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Gateway MasteringのBob Ludwigさんが愛用している事や個体数が極端に少なくポールのチケット並みに入手が困難なためレジェンドと化したマスタリングコンプレッサーのNTP 179-120です。所有している方も国内にはほとんどいらっしゃらないとは思いますが備忘録も兼ねて公開します。
COMPRESSOR AMPLIFIER 179-120
Instruction for Alignment Block Diagram
Normally the Compressor Amplifier will stay correctly adjusted,
except when a component has failed and has been replaced;
then it may be necessary to make certain adjus trnents.
Before attempting to make any adjustments, note the permissible indication errors stated in
Technical Specifications.
The functions of the trimpotentiometers are as follows:
P1 Bias adjustment of Op. amp A1
P2 Compensates for individual pinch-off of the F.E.T. ( Q1 )
P3 Compensates for individual slope △Rsd /△Vgd of the F.E.T.
P4 Linearity adjustment of the FET Attenuator circuit.
P5 Adjusts for minimum distortion of the FET attenuator.
P6 Adjusts the threshold level.
Do not attempt to make any adjustments until the current consumption has fallen to a steady level
approx 100mA after 60 sec.
Correct sequence of adjustments is as follows:
a) Bias adjustment of P1
Conditions: No input signal.
Recovery switch in position: 0.06 sec.
Connect a DC voltmeter (or DC-oscilloscope sens. approx. 20mV/div.) between TP 7 and TP 1.
P1 is adjusted until the voltage measured is the same whether TP2 is connected to TP9 or not.
b) Pinch-off adjustment of P2
Conditions: Input signal +6dBu 1kHz
Ratio switch in position: 1:1
Lim. level switch in pos.: "high"
P2 is adjusted until the output voltage is +6dBu (OdB amplification).
The adjustment range can be altered by connecting or disconnecting R15 and or R16.
c) Slope dB V and Linearity adjustment of P3 and P4
Conditions: Like referred under position b.
A floating external DC-source 0-6 V is connected between term. 3 and 5, term. 3 positive.
The DC voltage is set to 3.0 Volt, and P3 is adjusted so that the output level is -9dBu (15 dB attenuation).
Now the DC voltage is set to 6.0 Volt, and P4 is adjusted until the output level is -24dBu (30 dB attenuation).
Because of mutual dependence between P3 and P4 the adjustments are repeated until correct output level is obtained.
d) Threshold level adjustment of P6
Conditions: Input signal +6 dBn 1kHz
Ratio switch in position: 20:1
Lim. level switch in position: "high"
Compression switch in position: 15 dB
P6 is adjusted to an output level of +6 dBu
e) Distortion adjustment of P5
Conditions: Ratio switch in position 2:l
Input level and the other controls are set like under position d.
P5 is adjusted to minimum distortion.
Because of interaction between P5 and P2, the adjustment mentioned under position b is carried out once more.
上記a)～e)の５ステップで基本キャリブレーションは完了です。
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