Connecting an improved Pleiades filter to MD211

This is part 3. See nearby euroelectron posts for 1 and 2.


In the last part an inductance of 82mH in series with 140Ω was connected across the excellent MD211 mic's output. Then the usual Altec 4722 input transformer...


Signal path, setup:


Male singing voice (απόψε σε θελω - Marinela) - improved Pleiades filter (L,R) - Pleiades V6 with Altec 4722 input transformer - Sony TC-D5 Pro at XLR mic in - Sennheiser Hd580


The sound is very nice and it was decided not to rotate the 140Ω potentiometer from the 140Ω value assumed by chance.


After a few days, ie today, the setup was turned on again. Sound was great as usual perhaps a bit bass heavy at high registers of voice. (For men using falsetto voice there may be bass artifacts on any mic setup, increasing the distance of directional mics may help as bass is reduced.).


Another 82mH Pleiades filter was lying around near the Pleiades V6 head amp. It was connected after the 85mH inductor. The two inductor together (in parallel) make a turnover of less than 800Hz. The untouched 140Ω resistance creates a very gentle slope.


The sound was phenomenally nice too. Some of the falsetto bass artifacts disappearing. Ordinary non falsetto singing sounds amazing too. Natural.


It is very easy to hear what the L,R Pleiades filter does. By just disconnecting the crocodile clip to one of the resistor's terminals it is out of the circuit. The perceived sound is back to bass heaviness.


Reconnecting the filter bass heaviness disappears. And mid and treble is back.


Adding the extra inductor in parallel to the other inductor reduces some slightly annoying part of mid range.


These filters sound similar to what is done when engaging the HF boost on an Sennheiser MD441. It is not that the treble is boosted, it is more that some mid disappears etc. This is best observed while singing a steady note and playing with the filter.


More interesting experiments are needed to approach the ideal of flat frequency response from producer's brain to listener's brain.


The Pleiades reference at the time being is When I Fall in Love - Nat King Cole.


And the mic reference is the Grampian DP4/L connected to the 140mH input transformer pluged to the Pleiades V6 head amplifier.


For some reason the DP4/L does all that is needed without the need of any EQ rather than the usual 140mH shunt that works very well with its 25Ω voice coil.


Reference:


Flat frequency response from producer's brain to listener's brain, Sound Picture Recording and Resproducing Characteristics - D.P. Lowe and K.F. Morgan - J.S.M.P.S.E.