>> The monitor noise sounds strange... but disconnecting
>> the EXT IN leg from the SID should silence the background
>> buzz significantly. Or you might want to put a switch there
>> if you plan to sometimes actually use the input pin for
>> something :-)
>>
>
> Well this sounds even more interesting! How do I use the external
> in?? Is it tricky? Can I use the EXT IN in cybertracker?

Well, I haven't tried it myself, but the EXT IN pin (pin 26)
is connected to the audio in pin (pin 5) of the A/V connector.
You can mix external audio to the SID output and, most
importantly, run it through the filters. It's also possible
to daisy-chain multiple SIDs like this.

The Commodore 64 Programmer's Reference Guide will probably
tell you more. This place seems to have most of it, but it's
missing the appendices:

http://www.devili.iki.fi/Computers/Commodore/C64/Programmers_Reference/page_iii.\
html

I found the relevant appendice here: (search for EXT IN)
http://stud1.tuwien.ac.at/~e9426444/sidtech3.html

Stakker
stakker@...