Cassette I/O Reliability
A few people have written to us and have indicated that they
experience unreliable cassette I/O. As far as we are aware, if
everything is set up correctly, very very few errors should be
encountered at normal speeds. The same applies at double speed on a
Nascom 1 or 2400 Baud on a Nascom 2.
If you have cassette I/O reliability problems then the check
list below may help:–
Make sure that the tape transport is clean (wiping with a
tissue will do for starters) i.e. that the heads, the pinch
roller and capstan are free of loose tape material.
Check for earth loops. If the cassette recorder is earthed, and
the Nascom is earthed (it should be) and there is an earth
connection between them, then problems may arise. The safest
one to disconnect is the one(s) between the Nascom and the
recorder. That’s the safest, the best one to remove would be
the cassette mains earth. But on your own head be it.
The settings of the volume and tone controls can be quite
critical. Too much volume on record or play back may cause the
amplifiers in the cassette recorder to deliver a distorted
signal. Too little will not drive the cassette interface on the
Nascom. On recorders with one tone control (normally a treble
cut) this should be set at or near the max. treble end (i.e. no
treble cut). On others a flat or zero setting will normally be
On a Nascom 2, VR1 is best set up using an oscilloscope. Record
about five minutes of tone (plug in the recorder, and just
switch to record. Play back the tone, monitoring TP19 with the
“scope. Adjust VR1 to give as good a square wave as possible.
Use a reasonable quality tape. Since most cassettes are meant
for music/speech, using them to store very fast transitions
is not ideal. Some cheap tapes give a very low play back level
even when recorded at a good level. This its not critical for
sound but can cause problems for data.
A suggestion we have received from a member in Nottingham is to
load the cassette output (when the speaker output is being used) with
an 8 ohm resistor (or close to, but above this value) by connecting it
across the output plug. See ‘Cut that Noise’
elsewhere in this issue.
Cut That Noise
If you are using a signal output from a cassette recorder that
still has the speaker blaring away on play back then you may be
interested in this idea from a member in Nottingham.
Connect a Light Emitting Diode (LED) and a small ordinary diode
back to back with an 8 ohm resistor (or close to, but above this value)
in series across the speaker output. This will then give a visual
indication of ‘tone – data – nothing’ being output.