Adjustment Of Head Shielding; Channel To Channel Crosstalk - Revox G36 Service Manual

3.1.8 Adjustment of head shielding

This may sometimes be necessary in order to keep the operating hum levels at a
minimum. It should be noted also that since hum can be picked up by the electronics
on the underside of the recorder, care must be taken to screen the base when the
chassis is removed from its case, whether on the service bench for attention, or when
built into a cabinet.
To adjust the playback head shield, place two spools on the recorder with a half reel
of tape wound on each and without threading the tape depress the play and stop
buttons. The tape should remain stationary and the head shield may be adjusted to
give the lowest reading on a milli voltmeter connected to the cathode follower output.
If two meters are available it is advisable to check both channels simultaneously since
an improvement in one may bring about a deterioration in the other.

3.1.9 Channel to channel crosstalk

Certain physical limitation prevent one from achieving infinite crosstalk rejection. A
crosstalk figure of 50 db can be reached in practice and is generally considered
acceptable.
It may however still be irritating in such cases where extreme level differences exist
in the recordings of adjacent tracks.
When checking crosstalk, one should never listen to the "dead channel" with a wide
open monitor gain. Depending on the reserve gain available in the monitor system,
the slightest amount of crosstalk will thus become audible. Crosstalk behaviour can
be judged by exact measurement only.
To adjust the recorder for minimum crosstalk a reference recording at full modulation
(preferably music) is required on one track only. While making this test recording it
is important that the bias and audio signals are inoperative on the other channel.
(Channel-selector in position I or II respectively, level control of the unused channel
closed) . After re-winding, the recorded section is to be replayed while monitoring
the unrecorded track. By adjusting trimpot P6 (fig.14) reduce any audible crosstalk
until a minimum is reached. The optimum setting for P6 is found by repeating the
above procedure with a recording on the other track.