Passive preamp issues or?
I’d say without ever doing the experiment to see on the test bench or hear also, this 47kohm output impedance "could" be the problem. As it will also be "capacitor coupled" as well being tube which "could" make it even more of a problem if the caps not large enough, or an electrolytic, who knows, as it’s not following the output input >1:10 "rules" as we know them. Cheers George |
I put the pre-amp back in the loop. Dead quiet- decided I couldn’t live with the hum. FWIW- and I don’t clearly understand the logic behind this, if I keep the amp connected to the speakers and disconnect the dac from the amp, the hum is worse. Disconnected every that might contribute to the hum- no change. I may just look at better IC’s from pre to amp to see if I can wring some improvement. It’s really a pretty good system as it is- I may just need to tweak with the pre in the loop. |
As I asked you to put in your Blue Note 2 in, did you? (which also has volume) Direct into the poweramp, and then you can see if the problems disappears. If it does then the Jolida tube output is the problem, and even if it doesn’t make noise will still be an impedance mismatch at 47kohm with the input impedance of the Axiom pre also. Cheers George |
There it is! The problem is either the high output impedance of the Jolida at 47kohm (which is wrong for anything mind you) save the input impedance of Rogue M120 monoblocks, which are for memory 1megohm, or similar, they would give a good ratio of around 1:20. https://www.stereophile.com/content/rogue-audio-magnum-m-120-monoblock-power-amplifier-measurements Or maybe it’s the Jolida output coupling cap with that impedance, or could be earthing. But I don’t think you’ll ever find any manufacturer with a source product that has around 47kohm output impedance. Cheers George |
