Einherje wrote on 2021-09-08, 12:48:
Ydee wrote on 2021-09-08, 08:45:
Yes, I know, but I wonder what the modification brings - less noise, cleaner sound, more pronounced heights/bass or something else?
T74LS08 is a Quad 2-Input AND Gate.
I don't know a lot about IC, but what would you hope to achieve by routing one of the four data outputs back to to the power input?
A 74LS08 is in the digital side of things, so this capacitor does not influence frequency response, and also very likely not the noise level. A capacitor between a power input (a fixed voltage) and an output of a logic chip forces the logic chip to work harder when the output switches between low and high, because every time the output goes high, the capacitor needs to be discharged, and every time the output goes low, the capacitor needs to be charged. This extra work causes the gate to act slower, up to the point where short pulses are suppressed completely. So the purpose of this capacitor might be a slight delay of one signal, to allow more processing time for other signals, or to suppress short glitches on a signal.
Another purpose could be that when you power on the card, the capacitor is discharged, forcing the output pin to be at the same level as the power pin, which will create a short moment where the output is high, no matter what the inputs are.
While I have no proof, I highly suspect this capacitor is used to improve ISA compatibility with certain mainboards.