"Arny Krueger" wrote in message ...
Phil Allison wrote:
"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 !!

This article seems to throw quite a bit of cold water on the many claims of
dramatic sonic differences due to real-world variations in the loading of
SM57s by various preamps and cables.

I was under the impression that the interesting loads for the SM-57
were reactive rather than resistive. I think Mark McQ added some
reactive load (a low pass filter on the input for RF rejection) to his
RNP in part for this reason.

rossi