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GameSX.com => Audio Mods => Topic started by: panzeroceania on July 18, 2011, 06:06:28 AM

Title: Sega Genesis Model 1 with VA3 Motherboard - Trying to get rid of Audio Hum
Post by: panzeroceania on July 18, 2011, 06:06:28 AM
I recently got one of the earliest Sega Genesis Model 1s. The one with the 46E in the FCC ID Number, EXT Port, HD Graphics logo, VA3 Motherboard, etc.

This particular system (not every one, just this one) seems to have some issue with it's audio circuitry as there is a loud hum both through the headphone jack at any volume and through the Multi AV out.

I would like to find the source of this hum, clean it out, and if possible send out an unamplified stereo signal to my reciever and bypass as much as the Genesis circuitry as possible.

I know that the nature of the circuitry is that you can't tap digital audio as it is all done inside an IC. I have heard you could swap a better Yamaha IC out but that it wouldn't work. I was wondering if it would at least work with some games, or partially work, or if it would be completely 100% incompatible.

I am getting another of the old Model 1s in the mail soon, so I'd like to try the yamaha IC swap on one (if I can find the newer IC that is slightly compatible, I don't know where I'd get it)

and in the other Model 1 a more conventional analog audio mod.

I understand that these older Model 1s have 2 discreet ICs instead of the one integrated one used in all other Genesis models including most other Model 1s.

Does having these 2 discreet chips allow for a more sophisticated audio mod than usual?

I know the Crystal Clear Audio Mod is only for Model 2s, but I wondered if maybe it didn't work with most Model 1s as they have the integrated audio IC rather than the 2 discreet ones.

In short,

What would be the best method to isolate the source of the hum and remove it? What components am I going to need to buy to accomplish that?
Title: Re: Sega Genesis Model 1 with VA3 Motherboard - Trying to get rid of Audio Hum
Post by: l_oliveira on July 19, 2011, 02:43:57 AM
Things to notice:

It's DC 9v, not AC 9v. NES power adapters are NOT compatible. (powering it up with an NES adapter would cause no damage to the console as it contains an half wave rectifier (two rectifier diodes in parallel) to protect the two 7805 from voltage invertion. But due to lack of enough filtering capacitance you will get a pulsing variation on the voltage output which matches that of the mains voltage (would be 50hz in your case if you're really in Australia ...)

If you're using the proper DC power supply then the problem might be the usual dry electrolytic capacitors... You know the drill.

Gotta replace 'em all !
Title: Re: Sega Genesis Model 1 with VA3 Motherboard - Trying to get rid of Audio Hum
Post by: panzeroceania on July 19, 2011, 11:57:52 AM
well I don't get any buzz like that using the same power supply with another Genesis Model 1.

Replace the capacitors eh? fun fun. Thanks for the info.