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

  1. #391
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Quote Originally Posted by Eep386 View Post

    Either way, I'm pretty sure those caps on the VA2 aren't 4700pF.... 1000pF would give a 3.38 kHz cut-off frequency, when used with 47K resistors.
    Well I know that in order to reach the same LPF in the VA3, you have to change out the 5600pF with 4700pF. It may be that I forgot to take into account the resistors paired with the caps. In the VA3 the 10K's with 5600pF were a slightly more severe amount of LPF. So Ace said you just change the 5600's for 4700's. With all that said, what then in fact are the cap values in the VA2?

    Edit: Just checked your calculator and yeah, looks like I forgot to take into account the resistors. Looks like they must be 1000pF like you said. Sorry about that.
    Last edited by Firebrandx; 09-21-2018 at 08:46 PM.

  2. #392
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    No probs.
    What this also means is to get the 15.3 kHz 'unfiltered' setup on a ~VA2, you would need 220pF caps. Personally I prefer a 4.1 kHz -/+ 5% low-pass knee, which you can get with 820pF for the ~VA2 and 3900pF for the VA3 through VA6.8.

  3. #393
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    So this weekend I installed an M1 Double Mega into my primary Genesis. But that also meant I had to work on one of my other genesis systems to get a clean unmolested 2612 out of it. The other Genesis also has FirebrandX's bypass amp in it and had the same delays. I can confirm this is eliminated 100% on my va2 with the 47uf input caps in place and with both pins 1,2 and 7,8 removed from the socket that the 1034p chip sits in. On my va3 I did the same only it uses 33uf caps. It is mostly eliminated on that one as well. Boogerman has been used as a test for this because that game pretty much immediately starts to play audio soon as you power on the system. On the va2 the audio comes in just as it should. With the va3 fixed, it only has like a 1 sec or less startup delay. Honestly not enough for most people to notice as many games do not start up with audio that quickly.

    So I think Wolff has this without any other required changes being needed. He just needs to change the 100uf input caps to 47uf or 33uf as I didn't test the va3 with 47uf caps to know if the delay is increased slightly or not and to have all four of the above mentioned pins removed from his socket he provides for the 1034p to sit in for storage use.

  4. #394
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    On the pin removal of 1 and 8, I found an old problem cropped back up of noise floor being increased, so I can't really recommend it upon further review. The reality is I'm just going to have to make a new "M1 Mini Mega" that taps into the cap pads like the Mega Amp does. It would then have the mixing circuit on the board itself and completely isolated from the CXA chip. It just means people have to desolder or snip the existing caps on the Genesis board, just like they would in a Mega Amp install.

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