I had a pair of McCormack DNA rev a monoblocks years ago that did exactly what you described. It all started when a speaker connection came lose and and was grounded and blew a fuse. I replaced fuse. From then on it made a loud thump when turned on then high pitch noise that went away in a few seconds, but I never heard noise while playing music. I lived with it for a while since I left amp on 24/7. I did end up sending off for repair because I was scared something may go wrong in the future. I was told it had something to do with what they called "the rail".
Threshold SA/1 monoblocks cap issues, perhaps?
Few weeks back I bought these monoblocks and added to my system consisting of Metrum Adagio, EAR 868L, Focal 1038BE and laptop working as a source which will be replaced with a custom made computer based transport in few weeks.
But these monoblocks seems to have few issues though the seller told me that everything was fine with these monsters.
1. There is big thump when I switch on these amps one by one and also within a second I hear a high frequency sound like "ptakk" from both sides. This sound is there while switching off the amp though less frequently and intensity IMO.
2. Initially I thought the sound is only while switching on and off but later I found that it is also there in between while the music is playing. This is more like "karr-karr" like.
3. One day I also heard it even when I switched off amp while rest of system was on. So I am thinking it might be due to leaky caps. All the caps look like in really good condition and seller told me that there is no need to chnage these as these have hardly been used. Even I use these for 20-30 min per day five times week.
4. Once I removed EAR868 from the chain and same issue was still there indicating EAR is not the criminal here. Adagi was working fine with Parasound Halo A21 which I had earlier before I added preamp and monoblocks.
I do not have much knowledge but I can learn quickly. Need the advise of experts as I really love the sound signatures of these monos.
But these monoblocks seems to have few issues though the seller told me that everything was fine with these monsters.
1. There is big thump when I switch on these amps one by one and also within a second I hear a high frequency sound like "ptakk" from both sides. This sound is there while switching off the amp though less frequently and intensity IMO.
2. Initially I thought the sound is only while switching on and off but later I found that it is also there in between while the music is playing. This is more like "karr-karr" like.
3. One day I also heard it even when I switched off amp while rest of system was on. So I am thinking it might be due to leaky caps. All the caps look like in really good condition and seller told me that there is no need to chnage these as these have hardly been used. Even I use these for 20-30 min per day five times week.
4. Once I removed EAR868 from the chain and same issue was still there indicating EAR is not the criminal here. Adagi was working fine with Parasound Halo A21 which I had earlier before I added preamp and monoblocks.
I do not have much knowledge but I can learn quickly. Need the advise of experts as I really love the sound signatures of these monos.