Genesis 1 & Mega Drive 1 stereo mod no headphones volume control

[Ace]

Looking good. I think you've hit the spot for the Genesis Model 1.

[CkRtech]

Awesome. Thank you so much for your help, Ace. Feeling good. Now let's make a 16-bit ISA sound card from scratch... <ahem>.

All of the work for this circuit revision was done using a Sega Genesis Model 1 - VA 6.5 (IC BDM5 USA). Board date stamped Oct 18, 1992.

Helder - I am not sure if you are monitoring, but perhaps we could have a PCB revision for this should anyone need it? I can throw together the schematic in Eagle if you want, but it might be easier to copy/mod your existing file.

[Helder]

Awesome. Thank you so much for your help, Ace. Feeling good. Now let's make a 16-bit ISA sound card from scratch... <ahem>.

All of the work for this circuit revision was done using a Sega Genesis Model 1 - VA 6.5 (IC BDM5 USA). Board date stamped Oct 18, 1992.

Helder - I am not sure if you are monitoring, but perhaps we could have a PCB revision for this should anyone need it? I can throw together the schematic in Eagle if you want, but it might be easier to copy/mod your existing file.

Sure I can do a revision if you can give me a schematic to work off of.

[CkRtech]

Added schematic. Includes filter cap for VREF. Does not include possible filtering for VCC - I didn't try it with the extra caps on VCC, but it couldn't hurt.

I tried to keep the layout similar to the one you posted a few pages back. Let me know if you see any issues with it.

[Helder]

You're not using the TL072 anymore correct? I though you were using the TDA1308 opamp or was I mistaken? The VCC cap you're referring to is that 10uf cap?

[CkRtech]

Still using TL072, actually. Correct regarding 10uf cap.

[Ace]

A quick note, be sure to use 10Kohm resistors on both VCC and Ground if you're going for the TDA1308. This chip works best at half VCC for VRef unlike the TL072.

[Helder]

Still using TL072, actually. Correct regarding 10uf cap.

Here ya go:
https://oshpark.com/shared_projects/G5Ody7Ol

[CkRtech]

Awesome, Helder. This will make it easier should I want to do additional units. Humbly, I would like to submit that the circuit design is actually Ace's as every component in the circuit save the TL072P has changed.

Thanks again for everyone's help.

[Firebrandx]

Sorry to bump this old thread, but is this amp circuit finalized, and would it be kosher to use in my model 1 VA3? I've got rear RCA jacks that are tapped into the non-amped sound terminals from the chip, and I'm looking for something like this to properly amp the sound without resorting to tapping into the headphone output.

[CrossBow]

Sorry to bump this old thread, but is this amp circuit finalized, and would it be kosher to use in my model 1 VA3? I've got rear RCA jacks that are tapped into the non-amped sound terminals from the chip, and I'm looking for something like this to properly amp the sound without resorting to tapping into the headphone output.

Surprised you still need an amp on the va3. I've got both a va2 and va3 modded with their outputs off the RCAs straight from the 1034 as well. And they are literally at least 10db louder than a va6 and above are with this method. I've modded about 5 different console versions like this and the va2 and va3 are quite loud enough. At least as loud as my other consoles in my receiver rack volume setting wise.

[Firebrandx]

Surprised you still need an amp on the va3. I've got both a va2 and va3 modded with their outputs off the RCAs straight from the 1034 as well. And they are literally at least 10db louder than a va6 and above are with this method. I've modded about 5 different console versions like this and the va2 and va3 are quite loud enough. At least as loud as my other consoles in my receiver rack volume setting wise.

Well that is strange because my sound output is not anywhere near as loud as the headphone out at full volume. I recall Ace even mentioned my direct taps were going to be quiet because of this, and that I needed to add an amp circuit.

For reference, here's where I tapped in:

Genesis-Mods-RCAStereo-03.jpg

[Ace]

Surprised you still need an amp on the va3. I've got both a va2 and va3 modded with their outputs off the RCAs straight from the 1034 as well. And they are literally at least 10db louder than a va6 and above are with this method. I've modded about 5 different console versions like this and the va2 and va3 are quite loud enough. At least as loud as my other consoles in my receiver rack volume setting wise.

You're likely grabbing audio from the CXA1034's headphone output rather than directly from the preamp at pins 1 and 8 unlike what Firebrandx is doing. The only time the audio from the preamp is at a good volume is on the VA0, VA1 and VA2 boards with their overblown gain that causes major distortion in games with lots of bass and high overall volume. The reduced gain on the VA3 to VA6.8 boards means an extra amplifier stage is required to get line-level stereo audio that is unaffected by the volume slider (this would also apply to a gain-fixed VA0 to VA2 board).

@Firebrandx: You can use CkRtech's circuit on post 124, but with the following changes:

-All VRef resistors to 10Kohms
-Replace the TL072 with a TDA1308 or other equivalent audio-grade op-amp.
-Add some 100ohm series resistors to the outputs (to prevent directly shorting the op-amps to Ground)

[Firebrandx]

@Firebrandx: You can use CkRtech's circuit on post 124, but with the following changes:

-All VRef resistors to 10Kohms
-Replace the TL072 with a TDA1308 or other equivalent audio-grade op-amp.
-Add some 100ohm series resistors to the outputs (to prevent directly shorting the op-amps to Ground)

Muchas gracias! I will do up my own board in Eagle and make the adjustments. Cheers!

[Xaranar]

Muchas gracias! I will do up my own board in Eagle and make the adjustments. Cheers!

Would you mind sharing when you do? I have Helder's circuit installed in mine, and if yours sounds better, I'll want to use it