I got this hoping to "improve" it. It's in a metal case and has a CDM4 mech and Philips chips including a TDA1541A, but no digital filter.
As it turns out, possibilities are limited by the fact that it has no mains switch, with the "power" switch only isolating some of the circuits after the regulators.
I'd like to pass it on but feel I should do something about the frequency response first. I can't find a cheap manual, but I guess it's a common audio circuit. Op amps are SIL NJM2068 (dual, 6V/us, 25MHz).
Messing about with filters would be a new experience :)
Any ideas for simple improvement, please?
Some time later...
I took one of those dual inductors with adjustable slugs out coz it was impossible to measure otherwise. Still impossible...but some guesswork and my LCR bridge arrived at the circuit below, which simulates fairly close to reality.
The wiggles in frequency response shown in the first graph result in differential phase error beyond around 14kHz, as shown in the third. Middle graph is output from 1mA input.
I wonder if one of those notches beyond 20kHz should be at 44.1kHz? Anyway this demonstrates a typical problem for CD players without interpolation. There's plenty discussion done already. Choice appears to be between wiggles and noise.
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