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Old 16th June 2005, 07:47 AM   #1
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Smile New transformer question.

Hello again,

I have a question. I have found the following transformer and would like to know if it would be useable for a single channel of LM4780, brian gt kit, or an lm3875 p2p amp? Could I series/parallel wire several of these to get the amperage I need?

High quality power transformer features 120VAC primary and 2 secondaries. One secondary is 24 VAC at 2amps and the other is 36VAC (center tapped) rated 750mA. Open frame with metal mounting ears and flexible color coded wire leads. Size about 2.35"L (without mounting ears) x 2.26"W x 1.96" Tall. Brand new made by EPEC transformer.

They are selling locally for 1.99 each so I thought it might be worth looking into.

They also have this transformer for 6.95.

High quality open frame transformer by Magnatek features standard 115VAC primary and 25.2VCT at 2amp secondary. Size about 3" long (excluding mounting tabs) x 2.5" high x 2" thick. With insulated wire leads.

Thanks for your advice,

John
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Old 16th June 2005, 01:38 PM   #2
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Oh, I forgot to mention that the LM4780 kits are running a 4 ohm load and the LM3875's will run 8 ohm loads.
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Old 16th June 2005, 01:46 PM   #3
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You would have to series 2 of the 24v windings. This would net you a 50w or into 8 ohms so chip amp.
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Old 16th June 2005, 03:01 PM   #4
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Hello,

Thanks for your response. I have another question though, paralleling would give me an increase in current, but what equation can I use to figure how much? I am pretty sure it will not double, as in 48V and 4A. Also I was looking at the data sheets for the LM3875 and it has a power supply voltage rating of 70ma max, but an output current limit of 4a, so I take it I need to match my transformers to the output current and not the input current? Or is it better to have a larger availiable supply of current available? Also when building LM3875 my pcb calls for 1000u 50v caps, can I substitute larger caps of the same voltage rating such as 2200uf 50v???

Thanks again,

John
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Old 19th June 2005, 06:15 PM   #5
ctardi is offline ctardi  Canada
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Quote:
Thanks for your response. I have another question though, paralleling would give me an increase in current, but what equation can I use to figure how much?
Parallel will leave the voltage the same, and double the current.
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Old 19th June 2005, 06:16 PM   #6
ctardi is offline ctardi  Canada
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Also, where did you find those transformers? I could use a few of them...
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Old 19th June 2005, 06:23 PM   #7
paulb is offline paulb  Canada
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Default Re: New transformer question.

Quote:
Originally posted by juan_caliente
Hello again,
They are selling locally for 1.99 each so I thought it might be worth looking into.
At that price, buy 4. Use 2 for each channel, one each for the + side and the - side. No need to parallel transformers, which can be tricky. Unless you're really trying to save money (you'ved saved a bunch already with the price of those xfmrs).
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Old 20th June 2005, 02:16 PM   #8
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I found these at http://www.goldmine-elec-products.com/home.asp. They seem to have a pretty good selection of resistors and caps also. I was going to order 4 this week but they will only ship, I can't go pick them up. I am going to try Apache Reclamation again and see if I can find some toroids before I pay to have these shipped 6 miles.
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Old 21st June 2005, 06:08 AM   #9
ctardi is offline ctardi  Canada
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Thanks for the link, but with shipping to Canada, 6 of them, which woudl be what I need is about $60. [hijacking] I just emailed a whole whack of companies that make transformers, hopefully i'll get one from them. [/hijacking]
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Old 30th June 2005, 07:55 PM   #10
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Default transformer help

hey! I'm new here. I have just recently built an amp and I need a transformer for it. I was wondering how ( if its possible ) to step up the voltage from this transformer.
I have a transformer rated at 13.5 vac @ 5 amps.

is there a way to step that up to 40 volts DC @ ( ? amps ) ?

I know it will provide the 60 some watts I need for max output power. My amp is a TDA7264 built into a wallet tin. Its output power @ 22.2 volts +/- ( I adapted mine for single supply operation, so 44.4 volts) is 32 watts per channel (LOL , @ 10% THD *cringes* )


Currently Im using a 32 volt @ 940 ma ( .94 amp) printer psu to power it. It will put some major kick into my marantz sp1200's. I think Im only getting about 17 watts per channel max, the chip is rated at 25 watts per channel @ 20 volts =/- ( again, 40 volts single supply).

So.. is there a way to step up the 13.5 vac tranny I have to 40 volts @ a lower amperage? thanks LOTS for any help!
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