Nice write-up Guysonic! One thing I've noticed, and it may be a problem with my deck, is if the internal battery gets low, I start losing volume on one channel (I think the right channel?). I noticed in your write-up that the two channels have different self-noise levels - any theories as to why the channels should behave differently?
Thanks!
Mike
Hard to tell cause without circuit schematic diagram to know how analog output (gain) is being handled. From working the deck, forgot to mention LINE and PHONES output BOTH controlled by same volume up/down buttons simultaneously.
So we commence pure speculation on what could be happening.
Volume control of these two linked outputs may determined by dual channel varying voltage, or more likely just
one single mono channel voltage working into two or four voltage controlled LINE/PHONES amplifiers.
While same voltage seems to control both line/phones output, phones voltage output is almost half that of line output if I remember correctly, so maybe line and phones do have their own amplifier (two stereo amps) controlled by the same control voltage.
If this is the case, interesting to see if your LINE output also experiences unbalance with low battery voltage suggesting dual control voltages where one channel loses voltage regulation with low battery. If both line/phones affected then problem is likely with component(s) generating control voltage losing function. If just phones is losing balance, then likely problem with amplifier driving that output.
In any case, this should not be happening if deck continues to otherwise run OK (not shut down) at that lower battery level suggesting there is problem with sub-standard part, or less likely a design error.
It may be that MR-1 is not so different than R-09 in using just one master CODEC IC generating all or most analog input/output functions. If this the case, then quality control tests on this IC may be lacking low voltage regulation tests affecting critical performance.
However, all supply voltages inside MR-1
should be regulated to work until the deck shuts itself down, and in this case also likely the problem with a voltage regulator powering certain circuits is dropping regulation
too soon, before the deck is designed to know shut down point.