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DIY rackmount gear PSU question
Old 21st October 2013
  #1
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DIY rackmount gear PSU question

Hey
I have a question regarding a PSU im building to rack some channel strips.
I have found a good local source for 22-0-22 transformers, not sure of their exact specs re mA, but they are beefy and i fully expect them to be able to outperform the task i am assigning to them.

My question is in regards to wiring the 44ct trafo output wires for to the regulator circuit and to another circuit for the phantom (yet to be build or really even "designed", ie copied from somewhere on the internet). I have attached two poorly drawn pictures illustrating the two options I see. Would either of these work, and would one be superior to another? or is their a dangerous error that I am making?

much appreciated!
Attached Thumbnails
DIY rackmount gear PSU question-option-1.jpg   DIY rackmount gear PSU question-option-2.jpg  
Old 21st October 2013
  #2
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Hi
The only 'dangerous' error will occur if (when) you common 'ground' the 2 DC supplies.
This is because your AC has a 'common, which in the scenarios presented will end up 'shorting out' one or more of your rectifier diodes when you try to link DC 'grounds'.
Having 'half' the secondary feeding a bridge for the 24 Volt rail is OK, then you need a version of a 'doubler' to stack the 48 volt section 'on top'. I can't think how to do it at the minute. You would have been better off with 2 separate secondaries, but you already have it so.....
Matt S
Old 22nd October 2013
  #3
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brianroth's Avatar
 

What channel strips are you racking? Many/most channel strips require both positive and negative rails with a "common" (0 Volt) line. Exceptions would include things like old Neve modules that used discrete transistor circuits, and hence only a single 24 Volt rail.

Bri
Old 22nd October 2013
  #4
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Matt you totally lost me, i will reread your explanation tomorrow with a clearer head. I take it that you mean option 1 wiring would be bad? I take it the best option would be a torroidal transformer with 2 secondaries of 24 and 48 rather than one 44ct. I saw a double circuit somewhere, i will look it up again.

Brian, I am working on a "universal model" for a few different parts I have. Some are +24vdc like a spectra sonics 101 and a siemens v272, others are +/- (like a quad eight, the model eludes me right now). Mostly its all +24, some may be -24 like the scully 280.
I have been using external phantom adaptors but would like to include phantom in this next one, just seems a lot easier that way!

for regulators I have been using some from china via ebay. About $10 assembled and shipped. For the +48 I would have to assemble something, once I figure out the best way to wire the two circuits from the power outputs.
Old 22nd October 2013
  #5
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here are some examples for voltage doublers I had been looking at
Voltage Doubler,Voltage Tripler,Voltage Quadrupler circuit
Old 22nd October 2013
  #6
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brianroth's Avatar
 

You might start by looking at some of the existing kits being sold. Here is one:

PSU-2448mk2 Kit

The schemo is included in the instruction manual on that page:

http://www.fivefishstudios.com/pdf/P...k2Assembly.pdf

A similar kit (can't seem to find the schemo on the website tonight):

PSuniversal - $35.00 : Zen Cart!, The Art of E-commerce

The "Grandaddy" of all these is from JLM Audio, but I had trouble connecting a few minutes ago. I'll attach that schemo to this reply since it includes Joe Malone's website info, etc.

You will note that all three use a LM317 regulator for the phantom rail. I STRONGLY advise using a TL783 instead.

Bri
Attached Files
File Type: pdf ACDCVer2sch.pdf (21.4 KB, 153 views)
Old 22nd October 2013
  #7
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Richard Crowley's Avatar
What channel strips? How much voltage do they need? How much current?
What +/- regulator?
How much current is your transformer rated for?
If you can't accurately answer those questions, you appear to run a significant risk of toasting your channel strips. You seem to have a rather casual attitude about critical information. That does not predict success.
Old 22nd October 2013
  #8
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brianroth's Avatar
 

Yes, I had some similar questions, Richard. That's why I decided to steer Enginefire in the direction of several (very) similar designs in kit form. I've used or have seen all three kits in various DIY gear over the years.

But, there indeed some details that Enginefire needs to work out.

Bri
Old 22nd October 2013
  #9
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Hey Brian, Ive checked out those kits before, but i already have the components and enjoy the mental exercise of making do with what Ive got.
the TL783 looks like just the ticket.

