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Old 4th July 2009, 09:22 PM   #1
wicked1 is offline wicked1  United States
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Default 12v tx for 1875

I want to run my lm1875 amp on about 12v for some computer speakers.
The only 12v tx at parts xpress is 30va.

Does anyone know where I can find a larger one?

thanks!
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Old 4th July 2009, 09:54 PM   #2
Minion is offline Minion  Canada
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Do You mean a single Rail 12v Xformer ?? If you do then I don"t think you can run a LM1875 on 12v , I believe the LM1875 needs a Minimum of 16v DC , even 12v ac would give you 16v DC but it would drop to 14v or 15v under a load .....

If you mean a 12v ,0v ,12v Xformer then I know were I live I can get a 12v ,0v ,12v 4A Transformer at Radio shack for about $10 ......


cheers
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Old 4th July 2009, 10:15 PM   #3
wicked1 is offline wicked1  United States
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I mean 12,0,12. And I think I need something a lot bigger. Like 250VA which is, I think, about 20 amps. That sounds like a lot, so I could be completely wrong w/ my math, there.
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Old 5th July 2009, 12:50 AM   #4
wicked1 is offline wicked1  United States
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So, after a lot more reading, 250va is overkill, but still, I can't find any available over 30va. I think I need something around 180va.

I suppose I could go w. 15v, but I really don't need much power (And can't find any 15v large enough, either)
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Old 5th July 2009, 02:42 AM   #5
Minion is offline Minion  Canada
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30 Va per chip should be OK but 50Va would be better ...... You don"t need 180Va , At +/-15v DC you will only get about 8-10w into 8 ohms so you really only don"t need a huge transformer.......


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Old 5th July 2009, 03:29 AM   #6
kaos is offline kaos  United States
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Avel Transformers work ok and they take credit card phone orders. Check out the Y23 standard range listings.

http://www.avellindberg.com/transformers/y23_range.htm
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Old 5th July 2009, 12:27 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by wicked1
I mean 12,0,12. And I think I need something a lot bigger. Like 250VA which is, I think, about 20 amps. That sounds like a lot, so I could be completely wrong w/ my math, there.
110Vac:12-0,12-0Vac, 250VA is a 10.4Aac transformer.

Output { VA / Vac } = output Amperes

The 1875 will give about 10 to 12W into 8r0 from a +-16Vdc PSU.
It will approach 20W into 4r0 if the PSU can hold up.

Both of these, 8ohm or 4ohm, could be powered by a 30VA transformer.

If you require two channels then roughly double the transformer VA rating.
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regards Andrew T.
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Old 7th July 2009, 02:56 PM   #8
wicked1 is offline wicked1  United States
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Quote:
Originally posted by kaos
Avel Transformers work ok and they take credit card phone orders. Check out the Y23 standard range listings.

http://www.avellindberg.com/transformers/y23_range.htm

Thanks! I had written them, and they hadn't gotten back to me. They just did, and the price is GREAT! I asked for a quote on the 250va 12v + 12v, and the price is just barely more than the 30va 12v at parts express!!
Now that I know I can use an even smaller tx, it should be even better!
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Old 7th July 2009, 06:45 PM   #9
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Try MPJA.com for usable trans. at reasonable prices. You really dont need toroidal stuff always. I've used iron units without a problem . Take a look..
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Old 7th July 2009, 06:53 PM   #10
wicked1 is offline wicked1  United States
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I have no issues w/ a good old iron xfrmr, and started looking into that.

Is there a difference in the power supply if I go w/ a 12,0,12, vs something that has 12,0 + 12,0?
Would I just share that common ground?

(ive ordered pcb's from chipamp.com, but have not seen a schematic)
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