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drdagor 10th July 2004 02:59 AM

Chip Amp as tracking supply for preamp
OK This may be totally off the wall, but here's the idea....

I've been looking for a low noise power supply for an ultra low noise pre-amp I'm building. (Transistor/IC... Please don't turn up your noses.) This is +/- 15 volt job.

Anyhow... I was looking at the spec for the National chip amps, and realized that they are just low noise op amps with high current output. The LM1876 (dual 2 amp devices in one package) is actually a good candidate for a dual tracking regulator.

The idea would be to build a traditional op amp regulator circuit for using 1/2 of the LM1876... (Apply a voltage reference to the non-inferting input, give it enough gain to get up to +15 volts, and let its own internal regulation and some bypass caps take care of the noise.) To generate the negative rail, you make the other half of the LM1876 a voltage follower, and drive the negative side with the mid point of the two rails. So the negative rail always tracks the positive rail. There is a circuit in Horowitz and Hill that pretty much describes this.

Does this sound worthwhile to any body else? Love to hear some comments.

analog_sa 10th July 2004 07:26 AM

This has already been discussed. In fact you will find your proposed circuit in the OPA549 datasheet. No idea if anyone actually tried it.

DaKi][er 10th July 2004 10:53 AM

somthing like the psu in this maybe?

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