Crystal Clear Audio Mod for Sega Mega Drive 2 & Genesis 2, version 1.0

[Segasonicfan]

thanks for the pic, looks very nice!  I didn't even know the MD couldn't do FM in Mark III games heh. 

It would be nice to tackle this 315-5684, have you actually replaced it before or just wrote up the schem?  Finding the input caps in a CDX is such a pain..

-Segasonicfan

[Tiido Priimägi]

Somebody sent me an e-mail though this forum, but I don't think I could have just replied it so I posted the required info here. This applies for VA0 and VA1 MD2s (there's very minor differences between those 2, but in essence all is same). I have VA3 setup too, but i have not yet uploaded it, I'll upload it if its being asked for

[TrekkiesUnite118]

How difficult is this mod to perform? I've been thinking of trying it myself along with a few other idea's I've had but I'm terrified that I'd somehow kill my Genesis in the Process.

[jonatbaylor]

So finally, the mod reached version 1.0 state.

It does all what previous versions did, but at much louder volume and long cables will not have negative effect on high freqs anymore
Output is about as loud as MCD RCA outs, and I'm more than sure its sufficient enough

Only drawback is added complexity, you have many more components now (about 50 or so).

Anyway, if anyone feels like doing one, and runs into issues, be sure to contact me

I guess I have 2 questions. 1, why is this not done on mega drive 1 (why did you choose #2?) and then...why? lol

The Megadrive 1 has stereo output..sounds pretty good to me.

[kendrick]

Read the previous posts in the thread, please. The first model Megadrive/Genesis is widely recognized to have superior sound hardware to most of the subsequent revisions, but for whatever reason the model 2 console is more common.

Asking why someone implements a game machine mod is like asking why someone climbs a mountain. Most of the time, we do it strictly for the sense of achievement. Certainly, the well-tested and well-researched OEM hardware is good enough for most applications, but at GamesX we're hardly representative of the gaming public at large. We like SPDIF, we like channel-separated waveforms, and we like standardized connectors. When asked why, I counter 'why not?'

[Tiido Priimägi]

I did it on MD2 because MD2s have extremely poor sound, but comes out that after the mod, the MD2 that osunds the worst has the best sound from all the MD hardware there is.... ironic, hehe.
I only had MD2 when oding the mod, and I did it just to hear GOOD sound as I was very unhappy with the MD2 sound, I had a MD1 before which died and which sounded muuuuch better.

I've become a bit of an audiophile, MD1 has horrid output, very muffled and not exactly clean... I will look into making a mod for MD1 sometime....

[panzeroceania]

thought Tiido might find this interesting, this guy claims to have an early Mega Drive 2 that had very few models released and is kind of like a Model 1.5 as far as the internals go, or so he claims, I don't know enough about the hardware to varify this, but I thought I would show you guys.

http://retrocopy.com/forumthread/239-2/glitches-and-emulation-errors-in-mega-drive-retrocopy-0720.aspx#post_1520

[TrekkiesUnite118]

thought Tiido might find this interesting, this guy claims to have an early Mega Drive 2 that had very few models released and is kind of like a Model 1.5 as far as the internals go, or so he claims, I don't know enough about the hardware to varify this, but I thought I would show you guys.

http://retrocopy.com/forumthread/239-2/glitches-and-emulation-errors-in-mega-drive-retrocopy-0720.aspx#post_1520

That looks identical to my VA0 Model 2 Genesis.

[Tiido Priimägi]

it is a JP VA0 MD2, and I cannot imagine it sounding anything one would classify as "good"...

[zedrein]

I suppose I am a dumb dumb when it comes to electronics but isn't that huge cluster ball of resistors/capacitors/amps a good antenna for interference? Is this mod effectively one that seeks to drastically improve the signal-to-noise ratio of the MD while cleanly amplifying it?

[Tiido Priimägi]

Sorry for ultr@ late reply,

Yes, that cluster can pick up interference, but so far I've not got anything, especially with shielded cables in use. Most of the interference is in MHz range, and filtered out anyway, so it should not be an issue at all.
Only really sad thing is that FM signals carry great deal of noise from VDP when exiting from the chip.... damn Sega

[duo_r]

Is this mod appropriate for use with the Sega CD? Like will the audio for Genesis still be on the same volume level as Sega CD?

[Tiido Priimägi]

The sound levels are all good, but only problem is that MegaCD RCA outputs will not carry MD sound, but MD side will have all sound at correct levels, and clearer than what MEgaCD RCA's give (there's a small design choice that will muffle the sound a bit on the RCAs).

