Tape machine calibration is a process that involves matching the electrical characteristics of the machine to the tape you choose for recording. In order to do this, you will need the following:
- A small screwdriver
- A magnetic reference tape
- A sine wave oscillator
1. First you will need to clean the tape heads, but don’t use head cleaner on the rubber pinch roller. Then demagnetize by following the directions found in the tape machine’s manual.
2. Load the reference tape. After setting all of the channels to Repro/Safe, play the 1 kHz tone while paying attention to the VU meters. If you plan to record at the reference tape level, it’s best if all the meters read 0 dB. You can achieve this by adjusting the REPRO LEVEL pot on each channel. You can also attain a higher or lower level by adjusting the REPRO LEVEL until the meters read under zero by the amount you want to record over zero. (See the conversion chart below.)
|+9 = 520 nWb/m|
|+6 = 520 nWb/m|
|+5 = 520 nWb/m|
|+4 = 520 nWb/m|
|+3 = 520 nWb/m|
|+1 = 520 nWb/m|
|0 = 520 nWb/m|
Reference tape (n/Wb/m)
|Desired Operating Level||185||200||250||320||370||520|
3. Next, repeat this procedure for the 10 kHz tone, adjusting the high frequency REPRO pot. Repeat the procedure once again for the 100 Hz tone, adjusting the Low Frequency REPRO if it’s available on your recorder. Check the 1 kHz again and adjust as necessary. Also check the Sync/Cue playback using the Sync Level pots to achieve the same levels.
4. Load a new reel of tape for recording, and then set all channels to RECORD/READY. Make sure that the monitor switch is set to TAPE/REPRO. Use your oscillator to input a 10 kHz tone at 0 VU. While recording the tone, observe the meters. Turn the BIAS pot in a counterclockwise direction until you see the peak output on the VU meters. Then turn the BIAS pot in the other direction (clockwise) until the level peaks again and then begins to fall.
In the case that the needle hits the meter and stays there, lower the level from the oscillator during biasing. But make sure you remember to reset it to +4 (professional) or -10 (consumer), which is your reference BIAS level.
In order to find the Recommended Overbias, simply turn the pot clockwise until the level drops from the peak by the amount that is stated in your tape machines manual. Also make sure you follow whatever criteria is stated in the manual when it comes to tape type, etc. You will need to repeat this process for each channel.
5. Next set your oscillator to 1 kHz @ OVU. Then send the tone to the individual input of each track one at a time or through a bus or mult. Some decks offer a designated test tone input that you can also use.
While recording the tone, watch the meters in REPRO/TAPE and adjust the RECORD LEVEL/GAIN pots to reach 0VU on the meters for each channel. The meters should read the same when you switch between INPUT or TAPE monitoring.
Switch the oscillator to 10 kHz and record the tone while monitoring in tape mode and adjusting the HF RECORD EQ for OVU output. Then change the oscillator to 100 Hz and record another pass while monitoring in REPRO. Adjust the LF/LO FREQ on the Repro card, setting it to zero.
Check the levels again and adjust to 1 kHz if necessary.
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