cr1901 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://libera.irclog.whitequark.org/~h~yamahasynths
<andlabs> so what kind of math do I need to figure out what the actual resistance for these two circuits going into P66 and P67 are
<andlabs> for the neither-serial-nor-parallel resistros and capacitors
<andlabs> I know I need to figure out some multiple of the MAME cassette interface's read() function, whatever *that* returns
<andlabs> I *think* this is identical to Yamaha's MSX interface
<cr1901> BP is a DC-blocking capacitor. Ic22 is an op-amp in positive feedback configuration (has to be analyzed piecewise)
<qu1j0t3> that makes it a comparator amirite
<cr1901> Prob a Schmitt Trigger
<qu1j0t3> so a comparator with some hysteresis
<cr1901> Yea, and the negative terminal is biased to 2.5V
<cr1901> b/c of two equal resistors
<cr1901> (I'm ignoring the effect of the 5.6k resistors)
* qu1j0t3 is literally trying to work on a comparator circuit now
* qu1j0t3 has been frustrated today. "If what you're seeing is crazy, don't rule out the op amp might be just broken"
<qu1j0t3> are TL072's particularly fragile?
<qu1j0t3> at least my latest headscratcher was me just forgotting to install a resistor on + to ground
<andlabs> all that flew over my head
<andlabs> I'll worry about this part later
<andlabs> thanks
<qu1j0t3> andlabs: basically converts an analog signal into a digital signal by thresholding
<qu1j0t3> andlabs: the hysteresis removes instability near the transition
<qu1j0t3> andlabs: it's the hallmark of a Schmitt trigger
<qu1j0t3> andlabs: an op amp can be made to do this with positive feedback, but dedicated comparators can be used
<andlabs> hmmm
<andlabs> ok
<andlabs> more pertinent is that thing the other resistors are connected to ground or 5V
<andlabs> the line with slants underneath
<andlabs> rather than the usual ground symbol that's connected to the DIN
<qu1j0t3> chassis afaik
<qu1j0t3> for the purposes of those voltage dividers, ground
<qu1j0t3> and bypassing
<qu1j0t3> (the caps)
<andlabs> ah
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