Hello. Getting an odd issue. On the preamp side I’m using a sarno sms classic (basically an AB763 preamp section). This unit tests out completely solid. Here’s the issue: after a while when I switch to the preamp side I get very loud hissing. This takes a while to start happening. Again in isolation this preamp tests out immaculate. Each and every component and value. Any thoughts? Impedance?Isolation?
Everything in the chain has been replaced one by one to ensure no bad cables tubes etc. The amp on the amp side is a komet songwriter. The power station is an older one in great condition.
Head scratcher