Frequency respone trace

1

Hi

I have done some response of amps

I got the picture in attach

I can’t understand why from 1kHz to the high end the trace became thick

With both sw

Thanks

KIT3_DX_Risp_2,5watt
KIT3_DX_Risp_2,5watt1550×878 109 KB

2

Looks like some kind of instability.

It’s quite visible between 200Hz and 1kHz

3

The test was done on AudioNote Kit III, SEPP of 300B, and the doubt is about the secondary of OT where the 0 terminal is not to ground.

I will check, maybe this is the reason

Walter