All these microphones are balanced too.
They have an autotransformer to step up the impedance if needed but this does not change much.
If one looks at the schematic or measures the pins with an LCR impedance meter:
The voice coil (low impedance) is directly connected to 2 of the pins. So there are balanced as a voice coil is by definition balanced.
The high impedance part of the autotransformer (full coil) is also connected to 2 pins so it is balanced too as it is a coil too, (the only difference being it is a coil of more turns outside of the microphone voice coil).
In the above situations a pin is common to avoid the use of 4 pins. So everything is done on a Tuchel 3 pin or DIN 3 pin in the case of the M55. Same reasoning applies to the Grundig GDM311.
To summarize:
An autotransformer has 3 terminals.
The first two terminals are connected to the voice coil and the 2 output pins.
The end of the winding hi Z terminal is connected to the other pin.
It follows the other side of the auto winding is common. This is by manufacturer convention connected to the central pin of the output connector.
It follows the other pins are low Z and high Z.
The metal part of the microphone is not internally connected to any of these pins and this is good news for maintaining balanced output.
To summarize again:
There are 2 output options. The voice coil itself and the full autotransformer winding. Both are floating windings so they are balanced.
The fact that the voice coil is also connected in parallel with the low Z part of the autotransformer is not bad too as the latter acts as a Pleiades filter cutting some low end and making the microphone closer to flat (to listener's brain) frequency responce when singing is performed for example. It also electromagnetically damps the membrane making an effective pop filter.
From the above it follows:
To connect as low Z to XLR:
The central Tuchel pin is connected to either pin 2 or 3 of the XLR.
The other (low Z) terminal of the Tuchel connector is connected to either pin 3 or 2.
There is a fourth cable or connection. This is the metal part of the microphone and it is naturally connected to pin 1 of the XLR.
A very easy way to remember the XLR protocol is to remember 1,2,3 equals X,L,R, equals Xternal, Live, Return. So pin 1 is shield and the other pins are the signal pins, 2 being the live pin. When we design and make our own preamplifiers the chassis female XLR pin 1 must be connected to the 4th (nearest pin) which is the metal part of the chassis. In this way the microphone metal part is connected to the metal chassis through the cable shield. So everything is shielded and quiet. More information on the Jensen transformers website pin 1 literature. The chassis of equipment must be earthed for safety too.
You may experiment with swapping pins 2 and 3. It changes absolute phase but on some mics and preamp configurations it also may change the sound dramatically. A way to hear the difference is singing directly close to the microphone.
No comments:
Post a Comment