John Curl's Blowtorch preamplifier part II - Page 2199 - diyAudio
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Old 2nd April 2012, 06:36 PM   #21981
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Quote:
Originally Posted by john curl View Post
T, further consideration of the circuit that you just put up shows a true engineer's understanding of the problems, and a practical solution that could have been effected even in the middle 1960's without too much of a problem, since the 2N3819 was available even then.
John,
In my opinion, the information about the circuit ThorstenL posted is a bit misleading. I think it is his own variation on the themes "Sansui's way of pulling BJT bases apart" + "Borbely style 2nd stage" + "a tad of LH0033".
As far as I know, Accuphase never used that type of 2nd stage and they only used Jfet in front of comp.diff. input stage to (my guess) solve coupling caps / input Z issues. And no 2N3819's, by the way, just some 2SKxx.

I might be wrong, but then, ThorstenL is welcome to correct me and provide a reference.

Best,
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Old 2nd April 2012, 06:42 PM   #21982
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Elektroj, this is called 'quibbling' or making much of what you see, different, when it is really very similar. The 2N3819 has an American number, so the Japanese are not generally going to use it. However, it is a very old part and often sourced from many places.
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Old 2nd April 2012, 07:09 PM   #21983
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Originally Posted by john curl View Post
Elektroj, this is called 'quibbling' <snip>
I know, John, it is.
But then, it is not fair to come up with some self-brewed schematic and call it someone else's.
What's your own position with numerous clones and variations of your products, by the way? Are they allowed to bear "designed by John Curl" tag?

(flame trousers on)

Best,
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Old 2nd April 2012, 07:12 PM   #21984
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T's circuit is just an improved variation of what you put up. The essence of what T started from is contained in your schematic. It is good for a designer to give 'prior art' some recognition.
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Old 2nd April 2012, 07:13 PM   #21985
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Hi,

Quote:
Originally Posted by elektroj View Post
In my opinion, the information about the circuit ThorstenL posted is a bit misleading. I think it is his own variation on the themes "Sansui's way of pulling BJT bases apart" + "Borbely style 2nd stage" + "a tad of LH0033".
Perhaps. There are many influences in this.

I'm not particulary on Sansui, this is more Diamond transistor influenced.

The key to me are N-Channel J-Fet buffering symmetrical differentials.

These come from Accuphase. I do not claim the circuit is an exact copy of Accuphase's designs and the parts are based on what is inside of Tina-Ti and many others could be used. The VAS Stage is what I considered adding and has it's own advantages. Accuphase used a normal darlington VAS in the schematic I looked at E-305).

The circuit is about showing a principle, not a precise and exact implementation.

Ciao T
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Old 2nd April 2012, 07:16 PM   #21986
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Hi,

Quote:
Originally Posted by elektroj View Post
But then, it is not fair to come up with some self-brewed schematic and call it someone else's.
I was giving credit to the originators of the idea, in case the concept of crediting sources of inspiration is alien to you.

Some people...

Ciao T
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Old 2nd April 2012, 09:25 PM   #21987
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Quote:
Originally Posted by john curl View Post
Scott, it is obvious that you have not lived with a Quan-Tech noise analyzer on a daily basis for most of your life.
Perhaps you should look over his article in Linear Audio v3 giving noise measurements for high impedance sources.
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Old 2nd April 2012, 10:04 PM   #21988
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I hope to point out Noise Figure (a useful figure of merit in this case) with current with a typical low noise input transistor. Please note what happens with increasing current.
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Old 2nd April 2012, 10:39 PM   #21989
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Quote:
Originally Posted by ThorstenL View Post
I was giving credit to the originators of the idea <snip>
ThorstenL,
You weren't giving credit to originators of the idea, you published schematic and attributed it to Accuphase,
Quote:
Originally Posted by ThorstenL View Post
BTW, I cannot really claim that one, it's earlyish lower end Accuphase...
whereas in reality it only remotely resembled their product.

This is not the best practice to credit sources, I must say. Just use the proper wording and it will be fine.
Something similar to this would be much better:

"I did some thinking about this and came up with this... The idea to use Jfets in front of complementary differential stage came from manufacturer XXX."

Also, by keeping out words that describe from which end in your opinion the product might be, you will refrain from offending anyone.

Enough of this.

Let's stop tooting our own horns and get back to analysis of John Curls works, before he has changed his mind.

Best,
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Old 2nd April 2012, 11:11 PM   #21990
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Quote:
Originally Posted by john curl View Post
I hope to point out Noise Figure (a useful figure of merit in this case) with current with a typical low noise input transistor. Please note what happens with increasing current.
I was not talking typical, I was refering to the devices I mentioned last week. How to make bi-polars that are still improving beyond 25mA was demonstrated (and actually put into the public domain) over 25yr. ago. Unfortunately there was no money in this and no one ever used this information. Yes the application space is narrow.

EDIT - MPSA18 a choice for low noise input ???? If this is meant to dissipate confusion go for it.
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Last edited by scott wurcer; 2nd April 2012 at 11:22 PM.
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