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Old 12th January 2012, 11:21 AM   #31
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Jointdead,
You are not listening.
High supply voltages can and will kill the chipamp.
4ohms speaker loading requires an even lower supply voltage so that you don't kill the chipamp.

Have you read the datasheet yet?
Find out which parts you understand and ask specific questions about the parts you don't understand.
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regards Andrew T.
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Old 12th January 2012, 11:56 AM   #32
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The absolute maximum supply voltage is + and minus 30 volts.

I suggest that you purchase the correct transformer instead of monkey farting around. Purchase the correct transformer and you will be lucky enough to possibly make something that actually works. Purchase a transformer that is too large and too high a voltage and you will let the smoke out of your LM 1875 devices period. There are plenty of places to purchase a salvage transformer if your trying to save a buck. Primary concern in my opinion should be safety to yourself and others for one and safety of possibly others property by not starting a fire.
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Old 12th January 2012, 04:28 PM   #33
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I'm going to leave this to the Gain Clone fraternity.

I was offerring advice as to how to test the salvaged transformer.

For EURO 20.00 I would buy a brand new transformer of the correct voltage and VA rating. Maybe in Estonia they are more expensive.

By the time you have built a regulator and bought cheap transformers you will have spent more then the cost of the correct transformer.

I do appreciate that the DIY, re-use bug is very contageous but sometimes, common sense prevails.
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Old 12th January 2012, 05:00 PM   #34
johnr66 is offline johnr66  United States
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For every two channels with an LM1875 or TDA2050, you can use the Radio Shack 12.6-0-12.6, 2 amp transformer. On my TDA2050 amp, I get 10 watts RMS @ 8 ohms both channels driven (continuous sine wave) before clipping and 14 watts @ 4 ohms. Yes, the voltage is a low, but the trafo is $13 and easy to obtain.

For a 22 watt per channel as rated above into 4 Ohms, I bought 2 12v 5amp trafos from Parts Express and wound on some windings to bring the output voltage to +/- 20 volts no load on the DC side. It will sag some under load. This is as far as I'd push those 5 pin chip amps with 4 ohm loads. I also bolt them direct to the heatsink (no insulator) as thermal conductivity is better. The TO-220 case needs to transfer a lot of heat, so make it easy on it.

I never had much luck with trash picked transformers as the voltages or current is rarely right for the job.
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