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Thread: Introducing the Mega Amp - The universal Genesis audio circuit

  1. #1
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    Sonic Introducing the Mega Amp - The universal Genesis audio circuit

    Time for something big... something REALLY big. This is...



    THE MEGA AMP

    What is it?
    So what exactly is the Mega Amp? It is a universal audio amp designed to work in every Genesis ever made with minimal alterations. Put this in any Genesis and you will experience either the sound of a VA0 MegaDrive Model 1 or the full spectrum of the Genesis' sound hardware.

    How did this come to be?
    If you remember back in 2012, I posted a replacement audio circuit made specifically for the VA2 and VA2.3 Genesis Model 2s, of which only one console exists with this circuit and it's Mexico (no, it's not a Mexican Sega-16 member who has it). I then started working on a universal audio amp for use on GOACs, but now, it has become something bigger. After having been approached by Villahed94 to make something bigger than any of my previous two circuits and with his assistance, the Mega Amp was born. Working off those old circuits, which have become early Mega Amp prototypes, we now have the most complete replacement audio circuit for the Genesis.
    Three different circuit types are available, which are named "Filtered", "Unfiltered" and "System C-2." Same circuit, different low-pass filter, except for the System C-2 version which has dual filters and extra circuitry added on as a result. The filtered circuit uses a 3.68KHz low-pass filter to give that sound the Genesis Model 1 is known for while the unfiltered circuit uses a 21.16KHz cutoff frequency to get the full spectrum of the Genesis' audio hardware. The System C-2 version's dual filters include a 3.39KHz low-pass filter on the FM side of things and a 15.92KHz filter for everything else to bring the sound of the Sega System C-2 arcade board to the Genesis.
    Currently, the Filtered and Unfiltered Mega Amps are available for all YM2612 and YM3438 variants, but the System C-2 Mega Amp is only available for the ASIC YM3438 and discrete YM3438.
    The schematics of each circuit are below. Click on the thumbnails to view the schematics at full size.

    YM2612:



    ASIC YM3438 (also works on the discrete YM3438):



    ASIC YM3438 - System C-2 version (also works on the discrete YM3438):



    GOAC YM3438 (for Sega GOACs and GOAC-based Geniclones):



    GOAC YM3438 (for x-in-1 clones with GOACs):



    If you would like to build a Mega Amp but donít have access to a TL074, any quad op-amp (plus an extra dual op-amp for the System C-2 version of the ASIC YM3438 Mega Amp) or two dual op-amps (three for the System C-2 version of the ASIC YM3438 Mega Amp) with at least 3MHz bandwidth will work. The only exception to this is the LF347 which, while having 4MHz bandwidth, outputs horribly mangled audio when used with a 32X. As such, it is HIGHLY suggested to not use this chip. The recommended setup is a single TL074 or two TL072s.

    So, here's a general summary of the Mega Amp:
    -Simple design based around a single TL074 quad op-amp
    -Filtered circuits deliver the same sound as a VA0 to VA2 Genesis Model 1 minus distortion
    -Unfiltered circuits deliver the full spectrum of the Genesis' audio output
    -Audio levels louder than any previous mod, on-par with later Genesis Model 2s
    -Headphone support with the optional transistor buffers
    -Stereo and Mono audio outs for a complete replacement circuit

    Now for installation diagrams on consoles most in need of a new audio amp. Click on the thumbnails to view the shots at full size:

    VA7 Genesis Model 1 (use ASIC YM3438 Mega Amp with headphone buffer):





    VA0 to VA1.8 Genesis Model 2 (use ASIC YM3438 Mega Amp; headphone buffer optional):

    VA0


    VA1 and VA1.8


    Common


    VA2 Genesis Model 2 (use YM2612 Mega Amp; headphone buffer optional):



    VA2.3 Genesis Model 2 (use YM2612 Mega Amp; headphone buffer optional):



    VA3 Genesis Model 2 (use ASIC YM3438 Mega Amp; headphone buffer optional):



    VA4 Genesis Model 2 (use GOAC YM3438 Mega Amp; headphone buffer optional):





    VA1 Genesis 3 (use GOAC YM3438 Mega Amp; headphone buffer optional):







    VA2 Genesis 3 (use GOAC YM3438 Mega Amp; headphone buffer optional):





    Installation diagrams for GOAC-based Geniclones will be provided on the post below and diagrams for the CDX and Nomad will be added to this post at a later date.

