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

  1. #376
    Outrunner CrossBow's Avatar
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    Okay...I've got this installed into a va6 and it sounds like the bass might be too much on this revision? Attached per Epps suggestion is track 8 from SOR3:

    https://www.dropbox.com/s/90zez7mne9...8_va6.wav?dl=0

  2. #377
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    To be fair, the bass is naturally very high on the pre-VA7 Model 1's. This VA6 has it particularly pronounced though - are you still using the stock 5600pF filter caps? C45 and C48 are the caps for the low-pass filter. 4700pFs will raise the filter knee to 3.38 KHz, which will still sound very bass-heavy, but will also be very noticeably brighter.

  3. #378
    Outrunner CrossBow's Avatar
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    Yes this va6 is all stock minus the s-video and this bypass amp I added to it. BTW, I had my recording level at 80% but yet the actual recording meter never went above 45% during the actual playback and recording. I did not normalize either that is the raw volume from this Genesis now with this bypass amp in place.

    Also, this bypass amp still has the original 100uf caps installed on the audio input lines to it so it is the full fidelity. It does have a start up delay even without the 1034 installed, but it is only maybe 5 or 6 seconds at most.

  4. #379
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Was going to report that removing the 1034P from my VA3 did not fix the charge time delay. It works perfectly in the VA2, but does not help at all in the VA3. So clearly there's something in the mixing circuit that was changed starting from VA3 on. As I said before, I'm going to have to map out the schematic of the VA2 as the only one online that I found was I believe for the VA3. Then I can compare and contrast to see what's different.

    Moving forward, a 2.0 version of this board I'm going to have to approach the bypass the same way Ace does in the Mega Amp. It will effectively be an "M1 Mega Mini" because it will include the mixing circuit with my own output circuit as is on the current board. I'll have to give Ace full credit for the design since it will be a stripped down simple version of his original board. It will just be for people that want quality stereo output either from the headphone jack or via RCA jacks. No bells and whistles kind of deal.
    Last edited by Firebrandx; 09-11-2018 at 05:29 AM.

  5. #380
    Outrunner CrossBow's Avatar
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    I'm in the process of editing video for my YT channel on the process of installing one of these boards. But I did mention that in its current state it is really designed for those wanting to use or currently have RCA jacks for audio output. I do make mention that you would have to essentially cut all the wiring from the headphone PCB if you wanted to attach to that instead. Also I will make a short video tonight to put on the end in regards to some of these findings.

    For now I would just stick with 47uf caps on the input and output lines as you stated and not even worry about including the socket with the 2 and 7 pins removed. If you still wanted to keep a means for the 1034 to remain, then you would really need to provide a socket that has the input, output, and Vcc pins pulled. I actually tried this and it still prevented audio from going to the circuit for some odd reason. But I'm sure there is a way to pull enough pins to leave it effectively dead and grounded to the system, while providing enough pins for it to stay in place for storage.

  6. #381
    Outrunner CrossBow's Avatar
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  7. #382
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Happy to report the latest (and final) prototype for the "M1 Double Mega" has a FLAWLESS noise floor! It literally adds ZERO noise compared to the piggy-back method. So we now finally have a toggle mod solution for discrete 2612 or 3438 music! Here's a link to the sound check from both modes as the sound going out my Line Amp board:

    https://t.co/v04eUfNoSQ

    And here's the actual machine I used to make the recordings:


  8. #383
    Outrunner CrossBow's Avatar
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    Nice! Make sure to test a thunderforce II dedicated cart for floor noise. That game for some reason just brings it out when most others do not.

    And...when can I order one of these?! LOL

  9. #384
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    I just so happen to have a Thunder Force II cart to test with, so I'll be sure to give it a whirl. Although keep in mind it's not indicative of the actual noise floor, but rather the game code poorly interacting with the YM chip. Streets of Rage will have static during the intro, yet plays music in the sound test menu with no noise issues whatsoever. It's just dependent on how clean the code is for any given game.

    I need to get caught up on the pre-orders for the Line Amp kits, and then I'm going to code the sales and installation page for the M1 Double Mega. Keep in mind a LOT of work went into the design, and the 4-layer board is going to make it super pricey. My guess is around $75 since I have to source the YM3438 chips, and the board-to-board posts are strangely very expensive as well. Even so, I have to say it is my best work to date. The routing and design are top-notch. Audiophiles are going to have a blast playing with this thing on their favorite Genesis/MD tracks.

  10. #385
    Outrunner CrossBow's Avatar
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    Well..in my case I only need the board and stand off pegs. I actually have small stock pile of YM3438 chips on hand since I offer that as a mod for those that want it done.

