MKH 416 T - phantom power mod.

[MichelN]

The circuit on www.caban.nl takes the average supply current of the 416 (or other Sennheiser T model) and just attenuates the phantom supply such that there is approx 10 volts across the microphone terminals as required. Furthermore, the capacitors make the AC impedance equal for both terminals.

 

[Grim Reaper]

Yes! Finally...
How many do u want?
I think i have spare smt parts i can chuck in with the pcbs or do u want complete modules?

Complete modules. Cost? How do I PM you?

 

[Grim Reaper]

Zener Diodes are extremely noisy. So much so that they are often used as noise generators in e.g. synthesizers. To make things worse, the amount of noise rises with the rated zener voltage. In most circuits this is not good but for T powered microphones this is much more critical since EVERY noise, hum etc of the power supply is directly added to the audio signal. Placing a large capacitor parallel to the zener helps only a little because the internal impedance of the zener is very low and to suppress the noise in you need a really big capacitor (think of 1000uF or so).

If you do not trust the circuit from my previour post and you really want the zener based circuit, at least replace the 12 volt zener by 2 6.2 volt zeners in series. That helps a little. Better is to use leds for the voltage srtabilisation. A blue or white LED had a forward voltage of approx 2,5 .. 3.0 volt, so with 4 or 5 in series you also have a reasonable stable 12 volt with much less noise.

During the 1970s, I designed and built a 12v T-Power supply which uses a 12v zener diode and a transistor for voltage regulation. It has imperceptible noise. I used it with MKH416T and MKH816T microphones when I did professional sound recording. I have attached the circuit diagram.

 

[mrclunk]

During the 1970s, I designed and built a 12v T-Power supply which uses a 12v zener diode and a transistor for voltage regulation. It has imperceptible noise. I used it with MKH416T and MKH816T microphones when I did professional sound recording. I have attached the circuit diagram.

I've made the same to convert 12V Gefel mics to p48, worked well, tried it in a U87 to replace the zener and it made no difference to noise there.

 

[Grim Reaper]

I've made the same to convert 12V Gefel mics to p48, worked well, tried it in a U87 to replace the zener and it made no difference to noise there.

I could recalculate the resistor values to convert 48v to 12v but it would still be circuitry in a box. I want to install the circuitry in the microphone.

 

[MWohl]

Yes! Finally...
How many do u want?
I think i have spare smt parts i can chuck in with the pcbs or do u want complete modules?

I purchased a MKH416T years ago. I have the PSC 12T to 48v adapter. It works well, but it adds about 30% to the length of the mic. Not a deal breaker, but I find I use the mic less for on camera applications. If you have an option that fits in the barrel, I would definitely be interested (as long as install is not too complicated). I'm just above a noob when it comes to soldering.

Thanks.

 

[Grim Reaper]

I purchased a MKH416T years ago. I have the PSC 12T to 48v adapter. It works well, but it adds about 30% to the length of the mic. Not a deal breaker, but I find I use the mic less for on camera applications. If you have an option that fits in the barrel, I would definitely be interested (as long as install is not too complicated). I'm just above a noob when it comes to soldering.

Thanks.

I previously requested the conversion circuit boards, complete ones if possible, but although I was offered them and I replied to "mrclunk", I did not get a further response. I don't know why that happened. I also couldn't personal message to directly communicate with 'mrclunk", I think a minimum number of posts is necessary (10?) in order to do that.

 

[Spino]

The circuit on www.caban.nl takes the average supply current of the 416 (or other Sennheiser T model) and just attenuates the phantom supply such that there is approx 10 volts across the microphone terminals as required. Furthermore, the capacitors make the AC impedance equal for both terminals.

Could you elaborate further? I guess that the 2*6k2 make a voltage divider with the mic pin 2 resistance to ground? And I guess the out impedance of the mic is very low, otherwise pin 2 mixer side would see a higher impedance as pin 3 mixer side is just capacited to ground? Do you have out impedance and resistance to ground of the mic? And I guess the 6K2 + C on pin 3 to mixer will high cut signal on pin 3 to mixer? Or maybe I'm just dumb. Thanks for clarifications. (BTW, this looks like a mich simpler circuit)

 

[Grim Reaper]

Could you elaborate further? I guess that the 2*6k2 make a voltage divider with the mic pin 2 resistance to ground? And I guess the out impedance of the mic is very low, otherwise pin 2 mixer side would see a higher impedance as pin 3 mixer side is just capacited to ground? Do you have out impedance and resistance to ground of the mic? And I guess the 6K2 + C on pin 3 to mixer will high cut signal on pin 3 to mixer? Or maybe I'm just dumb. Thanks for clarifications. (BTW, this looks like a mich simpler circuit)

The circuit at www.caban.nl didn't make sense to me. I wonder why one 6k2 resistor is across the capacitor, pin 2 of mixer to the + side of the capacitor and pin 1 of the microphone to the - side of the upper capacitor and the other 6k2 resistor which has one side connected to pin 3 of the mixer and the + side of the other capacitor and the other side of that 6k2 resistor is connected to pin 1 of the microphone? My description probably makes as much or less sense as the drawing.

 

[MichelN]

I equiped all 10 my sennheiser t type microphones with this circuit and all work 100%. You should remember that looking from the cable the circuit should be symmetrical, so for both audio leads there is a 6k2 load parallel to a 22u capacitor. On the other side, the output of the microphone is not the same on both outputs. One pin is in fact a emitter follower while the other side is just grounded. The circuit described on caban.nl takes this all into account.

 

[Spino]

I equiped all 10 my sennheiser t type microphones with this circuit and all work 100%. You should remember that looking from the cable the circuit should be symmetrical, so for both audio leads there is a 6k2 load parallel to a 22u capacitor.

Yes, this seems valid if the circuit connects to identical stuff, which it isn't. Unless the stuff it connects to has not significant values. Or unless I don't understand, which is also very possible.

On the other side, the output of the microphone is not the same on both outputs. One pin is in fact a emitter follower while the other side is just grounded. The circuit described on caban.nl takes this all into account.

So you're saying that the 416 does not have a balanced output? Or that you're just grounding its pin 3?

 

[MichelN]

Indeed non of the sennheiser rf microphones has a true symmetrical output (like e.g. schoeps). Please look at the circuits that are easily available on the internet. The older microphones all have an emitter follower output on pin 2 (xlr version) and pin 3 is connected to ground. There is a RF filter in both outputs but they are irrelevant for audio frequencies. The caban circuit matches this output circuitry while at the same time makes a balanced load for the cable. And it only needs 4 components and there is no noise leven degrading.