to 20 mv and has a bandwidth of 150Khz. You will also need an assortment of adapters and cables, various hand tools. You also must have patience and some free time. I have been aligning all my machines for months now. There is a trial and error learning curve, but the results are worth it. You will gain a complete understanding of your machines that will help you in the long run. I just recently bought a tentelometer and 2 spring scales which let you know your tape tension is correct, you dont need them but at some point you will want them.
VP:cool:
 
lo.fi.love said:
I'm interested in aligning and calibrating my machines, and I'd like to know where to start on this. I've read the calibration article in the second Tape Op book and it gives what seems to be a good overview, but I'd like to have the opinions of people here.

So from what I understand, the following items are necessary:

1. MRL test tape
2. The manual for the tape machine being calibrated
3. Oscilloscope for doing azimuth adjustment
4. An oscillator

What else? Is this a difficult procedure for someone who is technically apt?
Click to expand...

You may occasionally want to check the bias frequency, to make sure it is close enough to the spec'ed value, so a frequency counter can also come in handy.

I have also found it handy to have plenty of unbalanced "mults" in a patchbay, so I can tie the oscillator output to every input on the machine all at the same time and not have to patch cables. I think I have eight of them in one old hard-wired 1/4" bay, each with four jacks tied together, so if I need to feed eight inputs, I can tie four of them together and then plug the oscillator in and then out to all the record inputs.

Cheers,

Otto
 
There are other ways to do the azimuth...I've used a freeware PC-based oscilloscope plugin that gets it good enough. I have a scope now so I'll be using that. There are other ways that I've used to but they are really for being more in a pinch.

You can get cheap or free tone generators for the computer too, or download test tones from analogrules.com.

The meter is the stickler. Needs to be a true RMS meter and have at least a rated bandwidth of 20-20,000Hz. Yeah, 150kHz is nice for checking the bias frequency, but that's $$$.

We'll help ya. Been through the exact same road as you.
 
I've been assembling all my stuff over the last couple of months...

1). Test tape (320 nWb/m) for my decks.

2). AC Millivoltmeter out of Hong Kong off eBay - not that expensive and really really useful (and you may find a 2nd hand one locally of eBay or Craiglist). I got one of these dual channel jobbies;

http://cgi.ebay.com.au/PRECISION-DUAL-2-CHANNEL-AC-MILLIVOLTMETER-LAB-NEW_W0QQitemZ370095185441QQcmdZViewItemQQptZUK_Consumer_Professional_RL?hash=item562b645e21&_trksid=p3286.m20.l1116

6ac5_1.JPG


3). I've got a Wavetek 134 function generator with sweep;

DATA316.JPG


4). and tonight I pick up my oscilloscope on the way home so I should be properly set.

I can already do the alignments on the Otari and the Revox with the test tape, the millivolt meter and the 1K & 10K internal oscillator from the Otari by setting up the Otari 1st and using that to set the PR99. They are all aligned for +4db but I'm contemplating dropping the PR99 to -10db (although it is output gain adjustable using the output gain pots). The Otari is switchable between the two. I also followed the alignment instructions in the manuals I've got for the machines rather than a generic process.

The plan is not only to keep on top of the alignments but to do all the maintenance like Cory does. That's why the oscilloscope, function generator and solder station / sucker and all those little tools as well.

I've also found a source of cassette alignment tapes (not cheap) and I've got one of those coming so I intend to use that to go through and check all my various cassette decks and adjust as neccessary / possible.

The millivolt meter is turning out to be a very very useful device. I've been using it (and the Otari's output calibrated 1k oscillator) to check the metering accuracy on lots of my pieces of kit. Otto's point about his cables is also the way to go. I've started to make my ones up myself, (might have to check out Otto's point about the frequency counter too).

All good :)

Geoff
 
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Wow, this is all very good information. I'm interested in getting my hands on an oscilloscope, an oscillator, and a voltmeter now.

I thought I was cruising along... thought I wasn't going to buy any more stuff for a long time except for maybe some more 1/2" tape. Guess I was wrong... ha ha ha! ;)
 
I've always liked Tektronix equipment. My summer job was building scopes for them when I was in high school and I later worked in a Tek wafer fab.

So I tend to get old tek hardware for my test setup. Just what I grew up with. And this stuff is outstanding even for 30 year old stuff (kinda like my decks)

It can also be boght off ebay for not too much and the manuals are very good.