Richard, if any of the information you requested was available or relevant to the post i would have provided it. seeing as there is no indication regarding the VA of the transformer, neither any manufacturer or hits from searching the numbers that are printed on it (no they do not seem to reveal any of the specs either), I can only eyeball it, which is something I learned from you actually! its not rocket science, neither am i doing this for someone else, its my personal hobby. If my attitude seems casual, in the words of Lawrence of Arabia, "its just my manner". maybe i am casual about it, I see it as a casual thing. the fate of the world does not depend on it, if it doesnt work or whatever, it will not stop the sun rising tomorrow. To be honest I care very little about most things these days, but the little that I do care about (when I care about it) tends to involve audio. Rather than tell me how you believe I am probably going to blow my channel strip (even if this were the case, the tone of your post seems to indicate that it would be forever irreparable, as if it would disintegrate), perhaps staying on the topic of the OP would be more positive and productive?

to ask again, as a clearer question, what would be the best way to use this 44ct transformer to power both +24v and +48? In terms of wiring the windings. Please forgive my ignorance of terms and best practices, i am not an EE, like I said, racking gear is more of a hobby than a profession.
Old 22nd October 2013
  #10
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Richard Crowley's Avatar
I would strongly recommend the instruction manual for the Fivefish PSU 2448 Mk2 kit
http://www.fivefishstudios.com/pdf/P...k2Assembly.pdf

It appears to do everything you are asking for, including variable rail voltages, and making 48V phantom power out of the center-tapped main supply transformer input (using a clever AC-coupling to "re-purpose" the transformer output)

Of course, you can buy the kit, but there is more than enough information there to roll your own from your own components. Assuming that you have a functional DMM to test things with. If not, that is an absolute prerequisite.
Old 22nd October 2013
  #11
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Thanks Richard, that schematic did clear up the wiring issue. CT connects to circuit ground and AC1 and 2 connect to the secondaries (44v spread in this case).

My concern right now is using the LM317 to step down the voltage, to get the 24vdc from the 44vac coming in. In your experience, is this something to be concerned about? dispite my nonchalant attitude, I still dont want to fry anything.

One other thing I am having trouble understanding is how the five fish supply gets +48 from a part that is rated only to +37v. Is it that the phantom power would draw so little current that they can safely push the part past its spec?
Old 23rd October 2013
  #12
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brianroth's Avatar
 

In the Fivefish (and JLM, etc. design) the positive and negative regulators are (in effect) each fed from only one half of the power transformer....22 VAC in this discussion. After rectification, the theoretical "raw" DC voltage into either regulator will be 22 * 1.414, or 31.1 VDC.

As for the 48 V regulator using a LM317 in any of the examples I posted, it's the "max input to output" rating of the regulator which is limited to 37 Volts. It's all well and good unless you happen to short the 48V output to ground, which will exceed the spec. Hence my suggestion of using a TL783.

Bri
Old 23rd October 2013
  #13
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Richard Crowley's Avatar
Quote:
Originally Posted by enginefire View Post
My concern right now is using the LM317 to step down the voltage, to get the 24vdc from the 44vac coming in. In your experience, is this something to be concerned about? dispite my nonchalant attitude, I still dont want to fry anything.
The regulator (LM317 or TL783) does NOT see the 44VAC. It sees the 22VAC * Sqrt 2 (1.414) which is 31.1VDC That is because it sees only "it's half" of the transformer (22VAC) and a capacitor-input filter yields 1.41 x the incoming AC voltage.

What is your source of these beefy 44VCT transformers? I might like to get a couple myself.

Quote:
One other thing I am having trouble understanding is how the five fish supply gets +48 from a part that is rated only to +37v. Is it that the phantom power would draw so little current that they can safely push the part past its spec?
As Mr. Roth said, the limit is between the input voltage and the output voltage. But it is always safer to use a more robust part that won't fry if you accidentally short the 48V bus.
Old 24th October 2013
  #14
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I can send you one if you like, they are from a local store. I think they were $7. Comparable in size to a Hammond 167L44, rated at 88 va.

DIY rackmount gear PSU question-uploadfromtaptalk1382589714342.jpg

Brian thanks for the clarification re 37v differential, makes a lot more sense now esp the warning of 48 v short to ground.

sent from my m-3500 using the gearslutz app
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