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Old 18th February 2012, 02:33 PM   #1
reins is offline reins  Germany
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Default reducing voltage

Hi,

I would like to reuse a broken amp as 1 Channel as E-Bass amp. I plan to built the pre-amp also in the housing. Now my question:
I have a regulated voltage of +-21V. Op-amps work only with max. 18V. Is there an easy way to reduce the voltage by 3V? Would a Zener work?

Thanx
Stephan
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Old 18th February 2012, 02:54 PM   #2
pdul is offline pdul  Denmark
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LM317 Current Calculator - Electric Circuit

Try to look at this link.
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Old 18th February 2012, 03:10 PM   #3
rcbuck is offline rcbuck  United States
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I would use a 78L15 and a 79L15. That should be sufficient to run the op-amps. If you need +/- 18V you will have to use the LM317 series as already suggested.
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Old 18th February 2012, 03:19 PM   #4
RJM1 is offline RJM1  United States
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There are a lot or op amps that work up to +-22V.
LME49860, MC34072, LT1078MH, MC33171DG
For example.
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Old 18th February 2012, 03:20 PM   #5
reins is offline reins  Germany
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I hoped fpr a somehow simpler solution ;-)

But it's ok then.

Stephan
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Old 18th February 2012, 03:46 PM   #6
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The easiest way is to put 5 diodes is series with the supply. If you have a symetrical ps you put 5 on the + and 5 on the -. Pls observe polarity.

Use silicium diodes only as they have a drop of 0.6V each (0.6V x 5 = 3V). 1N4xxx series will do and are common.

This is the most simple, though I'd prefer the 78xx and 79xx series. They are also available in 18V version.
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Old 28th February 2012, 02:56 AM   #7
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try using LM 7818 from NS (max. out current == 1 amp.) if you used LM 317, 1.5 amp max.
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