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Old 30th November 2007, 07:09 PM   #1
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Default buffered preamp power supply

Hello,

I want to add a buffer to my passive preamp, so that it can drive almost any power amp. I have found a design that uses the OPA627 on this page , and would like to build it. For the power supply, I came up with the attached design. Because I've never build a preamp PSU before, any comments are welcome.

I haven't figured out the values for the resistors yet. The 4u7 caps are tantalum (I have a bunch of those). Also, I would probably add one last small elcap and some small MKT's near the opamp. All diodes are 1N4001s.
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Old 30th November 2007, 07:51 PM   #2
TB is offline TB  United States
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Hello starbase218,
Check this article. It contains PSU schematic: http://www.stereophile.com/solidpreamps/54/index1.html

Another one:
http://headwize.com/projects/showfil...awliw1_prj.htm

Similar idea like yours. You can tune those PSUs to your need.
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Old 30th November 2007, 08:53 PM   #3
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The second article mentions that all the PSU electronics are for one channel only. For stereo, everything after the transformer is doubled. Isn't this overkill?

The reason I'm asking is that I would like to build the entire PSU in one enclosure, and the source select/volume/buffer electronics in another, so that both channels would be fed off the same PSU.
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Old 30th November 2007, 09:58 PM   #4
00940 is offline 00940  Belgium
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You might want to read this if you're going to use lm317 : http://www.acoustica.org.uk/t/3pin_reg_notes1.html
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Old 30th November 2007, 10:49 PM   #5
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Thanks for the link. I've updated the design to incorporate some of the changes. I think it's starting to look a bit like Rod's project 5B .

I've also come across some topics mentioning opinions on the OPA627 and other opamps, and their specific "sound". What I liked about the passive preamp was that it didn't have a sound of its own, and I would very much like to preserve as much of that quality as possible, while going active. But I am a bit unsure which opamp to use. Some described the OPA627 as sounding "dark".
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Old 30th November 2007, 11:44 PM   #6
kaos is offline kaos  United States
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The diode across your 337 (input to output) is backwards.
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Old 1st December 2007, 09:43 AM   #7
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You're right.. thanks .

Do you think this PSU would be suitable for a buffered preamp?
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Old 1st December 2007, 11:22 AM   #8
AndrewT is online now AndrewT  Scotland
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Hi,
opamps tend to perform better with very low noise power supplies.
This is particularly valid for pre-amps which have to work with low level signals.
You could look at discrete Vregs for the 627. Maybe even a CCS with shunt regulator. GK is running a thread on this now.
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Old 1st December 2007, 12:27 PM   #9
paulb is offline paulb  Canada
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Quote:
Originally posted by starbase218
Do you think this PSU would be suitable for a buffered preamp?
Yes.
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Old 2nd December 2007, 11:15 AM   #10
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Quote:
Originally posted by AndrewT
Hi,
opamps tend to perform better with very low noise power supplies.
This is particularly valid for pre-amps which have to work with low level signals.
You could look at discrete Vregs for the 627. Maybe even a CCS with shunt regulator. GK is running a thread on this now.
Ok, but how much is "enough"? Aren't regulators like LM317s widely used in preamps, even more expensive ones? Btw, who is GK?

Regarding opamps, I have read good things about the OPA2134. It's also less expensive than the OPA627, so I think I'm ging with OPA2134.
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