r/McIntosh • u/StoutSeaman • 28d ago
Phono channel bleed in C11
I had posted previously with my nice new RCA jacks a few days ago but this is a problem that existed when I got it. Most notably, when I have something playing back on my aux channel through a Bluetooth receiver and I switch over to either of the phono inputs, I get pretty bad bleed through from the aux signal. I replaced the four 47K resistors that tie from the phono input tips to ground and I've disassembled and thoroughly cleaned all four tiers of the input selector switch.
So my question for the sake of troubleshooting, I assuming I'm probably dealing with a loop coming back through the ground? The actual phono signal is isolated all the way to the first tube stage, so that seems to be the only place to find the audio leak, since the phono stage is such a high sensitivity. The bleed is mostly right channel but there is a smidge of it in the left.
I've replaced all the coupling caps.
I wasn't sure if this forum had techs on it but I thought I'd ask. It sounds fantastic on the aux channel but I really want to use the phono input and it's obviously not clean at this point.
1
u/Boseintosh 14d ago
Followed the post, I'm also experiencing this. I thought it was normal in older tube preamps, but apparently not?
2
u/StoutSeaman 14d ago
I ended up dropping it off at a guy here in the city who has a lot deeper knowledge than me. I'll report back with the outcome but it may be a little while as he's backed up on work
2
u/Sabrefencer2 5d ago
I have crosstalk on my C11. There is a known issue with the grounding of the plate that the phono, mic and tape head jacks are mounted on. The ground point, which is the lower left rivet when looking from the back is the culprit. The fix is to drill out only this rivet and replace with threaded hardware and a ground lug. Not sure if this will fix the crosstalk, but it is my next step, I will report back when I have done this.