Looking for small (low emi) torroid for single 2520 opamp

[JW]

Hey folks.

I finally finished a couple Solid State Pultecs. But the power transformers I have in them are way too big. Total overkill in terms of current and the emi is too much.

Does anybody know of some cheap dual 18-20V transformers for powering  single 2520 DOA, with low emi?

Thanks

 

[sahib]

I have a few toroidals. Where are you located?

 

[JW]

I'm in the US. Portland, Oregon to be exact. Probably not worth the shipping, I would imagine. . . . . thanks though.

 

[gemini86]

mouser sells a triad 25VA toroid that's only 3 inches in outside diameter. If I hadn't just placed an order two days ago, I could have ordered it for you and sent it up there to ptown...

 

[APEX JR.]

How bout a 42Vct 80Va Toroid at $ 10.00 each
http://www.apexjr.com/miscellaneous.html

www.apexjr.com
Steve

 

[mitsos]

2x18V, 10VA
http://www.antekinc.com/details.php?p=14

2x20V, 10VA
http://www.antekinc.com/details.php?p=15

or use a 2x15V and run them at 16V.
http://www.antekinc.com/details.php?p=13

 

[JW]

Awesome.
Thanks guys!

Question on the Antek transformers. If I'm connecting the secondaries in parallel for say, dual 18V, where do I get the 0V center tap for the input to the p.s.? Or does it matter?

I'm using Mnats' power supply for the +/-16V

 

[mitsos]

You wire the secondaries in series, joining the start of one with the finish of the other to make the center tap. Antek uses green and blue for both secondaries, and the leads should be in order (meaning the first and second wires shoudl be one secondary, and the other two the other.. you can check continuity with a DMM).  The two in the middle should be the CT. 

 

[nielsk]

Consider taking the power supply that you already have and putting it in a separate box. This will do a better job of lowering EMF noise that any transformer in the EQ enclosure, and you can run several pieces of gear with it.

 

[JW]

Mitsos,

I got a couple of the 2X18V Anteks you recommended.

There's not enough voltage when the secondaries are wired in series.

Can somebody tell me if I can wire the antek secondaries in parallel and just leave the CT connection on Mnats' power supply unconnected?

 

[Harpo]

There's not enough voltage when the secondaries are wired in series.

So you've either not wired the secondaries in series or there is a maybe short further downstream. Disconnecting the transformer from psu-pcb you will measure about 36-40V AC between the outer connections of your series combined windings and about 18-20V AC between the center tap connection and each of both outer winding connections.

Can somebody tell me if I can wire the antek secondaries in parallel and just leave the CT connection on Mnats' power supply unconnected?

Paralleling your transformers secondary windings will give you half of 'not enough voltage'.
You are connecting a single (maybe paralleled) secondary winding by connecting one lead to the center tap connection and the other lead to one (doesn't matter which) of the AC connections on pcb.

 

[shabtek]

+1 for what neilsk said

Consider taking the power supply that you already have and putting it in a separate box. This will do a better job of lowering EMF noise that any transformer in the EQ enclosure, and you can run several pieces of gear with it.

 

[JW]

I must have the primary hooked up wrong then. Can somebody take a look at the pdf sheet in the AN-0118 link?
Am I just supposed to use one pair? I currently have one pair of Red/Black hooked up to hot, and the other Red/Black pair hooked up to neutral.

 

[Harpo]

I must have the primary hooked up wrong then. Can somebody take a look at the pdf sheet in the AN-0118 link?
Am I just supposed to use one pair? I currently have one pair of Red/Black hooked up to hot, and the other Red/Black pair hooked up to neutral.

For 115VAC mains you'll have the primary windings in parallel (red+red hot, black+black neutral), for 230VAC mains you'll have the primary windings in series (red hot, black+red isolated, black neutral). Just to make sure, there will be a fuse and a mains switch in between wall outlet and your transformer as well.
Updating your profile with your location data might make it easier to help you.  This is an intercontinental forum and not only mains voltages differ.

 

[JW]

Thanks Harpo
That did the trick.

It's strange, one of the first things I tried was to wire the primaries r+r/b+b
However, I connected black to hot, red to neutral. (But I didn't think the polarity of the primaries mattered for AC.)
Is that not the case with some transformers, or do you surmise that there just an error in my measurement when I first tried it?

Hmmm