Why do some fine solid state amplifiers like Soulution have such low input impedance?

... does increasing the bias in a SS amp have an effect on input impedance? Or, put another way, could you increase the operating bias in an amp without raising the input impedance, and if you did that what would be the sonic trade offs?

"Increasing the bias" usually refers to the biasing of the output stage of a power amp or integrated amp. So it would not have any effect on the input impedance, which is determined by the input stage. Increasing the bias can of course affect sonics in various ways, depending on the specific design, but the range of acceptable bias points is limited by some combination of thermal considerations, the characteristics of the particular output devices, the voltages they are operated at, and various other aspects of the specific design.

Best regards,
-- Al

I can attest to Steve McCormack's use of low output impedance on his amp revisions.
When I got my DNA-1 monoblocks back the impedance was so low I now need to use a Jensen Transformer to covert the XLR signal to RCA in order to use my Vandy crossovers at lower impedance than I can get using balanced. A bit of a bummer. And, I still haven't had time to install everything. Ralph's MA-1's/MP-3 are so good that I have little impetus to change things.
Oh well, something to work on later...
Bob

Hi Guys - I just saw this thread and thought that I ought to chime in to (hopefully) clear-up any potential misunderstanding. All of the McCormack DNA amplifiers except the DNA-500 and DNA-750 monoblocks have a 100kohm input impedance, and this is true whether they are stock or upgraded. It is *only* when adding balanced inputs or converting a stereo amp to a monoblock that the input impedance drops to 10kohm, and this is because of the nature of the transformers I use for balancing and phase-splitting. I prefer these transformers to any other technique I have found, but it is true that the 10k input can occasionally cause some impedance-matching issues. Usually this only comes up when there is a speaker that requires the use of a passive high-pass filter before the amp input and the capacitor values must be matched accordingly (as in the case of the Vandersteen speakers with self-powered woofer sections). There have also been a few cases where a tube preamp had an unusually high output (source) impedance (over 1k), and this means that the impedance match (following the 10-to-1 rule of thumb) is less than optimal (even though it may still work well and sound good).
The technique I use for creating balanced inputs or a monoblock amp treats both the XLR and RCA inputs the same way, so both are the same 10k input load. I have made a few stereo amps with a switchable input feature so the user could have both a balanced 10k XLR input and an unbalanced RCA at 100k, and that has worked well for those folks.
Bob, I apologize but I am confused by your comment and don't understand why you felt the need for an additional transformer conversion. I'm glad you are enjoying your Atmasphere setup but if I can help you with your DNA-1 monoblocks, please let me know.
And, as always, if anyone else has any questions about my gear, feel free to contact me at SMc Audio.
Cheerio -
Steve McCormack