Here is what I use mostly:

Tek 465 Dual trace 100 MHz scope - I bought this broken for $75 and fixed it.
TM504 mainframe (free)
DM501 4.5 digit meter (free - broken but I fixed it)
DM502 3.5 digit meter (Free - and it was working!)
DC503A 110 MHz universal counter ($35 off eBay Working)
PS501 tracking power supply (Free!)
Signal generator (generic aerospace - $40)

This setup covers almost anything. The signal generator is levels which means that it keeps a constant output as you change the frequency. The DM501 reads has 4.5 digits to you can measure -10 dB as 0.3160 V and it gives true RMS to over 150 kHz.

I suppose that I'll get a FG501 function generator to replace the signal generator some day.

REgards, Ethan
 

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Impressive stack Ethan, how much'd the eggs cost?

Geoff
 
I've also found a source of cassette alignment tapes
Click to expand...

Geoff, what's your source for cassette test tapes?

Jeff, like Ethan told me long ago, one step at a time. And have fun!

It is rewarding and valuable to be able to maintain your own equipment. That's really what got me started is I was concerned nobody was going to care for it like I would...the analog equipment garners such little repect in general.

I personally wouldn't worry about a scope yet, but that's just my opinion. I've really just recently gotten to the point where it is necessary (for recalibrating my DX-4D's...another Ethan/Cory joint venture...I'm like the lab gopher...he's the brains).

A used Fluke 83/85/87 DMM (for example) will get you far as well as a couple freeware software utilities and that along with the test tape and some way to attenuate the test tones coming off the computer and you can cal your deck.

I made my own spring scales to do the brakes...a set of feeler guages from an auto parts store are good and get yourself an insulated "tweaker" (screwdriver)...Harbor Freight has sets of them for cheap.
 
I've had a Fluke DMM for a while now and it's OK, but I also have an HP analog AC voltmeter and I find the needle on a scale to be much quicker and more intuitive than red LED digits. YMMV.

Cheers,

Otto
 
sweetbeats said:
There are other ways to do the azimuth...I've used a freeware PC-based oscilloscope plugin that gets it good enough.
Click to expand...

I may also be interested in the DIY maintenance.

What freeware did you use?

Also, what's a reliable source for finding an alignment tape for my 38, through Tascam directly?
 
Here is a great PC-based oscilloscope/analyzer application...freeware.

Visual Analyzer

http://www.sillanumsoft.org/

I use it for setting up my decks…works great.

One thing though about the azimuth...
I've heard a some folks say that unless the heads are virtually brand new and/or have relief grooves cut...then don't mess with any physical head alignments, since the tape has already begun to cut a microscopic groove into the head based on its path (even if it’s not visible)...and once you start physically aligning a grooved head then you stand the risk of messing with your tape path because the tape could end up riding slightly out of the already formed groove (or the beginnings of a groove) and then all the other calibrations will be that much more difficult.

I just picked up a new ¼” half track, an Otari MX5050BIII-2, so I did a full check and physical alignment of the heads, and from this point on I will just be doing electronics alignments until it's time for new heads or a head relap.

Again...this is just what I've heard from a few guys in the past...but when you think about it, it does make sense NOT to mess with a head that's already "settled in".

I would love to hear some more opinions on this...
 
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Is there another way to test head alignment without the test tape right now, just to see if I even need an alignment?

I think I saw in the 38 manual that its fine if you just continue use the sync head for record and playback, all tapes are only playable on that machine using sync.

My understanding from the manual is that misaligned heads will cause a drop in dB (on the repro head). Of course, my understanding is limited. My original thought was to use a daw to check for phase cancellation of a tone played back on the sync head vs the repro head.

Just a (cheap) thought.

Any other ways?
 
sweetbeats said:
Geoff, what's your source for cassette test tapes?
.
Click to expand...
Almedio in Japan bought out all the TEAC Test Media business. It's a little tougher to match their catalog numbers to what you actually need, so some 1:1 correspondence to them for clarification might be necessary. It wouldn't hurt to start by referencing the old TEAC alignment tape part number, and work from there.

I bought a TEAC alignment tape or 2 before TEAC sold it off. I have the calibration tape for a 2x speed Portastudio and a 1x speed Portastudio,... by actual part number. I also councilled a little with a TEAC rep on the various part numbers of cal tapes, and was told that several of the different part numbers would be nearly compatible, so you might only need one, then use it on the similar decks. Say, if the 246 manual calls out a specific TEAC test tape , but the 688 calls out a different number,... logic tells you that each one should be similar enough to the other to just buy one to use on both.

