McCormack Amp question

For those of you with McCormack amps, are the difficult to mate with tube preamps because of their low impedance?
They work excellently with both tubed and passive preamps. They were designed for use with Steve's passives, but have a certain magic combined with tubes, actually.

Hello Ehoehn -

Most of my amps have a 100Kohm (high) input impedance and are easy to drive with any type of preamp. The only amplifiers I produce with a 10Kohm (low) input impedance are the DNA-500 and the SMc Audio-upgraded amps that include my new balanced input circuit or those that have been converted to monoblocks. I now use a transformer for input balancing and phase-splitting, and this results in a 10K input impedance. Most active preamps will drive this without any problem, and many transformer-based passive systems (like the Bent Audio NOH) also do a fine job. However, passive units that use conventional volume potentiometers or resistive-ladder attenuators (without active output buffering) and a few tube preamps with unusually high source impedance (over 1000 ohms) are not likely to give the best match.

Best regards,

Steve McCormack