The following spectrum is the Mani left channel RCA output (no input) with the Mani set to the low output moving coil gain setting (Gain stages 1 and 2 both at Hi).
In this high gain mode there is power supply rectification harmonics evident at the RCA outputs, with the Left channel being most impacted and the Right channel some 6 db lower.
I have identified the cause of the harmonics, this being the physical layout of the Bridge Rectifier and the main filter capacitor C1. Capacitor C1 is mounted horizontal on the circuit board and lays directly over the Gain Stage 1 OpAmp and associated components. While C1 is on the top face of the circuit board the input OpAmps are directly below on the other side of the circuit board. The high current transients resulting from the rectification of the 16VAC power supply input passing through C1 filter capacitor generates an EMI signal which is being induced into the Gain Stage 1 OpAmps and/or associated components. This issue is not a power supply design issue but one of physical layout dictated by the small size of the Mani case. I am in Australia so the power supply rectification harmonics are at 100Hz intervals.
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I have modified my Mani such that the power supply harmonics are now absent as shown in the spectrum plot below, also the 50Hz power supply hum component related to the 16VAC input power is also reduced.
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If anyone is interested I can supply further details on the approach I took to resolve this issue. I undertook this measurement after ordering a Hana ML moving coil cartridge and wondering what the Mani Hi Gain noise performance looked like. I think it sounds superior now, the best part is I can measure the difference!