John Curl's Blowtorch preamplifier part II - Page 2329 - diyAudio
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Old 26th May 2012, 06:22 PM   #23281
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My business partner demanded to remove magic eyes. Now the project looks blind for my tastes.
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Old 26th May 2012, 06:25 PM   #23282
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Quote:
Originally Posted by 1audio View Post
This?
I don't see gauges and controls.
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Old 26th May 2012, 07:14 PM   #23283
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Well, everybody's opinion has been interesting.
The first reason for NOT having an LED was that it added NO real usefulness, and it would be difficult to mount. We would have to drill an extra hole in the front panel, etc..
The second reason is that it would be difficult to POWER the LED, because we are using something like +/- 30V supplies, and current balance between the voltages is critical. The LED could actually offset the voltages, if put on one side only to 'ground'. The best solution would be to add two power resistors, one on each side of the LED, and use it as a floating load across the two supplies of one channel. However, what about the second channel? It won't have the same load. Is that important?
Third, my old friend Enid Lumley could hear LED's used as indicators. Was she crazy? Well, yes, but she could hear better than anyone I have ever known. Why cross Enid? Others have independently found the same thing.
Maybe we could suppress any 'RFI' or whatever else that might be generated in the LED by adding a sizable capacitor across the LED. Might help, who knows?
I hope that 'reasonable people' can see that it just was NOT worth it to add an LED, since there was no 'on/off' switch in any case, and just touching the top of either the power supply or control chassis would prove whether it is plugged in.
Now you know! '-)
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Old 26th May 2012, 07:33 PM   #23284
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OK, let me get this straight.

- The supplies in the BT are so poor that a 5mA current will "unbalance" them.
- Series connections between rails require resistors on each side, ignoring Kirchoff's law
- If a known crazy person says that she can "hear" a 5mA device with insanely low noise connected nowhere near a signal path, that should be the primary engineering consideration
- RFI (or some other emanation) that has never been detected in the physical universe should be addressed by bypass caps

And you wonder why I'm cynical about fashion "high end audio"?
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Old 26th May 2012, 08:05 PM   #23285
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And you wonder why I'm cynical about fashion "high end audio"?
To paraphrase a popular t-shirt slogan back in the 70's...

Just because you're cynical doesn't mean they're not all a bunch of hacks, quacks, and charlatans.

se
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Old 26th May 2012, 08:33 PM   #23286
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I thought it was well known that an LED which is more than a few volts away from ground suffers from electron tunnelling, so it turns into a microwave oscillator. That is why two resistors would be needed per LED, pus a cap across it.

Also, to get good channel balance the left and right power supplies have to be built at exactly the same time (and almost the same place) by identical twins running their soldering irons off the same mains spur. Any subsequent current draw imbalance will upset the built-in symmetry.

Ordinary mortals would of course be unaware of the special requirements of high-end award-winning audio.
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Old 26th May 2012, 08:48 PM   #23287
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I don't use a center tap. Perhaps you can try what happens in a simulation.
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Old 26th May 2012, 09:03 PM   #23288
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Quote:
Originally Posted by john curl View Post
I don't use a center tap. Perhaps you can try what happens in a simulation.
A center tap is not required for Kirchoff's Law to apply. At least in this universe.
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Old 26th May 2012, 09:13 PM   #23289
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I'm a symmetrical kind of guy. I don't like adding extras on one power supply only. However, my explanation of why I didn't add an LED from 'practical hassle' reasons should have been enough.
Actually, I would have liked to have an LED built inside a 2A circuit breaker, added to the AC input of each power supply module. It would look really 'cool', business like, and only add, maybe $500 to the cost.
It would seem that one cannot win. IF you avoid something, because it would just add hassle in construction, certainly do NOTHING for the sound quality, AND maybe cause a problem, I get criticized.
IF I do something that does cause time and effort to be expended as well as added cost, I get criticized. I can't win.
Speaking of the 'devil', I spoke to Jack Bybee this morning. He has a newer, even MORE expensive product, and he can't make them fast enough. He is on a mission to help audiophiles, and he can't break away to have lunch. That's the way it goes.
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Old 26th May 2012, 09:34 PM   #23290
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However, my explanation of why I didn't add an LED from 'practical hassle' reasons should have been enough.
Then why didn't you simply leave it at that?

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