[aodinets]

Is it possible to use transistors BC847B(BC850B) instead of 2SC945?

[KillingBeans]

This mod is the best thing that has ever happened to my MD2 

I used an OPA2134 instead of the 4558D. It sounds fantastic. At first the low tones was a little fuzzy, but now, after plenty of "break-in", it sounds like angels licking you in the ear.

If I had more money than brains I'd rebuild it with 2x LM394 and 2x OPA627 and feed it with some sort of yummy dual rail supply.
Probably wouldn't be able to hear the difference 

[KillingBeans]

I gave my MD2 a LM2676 for digital and video stuff and used the existing 7085 for all sound things.

This got me curious. So I gave my CCAM a 7805 of it's own, just to see what happended:



It killed the video hum completely! No more annoying buzzing sound when there's alot of white on the screen 

I can't recommend this addition to the mod highly enough!

[micro]

Tiido, the Thunderforce IV tracks sound terrific, great work! 

I've tried to apply the CCAM to my PAL VA0 Mega Drive 2. Unfortunately I don't get a sound out of the MD2 at all except for the "ZAP" sound when switching on the console.
On Sega-16's CCAM Thread I've found this diagram which I based the mod on.


On the MD2 mainboard I used following points to get power and the signals:


Does anyone realize what I might have done wrong? Is it important to connect to MCD- & 32X-L+R when testing the mod?

[KillingBeans]

The pinouts on your board does not match the 2SC945. Are you using a different kind of transistor?

On Sega-16's CCAM Thread I've found this diagram which I based the mod on.

The links/pics in the tread are dead 

[micro]

The links/pics in the tread are dead 

Here you go:

Mirrored for comparing to the bottom side:

The pinouts on your board does not match the 2SC945. Are you using a different kind of transistor?

No, not at all. I used this transistor (datasheet here) and that op amp (datasheet).

I thought the pinouts are ok. +5V to the collectors of all four transistors. PSG and FM(+22k) connected to the bases; emitter goes to the right side to the op amp...

[KillingBeans]

My mistake. Didn't look propper at your board.

(Note to myself: Don't try to be a smartass when you haven't slept in three days)

I guess there's only one way of finding the error. A continuity tester and a lot of patience.

[KillingBeans]

BTW, I've made this schematic. IMO it shows the signal paths and the function of the circuit a little more clearly:

[micro]

IT WORKS!  And it sounds awesome!

Thanks alot, that really helped. It turned out there was a problem with the 470 Ohm resistor that should be between GND and the center point of the two negative input pins. On my board both ends of the 470 Ohm resistor were tied to GND which rendered the resistor pretty useless of course.

The diagramm is kinda misleading concerning that resistor. The resistor is drawn small and is located between two holes. So I thought the resistor's leads should go through these two holes...

[KillingBeans]

Glad i could help 

[AlmostOriginal]

Does any one sell complete component kit or complete board? 

[KillingBeans]

TmEE might have some:

http://www.sega-16.com/forum/showthread.php?7686-Crystal-Clear-Audio-Mod-for-Sega-Mega-Drive-2-amp-Genesis-2-version-1-0&p=536804&viewfull=1#post536804

And there's this guy making SMD versions:

http://www.sega-16.com/forum/showthread.php?7686-Crystal-Clear-Audio-Mod-for-Sega-Mega-Drive-2-amp-Genesis-2-version-1-0&p=547716&viewfull=1#post547716

I'm also gonna make a batch of PCBs myself at some point.

[AlmostOriginal]

Thank you so much 

EDIT: Havent read all messages but Tiido Priimägi how the f*ck did you figure this out?

[Segasonicfan]

Im excited to see all the work still happening on this!   The new SMD boards are out, and they are sexy (see the Sega-16 thread linked above).  Im determined to get my CDX modded with this.  After fixing the video in that system for clean output I feel like this is the last thing needed to make it the perfect mini sega console 

-Segasonicfan

[Segasonicfan]

There should be 2x DACs there, LC7883 that is for CDDA(at least in MegaCD2, seems CDX uses something else) and LC78835 that is for PCM chip.

You can just put my circuit on top of the 315-5684, the volume levels of all signals are right so no adjustments need to be made, just desolder the chip, get rid of some extra components and those series and parallel capacitors everywhere on the audio lines and you're done.

