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

[Ace]

Anyone know if TL072 dual op-amps would be adequate for this mod? Here's the datasheet(also shows the TL071 and TL074): http://www.ti.com/lit/ds/symlink/tl071.pdf

EDIT: Just out of curiosity, I tried the older Audio Mod with no op-amp on a RetroN3 Version 2 and it looks promising. The only problem I've noticed is some distortion on low-frequency sounds(and, of course, the sound is very weak). Is this because the FM signal is too loud? Would I need to change the resistor value at the FM inputs to eliminate the distortion or would something else need to be changed?

[80sFREAK]

AFAIR TL07x is low-noise OP Amp's with J-FET. It's just OP Amp, but keep in mind they are static sensitive. If you feeding OP Amp with +5V, better to use low voltage IC's

[Ace]

These things are meant to run at 18V?! What would happen if you feed 5V to this kind of op-amp? I've seen them on a SoundBlaster 16 WavEffects sound card and I'm quite certain they're not being run on 18V on that thing.

[MEGADRIVE Jeroi]

I added now layout images directly to my layout post for reducing my ftp usage and the image folder was missing from my public ftp folder for a couble months.

Anyone know if TL072 dual op-amps would be adequate for this mod? Here's the datasheet(also shows the TL071 and TL074): http://www.ti.com/lit/ds/symlink/tl071.pdf

At from stats it seems it accepts 5v-18v and has 3mhz bandwith so it should work ok. TMEE could double check the datafile to be certain.

[Ace]

I added now layout images directly to my layout post for reducing my ftp usage and the image folder was missing from my public ftp folder for a couble months.

You think you could indicate the resistor values used in the layout? I can't follow your layout and TmEE's schematic to determine which resistor is which.

At from stats it seems it accepts 5v-18v and has 3mhz bandwith so it should work ok. TMEE could double check the datafile to be certain.

It seems to me like it would accept several different voltages. I'm gonna take a closer look at the datasheet myself to know for sure.

EDIT: Judging by some of the charts in the datasheet, it looks like the chip could take +5V for VCC. Guess it would work at 5V.

Now, Jeroi, would you have any idea what could cause distorted FM Synthesis on the older Audio Mod without the op-amp(might get the same distortion with the new circuit as well)? Are the input resistors too weak or something? I'd like to get TmEE's Audio Mod working on the RetroN3 as the on-board audio circuit(it's not even a proper amp) distorts low frequencies quite a bit at times, though it seems the FM Synthesis out of the TCT-6801 GOAC is stronger than that of the 315-5660 and equivalent Sega ASICs, so something would need to be changed to eliminate the distortion caused by a 100% unmodified Audio Mod.

[80sFREAK]

distortion=overload

[Ace]

So I guess I'd need to weaken the signal as in enters the circuit? Put a stronger resistor at the FM inputs or something along those lines?

[MEGADRIVE Jeroi]

Is tmee even supporting the old version anymore? Why to build one?

[TmEE]

I do not support older versions.

Regarding distortion, when FM is not too loud its not volume issue but rather opamp being not up to the task. You could try 100Kohm resistors instead fo 22Kohm on FM inputs, like you have to do on Genny3 to make CCAM 1.0 compatible with it.

[Ace]

Is tmee even supporting the old version anymore? Why to build one?

It's a leftover circuit I tried on a VA7 Genesis Model 1, and since I don't have the necessary components to build the new Audio Mod(yet), I just fitted the older Audio Mod on the RetroN3 Version 2 to see if the circuit would work right or not. I only tried the FM Synthesis as my wiring was too short to safely solder the PSG input, so I don't know if the PSG will be inaudible like it was on the Gen-X when I tried the older Audio Mod a while back. Which begs the question(this is for TmEE): if the PSG on the RetroN3 is inaudible through the new Audio Mod, what component would need to be changed?

Regarding distortion, when FM is not too loud its not volume issue but rather opamp being not up to the task. You could try 100Kohm resistors instead fo 22Kohm on FM inputs, like you have to do on Genny3 to make CCAM 1.0 compatible with it.

Considering I used the older Audio Mod without an op-amp, the distortion is most definitely caused by the FM signal being too strong out of the RetroN3's GOAC for the Audio Mod to handle. Now, before I go out and buy the components I need to build the new Audio Mod, could you tell me if the TL072 dual op-amp will do the job? Or would it be best for me to get a 4558?

[MEGADRIVE Jeroi]

Now, before I go out and buy the components I need to build the new Audio Mod, could you tell me if the TL072 dual op-amp will do the job? Or would it be best for me to get a 4558?

Look my layout post, it has suitable op-amp for this mod using 5v and from ebay rather cheap. Or use the 4558 like I did. Even tho officially it dont support 5v input but it still works. Try looking similarities in 4558 datasheet and your op-amp datasheet. I think the op-amp needs to have 3mhz bandwith and 5v input, also gain is to look how much volume is gained for output.

[TmEE]

TL027 is not going to cut it, its an old single section opamp. You would need a pair of them and all the support circuitry they need.
Distortion on the old version can be caused by overloading the outputs, as they are high impedance craps...

[Ace]

TL027 is not going to cut it, its an old single section opamp. You would need a pair of them and all the support circuitry they need.
Distortion on the old version can be caused by overloading the outputs, as they are high impedance craps...

TL027? Where the hell did you get that from? I asked about the TL072, which is a dual op-amp, NOT the TL027. Did you not see this datasheet I linked showing the TL071(single op-amp), TL072(dual op-amp) and TL074(quad op-amp): http://www.ti.com/lit/ds/symlink/tl071.pdf

Their bandwidth should be pretty good as I've seen the TL074 used to amplify the sound from a Yamaha YMF262 on some OPTi sound cards, and the sound that comes out of those cards is nice and clean. Other op-amps cause the low frequencies to become rough(LF347 - I know this chip has 3MHz bandwidth) and some cause the sound to come out as pure distortion(LM324, and I know these only have 1MHz bandwidth).

Either way, I think I'll just go with the 4558. I can't get the OPA2134 locally, so my only two options are the TL072 and the 4558.

EDIT: What should I look at in an op-amp's datasheet to know its bandwidth? Do I look at the Gain Bandwidth Product(GBP)? If I look at that, another datasheet I found for the TL072 suggests the minimum GBP is 2.5MHz while the typical GBP is 4MHz. Here's the datasheet in question: http://www.alldatasheet.com/datashee...ICS/TL072.html

[Ace]

Okay, I've tried the prototype Audio Mod again on the RetroN3, this time with 100Kohm resistors at the FM inputs and... the sound is perfect. Very clean, very crisp, no distortion. BUT, there's no PSG. I don't know if on v1.0 of the Audio Mod, the PSG will be too quiet, but if there's no PSG coming out of the system, what would I need to do to the circuit to make the PSG audible?

[Guntz]

Perhaps a transistor? Or an op amp? Have you tried them already?