I wonder what to make of this. Do you think it suggests that a suitable passive pre sounds better than a wire directly from the source? I think this is something along the lines of what Tony was saying, not that it’s sensitive about preamps, but that it’s betted with a preamp.
A 10K passive has a worst case output impedance of 2.5K and probably more like 1.8K in normal use, which is fairly active pre-amp-like. I was aware that the 50K one I was using was not optimum because the KSA50 has a 470pF capacitor at the input preceded by a 1K resistor and with the worst case 12.5K impedance before it this means worst case of -3dB @ 25KHz, probably more like 30KHz in normal use. This would mean probably 1dB down @ 18KHz or so, probably not too much of an issue for any of us over 25 or so! Not ideal though... (FM radio only goes up to 14.5KHz and Red Book CD to 21KHz ish)
In practice though something "weird" was going on and you wouldn't have believed it was the same amplifier with the two different value passives.
This gives some credence to TonyL's assertion that it's better with active pre amps.... or more likely that it likes low source impedance's such as those given by an active pre amp, or a 10K passive...
I don't know the details of your Theta DAC but assume you are using it directly driving the Krell and using an on board remote vol control on the Theta? I would assume that the Theta has a low output impedance, probably similar to that of an active pre as in fact a variable output at low impedance from a buffer on anything
is basically an active pre... just it's built into the DAC and has the DAC as its only source...
There are a variety of reasons why it
may not be ideal though. If the vol operates in the digital domain it may be restricting the amount of effective bits in use as vol is lowered, hence only giving its best at full volume and needing a pre of some sort after it to control vol.
Another possible is that it has an unusually high output impedance for such a unit... or maybe has a motor driven passive pot without a buffer at output and so is like a passive.... maybe of 50K!
The above are fairly unlikely though
So.... at the end of the day try whatever you like with it and see how you like the sound (yep I could have just said that at the beginning instead of the long preamble
). For me the 10K passive driven by my modded DPA Little Bit DAC was excellent! YMMV
Be sure to switch it off and leave it for a good couple of minutes before unplugging anything/plugging in anything new!
Hope that helps
Edit: As Tony just beat me to in far less words!