Phantom power for CH1 and CH 2 made out of CH4 power

[Andrew M.]

Phantom power for CH1 and CH 2 made out of CH4 power.

I have noticed that ch 1 and ch 2 without phantom power enabled doesn't have any hiss when phantom power is enabled on ch4

I was looking for 9V source for my phantom power box, so I don't have to use the 9V bateries and the best source for it is actually pahntom power from the ch4. Once filtered by phantom power power supply circuitry it doesn't produce any hiss.

So the next step was just taking out all content of the phantom power power supply and making the cable as per below diagram.
Once you remove power supply from phatom power box it is what is left:



UPDATE:
Looks like you don't need 2 X 47 uF and 100 uF capacitors. Apparently these are already inside the RED audio board.
However .1 uF capacitor 100 Ohm resistor and small inductor coil is a must.



Inductor could be omited if you use 100 ohm resistor made out of wire, not a solid resistive mass.
Otherwise use standard .2mH power supply inductive small coil.
6.8K resistors have to be paired to .05% tolerance if you want very very low noise on good mikes.

If you don't use standard RED mini xlr cable to connect to channel 4, use 600 ohm resistor instead 100 ohm, since RED cable has 600 ohm in series there.
You can connect to any pin on CH4 except of the ground.
This thing may not work if your mike needs more then 4-6 mA.

.1 mF capacitor is ceramic, all others are electrolite 100V. Polarisation of electrolites, plus is facing the +48 V and minus is facing ground or ch 1 and 2 pins.

I managed to put all these components in the large XLR connector on the mike side and I just added one more double wire going to the RED ch4 on top of existing CH1 and CH2 cables. All cables shilded.

So you can make phantom power, power supply out of the +48V supply from the CH 4 RED mike connector.
If you don't have experiance making this type of projects, contact Trewaudio maybe they will make one for you.

Ch4 will have hiss but headphones are set for ch1 and 2 so you don't hear it and you just extract cha 1 and 2 from the proxy files.


Andrew

[Joel Kaye]

Awesome. Can you take a couple pictures and post them too?

[Andrew M.]

I just closed the connectors, and it was a chalange.
I will be making one more like this tomorrow so if I do not forget I will take few pictures.
The best will be to put all the components in, on the cable, small 1/2" pipe
or small box. You can't blew up anything if you put 100 ohm resistor in the ch4 connector and the rest in the mike large XLR
Ch 1 and 2 is without the power so no problem there.


Andrew

[Joel Kaye]

Ch 1 and 2 is without the power so no problem there.

If phantom power was switched on in Ch1 or 2 could that cause any damage to anything?

[Andrew M.]

No you have 6K resistors there before you get to any pin of ch1 and 2
Also it was made out of the original RED cables that have 200K across and 600 ohm in series build in to protect the channel circuitry.
Only mike side is modified.

[Andrew M.]

Here are the pictures of the phantom power cable.
Works great, no noise at all, zero, null, nothing!!
I didn't have time today to make the second cable so I asked Harry (TrewAudio) to make me one
If you guys want to have one made by professional send e-mail to harryquan@yahoo.ca
harryquan at yahoo dot ca

He can also make you a cable that cancels the DC on the headphones plug.
Ask for Andrew's phantom RED cable and RED headphone cable.

I rather do some shooting.






The pink components are small inductance coils, you do not need bigger than that.
Remember to pair the 6.8K resistors to be almost identical, any noise from power source when distributed identically in to the mike balanced input will cancel itself and it cancel itself as good as this resistors are identical.
Any difference here will be translated to the audible noise if any on the power line.

BTW it is stereo 5 pin cable, it may be made as a mono cable only as well.

[Andrew M.]

Here it is, the screen shot from Audition and audio file sample using this cable.
Note Track 3 inverted on the right channel to produce the Left Right image from the MS mike L=M+S R= M-S
I do fine tune the phase here since camera body and fan noise is shifting the sound to the left, mike is on the right side of the camera, see phase chart on the far right showing sound gravity centre.
Track 2 is full Left, Track 3 is Full Right.
Recorded 3 channels M S and noise and exported from QT as a 3 dscreet channels.
The noise channel I use inverted and mixed in to the L and R channel to clean the fun noise and channels noise from the camera if any (less than -55dB).
Mikes set to -48dB

Sound file is in the next post.

[Andrew M.]

sound file is here
http://www.reduser.net/forum/uploade...1211649307.zip

Right click to safe, then rename from zip to .wav

Don't do unzip on it, it is not zipped.

[Cüneyt Kaya]

how much does this cable cost andrew...
nice find btw.

[Andrew M.]

Harry asked $65/h plus parts.
I gave him $200 for stereo cable.

Stereo phantom power supply is $300+

As to the DC bias cancelling cable, Male Female stereo, with two electrolyte 47uF capacitors inside (one for L and one for R channel) is $30
You need one if you do not want to demagnetise your headphones, if you have some expensive one. Headphone output on RED has DC bias 1.5V so on 15 ohm headphones will drain 100mA trough your headphones.
The headphone cable will prevent DC current to go through capacitor without stopping the signal.