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found a couple used SM58s REALLY cheap (about $3 ea.) but the catch was that they were in REALLY crappy condition (worn finish, dented grills, bits of rust). Anyway, was looking at them and noticed some things that seemed odd about them, namely a "DUAL IMPEDANCE 50 & 150 OHMS" marking around the band at the base of the grill plus what was apparently an extra orange wire coming from the internal transformer that did not appear to be connected to the XLR output at the bottom of the mic. So, after initially finding a sliver of info (a slight mention of "a secondary tap on the transformer that was eliminated about 15 or 20 years ago related to a 50 ohm output impedance condition that was no longer a factor") on the Shure site, I didn't turn up much. However, after more persistent digging, I finally turned up what looks to be the best and clearest info on this, so here it is for anyone that happens to wonder about this and look for information on this:
from Tim Vear of Shure back in 1995:
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A Short History of the SM57
The Shure Model SM57 is a unidirectional (cardioid) dynamic microphone.
It employs the Unidyne III cartridge, originally used in the Model 545.
The Unidyne III is the third generaton of the first Unidyne cartridge used
in the Model 55 in 1939. The Unidyne II was used in the "small" Model 55S
brought out in 1950. The 545 was introduced in 1959 and the SM57 followed
in 1965. The Unidyne III was designed primarily by Shure engineer Ernie
Seeler.
The SM57 was offered as a high quality microphone for speech applications
in broadcast, recording and sound reinforcement. Though the microphone
achieved some acceptance in the broadcast field, its ultimate success was
with live sound applications and recording. By about 1968, the SM57 had
been "discovered" by the fledgling concert sound industry. To engineers
at that time (and now as well) the microphone presented a very useable
tool: wide frequency response with an intelligibility enhancing presence
peak, a very uniform cardioid polar pattern to minimize feedback and other
unwanted pickup, and an affordable price (the original retail price was
about $85 with cable).
Over the years the SM57 has established itself as the second-most popular
microphone in the world (after the SM58). It is widely used in both live
sound and recording applications, in particular for vocals, guitar
amplifiers and snare drums. It is used in such a large variety of
situations that it often tops engineers' lists of "the one microphone to
be stranded with on a desert island."
Concerning changes to the SM57 since its introduction: there has not been
a major change to the basic microphone design. However, there have been
numerous small changes and improvements in the intervening 30 years. Here
are some of the more noticeable ones:
1. Original separate male XLR end cap was integrated into one-piece
handle casting (1960's).
2. Original metal closing ring (houses cartridge body) changed to plastic
(at least twice).
3. Plastic closing ring changed back to (current) metal (at least twice,
last time in the 1970's).
4. Brown "gooey" transformer potting compound changed to RTV silicone
(1970's).
5. Metal side screen eliminated from grille assembly (1970's).
6. Grille locking ring strengthened (1980's).
7. 50 ohm tap (orange wire) eleminated from transformer (1980's).
8. Black ground wire to cartridge replaced by ground tab on XLR connector
(1990's).
The essential cartridge parts (diaphragm, voice coil, magnet, pole piece,
acoustic resistance network, shockmount) remain as originally designed.
Output level has remained constant as has the polar pattern. The overall
frequency response of today's units is still within a few dB of the
original test curves.
Shure's basic philosophy on the SM57 (and other classics) remains: "if it
ain't broke, don't fix it!"
Tim Vear
Applications Group
Shure Brothers Inc
http://groups.google.com/group/rec.a...7c76ec5f45db0?
from Tim Vear of Shure back in 1995:
-----------------------------------------------------------------------
A Short History of the SM57
The Shure Model SM57 is a unidirectional (cardioid) dynamic microphone.
It employs the Unidyne III cartridge, originally used in the Model 545.
The Unidyne III is the third generaton of the first Unidyne cartridge used
in the Model 55 in 1939. The Unidyne II was used in the "small" Model 55S
brought out in 1950. The 545 was introduced in 1959 and the SM57 followed
in 1965. The Unidyne III was designed primarily by Shure engineer Ernie
Seeler.
The SM57 was offered as a high quality microphone for speech applications
in broadcast, recording and sound reinforcement. Though the microphone
achieved some acceptance in the broadcast field, its ultimate success was
with live sound applications and recording. By about 1968, the SM57 had
been "discovered" by the fledgling concert sound industry. To engineers
at that time (and now as well) the microphone presented a very useable
tool: wide frequency response with an intelligibility enhancing presence
peak, a very uniform cardioid polar pattern to minimize feedback and other
unwanted pickup, and an affordable price (the original retail price was
about $85 with cable).
Over the years the SM57 has established itself as the second-most popular
microphone in the world (after the SM58). It is widely used in both live
sound and recording applications, in particular for vocals, guitar
amplifiers and snare drums. It is used in such a large variety of
situations that it often tops engineers' lists of "the one microphone to
be stranded with on a desert island."
Concerning changes to the SM57 since its introduction: there has not been
a major change to the basic microphone design. However, there have been
numerous small changes and improvements in the intervening 30 years. Here
are some of the more noticeable ones:
1. Original separate male XLR end cap was integrated into one-piece
handle casting (1960's).
2. Original metal closing ring (houses cartridge body) changed to plastic
(at least twice).
3. Plastic closing ring changed back to (current) metal (at least twice,
last time in the 1970's).
4. Brown "gooey" transformer potting compound changed to RTV silicone
(1970's).
5. Metal side screen eliminated from grille assembly (1970's).
6. Grille locking ring strengthened (1980's).
7. 50 ohm tap (orange wire) eleminated from transformer (1980's).
8. Black ground wire to cartridge replaced by ground tab on XLR connector
(1990's).
The essential cartridge parts (diaphragm, voice coil, magnet, pole piece,
acoustic resistance network, shockmount) remain as originally designed.
Output level has remained constant as has the polar pattern. The overall
frequency response of today's units is still within a few dB of the
original test curves.
Shure's basic philosophy on the SM57 (and other classics) remains: "if it
ain't broke, don't fix it!"
Tim Vear
Applications Group
Shure Brothers Inc
http://groups.google.com/group/rec.a...7c76ec5f45db0?
Just looked inside one, and it seems to be the same color code (a blue to pin 2 and and red wire to 3, black wire to shield pin 1).
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