K8CC Voice Blaster Interface

zf8bs at twg.com zf8bs at twg.com
Fri Oct 7 23:27:41 EDT 1994

Has anybody here built the Voice Blaster drawn by K8CC in the Voice
Blaster documentation package?  I just did, and am having some problems
with it.  First off, when using a LPT port, it appears to me that LPT
pin 2 is never asserted, which means that relay K1 never closes.  Since
pin 3 does get asserted, relay K2 will close and so it is possible to
record a message which you can play back to a speaker.  But since
K1 never closes, you don't pull down PTT so it's all just an interesting

If, on the other hand, you use a COM port, then it appears almost the
reverse happens.  When you are recording, both pin 4 and pin 20 are
asserted, so you pull down PTT, MIC input goes to the Sound Blaster's
MIC input, and every thing is peachy.  But when you play back a recorded
message, only pin 4 is asserted; pin 20 is not.  So relay K1 closes and
you do pull down PTT.  But since K2 doesn't switch, you don't have a 
full Mic circuit from Mic In to Mic Out.  I do have the option selected
in the pop-up menu (option "X" toggled) that should allow this to 
happen.  What I can't understand is why I'm not feeding any signal to
the transceiver's Mic Input.  Obviously I've got more bugs I haven't
found yet.  At first I thought it might have to do with the audio
isolation transformer, but I don't see how I could record if that were
wired wrong.  (Note it's a 1:1 transformer, yet the package shows a 
different resistance on the primary than on the secondary.  Indeed,
it measures that way!  I wired the secondary to the Sound Blaster 
speaker output and the primary to the Mic circuit on K1B/K2A.  Is this
a problem?)

Another problem I've got is an excessive level of audio hum.  I was 
careful to keep microphone ground separate from all other grounds to
prevent this, but it's still a much higher level of hum on my recorded
messages than on the LTA-provided message.  And, interestingly, that
LTA message has much more hum than other .WAV files I have lying 

Comments from anybody else who has been down this same road?  This
software just came in the mail two weeks ago, so it should be pretty
                          AA6KX/Bruce Sawyer

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