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Old 29th May 2005, 11:20 AM   #21
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Sincerely, have tried with a resistance of 250ohm/20W and a choke with wire from 1mm of value about to 7-8 MH ( I not have not been able to it measure instrumentally ), and for generator to 50Hz has used an audio amplifier. Probably the "secret" is in the "Q" of the resonant circuit LC, and in the form factor of the 50Hz signal .
For the data that I have, from the curve 1 fig.3 seem that the energetic content to 50Hz is such by justify the 1000W of the resistance and the 15A of the choke.
Other point is the generator 50 Hz. Perhaps Hiraga has used a transformer or the pulsating output of a rectifier?

Mauro
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Old 29th May 2005, 02:04 PM   #22
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In the article, the LC is used as "1khz filter". Maybe it is mean for the signal can only pass 1 way.

How do you view the graph in your experiment? What "viewing" device do you use? A program in computer+soundcard? Scope? Neutrik? Audio Precission?
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Old 29th May 2005, 03:17 PM   #23
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Indeed, the circuit LC even to seem me a function of filter.
For what concerns the analysis, at home I prepare ( besides launch generating DDS and sine -90 dB and the usual analogic oscilloscope ) of a tool of oscilloscopes for PC with working (Pico Tecnology ADC216) in real-time FFT. With this (economic) tool analyses real-time and without problems the harmonics till 160Khz with dynamic of 90 dB ( has 16bit "realities" of vertical resolution ).
Naturally is not the precision one, but for this kind of measures not are of interest hardly ever the absolute value of a measure but her general "envelop" (the graphics are a very hard harmonics saturation!)

ciao

Mauro
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Old 30th May 2005, 10:18 AM   #24
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Quote:
Originally posted by mauropenasa
Indeed, the circuit LC even to seem me a function of filter.
[snip]ciao

Mauro

Yes, the filter is there to isolate the 50Hz generator from the amplifier, to keep the 1kHz out of the 50Hz generator, and to avoid that the 50Hz generator short-circuits the amplifier output, which would be a Bad Thing

Jan Didden
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Old 30th May 2005, 11:34 AM   #25
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I have made curious me. I will do of the tests the more ample, and if have resulted of relief there will show them.
In fact I hopes to verify the importance of this parameter (MFB immunity) in the "sonic" quality, and the adeguate topology to realized.
This are the intellectual "challenges" that like me!

Ciao

Mauro
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Old 30th May 2005, 11:41 AM   #26
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Quote:
Originally posted by mauropenasa
I have made curious me. I will do of the tests the more ample, and if have resulted of relief there will show them.
In fact I hopes to verify the importance of this parameter (MFB immunity) in the "sonic" quality, and the adeguate topology to realized.
This are the intellectual "challenges" that like me!

Ciao

Mauro

Mauro,

Very interesting! I'm looking forward to your findings!

Jan Didden
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Old 30th May 2005, 03:10 PM   #27
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Hi Mauro,

I'm also curious about what topology can give graph2 (AndyC too)

Wheter it can be reached with 3 transistor amp or 30 transistor amp or no feedback or feedback design, please tell us.
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Old 30th May 2005, 08:41 PM   #28
ingrast is offline ingrast  Uruguay
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Default Is it me only?

I am afraid I cannot discern the vertical scale for spectrum graphs as posted.

If for example fig. 2 range is 40 dB (a joke) then the test amplifier is outright bad.

Then if it is 140 dB (another joke), it is out of this world.

Rodolfo
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Old 31st May 2005, 02:26 AM   #29
jcx is offline jcx  United States
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Default ...gain is all you need

jeeze guys, the answer has only been known for over 60 yrs (70 yrs if you credit Bode and the boys at Bell having worked it out prior to WWII, just wasn’t well published before Bode’s book)

maybe some around here should really read up on feedback theory rather than repeat inanities they've picked up on the web and in audio magazines

all you need is low output impedance; anybody ever see: Vout = Itest * Zout in some textbook?

and of course there is only one practical method of achieving low output Z in a world of controlled current sources (like transistors or power fets) - that’s by applying lots of negative feedback, be it local or global

to get output Z low enough for the test current (or the norton -equivalent of "back EMF") to give "interface intermodulation" products down among the other distortion floor products all you need is gain - negative feedback loop gain around the output stage to be more specific

remember that emitter followers are 100% local negative feedback stages, go for a triple cfp/darlington output and most amps could do a good job if properly biased and compensated

http://www.diyaudio.com/forums/showt...ht=#post473194

shows more gain = lower Zout and lower “interface intermodulaion” even though the JLH and Graham’s modification don’t have a excess of output stage current gain, maybe some else here besides myself and amplifierguru could benefit from reading the references in that post

( I do have sims showing this “interface distortion” @ -140 dB – this is one case where spice has a good chance of getting the “distortion” number close to right since it is determined by Zout)
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Old 31st May 2005, 09:01 AM   #30
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I have tried launch amplifiers ( all with a tall degree of local or general NFB ) and the resulted on a range of 90 dB am as defined by jcx ( Low Zout = low "interface distorsion "). In practice not distinguishes a substantial variation of THD.
Even I believe that the strong THD of the curves publish are reproducible only in structures with high Zout & /or low factors of NFB ( totem pole & single ended without NFB?).
To show it I have to reconstruct some single ended.
If some disposes of this amplifiers and it may try, he is the welcome!


Ciao

Mauro
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