Help trouble-shooting a headphone amplifier

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Joined Oct 28, 2023
Hi, I lack experience in anything other than very old vintage guitar amplifiers, so was hoping for some help figuring out how to trouble shoot an SPL Auditor headphone amp. It passes signal as expected but only when the volume pot is set to full volume. Soon after you start bringing the volume down on the dial, the left channel cuts out. It's a fairly abrupt cut out (very slight scratchiness at the cut-off pint), and it's always at the same place on the dial - say after about 15% reduction from full volume. Is there a range of possible causes in this situation? I've tried to spray some deoxit into the volume pot which is the only control, apart from a mono/stereo toggle switch. Unfortunately it's pretty insulated so I can't really get too far into it. If I dissemble it further I'm likely to permanently damage it. From what I can tell, most of the diodes are working ok, and the ICs (LF411CPs) are each receiving the 18v at their inputs ok. Any ideas? Thanks in advance.

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