Analog Tape Machine Alignment (7)
Analog Tape Machine Alignment (7)
(Continued from previous article)
*In this article, I am dealing with 'Studer A80', an industry standard analog tape machine during 1970-80s.
Having just finished aligning the reproducer part of the tape machine to a reference standard via the alignment tape, we will now proceed to align the record side to the same standard. Remember, the goal here is to make the record and reproduce sides of the machine be as identical as possible so that 'what goes in, comes out'. This article will guide you through the process of aligning the record electronics of a tape machine. You will first do a bias adjustment, then a level adjustment, and finally a high and low frequency alignment. You will be adjusting the record electronics while monitoring the effects of your adjustments by watching the reproduce output.
1) Set up the signal generator to output a 1 kHz signal at a level of +4 dBv.
To do this, turn the generator frequency dial to "1" and push the frequency button labeled "x 1K". Use the output level control to adjust level. Read the level on the ACVM labeled "Input Signal Level".
2) Put the Studer Electronics into the Input mode.
At this point you want to make sure that the signal is indeed getting to the tape machine. You want to monitor the input to the tape machine. To do this, put the meter selector lever to "RECORD". You will find this control on the left side of the VU meter.
3) Make certain that the level of the input signal is 0 VU.
4) Return the machine to the Repro mode.
To do this, put the meter selector lever to "REPRO". You will find this control on the left side of the VU meter.
5) Set up the signal generator to output a signal of 10 kHz at a level of approximately +4 dBv.
This level does not have to be exact at this point.
6) Thread a reel of the tape type you will use for recording onto the machine.
Do not use the alignment tape.
7) Place the machine in the Record Ready mode.
This means we are enabling the record circuit. To do this, turn the rotary function control switch to the "READY" position. The green LED marked "READY" will be lit.
8) Put the machine into the record mode.
You will be doing the bias adjustment now.
To do this, press both "PLAY" and "RECORD" transport buttons at the same time. The red LED marked "RECORD" will be lit.
9) Adjust the bias level for an overbias of 3 dB.
To do this, locate the record adjustment electronics. Now find the control marked "BIAS LEVEL" for the speed at which you are recording (Fast). With your tweaker, turn the bias level control all the way counterclockwise (CCW) to the minimum level while monitoring the tape machine's output from the reproduce head. Notice that the signal falls below -20 VU and can barely beheard in the headphones, if at all. Now slowly turn the bias level control clockwise (CW) until the signal peaks. Continue turning the bias level control CW until the signal level drops back 3 dB from the observed peak.
10) When you are satisfied that you understand the nature of the overbias procedure and have done it correctly, stop the tape.
This is the completed bias adjustment. All subsequent audio signals will be recorded in the linear section of the hysterisis characteristics for the tape formulation you are using. Should you change tape formulations or recording speed after this point, you would need to do another bias adjustment.
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