Tape Recorder Alignment
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Definition Of Terms:

  • Azimuth - Rotation of head about the z axis (left to right).

  • Console - The big thing in the middle of the room with all the knobs and lights.

  • De-Mag - Short for 'demagnetizing'; the process of removing residual magnetization from the heads and related parts.

  • HF - High Frequency

  • I/O - Input / Output

  • LF - Low Frequency

  • MRL - Magnetic Reference Laboratory - A company that produces highly accurate, multi-frequency, full track test tapes for tape machine calibration.

  • Repro - Shorthand for Reproduce head.

  • Sync - Term used to indicate the playback mode of the record head.

  • Wrap - (or Tangency) Rotation of head about the y axis (side to side).

  • Zenith - (or Tilt) Rotation of head about the x axis (front to back).

Nazi Portable Radio
These are German policemen after WW1 trying out an early portable radio of doubtful practicality.
Image Courtesy Of The Douglas Self Site.


Process Overview:

  1. Clean and De-Mag The Machine
  2. I/O Alignment
    1. Input - adjust input to machine from console
    2. Output - adjust output from machine to console
    3. Meters - adjust machine meters to read 0VU
  3. Playback Alignment (from MRL tape or client tones)
    1. Level & Azimuth - 1kHz reproduce head & sync head
    2. HF & Azimuth - 10kHz reproduce head & sync head
    3. LF - 100Hz reproduce head & sync head
  4. Bias & Record Azimuth Adjustment
    1. 10kHz with machine in 'record' while monitoring repro head
  5. Record Alignment
    1. Level - 1kHz Machine in 'record' while monitoring repro head
    2. HF - 10kHz Machine in 'record' while monitoring repro head
  6. Repro check
    1. LF - Record 100Hz and adjust reproduce head & sync head



Clean and De-Mag The Machine

  1. Clean the heads, rollers, idlers, and pinch roller or pucks with the recommended substance (usually cotton swabs and 99% alcohol). A tape machine should be cleaned every morning and before every alignment, unless instructed otherwise by the assistant engineer or client. For digital machines, only foam-tipped swabs should be used. Cotton swabs leave small particles of lint, and with today's incredibly high digital track density, a small piece of lint can easily foul the data.

  2. De-magging removes residual magnetism from the heads, rollers, idlers, and anything else metal and magnetic in the tape path. This residual magnetism, if allowed to build up, can begin to partially erase tapes. The machine should be off, however it can be de-magged while on, but ONLY with the machine on 'Input' mode!! (Otherwise you'll fry the head electronics!) The de-magger should be 4-6 feet AWAY from the machine when it is turned on, otherwise it may permanently magnetize the heads! Once turned on, slowly bring the de-magger towards a head (some say to use a spiraling motion while approaching). Once at the head, slowly move the tip up and down a few times WITHOUT touching the head, then slowly move away again (spiraling if you desire). If the de-magger has an on/off push-button, power should be cycled before another approach. This should be done for all three heads, and any other magnetic metal in the tape path such as idlers, rollers, etc. A tape machine should be de-magged before the start of every new session or at least every few weeks on long sessions, unless instructed otherwise by the assistant engineer or client. Also, there should not tapes or other magnetic media within 10 feet of the de-magger while it is turned on.



I/O Alignment

  1. I/O alignment is designed to match the tape machine's I/O electronics with the console's I/O electronics. Performing an I/O alignment on a machine in the shop with shop test equipment is only accurate while the machine stays in the shop. Once the machine is moved to a control room, it's I/O characteristics will most likely change due to different loading characteristics of the room and console. Therefore, I/O must at least be checked, and usually re-calibrated, when a machine is moved from room to room. Various machines have slightly different procedures, therefore a practical world alignment of the Studer A-827 procedure will outlined here.

  2. Send 1kHz @ 0VU (+4db) from the console to the tape machine with it in input mode. With an AC voltmeter, measure TP 9/509 (on the audio card) and adjust Input cal (R131/631) for 0db (since the internal operating level of the machine is 4db down). Repeat for all 24 tracks.

