ELECTRICAL ADJUSTMENTS

When the mechanics work fine, it is time to look at the electrical adjustments.
There are a number of  "confusing" words and facts to learn if one is a beginner. Otherwise you will not know what you are doing...
One should have in mind that these adjustments can be "once in a lifetime job" , unless someone
else has tried to do some "adjustments" before you owned the recorder.
(It is wise to switch on the recorder for 30 minutes before doing any measurements, to make sure it is warmed up).

1. Speed.
Here, you need a test or "alignment" tape, and a frequency counter.
A tape for adjusting the speed is usually a recorded tone, often with the frequency 3150 Hz.
You play the tape while you have a frequency counter connected to "output" on either channel.
If the counter shows something else than 3150 Hz, you just have to adjust the speed.
To run the recorder at a correct speed is important if your tape will be played on other recorders.
As long as you always use your own recorder, it does not matter very much.
 

2. Playback and Record level calibration.
Now, things are getting a bit more complicated. Again, the idea is to make it possible for you to play tapes from other
recorders. The problem here is that there are several standards in the world.
The source of information for your recorder is your manual. Let´s have a look at the manual for a Tascam 34B:

The information tells us about several things (more on that later) and...Record Level Calibration.
It says that "0" on the VU meter "0 VU reference" should correspond to a magnetic energy of 250nWb/m on the tape.
That means, a tape played on another recorder will give the same reading on its VU meter if it uses the same standard.
(VU = Volume Units).

Playback calibration.
To calibrate a Tascam 34B recorder, you need a test tape manufactured for 250nWb/m.
You play the tape (which has a 1000 Hz tone recorded at exactly 250nWb/m).
As you run the tape, you measure the output voltage at the output connectors.
The manual says that the output voltage should be 0,3 V (0,316 to be exact).
If not, you adjust the outout amplifiers.

The purpose of adjusting the output level is to make it possible to connect the recorder to mixers, other recorders and so on.
By having a standardized level, it is easier to connect equipment.

Now when  the output level is correct, the VU meters can be adjusted.
There are amplifiers that run the VU meters. Adjusting them does not affect the output level. The purpose is to get a correct reading so that "0" on the VU meter corresponds to 0,316 Volt output.

Recording calibration.
Now when we know that the recorder gives a calibrated output, we have to adjust the recording level.
The "bad news" here is that we can calibrate the level for one tape type only.
This is because different brands of tape have different performance.

The calibration  is done by recording a 1000 Hz tone (you need a signal generator), and adjusting the recording amplifier
so that the VU meter shows 0dB when you play the tape. If the recorder has separate recording and playback heads, you can
monitor the playback at the same time as you are recording.

Remember, you are not to touch the output amplifier settings now, as we have already calibrated towards the reference tape.
Calibrating the recording level means that when you record at 0 dB VU, you will produce a tape with 250nWb/m.
If that tape is played on another recorder that has the 250nWb/m standard, that recorder will also show 0 dB if it is properly calibrated.
 

 
 
 
 
 
 

TASCAM 34B

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