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Old 26th November 2003, 10:07 PM   #1
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Default 7812/7912 regulator questions

I am using these regulators in the preamp section of my amp. I'm looking for some more power and I have some larger transformers around. Currently my rails are 19v, I want to attach a transformer that will give 58v rails. I only pull a few mA from the regulators so dissipation is not an issue. If the regulators do not produce +/-12v bad things will happen in the amp. Am I safe to attach this transformer?
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Old 26th November 2003, 10:09 PM   #2
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How bad?
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Old 26th November 2003, 10:42 PM   #3
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Those regulators will not survive input voltage that high. You will need to drop the voltage down with a preregulator or dropping resistors. If you know how much current these +- 12 volt regulators supply to the circuit just chose a resistor value to put in series with the regulator input that will give you about 18 volts or so on the input. Be sure that the resistor is high enough wattage to safely handle the heet generated.

You could just feed the regulators with the low voltage transformer you have now and power the rest of the amp with the higher voltage transformer. That way you don't need to change anything other than building a seperate highvoltage supply for the power amp.

Without knowing more about the circuit that's about all I can suggest.

Later BZ
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Old 26th November 2003, 10:43 PM   #4
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I think the maximum input voltage for these regulators is around 36V.
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Old 26th November 2003, 11:16 PM   #5
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Quote:
How bad?
Things like the entire amp latching and putting large DC currents on the output.
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Old 26th November 2003, 11:29 PM   #6
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Why don't you use separate transformer for the amp and separate for preamp section. Or if you are using toroid you might add extra windings to big transformer, just enough to provide voltage to 78xx/79xx regulators?
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Old 26th November 2003, 11:39 PM   #7
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Hi,

Quote:
Am I safe to attach this transformer?
No, but you could use some LMxxx to preregulate.

The 78/79xx series aren't really all that good sounding but I can't see how on earth that amp is going to be more powerful by changing the VA rating of the xformer and sticking to the same rail voltage and current ratings????

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Old 26th November 2003, 11:46 PM   #8
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With a new transformer he's increasing rails from 19 to 58 V. Don't forget to check electrolytics, if they can take the voltage jump.
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Old 26th November 2003, 11:49 PM   #9
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Gee, I think I hear an echo.
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Old 26th November 2003, 11:53 PM   #10
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Hi,

Quote:
If the regulators do not produce +/-12v bad things will happen in the amp.
So:

Quote:
With a new transformer he's increasing rails from 19 to 58 V.
Yes but sticking to say, +/- 12V is not going to give more output power to the amps though, is it?

Quote:
Gee, I think I hear an echo.
Or perhaps a misunderstanding on my part...

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