Converting Gravitar PCB to Black Widow - Cap / Resistor Mods

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Converting Gravitar PCB to Black Widow - Cap / Resistor Mods

From the retrofit manual here: http://arcarc.xmission.com/PDF_Arca..._Black_Widow_Retrofit_TM-232_2nd_Printing.pdf

I have heard that converting from Gravitar to Black Widow was just a ROM swap but the instructions from Atari list a couple more steps. Can someone explain the significance of performing these mods?

1. Use the digonal cutters to remove capacitors c28 (0.001 uf) and c34 (0.22 uf). These components are not used in the Black Widow game.

2. Use the soldering iron and needle-nose pliers to remove capacitor c27 (0.001 uf) and resistor r46 (10k ohm). Replace c27 with the 100 pf capacitor and r46 with the 22k ohm resistor from the kit.
 
Those are all modifications to the audio output circuit. Removing C28 and C34 gets rid of the low pass filters at those amplifier stages (so it'll play higher pitch sounds). Bumping C27 down from 0.001uF (1000pF) to 100pF will shift the frequency of that low pass filter up (again, playing higher pitch sounds).

Changing R46 from 10k to 22k will adjust the mixing of the audio output from the two POKEYs. I'm guessing each POKEY is used for different types of sound effects... so making this change will make some of them quieter relative to the others.

So... they're not critical modifications, but if you don't do them, the sounds will probably sound a bit different than a dedicated board (more bass and some sound effects will sound louder than they should).

DogP
 
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