    So yeah..pretty much board only for me.

  11. #386
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Crossbow's M1 Double Mega preview kit is on the way. In the meantime, I've found the significant difference in the mixing circuitry between the VA2 and the VA3 that MIGHT explain the cap charge time being removed when you disconnect the 1034P:



    In the VA2 board on the left, those are 47K resistors paired with 4700pF caps going into pins 1 and 8 of the 1034P. In the VA3 on the right, those are 10K resistors paired with 5600pF caps. So it's possible that lack of resistance in the VA3 plays a huge role in why the cap charge time delay still happens with the 1034P removed. I'll have to experiment by changing out the 10K's and putting in 47K's to see if that does the trick. I've already put in 4700pF caps on my VA3, so if I replace those resistors, I will effectively have restored the original VA2's mixing circuit.

    If this doesn't work, then the charge time delay must be caused by something else in the system. I'll just have to keep working on it and see if I can track it down.

  12. #387
    Outrunner CrossBow's Avatar
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    Didn't they change these values to combat the clipping issues with loud notes that the va2 suffers from by default?

    Also you said Pins 1 and 8? Those are the output lines and we bypassing all of that with your amp board since we taking in directly from the input lines to the amp on 2 and 7 right?

  13. #388
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Quote Originally Posted by CrossBow View Post
    Didn't they change these values to combat the clipping issues with loud notes that the va2 suffers from by default?

    Also you said Pins 1 and 8? Those are the output lines and we bypassing all of that with your amp board since we taking in directly from the input lines to the amp on 2 and 7 right?
    The mixing circuit references itself on pins 1 and 8, so even though we separate pins 2 and 7 from the CXA, the circuit still deals with pins 1 and 8. One thing I can try to test the theory is take a dual wipe and remove pins 1 and 8 along with 2 and 7, and see if we get the same relief of charge time on the VA2. If we do, then that definitely is the culprit.

    And yeah, some games were overly loud, so they dropped the 47K's down to 10K's. However, I think that overload was happening in the 1034P and isn't a problem with the Line Amp board. The 4700pF versus 5600pF on the caps is merely an LPF increase (which I hated), hence why I reverted my VA3 to the 4700pF caps.
    Last edited by Firebrandx; 09-20-2018 at 10:39 PM.

  14. #389
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Update: Confirmed removing pins 1 and 8 along with 2 and 7 had the instantaneous music reaction time with 1034P still onboard in the VA2. This means it HAS to be those 10K resistors causing the delay in the VA3 even when you remove the 1034P. So the final test will be to replace the 10K's with 47K's in my VA3 and try the 1-2-7-8 pin removal test with the 1034P intact. Since I don't want to hassle with 'borrowing' them from my VA2, I'm going to just order them from Digi-key and report back.

    BTW on my VA2, I re-installed the Line Amp mod using 4-line ribbon wire tacked to all the needed sources of the 1034P socket, and then routed the ribbon cable out the same 'gap' allotted for the power socket on the side of the board. Then I routed the ribbon cable back across the top and up into the Line Amp board. Seems to be a more efficient and clean install method that doesn't require removing the RF box (if you wanted to say use the headphone jack for line output). I may update my installation guide page to suggest this method, and of course removing pins 1 and 8 on the 2nd dual wipe socket as well to prevent the stored 1034P from interfering with the music.

  15. #390
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    Quote Originally Posted by Firebrandx View Post
    In the VA2 board on the left, those are 47K resistors paired with 4700pF caps going into pins 1 and 8 of the 1034P. In the VA3 on the right, those are 10K resistors paired with 5600pF caps. So it's possible that lack of resistance in the VA3 plays a huge role in why the cap charge time delay still happens with the 1034P removed. I'll have to experiment by changing out the 10K's and putting in 47K's to see if that does the trick. I've already put in 4700pF caps on my VA3, so if I replace those resistors, I will effectively have restored the original VA2's mixing circuit.
    Uh, wouldn't 47K resistors with 4700pF caps give a 720.8 Hz low-pass filter?

    The formula for calculating a low-pass filter frequency is 1/(2 * 3.14 * R * C)
    R is resistance in ohms, C is capacitance in farads. (1pF = 1/1,000,000,000,000th of a farad; 4700pF is the same as 4.7nF, which is 1/4,700,000,000th of a farad.)
    Or you can just use the calculator here: http://www.learningaboutelectronics....calculator.php

    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.
    Last edited by Eep386; 09-21-2018 at 11:40 PM. Reason: DERP

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