John Curl's Blowtorch preamplifier part II - Page 2350 - diyAudio
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Old 30th May 2012, 03:41 AM   #23491
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Originally Posted by Steve Eddy View Post
What about currents flowing into your reservoir caps? Is everything that comes after the transformer secondary going to be perfectly symmetrical?
I think we're getting at *why* this complication is used pretty well considering no drawing is in use. Well, there was a good drawing earlier.

The reason John Curl suggested thinking of batteries is that they float, and it's the floating that matters. Imagine a really messy noisy rectifier and cap followed by an appropriate filter. If this messy noisy power supply is truly floating no current will flow through its output terminals except that drawn by its load.

And what else floats? "A duck!" "Very small rocks?" "A witch!"

If power supplies are arranged so that *only* load current flows from its output terminals and she weighs the same as a duck, then she must be a witch.

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Old 30th May 2012, 03:53 AM   #23492
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In John's case it is a little bit more complicated. I usually have transformer, rectifiers, and stabilizers, in the same box that they power, even when they are in different compartments shielded from each other. John had relatively long wires from power supply to the preamp. According to US regulations safety ground has to be connected to chassis directly near power socket, so such simple star ground approach that I use is impossible.

However, there are always many ways to skin the cat, so John used his own one.
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Old 30th May 2012, 04:12 AM   #23493
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Originally Posted by john curl View Post
No Johnferrier, it just showed how 'flawed' the double-blind test was. Carver is still making vacuum tube power amps. Why? Is he really that corrupt? '-)
You don't think he switched to performance art ?


Click the image to open in full size.
Bob Carver's 900 watt monoblock amps on Ebay


.
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Old 30th May 2012, 04:21 AM   #23494
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That's another 'secret' SE. Of course, you or SY will not think much of it, so I think I will leave it off the list.
Then you shouldn't have mentioned it at all.

se
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Old 30th May 2012, 04:24 AM   #23495
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........... I've been swamped before ........
I've always said you're all wet.

se
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Old 30th May 2012, 04:29 AM   #23496
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Highly damped
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Old 30th May 2012, 04:37 AM   #23497
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Originally Posted by Chris Hornbeck View Post
The reason John Curl suggested thinking of batteries is that they float, and it's the floating that matters.
You can create a "center tap" with batteries just as you can with transformer windings. So telling someone to think about batteries doesn't inform them as regards "floating" any more than telling someone to think about transformers does.

Quote:
Imagine a really messy noisy rectifier and cap followed by an appropriate filter. If this messy noisy power supply is truly floating no current will flow through its output terminals except that drawn by its load.
Only if everything is perfectly symmetrical.

So as I asked previously, is everything after the transformer secondary perfectly symmetrical?

se
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Old 30th May 2012, 04:38 AM   #23498
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Originally Posted by Chris Hornbeck View Post
If a center tapped transformer is used to establish the center point of a dual polarity power supply, any imbalances, including AC ones, appear as current into the "ground". In a circuit with a single true star ground and no ground loops this is no problemo, but what real circuit has no ground loops?

Real circuits have two (at least) channels with their own signal grounds running off doing Lord knows what and having various other impure thoughts. Dirty current injected into an imperfect "ground" is only allowable without penalty with a ground loop free construction, a rare thing, usually requiring balancing or transformers. The dirty current injection is minimized by floating power sources up from ground until the last possible moment, then dropping 'em gently where they wanted to be all along. Isolation, then redemption.

Thanks,
Chris
Thats why you need to rectify, smooth and regulate the split secondaries first and combine them after that. Only signal return currents will then flow in the non-power ground, and if you bias everything up into class A (we are talking pre-amps here) only DC will flow in the supply rails - no signal related harmonics and wide band hash. Localized decoupling and filtering (no shunt regs please!) will further improve the overall noise performance.

Single secondary 'flipper' designs that generate a split rail suffer from more ripple and higher charging currents. And single rail, FWB rectified, smoothed and then split using a buffer to create a ground also have major compromises - especially so since the splitter is effectively in series with the signal.

You get nothing without paying for it somewhere along the line.
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Old 30th May 2012, 04:43 AM   #23499
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Originally Posted by vacuphile View Post
That is also how I see things, with the exception that I don't put snubbers across each rectifier, but small CLC's after them. Is there anything to say in favour of using the center tap as ground and saving 4 diodes?

vac
No
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Old 30th May 2012, 09:53 AM   #23500
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" . . . especially so since the splitter is effectively in series with the signal. "

ok - slight exageration - its the ground splitter circuit noise that appears in series with the supply rails, not the input signal. Still totally suboptimal in my book
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Last edited by Bonsai; 30th May 2012 at 09:57 AM.
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