Modding Dayens Ampino

[DECKY999]

I played a bit recently with this amazing little amp. I attached the pics of the original amp (taken from 6moon audio). It is based on a BJT pair 2SA1943/2SC5200 per side, in the output stage - around 25W in 8oms. Beautiful warm sound.

My goal was to re-box it and to improve the PSU. In addition I was planning to replace the volume control. I did all of that. I removed all components from the old PSU, volume control (carbon pot) and the input switching relay. I used the Twisted Pear Audio ladder attenuator (Joshua tree) which has a constant output impedance of around 750ohm.

After finishing I realised that there is a buzz - fairly high frequency one (5-6kHz). It was not the grounding issue, it was not the transformer capacitative or magnetic coupling (trafo is screened and shielded). The only thing the buzz was sensitive to was output impedance of the volume control. I put a 1K resistor in parallel to the volume output which made the buzz 50% quieter but it is still there. The original volume pot was a standard 10K unit. When the input to the amp (output from the vol control) is shorted the amp is absolutely quiet.

Does anyone have an idea what might have caused this buzz?