8-bit Software Disc Magazine (c) Duncan Webster DEC 1991
Issue 17 December 1991
Tech Tips Issue 4
One of the BBC's main bottlenecks was the rather poor quality speaker
built into the machine. Beleive it or not, a larger speaker can
certainly make a lot of difference and can make the Model B sound much
better. This article by E.M. Clark explains the steps that need to be
followed in order to fit a large speaker to your model B.
*** IMPORTANT ***
No responsability is accepted by the author or 8-bit Software for any
damage caused to machines whilst following the steps in this article.
Provided you have a little pre-knowledge of the inside of a BBC B and
are reasonably competent with electronics, then this upgrade should
not be too difficult. No Modifications should be attempted if you do
not possess the necessary skill/knowledge for such an upgrade.
ENHANCING THE SOUND OF YOUR MODEL B
Now that the shine and sparkle has vanished on this machine, perhaps
this simple modification will hopefully be of use to someone...or two!
First of all you will need about 1 Metre of screened cable, with both
ends bared. Solder one end to a 3.5mm jack plug, the screening going
to the body of the plug and the centre core to the tip. Solder the
other end to a 3 or 8ohm speaker, you can solder the wires any way
round. A 4 or 5 inch speaker is ideal, as long as it is not another
squeaky little toy as in the Beeb!
Next, make sure the machine is switched off, or better still,
disconnect it from the mains. Remove the top cover of the Beeb, then
remove the keyboard, after first unplugging it from the motherboard.
You will notice a small plug with wires attached going to the speaker,
unplug it, and fold it back. If you have another socket of this type
then solder two wires to it, each about 18" long, if you haven't got
one, then cut the wires on the existing socket leaving as much wire as
possible. Extend the length of these wires so that they reach the
back of the beeb, with a bit to spare. Don't forget to insulate the
joints. Next drill a hole in the back of the machine near to the ADC
socket, and fit a 3.5mm jack socket, solder the two wires to the
socket. Making sure there are no short circuits, switch on the beeb
and check for sound output. The sound output level can be adjusted by
the small vertical potentiometer VR1 close to the speaker plug, which
is PL15. Once the sound level is to your liking, switch off the
machine and replace keyboard and keyboard connector, and then the top
This little mod will give you better quality output. You can try this
mod out before finally drilling the hole in the case if you wish, if
you "float" the jack plug and socket and check to see if you are
satisfied before making it a permanent job. Don't forget to make a
drawing of the original wiring in case you want to return to it.
By inserting another jack plug into the speaker output socket but this
time connecting it to an amplifier, will give even greater output ...
providing you have an impedance match,or in other words, it is
This completes the article, if you have found it useful and would like
other articles in the future then please let Duncan know and thereby
me. It should be stressed again that this article is directed at
those members who are confident enough and knowledgeable enough to
make the necessary alterations to the computer. If you are in any
doubt then seek assistance from someone who is comptent enough to
undertake the job properly.
E.M. Clark K24.
QUESTIONS FOR FUTURE TECH TIPS
User 2GJ: Roger Pashby
Does anybody know what the command is to switch CAPS LOCK on and off.
I am sure that it is a simple *FX call or a VDU command, but i'll be
blowed if I can find it anywhere.
I want to include a password system for a menu I am building. I want
the user to be able to input his/her own password upon first booting
up and then then menu will auto save with the password built in, so
that in future it will request that password or hard break. The file
will also need to be protected so that is cannot be read and be
protected. Anybody suggest a routine?