Revox B215 Playback Calibration

 Revox B215 Playback Calibration

The image here of the B215 is just a general photograph - no commercial reference tape photographed here.

Outlined below are steps that can be used to calibrate the Revox B215 cassette deck - principally as a playback machine. Recording calibration is automatically achieved by the machine itself when you press Rec + Pause together, then Align. The machine will automatically perform tape level testing, bias, and equilisation.  

Playback Calibration Steps

(1) Carefully demagetize the heads, making sure the demagnetiser does not physically make contact with the heads. Follow the instructions as advised by the manufacturer.

(2) Clean the heads with an appropriate head cleaner - isopropyl alcohol works well, however it is not advised to clean the pinch roller with any type of alcohol.

(3) Insert your Dolby Level 400Hz, 200nWb/m (ANSI standard) reference tape - preferably a full-track professionally made cassette tape. 

(4) Note the type of tape: Type I, Type II etc - the B215 should automatically recognise this.

(5) Connect your B215 to either an oscilloscope or AC voltmeter - on playback of the test tape, the 400Hz test tone should register 775mV(rms), 1100mV peak, or 2200mV peak-to-peak.

My advise is to use an oscilloscope - you can visibly see the waveform and its stability. You may find that a voltmeter will appear to vary above and below a common value - this variation (if present) is caused by other factors such as wow/flutter/drop-outs etc.

(6) There are two playback adjustment potentiometers:

Left Channel R81, and Right Channel R36

Click on this image and download it to see more detail. 

Actual circuit board -

Using a completely electrically insulated flat-headed screw driver turn clockwise to increase (or anti-clockwise to decrease) the output at Dolby Level. Aim the output such that Left=Right=775mV. The 775mV figure is an ideal, technically it doesn't have to be exact. At this stage, you may also need to ensure that the outputs are balanced - carefully turn R42 to balance Left and Right.

Now that line out is .. Left=Right=0.775v, you will need to adjust the peak meter to reflect this Dolby Level, which is '0' on the B215.

Refer to the image above from the service manual, and locate potentiometer R26. Again, with an insulated flat-head screw driver turn the potentiometer slowly until the meter reads '0' from a lower level, ie from '-2' to '-1' to '0'.

Playback Circuit Diagram

Playback Level adjustment is a potential divider as shown above. I suspect the Bandstop filter is there to stop the high frequency bias 'carrier' from 'bleeding through' when 'Monitor' is pressed?

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