stereo chipamp channel separation

have built lm3886 based chipamp, on same pcb stereo.

thing is that when i unplug left channel ,signal from right channel input is heard at left channel output(and other way around),few db less than on right.

schematic is regular from datasheet ,100milion times checked and working in few other amps i make, only difference is it is on same pcb this time.

i am baffled and feel dumb ,but certain that i overlooked something very simple.
please help,ty
here is all,please focus on this stereo problem ,not rest of errors. thank you


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for now left channel only works without problems, right has still unindentified problem with hum, but both produce normal,fullrange sound, why not, maybe later i post measurments of working channel if i have time.

i have few new pcbs and slightly altered are mono and lot better than this. probably gonna sell few of those if tests/measures well.


2014-07-01 10:10 pm
At max output, the C = 100uF must not loose more than circa 1V. If the Hfe of the 2SC5200 = 50, the Ib must be 1/50 of the Ie = I speaker. With max speaker current = 7 A, the Ib must be circa 140 ma. The C of 100 uF will be unloaded within less than 1 ms with 1 V. This implies that this amp will only work at full output power till 1.000 Hz.

Did you really try this and did it work with 30 Hz at full output power? I cannot believe so.


2014-07-01 10:10 pm
Hfe ° 50 means: Ic = 50 x Ib. If Ic = Ie = I speaker = 7A max, then Ib should at least be 140 mA. And it is impossible to impose this current more than 1 ms through a 100 uF capacitor, unless diminishing its Q with the corresponding 1 V ==> This implies that you cannot output in full power low frequencies.
dr frost? what? ????
this works for real, on my bench speakers,speakers not good much below 50hz but they play as on other amplifier,what baffles me now how it works when shouldnt???? i am not that deaf i think i should hear 500hz cutoff.

on working channel noise is very low,cant hear it, also distortion i cant hear on my test song(hells bells). now i need to make measurment tool out of my soundcard to post measurments here when come home from work.