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Old 27th August 2005, 04:00 PM   #1
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Default Regulated PSU for Preamp

I have searched all the threads concerning regulated PSU for preamps used with NI LM3886 chipamps. I am confused by the sheer amount of information. Would someone please post a schematic for a PSU used in conjunction with OPA627/Buf634?

I have a 150VA 12-0-12 toroid, is there any way to use it? I know that the regulators usually regulate down by 3 or more volts; is 9volts enough?; is there an appropriate regulator to regulate from 12 to 9 volts? The speakers I am driving are currently being driven without a preamp and using a volume controlled line-out on my CD player (2.5V max). I would like the benefits of the preamp: switching inputs, modest gain, and clarity enhancement, etc., Any suggestions will be greatly appriciated.

Bob
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Old 27th August 2005, 04:11 PM   #2
VT67 is offline VT67  Belgium
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Hi Bob

For a simple OPA627/BUF634 combo and matching power supply look at Russ White's design.
Chipamp Pre

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Old 27th August 2005, 04:44 PM   #3
cyteen is offline cyteen  England
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Default Re: Regulated PSU for Preamp

Quote:
Originally posted by bostonflyer


I have a 150VA 12-0-12 toroid, is there any way to use it? I know that the regulators usually regulate down by 3 or more volts; is 9volts enough?; is the

Bob

Remember that after rectification you will get 12*1.414 volts DC so after regulation you should still be able to get a full 12 volts.
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Old 27th August 2005, 07:25 PM   #4
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Default Re: Re: Regulated PSU for Preamp

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Originally posted by cyteen

Remember that after rectification you will get 12*1.414 volts DC so after regulation you should still be able to get a full 12 volts.

It might be a little borderline, though, except if using low-dropout regulators.

3X7 regulators or similar need at least three volts more to regulate, in to out, and a slight AC line drop might take that away.

Better to get a slightly higher transformer or regulate to a bit less.


Carlos
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Old 28th August 2005, 01:13 AM   #5
BWRX is offline BWRX  United States
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well a 120VA transformer will also have a higher output voltage than 12*1.414 because it will not be loaded down a lot by the preamp electronics. so without accounting for the transformer regulation you'd have about a minimum of 12*1.414=17Vpeak-2V(2 diode drops)=15VDC. say it has about 10% regulation so you'd be more around 12*1.414*1.11=18.7-2V=16.7VDC to work with. don't forget that most of the low dropout regulators are guaranteed a maximum dropout of around 1.5V. i'd say your transformer is more than adequate for your application.

i use one 15VAC secondary of a plitron 120VA toroid in a power supply for an AMP3 (15Wx2 class D amp) and it doesn't cause the voltage to drop at all even around full output.
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Old 28th August 2005, 08:25 AM   #6
Nuuk is offline Nuuk  United Kingdom
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How about this one ?
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Old 28th August 2005, 02:27 PM   #7
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Quote:
Originally posted by BWRX
well a 120VA transformer will also have a higher output voltage than 12*1.414 because it will not be loaded down a lot by the preamp electronics. so without accounting for the transformer regulation you'd have about a minimum of 12*1.414=17Vpeak-2V(2 diode drops)=15VDC. say it has about 10% regulation so you'd be more around 12*1.414*1.11=18.7-2V=16.7VDC to work with. don't forget that most of the low dropout regulators are guaranteed a maximum dropout of around 1.5V. i'd say your transformer is more than adequate for your application.

i use one 15VAC secondary of a plitron 120VA toroid in a power supply for an AMP3 (15Wx2 class D amp) and it doesn't cause the voltage to drop at all even around full output.
You are considering positive 10% regulation only, when it should be +/-10%, IMHO.

How much wall AC drops might depend on many factors.

Low dropout regulators, as I also said, should be the way to go on this case.


Carlos
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Old 28th August 2005, 06:11 PM   #8
BWRX is offline BWRX  United States
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I've never come across a transformer that has a lower than specified no load voltage, but I suppose it's possible.
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Old 29th August 2005, 03:19 AM   #9
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Well, it looks like I'm on the ragged edge with the tranny. I've looked at some specs on low drop regulators and have not found one with the right input/output voltages, If someone knows of one please let me know. Thanks for all your posts!!

Bob
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Old 29th August 2005, 08:39 AM   #10
BWRX is offline BWRX  United States
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What about the LM337 and LM317 used in the supply Nuuk posted? There are a bunch of good ones from National and Linear. What exactly are the voltage and current requirements for your supply?
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