McCormack DNA 500 vs DNA 225 upgraded

@stevemcx  What are the rated RMS and peak currents? I’m by no means an expert, but I wonder why your amp was designed with a low input impedance (10k ohms), which tends to create an impedance mismatch issue. Since it is transformer-coupled, could the input stage be adjusted to increase its impedance?  Thanks.

I believe Steve is partially/mostly (trying to be) retired, like others of us, so you may not hear from him.  He has not had anything to do with the DNA 500 or 225 for many years as Conrad Johnson acquired McCormack Audio and took over those designs.  Steve’s company SMc Audio performed upgrades to both but maybe not the DNA 500 any more.

I will not try and answer your questions but as a former owner of the DNA 500 I can say it is effortlessly driven by virtually any solid state preamp, and that I have successfully used it with tubed preamps with output impedance as high as 600 ohms.  The old rule was a minimum of 1 to 10, output impedance of the source to input impedance of the load.  My personal goal was to keep that ratio at 1:20 or better.

Here are some specs for the DNA 500, FYI:

• Output Power:
  • 500 watts per channel RMS into 8 ohms
  • 900 watts per channel into 4 ohms
• Output Current: 50 Amps peak per channel
• Input Impedance: 100k ohms
• Input Sensitivity: 1.2V
• Frequency Response -3dB at 0.5Hz and 250kHz
• Rise Time: ±2µs
• Slew Rate: 50V/µs
• S/N Ratio: 88dB, "A" weighted
• Damping Factor: >100 (1kHz, 8 ohm load)

Thank you for the response, @mitch2.  Very kind of you. 

It is strange that the input imp. vary across the different model same series - 100k for DNA 225, 10k for DNA 500 and 13k for the mono DNA 750.  The measurements by Stereophile on the 225 show 91k ohm for its input impedance and ideally low 0.07 ohm for the output.  Don't quite comprehend the inconsistency.

Different designs. The DNA 500 and 750 are bridged designs while I believe the 225 is a stereo amp.