Need some help building a Power Supply??

Hi Guys, I am Pretty new to electronix so excuse me if my questions seem stupid....

I am in the Process of Building an Older version of the Green pre (MK1?) as my first real DIY electronix Project , I have Built Mics and replaced the Opamps in my Amp and Built a Battery Powered Phantom supply but nothing this complex....

What I want to know is I have some Small Transformers that I would like to use in the Power supply but they aren"t the Type used in the "Official" Green pre Power supply so I was wondering First If there was a way I can use these transformers in the Green and secondly what would I have to change in the Official Power supply to make it work with these Transformers....

The Transformers are 110v/220v to 2 x 26v rated at between .5 and 1 amp(I haven"t measured it with my DMM yet) and I have quite a few of them so I can use more than one if I have to...
I think I can get 2 x 26v or 52v when running off the 110v Leads so I should be able to get 2 x 6.5v or 13v when running the 220v leads off of 110v Mains....
I"m thinking I can use one Transformer and run it off of the 220v Leads and get 13v AC which should be about 16v DC that I can regulate to 15v which is what the green runs off of ,and I can use another Transformer in series to try to get the Power for the Phantom supply but I don"t know how I would do that?.?..

Does any of this make sence??

Is it possible without to much trouble??
If so How would I do it?? what Mods?

Or is there a way I can use these Transformers with the Green power supply without any real Modifications??
(I don"t think I can regulate 26v to 15v without frying the Regulator??)

Or is there a Schematic somewere for a Green that uses a 2 x 26v Transformer??

Any help would be great...

ThanX a Lot!!! :wink:

[quote author="Minion"]The Transformers are 110v/220v to 2 x 26v rated at between .5 and 1 amp(I haven"t measured it with my DMM yet) and I have quite a few of them so I can use more than one if I have to...
I think I can get 2 x 26v or 52v when running off the 110v Leads so I should be able to get 2 x 6.5v or 13v when running the 220v leads off of 110v Mains....[/quote]

No, you'd get 2 x 13V when running the 220V leads off 110V mains.

I"m thinking I can use one Transformer and run it off of the 220v Leads and get 13v AC which should be about 16v DC that I can regulate to 15v which is what the green runs off of ,

Click to expand...

It's a very rare regulator that will let you regulate 16V down to 15V; most regulators require more voltage than that across them. You also have to deal with line voltage that sags in the summertime.

and I can use another Transformer in series to try to get the Power for the Phantom supply but I don"t know how I would do that?.?..

Click to expand...

You said it yourself: The two secondaries of a transformer in series with each other total 52V; that'll get you about 71V, which you can regulate through a dropping resistor and a zener down to 48V (47V really, plus/minus the tolerance of your zener).

Does any of this make sence??

Click to expand...

Yes.

Or is there a way I can use these Transformers with the Green power supply without any real Modifications??
(I don"t think I can regulate 26v to 15v without frying the Regulator??)

Click to expand...

Sure you can, if you use a heatsink on the regulator. Actually you're looking at 34V from the raw supply, 37.4V at 10% overvoltage. Put in a second stage of filtering with a nice hefty power resistor and drop it down to 20V. Then use the regulator.

Peace,
Paul

Hi, Thanx for the answers, My Problems is I am such a Newbie at this stuff I don"t have a Clue how to Implement Any of these Ideas?.?.

Would it be possible for you to tell me how to Implement this but explain it like I am a total Idiot that Knows Nothing about electronix ,(With Pics or a schematic?)


ThanX

There are plenty of subtleties in the design of power supplies; I strongly encourage you to hit a library and find a copy of the National Semiconductor Power Supply Handbook.

In the meantime, here's a very simple pair of power supplies. The upper one is for phantom power, the bottom for +15V. To turn the bottom one into -15V, reverse the direction of all diodes, flip the capacitors upside down (+ terminals to the ground end) and use an LM337T regulator.

I left a number off the drawing; the voltage at the input of the regulator should be 20V, so you're dropping 14V across R2.

The key elements are R1 and R2, the dropping resistors. Once you know how much current you're drawing from each supply, maximum, compute the values of these using Ohm's Law:

R = V/I

where R is in ohms, V is the voltage you're dropping across the resistor, and I is the total current draw in amps. (Don't forget to budget 10mA extra for the zener and likewise for the LM317.)

Once you've computed the resistor value, figure out how much power it's dissipating:

P = R x I^squared

If you come up with something like 1W, use a 3W resistor -- leave yourself lots of margin.

You can do lots of refinements -- bypass capacitors and the like -- but this'll get you started.

Peace,
Paul

Thanx a Lot, That helps quite a Bit but I am still Pretty much totally Lost (Can"t do Math at all accept the Very Basics)....

So does the Picture you left me somehow incorporate into the Green PSU??

I guess I am going to have to Wire up these Transformers and see what type of Amperage they put out but it should not be much as they are very Small Transformers.....

If I have more questions (Which I will have many) I will post back...

ThanX for Putting up with my Stupid Newbie questions.....

Cheers

Not to worry about it. Meanwhile I realized I should make that drawing more useful and put in the stuff I left out before I had my coffee. Stay tuned.

Peace,
Paul

Okay, the more useful drawing is here.

