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Thread: Take your Genesis audio to the next level - The Mega Amp 2.0 is here!

  1. #166
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker zeruel85's Avatar
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    Hello,

    I have 9x (maybe 10x) Mega Amp Pro available right now.
    You can buy a DIY kit or a pre-assembled one, I have all the components, not only the PCBs.
    I can also provide installation on your consoles, if you need it.
    Contact me via PM if you are interested in them, thank you.


  2. #167
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker Nordak's Avatar
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    I'm a bit confused regarding the VA7 Model 1 passthrough diagram instructions. Based on the schematics I've seen, and verified by someone more knowledgable than me, audio is carried L/R by A29 and B29 on the passthrough. The diagram is stating to terminate on pins A27 and B27 for the L/R channels on passthrough. I'm trying to do an install for someone else and this is really the only thing I can't wrap my head around. I don't have a Sega CD to verify how this will work. Also, how far up the pins does the CD seat on the expansion and where is the best place to terminate for L/R audio? I'm nervous about tapping the pins directly and having them broken once the Sega CD is seated on the pins. I'm using Helder's board design.

  3. #168
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    You're confusing the Sega CD input to the internal amp (A29/B29) and the output from the preamp to the Sega CD (A27/B27). The transistor circuits from the Pro version are to be connected directly to pins A27 and B27. Solder your wires as high up the edge connector as possible so that you don't thicken the pads too much and either damage the pins on the Sega CD or make the pads too thick to allow the Sega CD to fit properly.

    Also, I completely missed this post by JamesF, so I'll answer it here:

    Quote Originally Posted by JamesF View Post
    Hi.

    I'm trying to understand how the stock system works with Sega-CD.

    If I understand correctly from the stock schematics of Model2 and Sega-CD 2, using the RCA on the back of the Sega-CD will use un-filtered CD audio but everything else is filtered with First-Order lowpass,
    BUT when using the A/V cable CD-audio will be filtered with First-Order and the rest will have Second-Order filtering (two first-orders in series)?

    Consequently, using the Sega-CD RCA jacks will make the Model2 have only First-Order lowpass filtering like the Model1 without actually modding anything, correct?
    Out of the Sega CD Model 2, if you're using as stock Genesis Model 2, you get the 2nd-order low-pass filter on the YM3438 (or YM2612 on the VA2 and VA2.3 boards) along with a 7.234KHz passive 1st-order low-pass filter (that is to say, basic RC filter instead of an active filter where the feedback on an op-amp has a capacitor and resistor in parallel with one another) between the second stage of the preamp that mixes in 2nd-order low-pass filtered FM, PSG and audio from the cartridge slot and the transistor buffers that send out the signal to the expansion slot (the amplifier stage itself has no filtering). On the VA2 to VA4 Genesis Model 2 audio amp, this 1st-order filter is an active filter on the headphone amp section of the 315-5684 and has a lower cutoff frequency of 5.882KHz.

    On the DIN, the filtering is 2nd-order from the YM3438/YM2612 and 1st-order from the final stage of the amp (3.785KHz on VA0 to VA1.8, 3.275KHz on VA2 to VA4). For some reason, Sega saw fit to completely omit a low-pass filter on the second stage of the amp except when the op-amps' outputs are split off. Adding a filter on the feedback instead would have helped reduce the awful hiss and crackling of the circuit, I'm sure (the separate filters for the Sega CD audio passthrough are bypassed out of the DIN).

    Quote Originally Posted by JamesF View Post
    With the Model1, a Mixing cable has to be used and Sega-CD will always be unfiltered because there is no CD-Audio inputs on the expansion port (A27/B27 or SL3/SR3) of the Model1, right?
    This isn't quite right because while the Sega CD Model 1's RCA outputs will have unfiltered CD audio, the internal audio of the Genesis Model 1 has 1st-order low-pass filtered audio that includes the Sega CD audio, so you get a mix of both. The Genesis' internal audio is likely more predominant due to its high volume compared to the Sega CD RCA outs, and I expect it to drown out the unfiltered CD audio from the Sega CD's RCA outs.
    HATES ATGAMES WITH A PASSION


    Mega Amp: An all-new audio circuit for your Sega Genesis/MegaDrive and clones.

    Note: If you want to contact me on Skype, identify yourself or your contact request will be rejected.

  4. #169
    Hedgehog-in-Training Hedgehog-in-TrainingSports Talker Nordak's Avatar
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    Ah, ok. Thanks for the explanation Ace. Just to verify, B27 is top pad, A27 bottom? Thanks again.

  5. #170
    Outrunner 0x15e's Avatar
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    I read through this whole thread but I'm still not sure of something. What do the filter options do?

    I'm asking because the original Mega Amp had an option that would filter like the System C-2 and since I'd like to use it to build a JAMMA Genesis, that's where I want to go with it. Does the 2.0 Pro have an option for that or should I build myself one of the old ones?