    For those interested in seeing what the unfiltered Mega Ampís spectrum is like, hereís a spectrum analysis done by Villahed of the circuit at 64KHz sample rate using Alien Soldier:



    And now for the obligatory audio samples:

    Sample Set 1
    Console used: VA2 Genesis Model 2
    FM chip: Discrete YM2612
    Mega Amp variant: Filtered YM2612 without headphone buffers

    Sample Set 2
    Console used: VA3 Genesis Model 2
    FM chip: Discrete YM2612
    Mega Amp variant: Unfiltered YM2612 without headphone buffers
    Samples provided by Villahed94

    Sample Set 3
    Console used: VA1 Genesis Model 2
    FM chip: ASIC YM3438 in Sega 315-5660
    Mega Amp variant: Filtered ASIC YM3438 without headphone buffers

    Sample Set 4
    Console used: VA3 Genesis Model 2
    FM chip: ASIC YM3438 in Sega 315-5660
    Mega Amp variant: Unfiltered ASIC YM3438 without headphone buffers
    Samples provided by Villahed94

    Sample Set 5
    Console used: VA1 Genesis 3
    FM Chip: GOAC YM3438 in Sega 315-5960
    Mega Amp variant: Filtered GOAC YM3438 without headphone buffers

    Sample Set 6
    Console used: VA4 Genesis Model 2
    FM Chip: GOAC YM3438 in Sega 315-5960
    Mega Amp variant: Unfiltered GOAC YM3438 without headphone buffers
    NOTE: There is some excess noise in this setup. This particular Genesis was the subject of a failed Neptune mod, so it behaves in a weird way.

    Sample Set 7
    Console used: VA3 Genesis Model 1
    FM chip: Discrete YM3438
    Mega Amp variant: Filtered ASIC YM3438 with headphone buffers

    Sample Set 8
    Console used: VA3 Genesis Model 1
    FM chip: Discrete YM3438
    Mega Amp variant: Unfiltered ASIC YM3438 with headphone buffers

    Word of note about Sample Sets 7 and 8: the Genesis used has a strange habit of dropping notes in some of Thunder Force III's music. It also does this with a YM2612.

    For reference, here are samples taken from some stock Genesis motherboard revisions:

    VA3 Genesis Model 1
    VA0 Genesis Model 2 (LM324 op-amps)
    VA1 Genesis 3

    Once Villahed and I get some PCB designs made for the Mega Amp, there will be two pre-modded Geneses in the Sonic's Bazaar section of the site which will each have the filtered and unfiltered Mega Amps, the first systems to receive completed Mega Amps. When the consoles are ready, I will link to the thread.

    NEW MEGA AMP VARIANT

    The Mega Mixer is here! This variant of the Mega Amp is designed for use on the TCT-6801 GOAC and has no amp, hence the name change to Mega Mixer. This takes advantage of the TCT-6801's on-board headphone amps to deliver the sound of the Mega Amp in the simplest way possible.

    Post updated on June 24, 2014 to add the System C-2 version of the ASIC YM3438 Mega Amp, include a simplified circuit for the GOAC YM3438 Mega Amp, include both the unfiltered and filtered Mega Amp variants for each chip on the same schematic and reuploaded all pictures to Imgur.

    Post updated on July 6, 2014 to add a few audio samples from some of Sega's stock audio amps.

    Post updated on July 28, 2014 to show more clearly what parts make up the headphone buffers so there is less confusion as to what parts need to be omitted if a headphone buffer is not installed.
    Last edited by Ace; 07-28-2014 at 05:22 PM.
    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.

  2. #2
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    **Post reserved for GOAC-based Geniclone solder points**
    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.

