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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.

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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.

  5. #395
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Ceramic and Electrolytic versions of the trimmed down Mega Amp style new boards. I will be testing both extensively to compare results:




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    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Updated the "Audiophile Edition" to use UKZ Nichicon "Muse" caps wherever possible. These are the very top level quality audio-specific caps Nichicon makes. They only go down to 10uF, so for the 1uF inputs, I used their next best audio caps called UFG "Fine Gold" by Nichicon. Here's the new board render from OSH Park:



    Link to Datasheet for UKZ caps:

    http://www.nichicon.co.jp/english/pr...pdfs/e-ukz.pdf

    Only C10 and C11 caps remain ceramic, but they are 47pF at C0G/NP0 dielectric, and their function is purely LPF. As such, they are perfectly fine for the job.

    To put it bluntly, this board is going to be an audiophile's wet dream for the YM2612 consoles. Combined with my M1 Double Mega, it will make the YM2612 consoles THE premiere audio station for everything Genesis. However as such, I have omitted/changed a few things from the Mega Amp 2.0:

    1. I do not include mono output circuitry. The goal here is minimalist design in both space and routing.

    2. I do not include toggle switches for filtering. I will be testing different values, but more than likely I will be sticking with 47pF. This is because YM3438 mode on the M1 Double Mega actually shines in the higher frequency ranges.

    3. The output circuitry is set to line-level applications at 330 Ohm + 47uF. I know Ace prefers 220uF cans, but I worked on this extensively with Ste Kulov, and 220uF is something you use for driving headphones. The fidelity will simply not be accurate for line-level equipment such as A/V receivers, TVs, and capture devices if you use 220uF cans into them from the board.

    With that said, the boards have been paid for, but it will take a couple weeks to get them back from fabrication. I'm VERY excited to test them out!

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    Forgot to add in 2.2k Ohm optional pull-down resistors for the YM inputs:



    Those pull-downs can be used in conjunction with the M1 Double Mega, and allow the red and white wires to be soldered from that board directly to this one. Speaking of the M1 Double Mega, I did a new test on the previous prototype where I left the board pins intact and soldered the lines to them:



    I'm happy to report this works without any noise floor increase! We're back to being 100% modular!

    The final prototype currently in fabrication will make use of these socket pins:



    This will allow the same plug 'n play action of dual wipe sockets, but with the added benefit of lowering the chip height to almost the same as soldering the chip directly to the board. The chips will only be less than 1mm higher than straight soldering, which will allow my 5mm heat sink for the 2612 to clear the top metal shroud of the Genesis console. You can see in the image below I have put a heat sink on the 2612 in my old prototype for testing, and it works great for keeping that sucker cool:



    Also in that image, I have replaced the voltage regulators with new 78S05s, and swapped out the old Genesis power brick with a much lighter more efficient new Triad PSU. It puts out a solid 9V at 2A, which is more than enough amps to power the console and all the mods added to it. Everything runs much cooler now. I'm very happy with it.

  8. #398
    Outrunner CrossBow's Avatar
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    Awesome! Glad I tipped you off to those pin sockets! Not only with this project but others as well, they will add a very professional look to an already excellent design and product.

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    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Quote Originally Posted by CrossBow View Post
    Awesome! Glad I tipped you off to those pin sockets! Not only with this project but others as well, they will add a very professional look to an already excellent design and product.
    Yeah those pin sockets were an excellent find! I will likely use them from now on in designs that need dual wipes, provided of course they keep plenty in stock. I'm also thrilled with the heat sink on the 2612. Even after a solid hour of playing music, it kept the chip lukewarm. As you know, that chip gets blazing hot! Is it TTL or something? I know the 3438 is CMOS and so it doesn't ever get hot.
    Last edited by Firebrandx; 10-06-2018 at 11:50 PM.

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    The YM2612 is NMOS/HMOS. It's a pretty hot-blooded device compared to the CMOS YM3438. Too bad I just don't care much for the more 'perfect' DAC, 'cause I'd love to take some of the heat off the aging LM7805s.
    Last edited by Eep386; 10-11-2018 at 01:47 PM.

  11. #401
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    Quote Originally Posted by Eep386 View Post
    The YM2612 is NMOS/HMOS. It's a pretty hot-blooded device compared to the CMOS YM3438. Too bad I just don't care much for the more 'perfect' DAC, 'cause I'd love to take some of the heat off the aging LM7805s.
    The M1 Double Mega doesn't replace the 2612. It is still needed for the timing in order for the 3438 to work properly. This add-n board allows a person to swap between the two chips as needed. You could even solder your own set of wires off where the switch is on the board to an external switch to make it easier.

    But I get what you're saying. Could always change out the 7805s with DC-DC converters and see if you can figure out the way to filter them additionally so they don't cause noise on the audio?

    Or at least just trying changing out VCC2 as I believe it is VCC 1 closest to the power switch that handles the power to the audio section.

  12. #402
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    For me, swapping the regulators out for 78S05's and then using a 9V 2A switching PSU has done the trick for eliminating the burning hot heat sink. However, on the 2612 itself, I recommend getting a 5mm-tall heat sink with some thin thermal tape. Works great to keep it from getting hot even after hours of nonstop use.

    Quote Originally Posted by Eep386 View Post
    The YM2612 is NMOS/HMOS.
    Researching the background history, it seems the chip is most likely HMOS technology as far as I can tell.
    Last edited by Firebrandx; 10-11-2018 at 03:27 PM.

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    Yeah, it's likely HMOS. On my VA6, I also replaced the Z80 with a CMOS Z84C004 (in the Genesis, it seems to be directly compatible) and the NMOS/HMOS Fujitsu VRAM chips with Samsung CMOS VRAMs, both changes also noticeably cooled down the heatsink. It's still pretty hot, but it's not quite as bad.
    I also replaced the original HMOS PSRAM chips with 25ns-rated Cypress CMOS SRAMs, but that didn't seem to make much difference.

    I had some wicked rainbow banding out of the composite output though before I replaced the capacitor at C79, that seemed to get rid of it. In my case that cap was obviously bad, but I don't believe that will fix rainbow banding on all consoles in every case.

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    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    I just thought of something stupid, but sort of funny: Hot-MOS and Cold-MOS :-P

    Anyway, the ceramic edition of the new board design arrived and I quickly populated it manually:



    Just waiting on the 'Audiophile Edition' that will use top-quality audio caps, which should be arriving in a week or so. Also just got notified the final prototype of the M1 Double Mega has shipped. I was talking to Ace about it the other day, but he has no interest in that project because he hates the 3438 chip sound with a passion. To each their own, but I like having the option to try both at the flick of a switch.

  15. #405
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    Quote Originally Posted by Firebrandx View Post
    I just thought of something stupid, but sort of funny: Hot-MOS and Cold-MOS :-P

    Anyway, the ceramic edition of the new board design arrived and I quickly populated it manually:



    Just waiting on the 'Audiophile Edition' that will use top-quality audio caps, which should be arriving in a week or so. Also just got notified the final prototype of the M1 Double Mega has shipped. I was talking to Ace about it the other day, but he has no interest in that project because he hates the 3438 chip sound with a passion. To each their own, but I like having the option to try both at the flick of a switch.

    Nice on the new prototypes already getting shipped! I will be very very curious to hear your results between this mega amp and the Nichi capped version. Though I'm sure they will be expensive, I'm likely to invest in one or both of them for my own setups here. As for the 3438.. I prefer the cleaner drum samples and improved stereo separation...plus with the audio amp bypass from Firebrandx installed...you thought the bass from a va2/va3 was good before...wow!

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