  3. With the same test conditions, monitor the tape return meters at the console and adjust the Output cal (R134/634) for 0VU at the console.

  4. With the same test conditions, monitor the meters on the tape machine and adjust the left-hand trimmer at the meter for 0VU.



Playback Alignment

  1. The first step in playback alignment is to adjust 'Repro Level'. This is done by playing a 1kHz tone either from an MRL tape or a client's tone tape, and adjust accordingly. If using a client tape, you align the playback electronics so the meters read 0VU. If using an MRL tape, you align for the proper flux level (see accompanying flux level pages). For instance, when aligning for a level of +6/185nW with a 250nW test tape, you would align the playback electronics so the meters read -3db.

  2. Rough azimuth is done now with 1kHz played from the repro head. See accompanying azimuth page for descriptions of the two main methods.

  3. If using a client tape, the same two adjustments (level and azimuth) are also performed on the sync head. If using an MRL, only azimuth is performed now, with all sync playback adjustments being done at the end.

  4. The second step in playback alignment is to adjust 'HF Repro EQ' This is done by playing a 10kHz tone either from an MRL tape or a client's tone tape, and adjust accordingly. If using a client tape, you align for 0VU. If using an MRL tape, you align for the proper flux level.

  5. Fine azimuth is done now with 10kHz played from the repro head. If using a client tape, the same two adjustments (HF Sync EQ and azimuth) are also performed on the sync head. If using an MRL, only azimuth is performed now.

  6. Some people skip this step entirely until the end, but it will be described here anyway. Low frequency characteristics change from one headstack to another due to wear patterns etc., and thus are unique to each headstack (even between headstacks of the same type). And since Low Frequency is a function of playback only and not a function of record, no adjustment of playback electronics will change how the low frequencies get recorded. Therefore, it is best to wait until the alignment is finished, then record a 100Hz tone and adjust LF at that point, thus compensating for that particular headstack's LF characteristics. In addition, MRL tapes are recorded full track (one giant track across the entire width of tape). When reading full track information, headstacks have a tendency to pick up low frequencies beyond their normal track width, calling this phenomena the 'LF fringing effect'. Every headstack produces the fringing effect to varying degrees, thus making a standard 'LF compensation factor' un-obtainable. Therefore, when using an MRL tape, LF must wait until the end of the alignment.


Bias & Record Azimuth Adjustment

  • Bias is performed by sending a 10kHz tone from the console to the machine while in record and monitoring the repro head. The bias control is first reduced, watching the meter rise until the peak is found, then the control is increased until the meter drops the required 'over-bias' amount from the peak. Bias is a relative adjustment, meaning it is not performed to a specific VU reading, instead it is performed relative to the peak. Since the scale of a VU meter is not linear, the oscillator level from the console should be increased so the peak is in the range of +2 or +3 VU, thus putting the peak in the highest resolution portion of the VU scale. This will allow a more accurate over-bias adjustment. The amount of over-bias is generally in the range of 1db to 3db. An exact figure can not be given here since the amount varies among machines and tape types. Using the same conditions, azimuth is fine tuned (on the record head) for the last time to perfectly align the record head to the playback head.


Record Alignment

  • Record Level is performed by sending a 1kHz tone from the console to the machine while in record and monitoring the repro head. Record level is always set to 0VU, since the operating level has already been set during the playback adjustment.
  • HF Record EQ is performed by sending a 10kHz tone from the console to the machine while in record and monitoring the repro head. HF Record EQ is always set to 0VU, since the operating level has already been set during the playback adjustment.


Repro Check

  • Now the machine is ready for the recording of the 100Hz tone. LF repro can be adjusted to 0VU while the machine is recording the tone and monitoring the repro head. If the playback alignment was performed using client tones, all that remains is LF sync adjustment (to 0VU). If the playback alignment was performed using an MRL, 1kHz and 10kHz must be recorded and played back on the sync head for Sync Level and Sync EQ adjustments, respectively.




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