At long last, I've traced everything inside the CDX to do this mod.  See the pics here:
http://s18.photobucket.com/albums/b134/Segasonicfan/?action=view&current=CDXCCAM3.jpg
http://s18.photobucket.com/albums/b134/Segasonicfan/?action=view&current=CDXCCAM2.jpg
http://s18.photobucket.com/albums/b134/Segasonicfan/?action=view&current=CDXCCAM1.jpg

It looks as though the 315-5684 doesnt mix the MCD L and MCD R (Sega CD audio).  The LC78835 outputs to an opamp on the subboard which mixes the audio into the 315-5684s audio outputs.  I havent desoldered the chip yet to double check, but the pins do not appear to be connected from what I can tell.  So my question is, can I just remove MCD L and MCD R from the circuit?  I think it should work fine that way.

FYI, I upgraded my opamp so yours will look different.  And Ive attached Tiidos very useful schematic which made all this tracing out possible.

-Segasonicfan

[Segasonicfan]

Alas, its been done!  I bought Retrogamer343s neat little SMD board of Tiidos audio mod and installed it in my CDX.  Works like a charm and sounds superb

I desoldered the 315-5684 and provided a pic below to show the traces underneath.  I was right about the MCD audio lines not being mixed in there.  Oddly though, pins 4 and 5 are not used as well, which has me scratching my head since those are supposed to be audio out pins. 

The last thing I have left is to mix the audio into the audio out jacks on the CD motherboard.  I thought it would do this after I connected it to the audio out on the AV port but I was wrong.  Really not sure how it does this natively since the only output pins on the 315-5684 for audio are run through some caps and resistors and into the...315-5619(?!) which is supposed to be a Z80.  Very strange.  Also, the pins connected the two boards have audio lines ties to the AV port, but somehow this isn't giving me audio on those jacks. 
Ah, worst case I can just solder to the jacks themselves!

-Segasonicfan

[Segasonicfan]

315-5684 Schematic now online!  Thanks to omp at Sega-16 forums there are schematics galore for Mega Drive, Mega CD, 32x, etc

http://www.sega-16.com/forum/showthread.php?23228-Sega-Service-manuals-16bit

[Segasonicfan]

Dont know if anyone is still reading this thread and following what I'm posting, but I'm excited about getting a CCAM into the CDX and hopefully someone out there is willing to help

Genesis mixing is done and works perfect.  Mixing into the CD has been a lot trickier though, since it is not clearly seperated like MD/Sega CD combos.  Apparently (after a looot of tracing and such) I've found the 315-5619 is a DAC for the PCM chip (315-5476A which is a RF5C164A).  It looks like this is the equivalent of the LC78815 in Mega CD2.  Figuring out the outputs to that is going to be a real pain, as will be mixing them properly.  I have a mix that works right now, although the quality is a little lower since the CCAM output is having to be fed into this mixing stage.  I am pretty sure Sega went this route to integrate a lot of the opamps used on the output stage of the DAC.  If anyone has any ideas on what this might be a "mock' rebranded chip of that would help though.

-Segasonicfan

[Fix_Metal]

It's been a while since I wanted to do this.
I made a layout using Eagle 6.1.0. I'm including pdf files for printing layout and infos for those who don't have the above.
CCAM Project
Best 

[RGB32E]

Seems like the best mod is to just buy a VA3 or 4 console.  My CXA1645M equipped stock VA3 sounds better than a CCAM modded VA2!

[Segasonicfan]

Finally figured out everything to adding a CCAM mod to the Sega CDX (for those crazy enough to try).  Details all here:
http://www.sega-16.com/forum/showthread.php?29425-Live-presentation-on-Sega-CDX-Hacking-%28Youtube%29&p=706463&posted=1#post706463

Thanks for your help Tiido!

[NFG]

Thanks for the update, segasonicfan!

But that page has an attached JPG which can't be viewed by anyone without an account there.  =(

[Segasonicfan]

Thanks for the update, segasonicfan!

But that page has an attached JPG which can't be viewed by anyone without an account there.  =(

Good point!  Here ya go:
http://s18.photobucket.com/user/Segasonicfan/media/Sega%20CDX/CCAMforSegaCDMixing_zps14fdea06.jpg.html
http://s18.photobucket.com/user/Segasonicfan/media/Sega%20CDX/CDXCCAM1_zps1a63fc52.jpg.html
http://s18.photobucket.com/user/Segasonicfan/media/Sega%20CDX/CDXCCAM2_zpsd628807b.jpg.html

this one is just explaining stuff: http://s18.photobucket.com/user/Segasonicfan/media/CDXCCAM3_zps6d952a10.jpg.html

Too bad attachments on this site are limited to 512kb   otherwise Id upload em here

[NFG]

Aha!  Well, I fixed that - the new limit is much larger.  Will 2MB be enough?  =)