Vibration noise from toroid transformer. Is it possible to get rid of it?
My homemade amplifier (D.Walton 300B
XLS MKIII schematic) is working normally with one exception. When I turn power
on the amplifier for the first 30-45 seconds appears vibration like silent but bored noise and this leads me
crazy. Others suggest not paying attention to this but I can't.
Maybe not quite well, I covered two
main toroidal transformers under one cover and sealed it with epoxy.
My attempts to find the source of the
noise were as follows:
I grounded inputs and verified
voltages – everything – OK.
1. Then I removed all the tubes,
turned power on – from the main transformers cover - dead silence - everything
is OK. No load - no noise.
2. OK - I inserted GZ37 only, turned
power on – after about 10 - 15 sec
appeared growing vibrating noise from the main transformer, which after 30
seconds became poorly heard.
3. Then I disconnected one of
toroidal transformers from the main. What was interesting I found high voltages
in completely from the main disconnected second transformer, only not standard
ones, but about 300 – 0 - 500 V. When connected again both transformrs, voltages
also have become standart 450 - 0 – 450 V on both transformers.
Maybe this electromagnetic
interaction between two closely fitting toroidal transformers under one cover
is the cause of noise? But I can’t do anything because these transformers are
already deadly buried in epoxy. Replacing them with new ones and making anew
different layout would cost me over 400 € and almost all of
the amplifier to be rebuilt. Is it possible to change something not so
painfully? Maybe the vibrational noise reason is different?