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PostPosted: Wed Nov 21, 2012 12:27 am 
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I just picked up a nice Twin Famicom. It's fantastic, but in Gimmick! and I assume other sunsoft games that use the DPCM channel for melodical bass, it sounds distorted or peaked. I've already clipped cap C205, and that did add more clarity in the upper range of the audio but it did nothing to help this problem.

I've recorded the tune Aporia from Gimmick! on my regular Famicom VS my Twin Famicom, here is the archive:
http://mikejmoffitt.com/mus/gimmick_compare.zip

Anyone have any insight into this and what I might be able to do to make it sound less awful? Maybe the triangle / noise / DPCM channel is being mixed in too strongly?


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PostPosted: Wed Nov 21, 2012 12:39 am 
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Maybe a stronger resistor from the CPU's second audio pin would lower the Noise/Triangle/DMC volume sufficiently?


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PostPosted: Wed Nov 21, 2012 1:58 pm 
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I think reducing the volume of the 2A03 audio outputs may help the situation; I listened directly to pin 2 from the 2A03 and it sounded better. I went to my regular Famicom and realised that the expansion audio is much louder, so helping the ratio between expansion and 2A03 audio will likely help.


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PostPosted: Thu Nov 22, 2012 11:37 pm 
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So having probed the triangle/noise/DPCM channel directly from the TF versus my regular Famicom, the audio differences are still there. I currently am not near the necessary tools to take pin 2 of the 2A03 out of circuit, but in-circuit this 2A03 alone sounds terrible. Could this be related to the revision of the 2A03?


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PostPosted: Fri Nov 23, 2012 7:05 pm 
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Would be neat to have an NSFPlay Twin Famicom mode as well...


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PostPosted: Fri Nov 23, 2012 9:25 pm 
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There -is- a Twin Famicom preset for NSFPlay, though I haven't changed any of the presets since I took over the project and I haven't really evaluated any of them. (I only have one Famicom and one NES to compare to, personally. If someone wants to edit some settings and vouch for their accuracy I can put it into the preset.)


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PostPosted: Sat Nov 24, 2012 10:56 pm 
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I tried Gimmick! in another Twin Famicom, and the DPCM sounds are the way they should be (the expansion audio is still too soft in comparison). Perhaps the capacitors in the pre-amplification stage circuitry near the cartridge slot need replacement. At least this does not seem to be a Twin Famicom-specific issue, but rather a corner case of this one Twin Famicom.


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PostPosted: Thu Jan 05, 2017 8:59 pm 
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I got another Twin Famicom, and it has this issue. It has an RP2A03G, nothing special. I probed the Tri/Noi/DPCM pin and the distorted DPCM is still there. Maybe this time I'll isolate the pin and see what's going on.


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PostPosted: Thu Jan 05, 2017 9:14 pm 
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It's possible that the inverter-as-amplifier is saturating, given that the DPCM range is usually much larger than any other component.

(Somehow I missed this thread four years ago?)


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PostPosted: Thu Jan 05, 2017 11:09 pm 
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I don't have an OG Famicom here to test, only a Twin Famicom and Fami Titler, but my TF has fine-sounding 2A03 & DPCM sounds, with little detectable distortion. I do hear some slight distortion/overloading on the FDS sound channel when FDS games are running.

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PostPosted: Sun Jan 08, 2017 9:08 pm 
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When I return home, I'll make a recording to compare my OG famicom with the TF. I'm going to be in Japan for two weeks, so maybe I'll try to pick up another :P


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