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[Russell Ault]

Hi all!

As my DIY antenna distro project slowly approaches completion (I'll report some results once I find a more thorough way to to test it), I'm starting to turn my attentions to power distribution. I'd love to not have to use 7 wall-warts for 7 receivers, but I'm assuming that simply taking a large enough DC power source and splitting it 7 ways is going to cause problems without some sort of filtering.

So my question is this: what kind of filtering would be required to supply several wireless microphone receivers off of the same power supply?

(Bonus, possibly stupid, question: what kind of filtering would be required to supply several microphone RX and an IEM TX off of the same power supply?)

Thanks all!

-Russ

[Rex Ray]

Hi,Russell!
   I researched this very thing a couple of years ago. Our rack department asked me to build a 16-out power supply for Sennheiser
mic recievers. It's pretty easy,but I'd recommend decoupling the individual oututs from each other. You'll most likely want to use a single large power supply of the correct voltage current rating for the number of units used,and decouple the rf from the main DC bus.
470pf caps at 15vdc should do it. I was surprised the first time I repaired a Sennheiser G3 distro/PSU that the DC outputs had NO decoupling. The zip cord was just soldered to a common rail.
Hope this helps,
Rex Ray
Sr. Engineer,Clair Nashville
[email protected]

[Russell Ault]

It's pretty easy,but I'd recommend decoupling the individual oututs from each other. You'll most likely want to use a single large power supply of the correct voltage current rating for the number of units used,and decouple the rf from the main DC bus.
470pf caps at 15vdc should do it.

Hi Rex!

That's hugely helpful! I'll admit, though, that my basic electronics knowledge could use some bulking-up. Do you have a schematic for your design? Also, would 470pf caps be suitable for 12vdc operation as well, or should I use a different value?

Thanks!

-Russ

[Rex Ray]

Hey,Russell!
  Check out some of the offerings from some of the pacific rim manufacturers such as Cosel,Phihong or Meanwell. I used Cosel open-frame switchers on a universal power supply for intercom that I built some time ago. They were a bit noisy at about 28khz so I added some filtering on the output to calm them down. We built 45 of those units,and in 17  years we've had one failure. 15 volts is the nearest voltage tolerance for a 12 volt circuit in capacitor land. You can always use greater voltage ratings,but too low a voltage rating will fail,sometimes releasing the magic smoke. The RF decoupling should go from the +volt rail to the 0v rail on the output of the supply. A 0.01uf capacitor across the +volts rail to ov will cool out the switching noise (if any) on the outputs. Try to put those caps as physically close to the supply as possible to cut down on radiation of the noise. Sorry,but the circuit belongs to Clair.
HTH,Rex

[Russell Ault]

Hi Rex!

Check out some of the offerings from some of the pacific rim manufacturers such as Cosel,Phihong or Meanwell. I used Cosel open-frame switchers on a universal power supply for intercom that I built some time ago. They were a bit noisy at about 28khz so I added some filtering on the output to calm them down. We built 45 of those units,and in 17  years we've had one failure.

Interesting idea! I was originally planning to use a non-switching, transformer-based power supply (to avoid noise), but I'm having trouble sourcing one with sufficient output, so my next thought was to use a desktop-style switching power supply of sufficient power to keep the project simpler. Is there an advantage to using an open-frame power supply vs. an external one (noise or otherwise)?

15 volts is the nearest voltage tolerance for a 12 volt circuit in capacitor land. You can always use greater voltage ratings,but too low a voltage rating will fail,sometimes releasing the magic smoke.

Ah, I'm sorry, I misunderstood and thought that you were suggesting a capacitor value based on a 15 V circuit, not its voltage tolerance; that makes perfect sense.

The RF decoupling should go from the +volt rail to the 0v rail on the output of the supply.

Just so I'm clear, then, there should be a decoupling capacitor between V+ and V0 before each output, correct? So a supply with 7 outputs would have 7 decoupling capacitors in it?

A 0.01uf capacitor across the +volts rail to ov will cool out the switching noise (if any) on the outputs. Try to put those caps as physically close to the supply as possible to cut down on radiation of the noise.

Perhaps this answers my question above about the advantages of an open-frame power supply. Will a noise-suppression capacitor still work if it's further down the line from the supply?

Sorry,but the circuit belongs to Clair.

Understood, and I greatly appreciate the help you've given me. I suspect this is going to be one of those projects with a learning curve...

Thanks!

-Russ

[Russell Ault]

Just a follow-up for anyone who's curious about what I did:

I ended up using an off-the-shelf 5a 12v switching power supply (5a is roughly 10x the power supplied by each of the 8 wall-warts I was wanting to replace, which leaves a little room for inrush current, etc.). The power supply is connected to a circuit I built into a project enclosure. The inlet of the circuit has a 47uF aluminum electrolytic capacitor and a 0.1uF ceramic capacitor wired across it (in parallel), and from there the filtered DC power is sent into 8 hard-wired power output cabless (the cables came pre-wired with the correct connector for my RX units), each output having a 470pF ceramic capacitor wired across it for additional filtering.

The result (much like DIY Antenna Distro) is not something I have the tools to test beyond voltage (which tested within 1% of 12v, both on its own and under load), but I can say that I've observed no negative side-effects of using it, and it has made for a much neater rack.

-Russ

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