I tried a 1K across the ghost channel RCA input and the output ghost disappeared. Yes a balanced connection would usually cancel out a ghost IF it existed on both +and - wires.
I lied when I said that with 1K shunt on the ghost input channel the ghost output was gone. Yesterday I saw a true shorting plug in my bench mess and tried that. Ghost output got cleaner. With the scope's minimum 10mV vertical res, I could now see that I missed something with the 1K plug. 4.4mV across 1K = 4.4uA! That's 4400x the op asmp's Ib. See pics taken yesterday before the following steps done yesterday and today.
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With four new input Rs (R13/130 and R6/60) and two new input Cs (C2 and C20) the new layout looks like the attached. The Left I/O occupies the bottom of the board and the Right I/O the upper part. Much more symmetrical. R13, R130, R6, R60, C2 and C20 are all new and were moved per the new ***'y re-org. C2 and C20 are now Panasonic metallized PP. The R/L Input connections are now shielded, lapel microphone coax.
Will provide pics tomorrow but the results are much like that taken for the above, #622 "1K plug" EXCEPT for the lack of the 1K plug. IOW, now with nothing occupying the Right input RCA the Ghost output signal is down into the single-digit mV range. A big improvement but it's still "there"..??? ~60dB separation.
Will provide pics tomorrow but the results are much like that taken for the above, #622 "1K plug" EXCEPT for the lack of the 1K plug. IOW, now with nothing occupying the Right input RCA the Ghost output signal is down into the single-digit mV range. A big improvement but it's still "there"..??? ~60dB separation.
Well, I lied again when I wrote:
Take a look at the pics and please critique, suggest, scorn, etc. Where is it coming from now? Also see the latest "The board layout 6/7/2025" and note the shielded input cables. The side-lane Gnds are now only used for the +/- 15V bypass caps and the Output RCA returns. The rearranged input Rs now use the fat backbone shield Gnd. I guess the RCA out returns could use that Gnd as well....
Post #622 pic titled "1K plug" showing 4.4mVpp was taken with a mistake present from the layout re-do. I forgot to remove the two original 63.4K R6s when I added the two new R6s so that pic and the other are with "R6" = 31.7K. Follow...? I'm sorry. I did not discover this goof-ball mistake until after I took a bunch of new pics of the board so today's pics show the old R6 in-place. I was too lazy to repeat them so please ignore or see if you can find them. BUT today's scope shots are with the old R6 removed. The new No plug Ghost is 9.2mVpp down from 70mVpp in post #613 . And today's "1K plug" is now zip - at least on the 10mV scale. That's a big improvement but still there. Not gone.
Take a look at the pics and please critique, suggest, scorn, etc. Where is it coming from now? Also see the latest "The board layout 6/7/2025" and note the shielded input cables. The side-lane Gnds are now only used for the +/- 15V bypass caps and the Output RCA returns. The rearranged input Rs now use the fat backbone shield Gnd. I guess the RCA out returns could use that Gnd as well....
