Introducing the Mega Amp - The universal Genesis audio circuit

[BlockABoots]

Yeah, ive just got the top off the MD2 and will turn it on and move the wires about and see it i get any joy

[BlockABoots]

Ok fixed!

The wire soldered to the R Output pad was lose, so reflowed the solder but then noticed that the audio was low and then noticed that the trace next to the R Ouput has lifted from the board so had to reflow solder arcoss the break.....



The solder didnt want to flow very well across the trace, probably need the iron hotter but didnt want to risk damaging the trace more by adding more heat. Not the neatest job ive ever done but works never the less

Ill probably upgrade to one of these MegaAmp soon any ways, look a lot neater install

[villahed94]

So I've bought a Mega Amp PCB from Helder and installed it in my Mega Drive 2 (VA0 board). Right from the start, I had a very similar issue like ComradeOj -- there was pretty much no sound from the right channel, whilst the left channel was much too loud, and distorted. I tried reflowing all OP-amp pins, which didn't change anything. While waiting for the replacement Helder kindly offered, I played around some more with the board, giving all parts a reflow multiple times. By now it only produces sound (on both channels) that is barely audible at all.

The replacement finally arrived, and I replaced the old install with it (including most wires). It sounded ... well ... strange. Fed up with everything, I completely uninstalled the Mega Amp, undoing all related changes (i.e., putting back in all resistors and capacitors) in order to check if the ASIC within my MD2 was still working properly. Fortunately, it was, and still is.

Next, I re-installed the replacement board to record an audio clip that I could put up here.

Voilà: Sonic 1 with replacement Mega Amp

As you can hear, the music is totally messed up. Just listen to that Marble Zone theme (starting around 01:10) ...

Here are pictures of my latest install (the wiring is all correct):

1 (2,2 MB)
2 (2,37 MB)

So ... anybody know what's going on here?

Thanks!

Check as with ComradeOJ's board the voltages on the voltage divider. Also check if resistors are not shorting.

[AlmostOriginal]

How about the missing 2,2Kohm resistors?

[villahed94]

How about the missing 2,2Kohm resistors?

They are not needed as this board is a VA0 Model 2. It's got an ASIC YM3438. The 2.2K pulldown resistors are only needed if there is a discrete YM2612 on the system and they're not present on the board.

[Helder]

Odd thing is I sent a known tested and working board, wondering if some component shit the bed so easily or maybe ESD when installing it. Ramsis look back about 3 pages and do the same tests as ComradeOJ especially the one on the op-amp voltage like Villahed suggested and post back.

[AlmostOriginal]

They are not needed as this board is a VA0 Model 2. It's got an ASIC YM3438. The 2.2K pulldown resistors are only needed if there is a discrete YM2612 on the system and they're not present on the board.

Ahh! My bad!

[Ramsis]

For some reason, it sounds like PSG is either shorted with the YM3438 left input or the mixing is off. Do you have a multimeter on hand? Measure the two 100Kohm resistors for PSG mixing and the 51Kohm resistor on the YM-Left input (the silkscreen says 39Kohms, but ASIC YM3438s need 51Kohms).

Thanks, Ace, for a hint that resolved my issue. Turned out the lower one of the two 100KOhm resistors was shorted. Once I'd desoldered that resistor, I could even see a tiny string of solder going alongside its lower surface. I gave it a reflow, and now everything seems to be fine.

I'm not at my own place right now, but as it's too good to last, I'll test the install thoroughly with my 32X and Sega CD once I'm home (sometime during the weekend).

Thanks again!

Ramsis

[Helder]

Glad you got it all sorted out thanks to Ace. I have something that might interest people I've been working on, it's the next revision of the Mega AMP and they aren't for sale yet as I'm still testing and refining little details but here is a sample of what it looks like:

Original 1.1 currently being sold:



The New 1.2 with smaller size and smaller components and a pair of slide switches to switch between filtered and unfiltered with ease and on the fly:



The 2 boards side by side:



Now if some one wants the other 2 I have from the 3 boards I received I will sell these at the same price as the current version but first come first serve, you can buy them in the thread I have in the Bazaar. Be sure to state you want the 1.2 along with the motherboard version you have.

[ComradeOj]

^ A built in filtered/unfiltered switch is a cool addition!

Are you going to make one with headphone buffers eventually? That way you could put one in a model1, CDX, nomad and be able to use headphones still.

[Helder]

That is the part I'm thinking of tweaking, but I might just make a small batch with the headphone amp with the same design since I don't sell to people all that often with the VA7 Model 1. It will be extra parts and work on my end to incorporate it all into one board that hardly uses those extra parts. I will mess with the design a bit to see what I can come up with, oh the slide switch works on the fly so you can hear the difference instantly.


Edit:

Villahed94 or Ace do either of you have Super Street Fighter II ? if you do could you do some audio clips from stock audio of an MD2 with a YM3438 and the Mega AMP? One of the forum members would like to see if the Mega AMP can fix some of the shit audio in the game.

[Ace]

I have the game and a good number of unmodified Genesis Model 2s with shit amps. I can get those for you later in the week. Are we talking ASIC or GOAC YM3438 here?

[villahed94]

That is the part I'm thinking of tweaking, but I might just make a small batch with the headphone amp with the same design since I don't sell to people all that often with the VA7 Model 1. It will be extra parts and work on my end to incorporate it all into one board that hardly uses those extra parts. I will mess with the design a bit to see what I can come up with, oh the slide switch works on the fly so you can hear the difference instantly.
Edit:

Villahed94 or Ace do either of you have Super Street Fighter II ? if you do could you do some audio clips from stock audio of an MD2 with a YM3438 and the Mega AMP? One of the forum members would like to see if the Mega AMP can fix some of the shit audio in the game.

I have the game, I could test with even a YM2612 if need be. Both with MegaAmp of course, but the clips might take a while (I'm a bit busy).

[Helder]

No rush guys, it would be the standard non GOAC but if you're feeling generous and have some free time why not do the GOAC as well but like I said the ASIC is fine. Thanks guys.

[villahed94]

^ A built in filtered/unfiltered switch is a cool addition!

Are you going to make one with headphone buffers eventually? That way you could put one in a model1, CDX, nomad and be able to use headphones still.

Did you manage to get that MegaAmp working?