Fostex A-8 - Page 41

Specification: 72dB weighted
60dB unweighted
6.4.10 T.H.D. measurement
1) Set the front panel NR INT/EXT switch to INT.
2) To adjust TRACK 1, for example, apply a 400Hz, -lOdBV (0.3V) test signal to
INPUT jack 1, record it, playback the recorded tape and apply its output from
OUTPUT jack 1 to the distortion meter.
Specification: T.H.D. 1% or less
3) If it is not within spec, demagnetize the head, check the bias trap adjustment
and record level.
If it still does not fall within spec after making the corrective measures above,
readjust the bias current by the procedures in the previous Section 6.4.6.
4) When the Section 6.4.6 adjustments are made, it is necessary to go through pro 
cedures in Sections 6.4.7 and 6.4.8.
6.4.11 Erase measurement
1) Set the front panel NR INT/EXT switch to INT.
2) To adjust TRACK 1, for example, apply a IKHz, OdBV (1V) signal which is lOdB
higher than the reference level, to INPUT jack 1 and put TRACK 1 in the record
mode.
Partially rewind the tape to retain a section of the IKHz signal and then record
over the remaining section without any signal at the input.
3) Rewind to start of recording, playback the tape, insert a IKHz bandpass filter
between OUTPUT 1 and the level meter to measure the output.
4) The level ratio between the IKHz recording and the no-signal recording is the
erasure figure. It is in good normal condition if erasure is higher than 70dB.
5) If it is less than the spec, increase erase current about 10% by the procedure
of Section 6.4.5. Monitor the erase current waveform on the oscilloscope at
adjusting and set the core just before the waveform begins to deteriorate. A
higher current will heat the erase head and result in damage to the tape.
6.4.12 Sync crosstalk measurement
1) Sync crosstalk is the relative figure against the reference level on how much
of the recording signal from the track in the recording mode is leaking into the
track being reproduced.
When sync crosstalk is excessively high, playback output during overdubbing will
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