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Thread: DIY Alignment and Calibration

  1. #1
    lo.fi.love's Avatar
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    DIY Alignment and Calibration

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    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?

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    Victory Pete is offline Banned
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    Quote Originally Posted by lo.fi.love View Post
    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?
    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

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    ofajen is offline Daddy-O Daddy-O Baby
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    Quote Originally Posted by lo.fi.love View Post
    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?
    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

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    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.

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    jedblue's Avatar
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    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-DUA...3286.m20.l1116



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



    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
    Last edited by jedblue; 07-30-2009 at 19:04. Reason: typo's

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    lo.fi.love's Avatar
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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!

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    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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    In Sunny Vancouver ..... (Washington)

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    evm1024's Avatar
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    Quote Originally Posted by jedblue View Post
    Impressive stack Ethan, how much'd the eggs cost?

    Geoff
    5 dozen for $5.99 on sale at Winco.

    That crate holds parts very nicely!

    --Ethan
    In Sunny Vancouver ..... (Washington)

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    I've also found a source of cassette alignment tapes
    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.

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