48 Volt Phantom Power Supply with Photo-Schematic. Transformer Question.

Thread Starter

alanbcooper

Joined Jan 21, 2016
2
Hey guys,

This is my first post and I am happy to have found this website. I am currently working on a project using a PCB and jumper wires to make a 48v Phantom Power supply to be used with multiple condenser microphones. To make a long story short, I found a "mostly" detailed post on another site of someone creating the power supply using a 120v to 25v step down transformer. My main concern is the amperage. The instructions call for a power supply with 1 Amp while the power supply I ordered and have received is 1.6 Amps. Will this cause any problems? Also I am confused as to what is going on in the middle of the picture of the photo-schematic. My transformer only has two contact points and a ground (on the step-down side). It appears as though there is a 3rd wire coming from the transformer traveling through the middle of the picture. Also just to be clear, whoever made the original supply used a turret-style board while I am using a PCB with jumpers like I mentioned earlier. Also I understand I could just buy a wall-wart power supply but I am making this so I can learn more about circuits and PCB's. Hopefully someone will be able to help.

Link for details and parts list: http://www.tangible-technology.com/power/Phantom_frying.html

Picture of "photo-schematic" power_v3a.JPG

Thanks in advance,

Alan
 

Thread Starter

alanbcooper

Joined Jan 21, 2016
2
Thanks for the link. It was a simple misunderstanding on my part as far as the amperage question. I am still confused however as to whether or not a center tapped transformer was used? If not, once again I am still confused as to what the pink line in the middle of the board is supposed to represent?

Thanks again,

Alan
 

#12

Joined Nov 30, 2010
18,210
The transformer seems to not be center tapped, but the DC supply is center tapped. The pink line is the zero voltage line compared to the positive and negative DC voltages.
 

Kermit2

Joined Feb 5, 2010
4,162
It does appear that the PCB has two power rails (37 and -37) and the caps and zener connection indicate a 99.9% for certain center tapped arrangement.
 

Kermit2

Joined Feb 5, 2010
4,162
There is a grounding lug for the center tap on the board. So you could use a center tapped one without any mods as far as I can see.

 

BR-549

Joined Sep 22, 2013
4,938
I don't believe the transformer is center tapped. Ground is point B. Point C (the pink line) is +37 V.

The top of C3 is 48 V reg.
 

analogdude

Joined Jul 14, 2015
14
Disagree. What I see is a single end of the secondary used as, "common" with one diode going each way from the other end to make a pair of half wave rectifiers. Like this:
Yes, but the polarity of the lower capacitor inverted.
Disagree. What I see is a single end of the secondary used as, "common" with one diode going each way from the other end to make a pair of half wave rectifiers. Like this:
Yes, but the polarity of the lower capacitor of your diagram should be inverted. Point C is the common of the +ve and -ve capacitor pins, and the transformer winding.
 
Last edited:

#12

Joined Nov 30, 2010
18,210
the polarity of the lower capacitor of your diagram should be inverted.
I disagree again. The board is arranged with the most positive DC at the top, the pink line being a center position, and the most negative voltage at the bottom. The capacitors are correctly oriented.
 

bertus

Joined Apr 5, 2008
20,567
Hello,

In the link in the openings post, the schematic is also given:

phantom1.JPG

There are no values given in the schematic, but the two times single rectifying are used as voltage doubler.

Bertus
 

AnalogKid

Joined Aug 1, 2013
8,487
Agree with Dave. Caps on the original schematic and the photo are correct.

Unless there is a lot of signal conditioning going on at the mic, 1 A is a ton of phantom power current.
 

GopherT

Joined Nov 23, 2012
8,012
Why use 48V when the link on the first post says everything from 9 to 48V works and Never ever exceed 48 volts. I would use something between 9 and 35. 9 seems pretty easy.

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