ChanServ changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://freenode.irclog.whitequark.org/~h~yamahasynths
<cr1901_modern>
The only ecp5 board I have has broken hyperram :(
<TD-Linux>
my main target is ulx3s with 32MB SDRAM
<cr1901_modern>
was there a run of pre-populated boards?
<TD-Linux>
no I made one myself via oshpark
<cr1901_modern>
Hmm maybe I should try to make one... been a while since I reflowed anything for "obvious" reasons
<TD-Linux>
it was not particularly difficult. though the bga reflow failed and I had to redo it
<cr1901_modern>
yea, that's why I hesitate. I've only successfully done rework once
<cr1901_modern>
although that was the last time I did rework, so I guess I'm getting better?
<TD-Linux>
fyi I got a chip from the gacha and it works
<cr1901_modern>
The gacha bugs the hell out of me, and I can't really put into words why
<cr1901_modern>
Yea I'm no fun
<TD-Linux>
none of the chips in it are rare enough for it to make any dent on availability
<cr1901_modern>
I wonder how SID and AY-3 stocks are doing
<cr1901_modern>
(no they aren't in the gacha AFAIK, just curious)
<TD-Linux>
AY-3 seems pretty common. SID not
<cr1901_modern>
I have two SIDs I got as my birthday present in 2010. They cost $90 for two of them IIRC
<cr1901_modern>
or something ridiculous
<cr1901_modern>
Still haven't put them to use :(
<TD-Linux>
there are versions of the AY-3 still in production. some have different pinouts but worst case you can make an adapter
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<ValleyBell>
KitsuWhooa: re ladder-effect: It's actually just a reduced resolution of the DAC.
<ValleyBell>
You get 9 bits per channel, so it introduces some aliasing.
<ValleyBell>
(vs. 14 bits internally, IIRC)
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<KitsuWhooa>
ValleyBell: do you have any examples that I could use to compare?
<superctr>
you know
<superctr>
i sent you an example back when we were testing it
<superctr>
Sonic 3D Blast - the final fight
<superctr>
at some point the song breaks down to just the bass, which pans between left and right
<superctr>
and you only hear the ladder effect on the other side
<KitsuWhooa>
superctr: I actually couldn't hear it
<KitsuWhooa>
:p
<superctr>
in any case it's a problem with the 9-bit DAC. It uses one's complement math internally, and there is a voltage difference in negative 0 and positive 0
<KitsuWhooa>
ooooooooooh
<KitsuWhooa>
so it's the background noise
<superctr>
additionally, when the waveform phase is negative, you hear the difference between negative and postive 0 on both channels
<superctr>
even when it is panned left or right
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<andlabs>
what am I listening to
<superctr>
<superctr> Sonic 3D Blast - the final fight
<superctr>
i think it's a good song to demonstrate the ladder effect since it is audible even without headphones
<andlabs>
yes I know htat
<andlabs>
but what did you do there
<andlabs>
circuit bending?
<andlabs>
and what is this ladder effect that has to do with the DAC? are you referring to the repeated notes with decay?
<KitsuWhooa>
first time in the track is with an emulated 2612
<KitsuWhooa>
second one is with an emulated 3438
<KitsuWhooa>
one has the stuck note, one doesn't :p
<superctr>
if you look at the context, i already explained the ladder effect
<andlabs>
oh
<andlabs>
yeah sorry I just got confused
<superctr>
the YM2612's output is 14-bits internally, but the DAC output is 9-bit. So it is clipped. However when the output reaches 0, there's a difference between negative and positive 0 which is audible
<superctr>
i should say, the output is shifted right, not clipped
<andlabs>
here's the confusion
<andlabs>
the channel 6 PCM mode is also called "DAC mode" in some circles
<superctr>
in this case, DAC stands for digital/analog converter
<superctr>
the "DAC mode" might be called such because it bypasses the FM and data written to that register goes directly to the DAC
<cr1901_modern>
Of course if you have "DAC mode", you should use it, but other chips can get a DAC by pausing the phase generator at the peak of the sinusoid (i.e. the last entry in the 256-bit ROM table since it's a quarter sine).
<cr1901_modern>
I don't know how to do this consistently, but some adlib games did it
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<m4t>
ooo snap
<m4t>
i got a 2019 batch of ym2612
<m4t>
:-]
<whitequark>
lol
<m4t>
hot off the fab
<m4t>
yamaha isn't bold either. fail.
<m4t>
that and the bottoms of the chips are filthy.
<m4t>
i think the opl3 and yac512 are fine tho
<m4t>
the ym2610's are from 2012 ;(
<m4t>
bold yamaha
<m4t>
the m27c128a eproms might be original
<andlabs>
#BootlegChipGallery
<m4t>
acetone and ipa don't seem to be removing anything on the ym2612
<m4t>
korea + 94 stamped on the circles on the bottom, but YAMAHA JAPAN / YM2612 / 1901 AADB on the top
<m4t>
maybe sanded but not blacktopped?
<m4t>
i think these eproms are actually NOS, or very clean pulls. will see if they have data on them.
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<m4t>
ym2610's definitely blacktopped and retinned. will post some pics in a bit.