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Old 28th July 2005, 03:10 AM   #1
asc is offline asc  United States
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Default 4780 smoked a transformer

Well, I was beta tesing my newly assembled LM4780 circuit with a guitar and an 8 ohm speaker the transformer went up in smoke after about a minute. The first minute sounded really good, btw. The x-former was rated at +/- 24V (48V with CT) @ .63 amps. After that was rectified, it was about 38.2VDC without a load, on a snubberized PS kit board. The specs on the 4780 said 80V max, so I tried it with an 8 ohm speaker load and the transformer overheated. Quickly I hit my handy power strip switch and I think everything is still ok.

The question: Will I need 2 or more amps at 38V?

Has anyone had marvelous success feeding a 4780 (chipamp) board? And at what current/voltage did you supply it?

Also, I have two 8 ohm speakers that I could either make into 16 (series) or 4 (parallel). What would be the best scenario?

-ASC
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Old 28th July 2005, 03:14 AM   #2
agent.5 is offline agent.5  United States
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0.63A?

I think you want about 10A
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Old 28th July 2005, 05:00 AM   #3
Stocker is offline Stocker  United States
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To be more precise, and to be safe, you want at least as much rated current capacity as the electronics are rated to produce. If your amplifier datasheet says it can put out 3 amps, get at least a 3A rated transformer.

If you get one that is rated for at least 2-3 times the current (e.g., 10 amperes), then the voltage will tend to droop much less and you will have good things like "less clipping" and "punchy bass" and "non-smoking transformers" etc.

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