INMC 80 News


June/July/August 1980, Issue 1

Page 44 of 48


Cassette 1/0 Reliability

A few people have written to us and have indicated that they experience unreliable cassette 1/0. As far as we are aware, if everything fs set up correctly, very very few errors should be encountered at normal speeds. The same applies at double speed ona Nascom 1 or 2400 Baud on a Nascom 2.

If you have cassette I/0 reliability problems then the check Tist below may help:–

1) 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.

2) 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.

3) The settings of the volume and tone controls can be quite critical. Too much volume on record or play back may cause the amplifiers fn 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 best.

4) 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.

5) 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 biaring away on play back then you may be interested fn 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 serfes across the speaker output. This will then give ae visual indication of ‘tone – data – nothing’ being output.

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Page 44 of 48