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Old 11th December 2011, 05:27 PM   #18971
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Hi,

Quote:
Originally Posted by simon7000 View Post
Many years back there was an IEEE conference with two co-chairs. The first one's biography was a page long and listed bunches of technical awards, accomplishments and positions held. The other chair's bio was very short. He had won the Lenin and Nobel prizes.
I think I can do wout the Lenin one, or the Order of Karl Marx at that (the east german equivalent). I wouldn't mind a Nobel.

As I get older I find what I give out as Bio/CV gets shorter as I get older. Very little is really worth mentioning.

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Originally Posted by simon7000 View Post
Now T & JC while giving out secrets, I should continue my power supply tests with some low noise diodes. Any suggestions?
I personally use pretty generic schottkies, like 21DQ100 or such, depending on power levels.

But I also design significant DCR into the custom transformers for my gear (precise details are not up in public, you can PM me) and have the wound fully symmetrical and electrostatic screens, so noise on the primary does not pass easily to secondary.

Using generic transformers I try using cancellation of leakage (works well with mummified doughtnuts) and add external resistor to get the DCR up enough.

I also tend to follow the actual rectifiers with a "small and low inductance" capacitor in a small loop before things go into the main reservoir cap's, usually with judicious slices of Ohms designed into the PCB or very thin wires to damp any unwanted tank circuits.

To be honest, designing PSU's into PCB's or normal 3d Space is a bit of an art, it helps to be able to really visualise the different elements. The difference can be many dB for what may seem trivial changes...

Ciao T
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Old 11th December 2011, 05:37 PM   #18972
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...and sometimes even read in between the lines of John's comments
Reading between the lines becomes very important in many reviews.

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Originally Posted by ThorstenL View Post
I wouldn't mind a Nobel.
Are you expecting one any time soon?
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Old 11th December 2011, 05:42 PM   #18973
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Quote:
Originally Posted by Bob Cordell View Post
One thing I really like is the fact that you incorporate a standard loudspeaker load emulation into your frequency response tests for amplifiers. It is tremendously helpful to get an idea of what kind of coloration mught result from a given amplifier's output impedance (as opposed to the benign resistive load).
Are you sure Bob that John interprets your sarcasm properly?
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Old 11th December 2011, 05:46 PM   #18974
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Hi,

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Originally Posted by Pano View Post
Are you expecting one any time soon?
I rather doubt it.

Audio is not a field that win's you Nobel's and I sure hope I never qualify for one in politics or the likes...

I merely said I would not mind being given one.

Ciao T
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Old 11th December 2011, 05:49 PM   #18975
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Peak like resonance of cartridge inductance with cable capacitance, or something else?
Yes, I will try to find the original again (getting pretty yellow).
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Old 11th December 2011, 05:54 PM   #18976
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Originally Posted by Wavebourn View Post
Are you sure Bob that John interprets your sarcasm properly?
Not sure what you mean. There was no sarcasm intended. Everything I said was intended to be positive and constructive. Are you referring to my use of the term "benign resistive loads?" Everybody agrees that they are relatively benign loads for amplifiers, including John.

Cheers,
Bob
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Old 11th December 2011, 06:01 PM   #18977
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Quote:
Originally Posted by Bob Cordell View Post
Everybody agrees that they are relatively benign loads for amplifiers, including John.

Cheers,
Bob
Yes, dummy loads may be much more revealing.
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File Type: png distortion_dummy.PNG (68.7 KB, 147 views)
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Old 11th December 2011, 06:06 PM   #18978
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Quote:
Originally Posted by Bob Cordell View Post
Not sure what you mean. There was no sarcasm intended. Everything I said was intended to be positive and constructive. Are you referring to my use of the term "benign resistive loads?" Everybody agrees that they are relatively benign loads for amplifiers, including John.
I agree that it is a good idea to test amplifiers on real loads, but what is the point in frequency response curve of an amplifier loaded on some complex load? What would you get loading any "standard" signal generator on such a load? How useful will be the curve? And, finally, what is "Standard speaker"? Which one? Even if you limit choice of speakers by a single dynamic full-range cone speaker, which one is "standard"?
In my mind, it is much better to tell the man that he is wrong, instead of making fun behind his back.
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Old 11th December 2011, 06:16 PM   #18979
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Yes, dummy loads may be much more revealing.
Yes, if you want to see distortions of 2W SE amp loaded on horn speaker, or 100W P-P amp loaded on some 3-way speaker with complex crossovers that have dips in impedance that engage overload protection. But what's the point of frequency response curve output vs input of an amp loaded on some complex load?
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Old 11th December 2011, 06:22 PM   #18980
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Yes, if you want to see distortions of 2W SE amp loaded on horn speaker, or 100W P-P amp loaded on some 3-way speaker with complex crossovers that have dips in impedance that engage overload protection.
Anatoliy, you might be surprised. No need of testing 2W SE tube amps only or overload protection function. Try it and you might be surprised.
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