I have three spider valve mkii 112 combo amps and each of them are exhibiting a high pitched sound around 3khz-3.5khz when the amp is on. For the most part it is in the background, but at various times it can get higher in the mix where it can be a distractor or even painful.
The tubes have been switched out and verified as the correct tubes and re-biased and the noise still persists. I switched cables, guitars, used a power conditioner, but the sounds still persists. I believe the sound may be somehow connected to the master volume. When I use the amp live I can hear the sound. However, when I use the amp and use the direct output feature (via studio or performance mode), the high pitched noise no longer persists.
Has anyone else experienced this issue or have any potential fixes?
Thank you.