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Old 6th May 2011, 02:30 AM   #1
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Unhappy OOPS! bought transformer without dual secondaries

I purchased an 300VA AnTek AN-3440 for my stereo LM3885 kit with single power supply (so far). It looks like I can have dual secondaries if I want 40V (which I don't) but only single secondaries for 12V or 18V (which I want). Can I split one of the secondaries between the "top" AC1 and the "top" AC2, then split the other secondary between the "bottom" AC1 and "bottom" AC2. Well, of course I can, but I mean, Will it work if I do? Looking at the power supply schematic, it looks like it will work, but I'm afraid of frying something.

Do I need to buy another transformer with dual secondaries?
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Old 6th May 2011, 03:46 AM   #2
tinitus is offline tinitus  Europe
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that is dual secondary

switch the positive and negative symbols placed on the grounds and it looks right

if its single secondary you need, just use one for each channel

but you post is a bit confusing to me
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Old 6th May 2011, 03:49 AM   #3
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I think you should look at returning the transformer without at least a centre tap you would need to implement a voltage doubler type rectifier circuit which as far as I am aware is only suitable for low current.

You certainly can't wire up a single secondary to those two bridges and get your +ve and -ve rails.

Also torroidals with main windings (seems your main windings are 2 X 40V) and then additional lower voltage windings, usually have much lower current capability on the lower voltage ones.

BTW did you mean LM3886?

edit: tinitus, I checked out the spec on the transformer, and it has dual 40V secondaries, but only one single 18V and one single 12V and he want's one of those lowever voltages...

Tony.
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Old 6th May 2011, 04:02 AM   #4
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Its a nice tranny for a solidstate amp, HV for outputs, LV for signal stages.
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Old 6th May 2011, 01:45 PM   #5
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by wintermute View Post

edit: tinitus, I checked out the spec on the transformer, and it has dual 40V secondaries, but only one single 18V and one single 12V and he want's one of those lowever voltages...

Tony.
yes, thanks, I checked too, and it appears to be so

specs on Antek site are not very clear, and makes it hard to order
for whatever reason I cannot open pdf file with detailed specs

maybe 2215 or 2218 would have been a more obvious choise
but then I can't see the difference between AS and AN versions
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Old 6th May 2011, 02:15 PM   #6
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Not hard to modify the design for single ended supply.

paul
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Old 6th May 2011, 02:34 PM   #7
macboy is offline macboy  Canada
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If you need to use this transformer, use the two 40 V secondaries in parallel, to create a single supply of approximately 56 VDC. This is an ideal voltage to run a pair of LM3886 bridged into 8 ohms. And a single supply is also ideal for bridged output since you don't need output capacitors. If you use the single supply without a bridge-tied-load then you need the large output capacitors.
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Old 6th May 2011, 04:28 PM   #8
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Default Thank's everyone

Thank you, everyone for the help.

I didn't mention that the diagram is from Chipamp.com, and the transformer does not represent my transformer. I want the lower voltages, because Chipamp.com states this will lead to a more stable amp into 4 ohms, and the 4 ohm speakers are already built. The power supply is already built, so I'd like to use it as is. I didn't know that additional secondaries often have lower current capabilities than the higher voltage secondaries. That's good to know.

I actually bought a pair of these transformers used, so I can't return them, but at least I didn't pay much for them! I can use the pair to test my amp, then replace them with a more suitable transformer before I put them in a case.

The Anteks will just have to wait for my next amplifier project
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