🚀 go-pugleaf

Eric Lindsay (eric@zen.maths.uts.edu.au) wrote:
: In <16B7E7CBB.A8637710@tscc.macarthur.uws.edu.au> l.gudiksen@uws.edu.au writes:

: >I have a PC which uses a pezo spearker. Lately I have loaded some programs
: >which have some good sound included in them, but naturally to sound quality is
: >poor.
: Using an 8 or 16 bit DAC gives good sound, but I guess you don't want to hear 
: from people whose computer have real sound capabilities 8-)
: >What do I need to look out for when changing it over to a coventional speaker,
: >such as impedence, audio drive, etc.
: I take it you don't have schematics for your clone?  Instead of just adding 
: a speaker, I'd add a high impedence amplifier.  On the assumption that the 
: square wave drive is coming from something that is TTL equivalent, dump it 
: through a capacitor (0.1 uF monolithic, since you are likely to have some 
: on the bench), then a 200k pot, into an LM377 or LM378 or equivalent 
: audio amplifier (cheap little 2 or 4 watt 14 pin stereo amplifier ... with 
: a PC, you don't have any use for the second channel ... but I'm not sure of 
: the number of a mono equivalent).  Oh yes, with the power supplies on PCs, 
: you will probably need close attention to the noise on the power rails.  Or 
: maybe you can just find one of those little "self powered" loadspeaker boxes 
: they sell for Walkmen(T.M.) and add one of those?

this is the way i'd suggest too - the mono version of the 377/378 is the
LM380 - dirt cheap and something could be roughed up in veroboard - make
sure that the +12 volt rail is well bypassed with tantalum & ceramic caps
to filter out the HF hash from the switch mode PS. alternatively, jaycar
and the like cann probably supply a stereo or mono kit using the same or
similar ics - if you go with the stereo option and decide to use a half
way decent 4" speaker, why not bridge the channels and add a pot up
front for level control (keeping in mind that the audio quality of the
original signal from the PC won't be great - only a filtered square wave
after all).

by the same token, i would guess that the original PC circuitry would
drive a small high impedance (say 60 ohm) speaker anyway - why not try 
it and see?



-- 
richard lindner                   ,-_|\            rjl@spectre.apana.org.au
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