Potentiometer Genesis Overclocking and ramifications.

For hardware talk only (please avoid ROM dumper stuff)
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Count SymphoniC
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Potentiometer Genesis Overclocking and ramifications.

Post by Count SymphoniC » Tue Oct 28, 2014 2:51 am

Someone has offered to do some modding on a Sega Genesis model 2 and donate it to me for the tracker project. On the table amongst other nifty mods are a potentiometer to overclock the Genesis. But this has raised concerns.

What would the ramifications of this kind of a mod be on the sound chips' clocks? It's wondered if this will alter the pitches/frequencies of the notes and the timing system for tracker playback. I also don't understand the precision of a potentiometer as far as how it affects clock speed... I need answers and hardware itself is not my area of expertise here. Thanks in advance guys.

EDIT: I have some more information from this person via email. I'm not very well versed in this stuff so forgive my ignorance on the topic.
"Honestly, I had just planned to add in a 10K pot, desolder the crystal,
throw it on the pot, and then add in the mod.

This way, a mid-range setting would be the default, and you'd be able to
push it higher or lower if need be.

It would in no way be a permanent/fixed oc."

Mask of Destiny
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Post by Mask of Destiny » Tue Oct 28, 2014 6:03 am

I'm not sure what use a potentiometer is for overclocking something. A potentiometer is basically a resistor that varies based on how much you turn it. I mean I suppose you could have something that measures the resistance of the pot and uses that to determine what clock divider you want to use or something of that nature, but the description you quoted doesn't really make a lot of sense.

Also, you really don't want to mess around with the master clock as that will overclock everything and screw up the display signal timing. You just want to overclock the 68K.

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Jorge Nuno
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Post by Jorge Nuno » Tue Oct 28, 2014 5:07 pm

I have seen a variable oscillator IC taking a variable resistor as a means to control the output frequency, so it could be that. However, I doubt it has the accuracy/stability given by a crystal oscillator (no way)

mikejmoffitt
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Re: Potentiometer Genesis Overclocking and ramifications.

Post by mikejmoffitt » Tue Sep 29, 2015 6:46 pm

I clocked my YM2612 with a function generator. It did exactly what you expected - controlling output frequency. I suspect the envelope generator will be scaled accordingly as well.

https://www.youtube.com/watch?v=ve5YBiFyLX4

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