3M DELTA Series - Program Record Bias; Program Record Equalization; Cue Bias; Cue Master Levels

d. To accommodate lower input reference lev 
els, connect wire jumper W1001 (and W1002
for stereo) as indicated on the Record and
Meter amplifier board drawing.
2. Program Record Bias
NOTE: This procedure adjusts Program Record 
ing Bias according to generally accepted prac 
tice for commonly available tape formulations.
The procedure yields acceptable record perform 
ance (noise, distortion, and frequency response)
on many of the tape oxide formulations avail 
able. However, this adjustment may vary slightly
from one tape formulation to another, and exact
procedure should be determined by consulting
the tape manufacturer.
a. Prior to making any bias adjustments, con 
firm that the recording head azimuth (phase
alignment) has been correctly adjusted as
outlined in Section III.
b. While monitoring the respective playback
output channel with a high impedance volt 
meter. begin recording a 10 kHz tone at an
indicated -10 VU level (front panel meter).
Be certain the cartridge selected is typical of
the type to be used in the machine; espe 
cially the type of magnetic tape.
c. Turn R1107 (mono or left channel) until a
maximum output level of the 10 kHz tone is
observed. Once this “ peak" bias setting is
found, continue to turn in a clockwise direc 
tion until the average level of the tone de 
creases 2 dB.
d. Repeat this procedure on the right channel,
using R1 108 to adjust the bias.
3. Program Record Equalization
a. Connect the high impedance AC voltmeter to
the respective playback program channel
output. Be sure to properly load the output
with 600 ohms.
b. Set the test tone generator to 1 kHz and set
the front panel indicated Record level to -10
VU.
c. Observe the playback level on the voltmeter
and adjust its range switch to a convenient
reference reading.
d. Set the test tone generator to 10 kHz and
observe the level on the external voltmeter. If
the 10 kHz level differs from the 1 kHz tone
level, adjust R 1005 on the Record/Meter Amp
PC board until the 1 kHz and 10 kHz tones are
indicated at equal levels.
e. Repeat this same procedure for the right
channel using R1006.
4. Cue Bias
a. Swap the left program playback head cable
with the cue playback head cable.
b. While monitoring the left program playback
output with a high impedance AC voltmeter.
begin recording a continuous 8 kHz (tertiary)
cue tone.
c. Adjust the cue bias potentiometer R1 131, lo 
cated on the Bias Amp PC board, until a
maximum output level of the 8 kHz cue tone
is observed.
d. Alternately record a Primary cue tone and a
tertiary cue tone. The 8 kHz cue tone should
be 10 dB lower in level than the 1 kHz tone.
The 1975 NAB standards call for -10 dB nom 
inal, -9 dB maximum, -13 dB minimum.
NOTE: The program playback amplifier
must first be properly equalized from a cal 
ibration tape in order to make this adjust 
ment.
5. Cue Master Level
The cue oscillator tones are generated by the
microprocessor and are digitally controlled. The
microprocessor determines the correct frequency
and level. Therefore, there is only one control to
adjust the cue oscillator circuitry. This control sets
the levels of all other cue tones in proper rela 
tionship to the primary (1 kHz) tone.
a. With the head cables still connected as out 
lined in the previous Cue Bias procedure,
record a 1 kHz Primary cue tone and observe
the output level.
b. The Primary cue tone must playback at the
same relative ouput level as the 1 kHz refer-
5-2