I have an issue with my F5 and pre-amp (well pot with buffer to be precise) combo and I can't make sense of it.
Warning: This is my first power amp and pre-amp, though I have built some headphone amp kits, so it could be quite obvious to you guys... Also, English is not my first language (having moved from continental Europe to the UK) so please excuse my lack of suitable vocabulary at times.
Laptop --> Audioquest Dragonfly --> F5: All good. Centred image (mono test track), no hum (by ear with my Tekton Lore Reference, 96dB [email protected] claimed).
RaspberryPi w/ Allo Boss 1.2 DAC --> ACF 12Vac --> F5: Hum on both channels and image is slightly to the right (from listening position).
At first I thought it must be the pot or the pre, but there was no issue with the previous amp (Onkyo A-9010), nor with my Bottlehead Crack headphone amp. Hence the conclusion that it must be the "interaction" between pre and F5.
Following THIS presentation it sounds like a cross-channel ground loop. I tied the input grounds together at the chassis with a clamped on wire to try to solve it, but there was no noticeable effect. Not sure if the F5 has hum breaking resistors on the PCB... and how would that affect the channel balance / centre imaging? Maybe one side is oscillating?
The hum is not very loud, so I could live with it if I have to, but not with the off-centre imaging.
Please find some pictures attached. The case of the ACF 12Vac is connected to the star-ground on the PCB through a 3W resistor/cap under the board (so not visible).
Warning: This is my first power amp and pre-amp, though I have built some headphone amp kits, so it could be quite obvious to you guys... Also, English is not my first language (having moved from continental Europe to the UK) so please excuse my lack of suitable vocabulary at times.
Laptop --> Audioquest Dragonfly --> F5: All good. Centred image (mono test track), no hum (by ear with my Tekton Lore Reference, 96dB [email protected] claimed).
RaspberryPi w/ Allo Boss 1.2 DAC --> ACF 12Vac --> F5: Hum on both channels and image is slightly to the right (from listening position).
At first I thought it must be the pot or the pre, but there was no issue with the previous amp (Onkyo A-9010), nor with my Bottlehead Crack headphone amp. Hence the conclusion that it must be the "interaction" between pre and F5.
Following THIS presentation it sounds like a cross-channel ground loop. I tied the input grounds together at the chassis with a clamped on wire to try to solve it, but there was no noticeable effect. Not sure if the F5 has hum breaking resistors on the PCB... and how would that affect the channel balance / centre imaging? Maybe one side is oscillating?
The hum is not very loud, so I could live with it if I have to, but not with the off-centre imaging.
Please find some pictures attached. The case of the ACF 12Vac is connected to the star-ground on the PCB through a 3W resistor/cap under the board (so not visible).