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Old 16th March 2013, 07:07 AM   #36741
1audio is offline 1audio  United States
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Ed-
Do you have a current probe? Monitoring the current waveform can show a lot of what is happening. The interactions between conduction angle, load, transformer saturation etc. are easier to visualize as waveforms than spectra.Usually the stiffer the voltage the bigger the current peaks, and as such more radiated noise. If you have a scope with waveform math you can display the instantaneous power which is also very interesting. Sinewaves are not the best source for rectified power.
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Old 16th March 2013, 12:15 PM   #36742
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Quote:
Sinewaves are not the best source for rectified power
Demian,

do you care to elaborate on this?

Three phase (sinusoidal) power distribution is considered by many to be best. Single phase with PFC comes close, especially for low power applications. What's wrong with sinewaves?

Thank you

Giorgio
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Old 16th March 2013, 01:12 PM   #36743
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I assume he complains against FFT.
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Old 16th March 2013, 01:16 PM   #36744
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Quote:
Originally Posted by S.A.G. View Post
Demian,

do you care to elaborate on this?

Three phase (sinusoidal) power distribution is considered by many to be best. Single phase with PFC comes close, especially for low power applications. What's wrong with sinewaves?

Thank you

Giorgio
the conduction period of the rectifiers when used to charge the capacitors of a DC supply that follows. You get a short conduction phase with a very high peak current followed by a period of no current in the diode. a swinging choke would help, but at the currents involved in a power amp it soon gets big and cumbersome.

It the incoming mains is rich in third harmonic then the diode gets more time to charge the capacitor.
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Old 16th March 2013, 02:05 PM   #36745
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Oh dear, a three-phase PFC bucking horse it is.

Ultimately, audio amplifying is all about efficiency and cost (leaves more cash for gigantic loudspeakers)
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Last edited by jacco vermeulen; 16th March 2013 at 02:11 PM.
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Old 16th March 2013, 03:09 PM   #36746
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Demian has a good point. While I appreciate the time and effort that Ed is putting into these power supply examples, they are (for me) difficult to interpret, and ANOTHER VIEW might be equally revealing and add to the real understanding of the problems and tradeoffs. Decades ago, somebody gave me a HP current probe from the early '60's that used obsolete (mercury)batteries and was germanium based. It was difficult to get going, yet, it gave me SERIOUS INSIGHT as to the difference between typical and high speed rectifier diodes. It was SO OBVIOUS with the current waveform that I then stopped using ordinary diodes in my best designs. You will find that the Blowtorch, Para JC-1,2,3, all use high speed-soft recovery diodes, everywhere where they are in continuous use such as in rectifier service.

I would like to point something out to Gapapag, something of interest. Last night, watching a TV program on 'How They Do It' they showed the construction of AIRSTREAM trailers, a popular travel trailer type from the 1930's. They specifically pointed out that they construct them with AIRCRAFT GRADE ALUMINUM, yet they are just a trailer. Why? I think it is the why they can be polished to a quality finish as well as other physical qualities. They would not use 'trashcan grade aluminum' or whatever, if they could get the same results. Our choice of AIRCRAFT GRADE ALUMINUM was made for us by the machinist that we went to, not by us. In mentioning it, here, in context of the CTC Blowtorch, I was only passing on what I was told, and the fact that someone who tried to make the same sort of case for themselves might consider that there are different grades of aluminum.
The 'heart' of our 'success' with the CTC Blowtorch, by anyone (so far as we know) who has used it, is because we DID OUR BEST to make it as good as possible. Not for some commercial enterprise, where cost vs quality, or 'proof' of WHY we chose the most exotic and expensive passive parts in many locations (so that we made no 'knowing' oversights at the time of its design and construction) because we were serious about making the best preamplifier that we could.
If I were making a recording, and it was my job to be a technical consultant, as I have done on several occasions, I would try my best, in the same way, to do the BEST JOB POSSIBLE, not to some typical commercial standard, or the most cost effective way.
By the way, this can 'tick off' the regular people who make audio for film, recording, and PA when you insist on 'the best way' rather than settling for the status quo, and I am pretty sure I would 'tick off' a number of people here, who do/or did audio for a living, commercially. That is the trade-off for doing a 'world class' effort in a commercial world.
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Old 16th March 2013, 05:25 PM   #36747
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Quote:
Originally Posted by john curl View Post
I would like to point something out to Gapapag, something of interest. Last night, watching a TV program on 'How They Do It' they showed the construction of AIRSTREAM trailers, a popular travel trailer type from the 1930's. They specifically pointed out that they construct them with AIRCRAFT GRADE ALUMINUM, yet they are just a trailer. Why? I think it is the why they can be polished to a quality finish as well as other physical qualities. They would not use 'trashcan grade aluminum' or whatever, if they could get the same results. Our choice of AIRCRAFT GRADE ALUMINUM was made for us by the machinist that we went to, not by us. In mentioning it, here, in context of the CTC Blowtorch, I was only passing on what I was told, and the fact that someone who tried to make the same sort of case for themselves might consider that there are different grades of aluminum.
Oh please, John. "AIRCRAFT GRADE ALUMINUM" is just an overly-hyped buzzword for 6061, which even Wikipedia notes is "one of the most common alloys of aluminum for general purpose use." I'm sure they even make trash cans out of it.

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Old 16th March 2013, 05:38 PM   #36748
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OK, can I have one in Sealium then ?
(also sounds way more exotic than 5383-H116)
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Old 16th March 2013, 05:59 PM   #36749
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Steve Eddy,
You are correct that all 6061-T6 aluminum should be made to the same standards whether the aircraft grade name is applied or not. But that is to say that you couldn't use 7075-T6 in its place, wouldn't really make any difference in an audio chassis, but in a plane the two alloys have different properties that are chosen for specific purposes. Yes aircraft grade would somewhat distinguish this material from junk recycled material that is just cast aluminum, but it is an oft overused term at this point in time.

ps. In aircraft the designation is only used along with chemical analysis and quality control to have a paper trail and certification of the material that it does in fact meet specific standards. It is a traceable quality standard. The aluminum coming into a qualified shop sure better be marked with grade and producer if you are going to use it for a flyaway part.

Last edited by Kindhornman; 16th March 2013 at 06:02 PM.
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Old 16th March 2013, 06:02 PM   #36750
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Originally Posted by jacco vermeulen View Post
OK, can I have one in Sealium then ?
(also sounds way more exotic than 5383-H116)
Or how 'bout "MARINE GRADE"?

se
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