"Arny Krueger"

An interesting related article can be found at
http://www.eetasia.com/ARTICLES/2002...MSD_POW_AN.PDF

Most interesting is:

"Figure 3 shows the effect of preamp input resistance (and capacitance) on
frequency response of a Shure SM57 with 100 feet of common cable. The
upper
curves, 10 kS and 3 kS, are typical of transformer-less mic preamps while
the lower curve, 1.5 kS, is typical of a transformer input mic preamp.
Note
the ultra-sonic peaks in response caused by insufficient damping".

This chart gives some insight into the output impedance of a SM57. To
summarize, there is negligible change in response at 3 KHz with load
impedances varying from 1,500 ohms to 10,000 ohms. IOW, the source
impedance
of a SM57 in the normal audio range (20 KHz) is quite small. Other
sources
give it as being 150 ohms or 310 ohms. It may be even less - perhaps 75
ohms or less. The same charts show an approximate 5 dB range of response
at
20 KHz but less than 1 dB variation at 10 KHz. None of this is all that
audibly significant.


** Fig 3 in the Jensen article shows an overall variation of less than 2dB
at 20kHz for the three load impedances at the end of 100 feet of cable
driven by an SM57. At 15 kHz, or the highest frequency an SM57 actually
reproduces, the variation is less than 1 dB while at 10 kHz that variation
is less than 0.5 dB.

The HF response variation between different samples of the SM57 is a lot
greater than that !!



............. Phil