[dwicin]

In the STEREOPHILE review of January 2008 on page 141 of the "measurements" by John Atkinson, he states in the second paragraph that "The input impedance was lower than specified, at 7.5 ohms unbalanced, 10.2 ohms balanced.  This will result in a slightly lean bass with some tubed preamplifiers."  I use a McIntosh 220 tube preamplifier that has an output impedance of 250 ohms.  A tacT RCS 2.0 digital preamplifier has 66 ohms balanced output impedance.  Why would the difference affect only the bass and not the complete spectrum?

[James Tanner]

In the STEREOPHILE review of January 2008 on page 141 of the "measurements" by John Atkinson, he states in the second paragraph that "The input impedance was lower than specified, at 7.5 ohms unbalanced, 10.2 ohms balanced.  This will result in a slightly lean bass with some tubed preamplifiers."  I use a McIntosh 220 tube preamplifier that has an output impedance of 250 ohms.  A tacT RCS 2.0 digital preamplifier has 66 ohms balanced output impedance.  Why would the difference affect only the bass and not the complete spectrum?

Hi,

The lean bass could occur because the tube preamp has output capacitors.  The input impedance of the amplifier could form an R/C filter with the capacitor with a cutoff frequency in the audible range. 

All 28B SST's now have the input impedance corrected to the proper specs.
 
cwr