[AMRadio] Mic opinion

[Jim Candela]

 Charlie,
    I can only make one point, and that is the position of the volume control knob can have an effect on the linearity of the next stage. This might sound crazy, so let me splain. The audio drive has a source impedance, and the next stage has a load impedance. When the audio gain pot is at the limits (0 or 100%), the source impedance is zero ohms. With the pot in the middle, the source impedance is no less than 1/2 the resistance of the pot end to end. If the pot is 500K, then think like 250K source impedance plus the plate resistance of the driving stage. Then consider the next stage is a triode, and it might have 2-5pf grid to plate capacitance, and something similar from grid to ground. That 250K + source impedance will draw down the signal as the peak approaches the point where the control grid draws grid current. For some tubes, this happens several volts before the actual knee of grid current is achieved. This means one half of the signal gets attenuated more than the other. Then consider what happens at 100hz versus 3Khz were the capacitance of the load causes a low pass where the Fc point is lowest when the source impedance is highest (mid way on the volume control).
Yep, I should be shackled, and put in a rubber room!
JimWd5JKO
    On Monday, July 26, 2021, 6:27:04 PM CDT, CL in NC via AMRadio <amradio at mailman.qth.net> wrote:  
 
 A friend of mine has a Collins SM-2 mic feeding a 32S-3 that appears to be anemic audio output wise so he is looking for a new mic.  I have a Shure mic made for Collins (yea, its gray and says Collins on it, whoopee) and it put out plenty of signal such that the mic level pot is lower than 12 o'clock on the dial, while the SM-2 is around 4 o'clock.  What is the consensus on the Heil Sound GM-VINTAGE for tube gear?  I did post this on the Collins email chain, but sometimes a viewpoint not muddied by love of Collins helps.  Anybody have a line on a good tube gear mic company that is not Heil?

Charlie, W4MEC in NC
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