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Old 21st July 2003, 04:20 PM   #1
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Default Good supply for preamp, Comments?

I'm about to begin my new Classe Preamp Clone and I want your comments on my Power Supply. This is what can probably be called an overkill supply, but I got most of the parts in stock. Let me know want you think and how can I improve it further.

I will post two parts of the gif picture (before and after the regulator). The complete pdf file will also be posted.

Thanks in advance...
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File Type: gif power_1.gif (31.7 KB, 1467 views)
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Old 21st July 2003, 04:22 PM   #2
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Default After the regulator

Here the "after the regulator" gif file
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File Type: gif power_2.gif (17.8 KB, 1420 views)
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Old 21st July 2003, 04:24 PM   #3
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Default Complete Schematic in pdf

Complete Schematic in pdf
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File Type: zip power supply.zip (21.9 KB, 161 views)
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Old 21st July 2003, 04:51 PM   #4
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No, it is not an overkill at all. PS transformer rating is way too low to qualify as an overkill. Caps following the regulators are really excessive. 317/337 provide some kind of minimal acceptable sound quality in general, but it really matters what exactly are they going to power in this case (sorry, unfamiliar with Classe circuits). There are many fast opamp- pass transistor based circuits on this forum, which will beat a 317 unconcious. There are also interesting shunt regulators. If you do some search you'll find a wealth of regulator info here. Just curious: why a Classe clone?

cheers
peter
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Old 21st July 2003, 05:09 PM   #5
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It simply seems overkill from the amount of parts used, when comparing for instance to a simple supply used in Pass preamps: http://www.passlabs.com/pdf/aleph/apserv17.pdf

Getting really good regulation doesn't necessarily have to produce good sound. Some people already commented that a simple pass trsnsistor provides for very good sonics.

I would imagine that the best ways to figure out the merits of a supply is to built few of them and check with a circuit how it sounds. Then you can add additional stages of filtering and bypassing.
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Old 21st July 2003, 05:32 PM   #6
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Quote:
Getting really good regulation doesn't necessarily have to produce good sound
Very possibly. But a set of 317/337, although ubiquitous in commercial amps sound positively 'grey' and dynamically challenged.
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Old 21st July 2003, 05:35 PM   #7
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Does Nelson Pass get credit for the pass transistor concept ?

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Old 21st July 2003, 05:59 PM   #8
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I am not familar with the Classe preamp as well. I assume that it draws minimual current just like an ordinary preamp (see 100ma?).

a few observations:

1) the R1/R2 (100ohm each) seem to be awefully big. With good ripple rejection of the 317/337 regulators, you probably don't need them.

2) if I have to, I would put big caps after the LM, not before.

3) I think overall the circuitry is complicated (too complicated?).
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Old 21st July 2003, 06:28 PM   #9
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Quote:
2) if I have to, I would put big caps after the LM, not before.
And why exactly? Even the datasheet doesn't endorse that.
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Old 21st July 2003, 07:55 PM   #10
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Quote:
Originally posted by analog_sa


And why exactly? Even the datasheet doesn't endorse that.

did the datasheet recommend BG caps, gold-plated RCA, aluminum pads, or heatsinks dipped in dielectric oil?

Seriously, my thinking or guessing is that a regulated PS will have high transiant internal resistance (it cannot output a lot of current for a very brief period of time). Having a large "resevoir" after the regulator will help cure that.
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