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
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