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

  1. #31
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    Use 75Kohms. That gave me the best results with a TL072 while I was experimenting with this (though I did this a good bit before Jeroi posted this circuit using VRef from the motherboard, which I suggest you don't use; in fact, I suggest you don't even use 2.5V VRef, but rather something a bit closer to 3V as in my experience, 2.5V results in a somewhat clipped waveform - you could use the VRef circuit from the Mega Amp).
    HATES ATGAMES WITH A PASSION


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  2. #32
    WCPO Agent Helder's Avatar
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    I don't have that value but do have a 100k variable resistor and will try that, also I'm not using VRef from the motherboard just the left and right channels from the chip.

  3. #33
    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Nope even 1.9V is good Vref for normal Line out. The normal line out is .7vp which means there is plenty space for gain. 2.5 more than sufficient so Ace's point is not valid. At the moment there is problem that we do not know the amplitude of thos mix lines. If we knew these then amp level can be calculated that is needed.
    Last edited by MEGADRIVE Jeroi; 07-18-2014 at 05:30 PM.
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  4. #34
    WCPO Agent Helder's Avatar
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    I posted the links to order the boards if you want to order yourself a set either smd or through hole and we can try to tackle this and get a final working design.

  5. #35
    WCPO Agent Helder's Avatar
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    Ok so I got around to testing the different pots and 100k didn't do much so I used a 470k pot and low and behold 430k is loud enough for me, it finally had some balls at that setting. If you want to mess around a bit more with it be my guest but I think that is the sweet spot.

    Edit: The sound is nice and loud and treble sounds good but the Bass needs a boost, so what component on the schematic controls that so we can tweak it also.
    Last edited by Helder; 07-27-2014 at 11:05 PM.

  6. #36
    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Quote Originally Posted by Helder View Post

    Edit: The sound is nice and loud and treble sounds good but the Bass needs a boost, so what component on the schematic controls that so we can tweak it also.
    The input caps, you wil need to repalce C45 and C46 with 10uF. It is nF cap located in the motherboard.
    And you could change 10k to 1K and 430k to 43k. Audio respones are better with lower resitance values.
    Last edited by MEGADRIVE Jeroi; 07-30-2014 at 06:34 AM.
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  7. #37
    WCPO Agent Helder's Avatar
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    Are you sure about changing the 10k and 430k? won't that bring the volume down again?

  8. #38
    Road Rasher Xalphenos's Avatar
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    But wouldn't changing both ends like that be essentially the same? Anyway this looks very interesting. I've got a couple model 1s I wouldn't mind shoving this into. Thanks for doing all the legwork with testing Helder. And thanks MEGADRIVE Jeroi.

  9. #39
    Creator of the Mega Amp Raging in the Streets Ace's Avatar
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    Quote Originally Posted by Helder View Post
    Are you sure about changing the 10k and 430k? won't that bring the volume down again?
    The gain will still be the same. If you divide 430K by 10K, you will get a gain factor of 43. The same thing happens when you divide 43K by 1K; you get the same gain factor of 43.
    HATES ATGAMES WITH A PASSION


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  10. #40
    WCPO Agent Helder's Avatar
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    Ah makes sense now, so the 10uf will bump up the bass then? I have some resistors of these values in the correct SMD values so this will be a nice little board once everything is set. So on the schematic there are three 10k resistors so changing the three to 1k will produce the results mentioned above?


    Edit: Here is how big the board is:
    Last edited by Helder; 07-30-2014 at 01:06 PM.

  11. #41
    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Quote Originally Posted by Helder View Post
    Ah makes sense now, so the 10uf will bump up the bass then? I have some resistors of these values in the correct SMD values so this will be a nice little board once everything is set. So on the schematic there are three 10k resistors so changing the three to 1k will produce the results mentioned above?


    Edit: Here is how big the board is:
    Well replace the input caps with 10uF caps and see results.

    Quote Originally Posted by Ace View Post
    The gain will still be the same. If you divide 430K by 10K, you will get a gain factor of 43. The same thing happens when you divide 43K by 1K; you get the same gain factor of 43.
    Also reducing the resitor values makes more base because smaller resistance makes the base cut frequency more lower than higher ones as I said in previuous post already: frequency response gets better with lower resistance values.

    Also I would suggest you to add STEREO RCA jack mounts to the mobo. It would be nice to just screw RCA's to back and the mobo is connectect directly to the jacks. Also make 0' degree jacks there so that mobo is lifted to fit in the case more easier.

    phs10w.jpg
    Last edited by MEGADRIVE Jeroi; 07-30-2014 at 01:46 PM.
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  12. #42
    WCPO Agent Helder's Avatar
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    I actually have 3 RCA jacks in my case one for composite and the other 2 for Audio, but you still haven't responded to my question about the three 10k resistors on the schematic: Should all three (3) 10k resistors be changed to 1k or just the ones on the audio lines?

  13. #43
    Take it apart! WCPO Agent MEGADRIVE Jeroi's Avatar
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    Only the Audio resistors. The divider needs to be 10k for low current usage.
    #MEGADRIVEJeroi @ Quakenet irc server.
    Be true to yourself. GFX doesn't matter, the game does. If you are intrested to donate one NTSC Genesis for hardware testing purposes, please pm me.

  14. #44
    WCPO Agent Helder's Avatar
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    Ok so I changed the 430k to 43k and the 10k to 1k and the audio is very noticeably lower so that didn't work and I compared it to a model 2 with Mega Amp installed so I have something to base it on and again it very noticeable the difference. Keep in mind this is a good audio model 1 and the bass is still low, which way to install a polarized 10uf cap in place of the ceramic nf caps? basically where would the negative and positive go on the pads?

  15. #45
    WCPO Agent Helder's Avatar
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    Well after putting a 470k pot on the 10k and 33k resistors I tweaked them both till I had it close enough in sound to the Mega AMP Model 2, so now it has some bass and good treble but any higher than 17k on the 10k resistor will make it too high pitched. So the results are as follows:

    The 10k resistors on the audio lines should be 17k but that's a hard value to find so 16.9k is useable for a cheap price.
    http://www.ebay.com/itm/0805-2012-Me...item461c79196b

    The 33k resistors should be 453k and anything higher will cause the high pitch treble and loose bass, less is ok.
    http://www.digikey.com/scripts/DkSea...23554383923657

    Still have the bass that needs a little boost to make it more comparable with the Mega AMP and haven't tried any changes to the motherboard caps yet.

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