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    Question calibration

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    Hi,
    i just got a tascam 388 (for 100) and was wondering if anyone could tell me how to calibrate it. i have NO idea how to do this and am quite new to the 388, so try and explain it to me as if i were 5.
    Thanx

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    Arrow Ummm,...

    It's a little more complicated of a process than can be adequately explained on a bbs, but I'll give it a try.

    First, it's a good idea to do some record/playback tests to see where you stand, and determine if you actually need a calibration. However, as an experienced gearhead and DIY'er, I can say that almost without doubt you'll need some minor adjustment & calibration to get the 388 right on spec.

    (Start with DBX switched OFF),... Using a keyboard or test tone generator, record a 1kHz test tone on all tracks simultaneously at 0VU. Rewind and play back the tape, and note how much each track's volume has dropped off, or comes up short of 0VU. This is your basic preliminary test. You may expect that the tracks may be deficient an average of 3~5db short of 0VU on the meters on playback. This is what I've typically seen.

    Then, run a 1kHz/0VU signal (3.16V) directly into each of the PGM IN connectors, one at a time, while adjusting the VU-meter adjustment pots on the left side. This will assure your meters are reading correctly, at the outset.

    Next, load your MRL 21T204 multifrequency calibration tape, and adjust playback amps to read 0VU on playback of the standard 1kHz/0VU test tone.

    Then, on the multifrequency test bands of the cal-tape, check and adjust the playback EQ, using the 12.5kHz reference tone. I've found that adjusting with the 12.5kHz tone gives overall flattest frequency response on playback. You may expect a dropoff at/above 16kHz and below 60Hz, with maybe a little exagerated bump at 125Hz, and this would be normal.

    Having done that, you then move to the record-side adjustments. This is done by recording a 1kHz/0Vu test tone onto a blank tape, and playing back to see what you get, then adjusting the record-amps as necessary. It's your goal to have a 0VU playback when recording a 0VU signal onto tape. This involves a lot of recording of short clips, rewinding, adjusting, and repeating the process until you get a 0/0 record/playback response.

    That's the most basic of setting internal levels, and hopefully that will improve the overall record/playback response of your 388.

    Then, there's the matter of head alignment, which will help aid the edge-tracks 1 & 8 to come back into spec, if they're a little dodgy. However, this requires a dual-trace oscilloscope, and may be beyond the typical DIY'er. (Using the calibration tape again)... You'd connect a probe to tracks 1 & 8, and adjust the gross head alignment for maximum and balanced output on tracks 1 & 8, based on the VU meters. Then, you'd connect the probes to tracks 2 & 7, and adjust the azimuth setting, which should give you an A/B conglomerate signal that looks like a straigt line from the lower left to the upper right quadrant. I'd not advise touching the heads unless you're prepared with the right tools and have some basic-to-moderate experience with electronics. I'd not advise messing with the head alignment unless absolutely necessary.

    Further, there's the matter of adjusting the bias. It always says in the manual that bias is factory set, and should not need to be touched, which is probably true, which is fine by me, but people often want to check and set the bias anyway. This is done by recording a 10kHz test tone in short segments onto a blank tape, on all tracks simultaneously. There's an inductor that you'd adjust to get each track's response to peak at "anything", as long as you note where the peak is,... then keep adjusting clockwise until the test tone bursts note about a 4db dropoff from "peak". This is a long and arduous process, and it will take quite a while to get it in the right zone. There are many record/rewind/playback loops that must be made to adjust all 8 tracks, and it's a lot more touchy than just adjusting record-levels. Again, I'd not advise adjusting the bias unless you have the minimum requisite experience.

    Record EQ is set in a similar fashion to Playback EQ, only using a record/rewind/playback series of test tone/adjustments.

    The full calibration of the 388 is quite an involved process, and the 388 manual has the full writeup of it. This is the best I could do on the spot, with a layman's condensed version of the steps, based on my own reading of the manual and actual experience tinkering around and adjusting the 388.

    Calibration of this sort is not advised for the less experienced techy DIY'er. Basic-to-moderate DIY skills with electronics is the minimum you'll need to achieve your goal.

    The most correct order to do all the adjusments would probably be:
    Meters,
    Playback levels,
    Playback EQ,
    Record Bias,
    Record levels,
    Record Eq,
    Playback levels, (again).


    Summary: more often than not, (1) meter calibration, (2) playback levels, (3) playback EQ, then (4) record level adjustment may be all you need to bring the 388 back to satisfactory performance.

    Myself, not being an expert by any stretch of the imagination, I'd always consult the manual. Also, a Google search of "tape calibration" will turn up a wealth of information by real experts, for more general reference.

    This is just what I could write up, off the cuff, and is not intended as a standard reference text.

    Hope that informations helps give you the basic idea of what's involved. It's preferrable to read this synopsis, then consult the 388 manual for the full instructions.


    Last edited by A Reel Person; 09-12-2005 at 06:36.
    Quote Originally Posted by Lt. Bob
    ... subtleties of sound make a difference to those who really listen.

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    thanx for your help, i'll give it a try.

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    tape deck alignment

    Hi
    When I worked as an engineer at the BBC we were also told to clean the entire tape path, especially the guides near the heads (to remove oxide which had shed from the tape) and also to do a full demagnetise of heads and anything vaguely magnetic in the tape path. This was crucial before you lace up your very expensive squeak tape (frequency alignment). Even though the BBC used to make their own alignment tapes in their own test room, they were still worth a fortune.

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