  3. #3
    YM3438 Master! ESWAT Veteran evildragon's Avatar
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    Which version should I use for my discrete YM3438 modded system?
    Customized Sega Genesis Model 1 - VA3. Energy efficient with buck converters instead of LM7805's.


  4. #4
    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Discrete YM3438, if you want model 1 like filtering use the filtered version. We're sure it'll sound perfect and distortion free.


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

  5. #5
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    Actually, it's ASIC YM3438. Those circuits work on both the ASIC YM3438 and the discrete YM3438.
    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.

  6. #6
    The hippies were right. Raging in the Streets AlecRob's Avatar
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    Perhaps Villa Head Ninety-Four will mod my VA7 for free if i threaten to send him AES games in the mail.
    Last edited by AlecRob; 01-02-2014 at 12:07 AM.

    Quote Originally Posted by Guntz View Post
    That console is a thing of beauty, not a slut...

    My feedback thread

  7. #7
    Road Rasher superandroidtron's Avatar
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    The OP mentions that this circuit replicates the VA0 - VA2 model 1 sound. Is my VA5 model 1 somehow inferior to those boards? I thought all model 1s had the same sound excluding VA7.

  8. #8
    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Not really. VA0s have different low pass filtering than VA3 onwards. IIRC VA3-VA6.8 have a LPF of 2.89khz


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

  9. #9
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    The filters are slightly weaker on the VA0 to VA2 boards, but those have excess gain on the pre-amp which causes distortion. The filtered Mega Amp brings the lighter low-pass filtering of the VA0 to VA2 Model 1 boards with the corrected gain of the VA3 to VA6.8 Model 1 boards. The best of both worlds.
    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.

  10. #10
    ToeJam is a wiener Hero of Algol Guntz's Avatar
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    Quote Originally Posted by villahed94 View Post
    Not really. VA0s have different low pass filtering than VA3 onwards. IIRC VA3-VA6.8 have a LPF of 2.89khz
    I guess the idea Ace is going for is to give everyone a Genesis which sounds like the original, the one and only VA0 Mega Drive, released in 1988.

  11. #11
    Hero of Algol TrekkiesUnite118's Avatar
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    How does this compare to the Crystal Clear Audio Mod for Model 2's?

  12. #12
    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Quote Originally Posted by TrekkiesUnite118 View Post
    How does this compare to the Crystal Clear Audio Mod for Model 2's?
    Even less filtering (CCAM is around 15 khz) and easier to make from scratch. Also lower power consumption.
    It has a louder output and even without the headphone buffers it can drive headphones quite nicely.


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

  13. #13
    Road Rasher AlmostOriginal's Avatar
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    Yes! Btw Does the GOAC YM3438 *********** (for x-in-1 clones with GOACs) works with the TCT-6801? Is it the same as the Retron3?

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    Nameless One DemVil12's Avatar
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    Can i use MC33079D op-amps as i hate the TLxxx series and really don't want to use them?


    Consoles:
    1. Sega Genesis II VA2.3 Malaysia
    Video - SKA2195 ( No jailbars oO )
    2. Sega Genesis II VA3 China x5.
    Video - Sony CXA1145, 1645.
    3. Sega Genesis II VA3 Japan x4.
    Video - Sony CXA1645.
    4. Sega Genesis II VA3 Thailand.
    Video - SKA2195.
    5. Sega CDX + Infrared Controllers.
    6. Sega Nomad boxed.
    5. Sega Saturn Launch Edition Boxed - ( USA ) - Made in Japan.
    6. Sega Dreamcast Boxed - ( USA ) - Made in Japan.

  15. #15
    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Quote Originally Posted by DemVil12 View Post
    Can i use MC33079D op-amps as i hate the TLxxx series and really don't want to use them?
    Sure, there is no problem about that.

    Quote Originally Posted by AlmostOriginal View Post
    Yes! Btw Does the GOAC YM3438 *********** (for x-in-1 clones with GOACs) works with the TCT-6801? Is it the same as the Retron3?
    Yes, it's been tested on systems with that GOAC and it works just fine.


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

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