It was expensive, though. On the same price level as a reel MRL test tape, or thereabouts./DA:eek:;)
 
fstrat76 said:
Is there another way to test head alignment without the test tape right now, just to see if I even need an alignment?

I think I saw in the 38 manual that its fine if you just continue use the sync head for record and playback, all tapes are only playable on that machine using sync.

My understanding from the manual is that misaligned heads will cause a drop in dB (on the repro head).
Click to expand...

Record a test tone, and then compare the levels going in VS the playback levels. That's a simple/basic check, but it only reveals one aspect of electronic alignment...there are other steps that a calibration tape will be needed for.

Using the Rec head for playback will not give you as good quality as the standalone PB head...the Rec/sync is mainly a cue/reference signal for your tracking.
 
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miroslav said:
One thing though about the azimuth...
I've heard a some folks say that unless the heads are virtually brand new and/or have relief grooves cut...then don't mess with any physical head alignments, since the tape has already begun to cut a microscopic groove into the head based on its path (even if it’s not visible)...and once you start physically aligning a grooved head then you stand the risk of messing with your tape path because the tape could end up riding slightly out of the already formed groove (or the beginnings of a groove) and then all the other calibrations will be that much more difficult.
Click to expand...

Well, John Stephens carried this idea to it's logical conclusion on at least some of his machines... the heads were carefully aligned and then glued in place. No physical adjustments were needed or really even possible unless you were doing major work on the heads.

I've made occasional adjustments to azimuth (at least to check, especially when a machine gets moved or heads are relapped and then optically aligned first.) I haven't noticed those adjustments causing problems in doing the electronic alignment.

OTOH, probably there is little risk in leaving the heads in place if the machine isn't moved and the heads aren't pulled or relapped, etc. The exception would be if the head mounts and adjusters aren't as secure as they should be.

Cheers,

Otto
 
Good stuff so far.

Welcome to miroslav!

You definitely need a calibration tape from MRL or TEAC. Unfortunately that is one costly thing you can’t do without.

I listed a few things in the threads below some time ago

https://homerecording.com/bbs/showpost.php?p=1579981&postcount=9

https://homerecording.com/bbs/showpost.php?p=2052052&postcount=6

Radio Shack keeps moving their links around (How do they stay in business ?)
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=22-811

And here is another O-scope
http://www.dsp4swls.de/download/oszilight.zip

Can't find Winscope anymore. The people at archive.org should be shot for making robots retroactive. IMO, they either have it archived or they do not. Once they have it (which they did in this case) they should keep it. To freeze time... that's what they're for. It's down right un-American!

/Rant (sorry)

I've only used PC-based O-Scopes for a few years now. They do the trick for tape deck alignment.

One thing to add about using sync or repro heads. It depends on the design of the machine. As a rule the repro head is better, but Tascam broke that rule with a few of their decks. Machines like the 38 and 48, use the same part number for both sync and playback heads. So, you don’t get the same advantage by using the repro for playback as you would with a machine that has a specially designed Repro head.

In a private studio environment your calibration will hold for a long time. When getting a new/old machine I recommend doing a full align (usually needed, but not always). After that you will just check it maybe every six months to see that it is still right on. I go for three years never having to tweak anything.

Yeah, about azimuth... I just go by the scope. If it stays within spec you don't have to mess with it all the time. The surface of the head will change with wear, so it may need a bump now and then over the long term.

~Tim
:)
 
Thanks Beck!

I have that Radio Shack digital multi-meter (or one very similar to it)...it also has the option to read signals as dBm, so it saves some time.


ofajen said:
Well, John Stephens carried this idea to it's logical conclusion on at least some of his machines... the heads were carefully aligned and then glued in place.
Click to expand...

While I didn't actually glue the heads, I did drop some nail polish on each of the adjustment screws...though like something someone else once said...they've never seen a screw turn itself, even during transport! :D
But I guess a good bump or two could make 'em twitch a little.

I only put the nail polish on the screw heads 'cuz I can be somewhat anal about stuff like that! ;)
But I'm the only one touching my studio gear for the most part, and I'm pretty gentle, so I don't expect the screws/heads to ever move physically once they are set.

I'll be doing my 16-track soon, which has seen some use, but even that deck is pristine, and will probably only need a touch-up on the electronics.
 
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