  6. #171
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    If you want to have sound like the System C-2 with the Mega Amp 2.0 Pro, you would need to alter the circuit to where the preamp has an approximately 3.3KHz low-pass filter, the final mixing stage with the TDA1308 has an approximately 15KHz low-pass filter, change the output capacitors from 220uF to 1000uF and redirect PSG to the TDA1308. If you want, I can bust out my test circuit and figure out some values for you.
    HATES ATGAMES WITH A PASSION


    Mega Amp: An all-new audio circuit for your Sega Genesis/MegaDrive and clones.

    Note: If you want to contact me on Skype, identify yourself or your contact request will be rejected.

  7. #172
    Outrunner 0x15e's Avatar
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    Quote Originally Posted by Ace View Post
    If you want to have sound like the System C-2 with the Mega Amp 2.0 Pro, you would need to alter the circuit to where the preamp has an approximately 3.3KHz low-pass filter, the final mixing stage with the TDA1308 has an approximately 15KHz low-pass filter, change the output capacitors from 220uF to 1000uF and redirect PSG to the TDA1308. If you want, I can bust out my test circuit and figure out some values for you.
    That would be great! Thank you!

    If it makes things any easier, doing this on a Mini would be fine too. I don't intend to ever hook up a CD or 32X to this one.

  8. #173
    Nameless One BRNexus7's Avatar
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    "This setup is unnecessary, but recommended if you want to add Sega CD audio passthrough on the Genesis Model 1 without using a patch cable."

    But Sega CD audio does passthrough on Model 1 Genesis without the need for a patch cable. Just run a 3.5mm to RCA from the headphone jack and you are fine.

    The only drawback is Sega CD music also gets filtered.

  9. #174
    Road Rasher ironnick23's Avatar
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    Quote Originally Posted by BRNexus7 View Post
    "This setup is unnecessary, but recommended if you want to add Sega CD audio passthrough on the Genesis Model 1 without using a patch cable."

    But Sega CD audio does passthrough on Model 1 Genesis without the need for a patch cable. Just run a 3.5mm to RCA from the headphone jack and you are fine.

    The only drawback is Sega CD music also gets filtered.
    So the Sega CD redbook audio passes through the Model 1 and out the aux, and then back through the SCD out the red and white cables?

  10. #175
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by ironnick23 View Post
    So the Sega CD redbook audio passes through the Model 1 and out the aux, and then back through the SCD out the red and white cables?
    All the Sega CD music will come out the Stereo Headphone Jack on the Genesis. You don't need to use the patch cable or the RCA outputs on the Sega CD unit.

  11. #176
    Road Rasher ironnick23's Avatar
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    Thatís odd, well the intro music on bios 2.0 if the volume slider is set to 0 half the music disappears and you only hear the bass. I occasionally use the aux to output music to my receiver, though tbh I have not tried it with the SCD though I assumed I would be missing the bass part of the bios music. The manual suggests setting the volume at 7 or 8. Studies posted on this forum show distortion when using the volume at full.

    So if I am listening to an audio cd through the aux port on my model 1, itís going through a low pass filter designed specifically for ym2612 fidelity? Wouldnít that mean the cd audio quality suffers?

  12. #177
    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by ironnick23 View Post
    Thatís odd, well the intro music on bios 2.0 if the volume slider is set to 0 half the music disappears and you only hear the bass. I occasionally use the aux to output music to my receiver, though tbh I have not tried it with the SCD though I assumed I would be missing the bass part of the bios music. The manual suggests setting the volume at 7 or 8. Studies posted on this forum show distortion when using the volume at full.

    So if I am listening to an audio cd through the aux port on my model 1, itís going through a low pass filter designed specifically for ym2612 fidelity? Wouldnít that mean the cd audio quality suffers?
    Yes, Sega CD music "suffers" in that when fed through the headphone jack it gets filtered, but that just means it matches the YM2612 audio in terms of filtering. I think the only benefit of using the patch cable and Sega CD RCA outs is if you have a Genesis with unfiltered Mega Amp, or if you just want to use the Sega CD to play CD music, which I don't know why you would when there are better consoles for that.

  13. #178
    Road Rasher ironnick23's Avatar
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    I donít have any cd audio music from my scd coming out of my headphone aux, only from rca. is this something to expect if I where to install a mega amp? Btw I can certainly hear a difference between a lossless digital playback and Cd played through scd. Works great with 90ís hip hop.

    Also, blasting silence from the aux out I can certainly make out a hum or buzz on the line.

    My system is recapped and using 4700pf caps va3 model 1

  14. #179
    Nameless One BRNexus7's Avatar
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    You need to remove the patch cable and rca plugs from the back of the Sega CD. If you have the patch cable hooked up to the Sega CD unit it will redirect the Sega CD audio to the RCA plugs.

  15. #180
    Road Rasher ironnick23's Avatar
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    The filtering used by the amp is designed for the ym2162 to create that signature sound. AFAIK the Sega cd uses the Ricoh RF5C164, and pushing that through the md amp wouldnít sound as intended? For the full setup Iím simply missing a ferrite bead on the mixing cable (not sure that does much). The 32x sound has to run through all three and out the scd. Ironically the video of the scd has to run all three in the opposite direction. In my experience the md needs the most treatment to minimize sound and video flaws.. it would be interesting to have someoneís take on the SCD audio filtering

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