At your own risk. Take ultimate care of your microphones and most importantly of your ears.
On previous Pleiades experiments many world class microphones sounded worst than they should when connected to the very analytical Pleiades V6 booster amplifier.
By connecting an AKG D1000 E the sound was immediately very clear at mid bass when proximity compensation was done by the the mic's internal switchable filter instated of relying on the input transformer of the V6.
A logical step was to unplug the (1:10, 140mH input transformer) and plug in the green Altec 4722. The massive bass when the mic was used at a few inch distance was compensated by reducing the coupling capacitor from the transformer secondary to the grid of the EF183 electron tube.
The input impedance of the grid of the EF183 on the V6 booster amplifier is typically 100KΩ. The 6dB/oct low cut or high pass filtering action is produced by the coupling capacitor and this resistance forming an RC circuit.
A variable Heatkit switchable capacitor box (condenser substitution box CS-1) was connected. Each of the many internal capacitors can be inserted in the circuit by the Rotating the switch while listening in real time. A very useful parametric filter. The results of best sound for close use of microphones are as follows:
(A proximity compensating filter should not be confused with an ordinary low cut at 100Hz. The proximity effect can boost even 500Hz for example, as can be seen on any directional microphone published curves, making a world class mic sounding unusable at a few inch. Their slope is gentle at
only 6dB per octave. An 6dB/oct 100Hz low cut is already present on the Pleiades V6 by the interaction of the electron tube output impedance and the input inductance of the output transformer).
For male voice
Mic Capacitor value
Paso 980 3in-4in 2.2nF
MD441 various close distance 1n
D112 2in,1n 9in,1.5n 2ft,2.2n
SM58 Mexico 1n as D112
515SB (Unidyne B) US 1n,1n 3in,1.5n 1ft,2.2n
Unidyne III (vintage SM57) 2in-4in,1n
SM200 (Schaub Lorentz) as D112
A following up experiment may be connecting a capacitor directly to the mic output so that the primary of the input transformer receives a clean non bass heavy signal. Or for example, how would it sound like by connecting a capacitor in series with the low Z(25Ω?) voice coil of the Shure SM58 and then normally connect to the internal mic stepup transformer?
(Later addition)
After substituting a descrete 1nF capacitor to the above setup buzz noise was of course reduced but some hiss was revealed.
Also a preliminary test was done with an MD441 U3 (the one with no internal low cut filter) directly connected to a capacitor. The Altec input transformer was then fed. The sound was nice on mid and especially high frequencies but not too great on low frequencies. Some hiss was apparent too. The best sounding capacitor values were 200nF to 150nF to 100nF. At some stage this experiment may be repeated with 2 capacitors on each 2,3 pins as this is a balanced circuit.
As of now possibly the best Pleiades setup is the one with the Grampian DP4/L for omni mics and AKG D1000, Schaub Lorenz SM200 for unidirectional mics, and Grampian GR1/L (stepped up as described on a previous post).
Therefore the best sounding Pleiades setup so far is possibly:
Grampian DP4/L at 1in-6in - Pleiades V6 with 1:10, 140mH input transformer - Sony TC-D5 Pro - Sennheiser HD580
A very natural, full sound and low noise too.
No comments:
Post a Comment