Phantom PCB

[ruffrecords]

Both parcels shipped Wednesday 17th.

Cheers

Ian

 

[letterbeacon]

What transformer are people using for this board?  I'm not having much luck finding a toroidal on Mouser that outputs 50vac.

 

[Igor]

2x24V, 15va should work for this.

 

[letterbeacon]

Great, thanks Igor!

 

[morbleu]

Pcb arrived today!
Thank you

Andreas

 

[baadc0de]

With a double secondary toroid (2x25V) I should probably join 25V from the first secondary with the 0V of the second secondary so that the 0V of the first and 25V of the second primary give together 50V AC?

Thanks,
B.

 

[ruffrecords]

With a double secondary toroid (2x25V) I should probably join 25V from the first secondary with the 0V of the second secondary so that the 0V of the first and 25V of the second primary give together 50V AC?

Thanks,
B.

Yes, that should work OK. Just check with a meter to make sure.

Cheers

Ian

 

[letterbeacon]

This may seem like a silly question, but should I use a separate fuse for phantom power, or can I get away with using one fuse for the phantom power as well as the pre amp?

 

[chrispsound]

I was wondering if it would be OK to make a point to point version of your phantom power supply from the schematic posted for my own personal use?  Also the capacitor listed in the schematic is 4700u but the one used in your proto is 470u,  will the 470u work?  Thanks, ChrisP

 

[ruffrecords]

This may seem like a silly question, but should I use a separate fuse for phantom power, or can I get away with using one fuse for the phantom power as well as the pre amp?

I guess it depends on the degree of protection you want to include. Obviously you have a fuse on the primary side of your mains transformer so if any of the secondaries is shorted this will blow. This will work even if you have a separate transformer for the phantom supply. If the phantom PSU dc output is shorted the the regulator chip will go into thermal shut down and limit the current. If you know the maximum current that will be taken from the phantom supply then you could include a fuse on the secondary side to ensure this is not exceeded.

Cheers

Ian

 

[ruffrecords]

I was wondering if it would be OK to make a point to point version of your phantom power supply from the schematic posted for my own personal use?  Also the capacitor listed in the schematic is 4700u but the one used in your proto is 470u,  will the 470u work?  Thanks, ChrisP

Yes, I am happy fro you to make a  p to p version for yourself.

The 4700uF was designed to allow for supplying up to 20 channels with phantom power. If you only have a couple of channels the 470uF will be fine.

Cheers

Ian

 

[baadc0de]

Is it better to switch phantom AC in on/off or the DC out path to the mic on/off?

I have a balanced-T 200 ohm attenuator before my preamp in. I assume 48V and the resistors must be connected at the XLR mic in before the attenuator?

Thanks in advance,
B.

 

[ruffrecords]

Is it better to switch phantom AC in on/off or the DC out path to the mic on/off?

I have a balanced-T 200 ohm attenuator before my preamp in. I assume 48V and the resistors must be connected at the XLR mic in before the attenuator?

Thanks in advance,
B.

It is normal to switch the dc path. In most designs the +48V goes through a switch then a series resistor of about 100 ohms and the to an electrolytic capacitor of about 47uF to ground. This provides a little extra smoothing and also reduces turn on and turn off clicks.

Cheers

Ian

 

[baadc0de]

So, I would do something like this I presume:

http://en.wikipedia.org/wiki/Filehantom_power.svg

In A and In B go to the mic, out A and out B go to the attenuator and then to the mic input transformer right.. the attenuator is 200:200, R3 = 0, C1 = C2 = 4.7uF, C3 = 47uF, R1=R2= 6.8k

Would this do?

 

[ruffrecords]

Would this do?

Yes, that should work. R1 wants to be 100 ohms or so. You can put the attenuator before the caps if you wish - depends what the mic pre input circuit looks like.

Cheers

Ian

 

[baadc0de]

Would this do?

Yes, that should work. R1 wants to be 100 ohms or so. You can put the attenuator before the caps if you wish - depends what the mic pre input circuit looks like.

Cheers

Ian

It's a straight ahead REDD fourseven..

 

[ruffrecords]

It's a straight ahead REDD fourseven..

In which case you don't need the caps at all. Just connect straight to the input transformer.

Cheers

ian

 

[baadc0de]

So, like this? Sorry for being dense but I'm not really confident in my "designing" skills quite yet.

 

[ruffrecords]

So, like this? Sorry for being dense but I'm not really confident in my "designing" skills quite yet.

Yes, that circuit is spot on.

Cheers

Ian

 

[letterbeacon]

I'm hoping to connect up the phantom PCB this weekend, but I wondered if I could run this by you:

I'm using a toroid transformer with dual 0-25VAC secondaries.  I connect the two 25VAC leads to the two VAC inputs on the phantom PCB.  I tie the two 0V leads together, but where should I connect those?  At the star ground point in my pre amp that's connected to the chassis?

I'm using the 48VDC to connect to a JLM go between kit.  Where shall I connect the 0VDC?  Pin 1 of the XLR input?

Thanks for your help.