MX110z Phono 1 Static

[pappyland]

Hi there!

I’ve had my MX110z for a few years - most recently serviced by Audio Classics in 2020. Recently, I’ve noticed a faint static noise in the right channel - and only on Phono 1. The noise increases /decreases with volume control.

I’ve ruled out the input cable and record player leading to Phono 1 (as the noise persists when I unplug both cables, and reversed the input cables from left to right). The noise *does* reverse channels to left if I reverse channels using the output switch on front of the MX110z. I also don’t hear any noise when set to Phono 2 w/o input.

So:
1. Is there an obvious tube that may be at fault? (Doubtful AFAIK since it’s limited to one phono input)
2. If not, is there anything else I can try testing/swapping before sending out my amp to a professional? RCA jacks were replaced in 2020, and they look pretty clean to me.

Thanks!

 

[Bob the Tech]

You're right that there's one tube for PH preamp L and one for PH preamp R, so there's no magic tube that's causing PH1 issues without PH2 issues.

In fact the PH1 / 2 circuits are exactly the same except for two things - the PH1 has the 2nd input for XTAL with an added series capacitor (should have no effect on this), and PH1 and 2 have different PH level pots after the PH preamp. Otherwise everything is identical.

Unless something is obviously wrong with the new PH1 R channel input (connector is loose, for example), I'd guess you have a dirty input select switch or dirty R channel PH1 level pot. Try cleaning / lubricating these if you're handy, and if not you can try working them a bit by rotating the switch through all the inputs and back a dozen times or so, and running the pot up and down in level a few times before settling back where it was. See if either of those cleans it up.

Bob