GuitarBird64

I do have the output set to instrument, as that is the level I always need for my applications. Lowering channel volume does remove squealing, but when I am sculpting a tone, sometimes you want the channel volume to be higher. But this squeal happens even when the channel volumes are reasonable, such as 7 or 8. I am able to get this squeal even without using the Line Selector, that is, plugging in directly from guitar and then going right into my amp is not distorted or having heavy gain. Thanks for the replies though.

Using an HX StompXL in one of the loops on my Boss LS-1 Line Selector. Getting high frequency squeal even at low volumes when using High Gain tones. I have the LS-1 loop gains at halfway position and my XL output knob is set about halfway. I have the tones main output levels set about 0db, amp. model master volumes relatively in the middle. None of the effect tone blocks have their level cranked either. I am diligent about gain staging as I am an experienced audio engineer. But on some models of amps I get non-musical squealing that sounds like typical microphonic squealing from bad pickups or cables. But I checked all guitars and cables using a couple different high gain tube amps with gain maxed and I don't get this kind of squealing. This nasty squealing is not from audio feedback as it occurs at low volumes, and with different guitars with different pickups. I use good cables too. I use the Factory supplied wall-wart power supply. I don't have this problem when I swap in different high gain amp simulator pedals like the UA Lion or the ToneX, or high gain distortion boxes in place of the XL in the loop of the LS-1. I am beginning to think their is some weird issue with the XL itself. Any ideas?