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#1 2012-02-23 01:27:41

Coralio
GI-Joe
Registered: 2012-02-20
Posts: 17

SID audio in - usage and protection

Hello,

It seems that few people are using the audio in function of the SID, as mostly it just comes up in context of grounding it for noise reduction, and occasionally the feedback mod.

I may be thinking nonsense, but letting signal through the unique SID filter may provide fun and cool-sounding effects... I'm a newbie to SID programming, but if it's anything like a "big" synth, then I should be able to regulate the filter with the LFO and voila, programmable trancegate and more! big_smile

So mostly I'm interested in whether anyone uses the audio in for something regularly in his musicmaking, and also how to protect the damn thing. smile

Ground loop isolation is by default, but I read that it should be 0.7V peak to peak! That sounds like a really low threshold. If I'm not mistaken, even the SIDs own audio out is 2V peak to peak! I'm afraid if I plugged my digi piano or my Mac audio out in, it would fry the SID in no time, let alone some brutish mixer. big_smile Is there a way to protect it from voltage peaks, or should I just turn the volume really down when connecting to the SID?

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#2 2012-03-06 11:06:33

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: SID audio in - usage and protection

I sucesfully tested the audio in connected to an MP3 player via a ground loop. If you want to limit the voltage input you could apply a zener limter (2 opposing zener diodes) to the secondary side of the ground loop (the side connected to the C64). Some reference:
http://hyperphysics.phy-astr.gsu.edu/hb … miter.html

Just choose the right zener voltage. Also a series resistor could help in dissipating the resulting excess current caused by the overvoltage. Not sure about this, thou, the resistance of the ground loop might be enough for this. Some fine tuning and tesitng with an oscilloscope would help.

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