As for math... the main thing you need to do is figure out how much current the Green Pre will draw. That means deciding how many channels you're going to build and looking up in the spec sheet how much current each chip draws. Add them up, then add .01A for the regulator and .02A for maximum signal draw (just a guess on my part) and that's your current draw. Let's say it's .038A (38mA) per channel, and you're building two channels. 2 x .038A = .076A.

You know from the diagram the voltages on the two ends of the resistor, so subtract the lower one from the higher one and that's the voltage drop. Ohm's law:

R = V / I

V is your voltage drop, I is the total current for all channels. If V is in volts and I is in amps, then R will be in ohms. Calculate power dissipated as in the previous post. Do the same set of calculations for the phantom supply -- figure out maximum current draw for your microphones, then add .01A for the zener.

Peace,
Paul

To be quite honest - if its you first project and you are having trouble and just want to build it
Transformers for the value required in the Green are probably about £5 - ie the cost of a packet of cigarettes or a gallon of petrol or two beers

[quote author="uk03878"]To be quite honest - if its you first project and you are having trouble and just want to build it
Transformers for the value required in the Green are probably about £5 - ie the cost of a packet of cigarettes or a gallon of petrol or two beers[/quote]

Maybe were you Live but were I live you can"t even Find Transformers unless I salvage them from Other Stuff or I use AC adapters that I find at the Salvation army....If I order one for the Lame electronix store here they will charge me close to $50 for a Single Transformer (they also Charge $2 each for Transistors and 0.50c for a Single Resistor)

Is there a way I can use an AC adapter Like a 16v or 18v?? Would I need 2 of them ??

pstamler: I really appriciate your Help but I guess I am too new at this (Or stupid) to really understand how to Incorporate Your Ideas into a power supply even though I"m sure it is Easy....I could Probably do it if I had a Full schematic of the Full PSU but I wouldn"t ask anyone to do that For me.....


ThanX

Well I think I solved my Problem... I just found a Schematic for a Power supply that will use my Center Tapped 26V AC adapters and that will let me output 48V Phantom Power and 15v+/15v- and another Voltage selectable By a Resistor which i will probably not use or set at 15V to run a seperate Channel of Preamp....

Here is the Schematic I am going to use:

http://www.vintagedesign.halmstad.net/diy/Uni%20PSU.pdf


Can someone Verify that this Power supply will be Good enough to run a couple Channels of Green Pre??

It seems easy enough to build and the PCB design and stuffing Pattern is there but It also says that this Power supply has not been Tested Yet (It should be by now though)....

ThanX a Lot Guys.....

Cheers

[quote author="Minion"]Well I think I solved my Problem... I just found a Schematic for a Power supply that will use my Center Tapped 26V AC adapters...[/quote]

It will not work this way. As stated in the schematic it is for separate windings, not for center tapped transformers.
Have a look at http://www.beatbazar.com/guests/ssltech/kps-1/index.htm for a center tapped version, and exchange 7818/7918 by 7815/7915 for 15V dc or use the 317/337 with the voltage setting resistors in your schemo. For further advice have a look in the Meta for power-supplies.

I don"t think you read the Whole Schematic Because there is a Design for use with 2 seperate Transformers AND there is One for running a Center Tapped Transformer.....

They actually use the same PCB accept for a couple Modifications were the Input from the Transformer is...





You should be able to see at the Bottom that is says "2x24v with Center Tap" and mine are 2x26 center tapped....




But if you still think the other one would be better then I will try that one....

ThanX

Actually, what I posted was pretty close to a full schematic, missing only the primary wiring (AC plug, fuse, switches if desired).

Can I make a suggestion? You've said you're a newbie and just beginning to get your feet wet in this stuff. Before setting out on this project, order a copy of Charles Hansen's The Joy of Audio Electronics and read through it several times. I think you'll find a lot of very useful information there.

Peace,
Paul

Would 2 x 13V not be enough for the green? Mine only runs at about 14V

I'm no power supply expert, this is purely out of curiosity.

13v rectified will give 18v DC at the output of the rectifier, plenty to work into a 317/337 pair

Peter

Peterc, Does that mean I can use my 2x13v AC Transformers In the Green Pre Power supply??

This is the Green PSU I was looking at:

http://1176neve.tripod.com/id11.html

It looks like the Power supply needs a 2x15v with seperate Windings were mine is center tapped so how do I incorporate my Center Tapped Transformer into the PSU that needs seperate windings??


ThanX

That's what it means

Hi, But how do I incorporate my Center Tapped Transformers into the PSU design Cuz it seems to take a Transformer with 2 seperate 15v Windings (The schematic needs 4 wires going into the PSU were mine have the 2x13v Leads and a Common lead, Note the Pic I posted above)....

Can you Let me know how I would do this?? (I guess I could use 2 Transformers??)


ThanX


PS: Ptownkid: E-amil me with the Total + shipping for those Transistors and I will send you the Payment....

The newer green pre psu takes three wires, I'll e-mail you the deets.

The newer green pre psu takes three wires, I'll e-mail you the deets.

Click to expand...

Great...ThanX a Lot


PS: I actually thought when useing a Center tapped transformer you just use 2 Wires?? Maybe I"m just Stupid??