What is a nice sounding distance and Pleiades inductance for Shure Unidyne III

This experiment started by singing to Shure Unidyne III, amplifying it with Pleiades V5 and then directly driving a cassette recorder stereo head kissing with the playback head of Sony TC-D5 pro. This is described on the previous post and is a first attempt to analog simulate analog tape recording in real time with no tape moving or other moving parts.


The analog simulation gave a loud sound.


The Pleiades V5 has an input inductance of only 47mH making a very bright sound out of the Unidyne III.


After the tape simulation experiment the V5 was directly connected to Sony TC-D5 Pro for comparison as follows:


Signal path, setup:


Living room with Pleiades membrane absorbers - male voice singing the end phrase of Words - Bee Gees - Shure Unudyne III hand held at various distances - Pleiades V5 with its output pad - Sony TC-D5 Pro to its XLR transformer input, at mono - TDK type II cassette - Sennheiser HD580


The sound was nice but very bright.


It was decided to increase the inductance the mic sees to get more bass.


So the mic was directly connected to Sony TC-D5 Pro using only various Pleiades filters.


Setup same as above with the following difference:


...- Shure Unidyne III - Pleiades filter - Sony TC-D5 Pro -....


Naturally the first Pleiades filter tried was 52mH which is very close to the 47mH input transformer primary inductance of the V5 prepreamp.


The sound was similarly bright but weaker and the TC-D5 rec level pot had to be at max for full modulation compared to 3-4 when using the V5 with its output pad.


Next an 82mH Pleiades filter was connected and the mic used at 2 in with better sound.


Then 135mH corresponding to about 200Hz turnover. The best distance was about 3in and the sound was fuller.


Then 333mH or about 100Hz 3 dB cutoff point was used with the mic sounding best at 4-5in and full bass and treble and mid range sound. This seems to be the sweet spot combination.


Then ni Pleiades filter was used. The sound was very bass heavy due to proximity effect even at 12in.


Summary:


The best combination was a mic mouth distance of 4-5in and a Pleiades shunt inductance of 330mH or 100Hz cutoff.


The use of Shure Unidyne II was inspired by Brian Wilson using it for vocals on Pet Sounds and Bruce Springsteen on Nebraska (SM57).


Very beautiful mic. With a Pleiades filter it becomes very bright at very small distances. The 4-5in distance may be the optimum for the particular setup described.


If the Pleiades V5 is to be used with this mic the primary transformer should be redesigned with more primary and secondary turns or a larger core so that the input inductance is of the order of 330mH.