It appears that the VPC-1 has a total resistance of 10K. I suspect that the problem will not occur with that in place, which would help to confirm the diagnosis I proposed.
However I suspect that 10K is too low a value to be a permanent solution. Interaction of the 10K load with the rise in the preamp's output impedance that most likely occurs at deep bass frequencies, as a result of the coupling capacitor it probably uses at its output, will probably result in perceptible rolloff of the deep bass.
I don't think that would occur with the approximately 33K input impedance of the 10 db Rothwell attenuator (as measured by me, using a not particularly accurate analog multimeter).
Also, since the Rothwells would be inserted directly into the input jacks of the power amp, with no intervening cable, the possibility of sonic effects resulting from interaction of the VPC-1's output impedance with the capacitance of the cable connecting it to the amp would be eliminated.
Best regards,
-- Al
However I suspect that 10K is too low a value to be a permanent solution. Interaction of the 10K load with the rise in the preamp's output impedance that most likely occurs at deep bass frequencies, as a result of the coupling capacitor it probably uses at its output, will probably result in perceptible rolloff of the deep bass.
I don't think that would occur with the approximately 33K input impedance of the 10 db Rothwell attenuator (as measured by me, using a not particularly accurate analog multimeter).
Also, since the Rothwells would be inserted directly into the input jacks of the power amp, with no intervening cable, the possibility of sonic effects resulting from interaction of the VPC-1's output impedance with the capacitance of the cable connecting it to the amp would be eliminated.
Best regards,
-- Al