A method to gently low cut the Sennheiser MD21 HL

At your own risk.


The Sennheiser MD21 HN is one of the best microphones on the planet.


For a not loud singing voice and loud acoustic reproduction it can sound bass heavy to our brain due to Fletcher-Munson, voice effort curves.


One way to get flat frequency response from producer's brain to listener's brain is their following:


We exploit the fact that there's is an internal transformer stepping up the voltage. So we may connect the hiZ out to a JFET or electron tube. So we have a world class signal to noise ratio. See Pleiades K117, Pleiades V4, V6 etc.


We may then use the low Z output of the transformer for filtering the excess ear brain bass. For example an LR (L in series with R) Pleiades filter can be connected, (see previous posts). So without doing any modification to the microphone a 3 conductor and screen cable can be used and everything can be implemented on the other side. We may use the fact that star quad cables have 4 conductors if we cannot find a high quality 3 conductor cable.


If we use a Pleiades K117 JFET head amp it can be powered by the mic in of devices for electret mics. Or we can use an AA battery power supply inside those plastic barrel box adapters etc. Then we may feed a world class Sony TC-D5 M, Maractz PMD430 or Uher 4200 possibly obtaining an amazing signal to noise ratio and flat frequency response from producer's to listener's brain. It might be possible to use the input resistor of a Marantz PMD430 or CP430 etc as the load resistor, further reducing the number of components, see relevant Marantz post. Or a Nuvistor 7586 electron tube can be connected to the hiZ MD21 through a capacitor to control grid. use Pleiades bias and all we need to do then is power the heaters and anode with about 4 volts. ;The anode resistor may be the device in out resistor). See previous Pleiades V6 Nuvistor posts. A fuse should always be used is series with a battery for safety. See relevant post.


Of course we may also make an XLR female to male adaptor and include inside the Pleiades LR filter (see previous posts) and then feed a balanced mic in low Z input. Even with only 82mH in parallel the MD21 can sound brilliant, but it is best to include a series resistor to the inductor to control the slope. Signal to noise will depend on the front end amplifier. An ultra low noise front end is the Pleiades V6 electron tube head amp. Recently 22nF is used and a Pleiadss biasing anode to grid resistor of 6MΩ.





Bibliography:


Flat frequency response from producer's brain to listener's brain, Sound Picture Recording and Reproducing Characteristics - D. P. Lowe, K. F. Morgan - JSMPE