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Akira
Registered: Oct 2003
Posts: 52 |
8580 digifix woes
I just tried to apply the 8580 digifix but I am running nto trouble.
Basically it works, boosting the digis, but everything else goes quiet.
I must be doing something wrong. I basically just connected a resistor to the EXT-IN pin (which I lifted) onto the GND pin of the SID. I noticed that if I remove the resistor then I can't hear anything. Maybe it is the wrong resistor, but why grounding the pin yields no audio?
Am I supposed to lift the GND pin too?
I wanted to put this on a switch so I can have noise reduction or digifix selectable, as I know the digifix will break a bunch of 8580 tunes.
My SID is a 8580 R5 and the motherboard is a REV.B ASSY 250469
There's no problem with the machine since after I got scared I blew a SID, I reverted the whole process (I had applied the mods through an intermediary socket, as suggested by Lemming) and it's running fine. I noticed Lemming mentions PIN22 on his article on VN#58 but every schematic online denotes pin 26 as EXT-IN and I used that (pin 22 is D7 or something) |
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algorithm
Registered: May 2002
Posts: 707 |
This may be offtopic but software based digifix can be done if digi is purely just $d418 digi without sid music playing for the older demos.
Most of the newer stuff is via the waveform 8 bit method which works well for all sid revisions without modification
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
~750 kOhm and +5V und nicht an GND.
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Akira
Registered: Oct 2003
Posts: 52 |
Sorry man, I am afraid to blow up the SID if I connect the EXT IN pin to 5V, resistor notwithstanding. Also contradicts most info online. Would appreciate a bigger background to that. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Pulling EXTIN to GND is supposed to remove some noise from the audio output.
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Akira
Registered: Oct 2003
Posts: 52 |
I know it does that, but driving 5 volts to the ext-in sounds like a sure-fire way to blow up the SID, regardless of resistors in between.
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Have to look up some old schematics again, maybe they used a voltage divider to drive x volts into EXTIN.
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
470Ohm (or anything about that) to GND works :) voltage divider would be cleaner though, indeed :) |
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Akira
Registered: Oct 2003
Posts: 52 |
But a lot of people say 300 kilo Ohm. The difference is really big. I don't get it why there's so much different information around.
I tried a 1k resistor and all I heard was digi. |
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lemming
Registered: Oct 2009
Posts: 44 |
Whoopsies, there seems to be a typo in VN#58 then, sorry about that :) the EXT-IN pin is definitely 26 and not 22 (third from the top right).
There are many ways to do this, a 330Kohm resistor between EXT-IN and GND is one way and 750Kohm between EXT-IN and +5VDC is another.
Using a switch is a good idea, because the "digifix" does mess up with the richness of the sound output, so you wanna turn it off when you don't need it.
Same pinout applies for 8580, only pin28 is 9VDC.
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
Quote:There are many ways to do this, a 330Kohm resistor between EXT-IN and GND is one way and 750Kohm between EXT-IN and +5VDC is another.
and the numbers you mention show again that *actually* its quite irrelevant what resistor you use, and were it is connected =) what matters is that you somehow inject leak voltage. other than that you can pretty much use any resistor, as long as you DO use one (dont connect ext-in to VDC directly) |
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