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Old 31st January 2013, 08:19 PM   #2681
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by myhrrhleine View Post
Hi Scott,

The information Ive seen showed improvement for extremely low distortion levels, like around -100db.
Takes the falling fb/response/phase shift associated with it out of the picture -->

THD cancelling.jpg

(A.Sandman)
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Old 1st February 2013, 08:35 PM   #2682
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Originally Posted by RNMarsh View Post
Takes the falling fb/response/phase shift associated with it out of the picture -->

Attachment 327400

(A.Sandman)
What does that have to do with cap load drive? Put some practical numbers up there for say an RL of 600 Ohms and net gain of 20dB. An amusing conceptual circuit but not practical in many cases. Do a noise analysis for instance, or if the summing resistances are much less than RL you get all the distortion back by shoving most of your current into the correction amp.
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Last edited by scott wurcer; 1st February 2013 at 08:38 PM.
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Old 2nd February 2013, 12:37 AM   #2683
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For those of us without EE degrees, it would be nice to know what is the external compensation (output back to minus input and the resistor to ground. IE values for R13 with C3 of 15pf in parallel and R6 on D5BB schematic) for 10db of gain, 20db of gain and 40db of gain. Thanks, Ray
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Old 2nd February 2013, 03:00 PM   #2684
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Correction: External compensation for unity gain with the + input grounded and then , 10db, 20db, 40db as in normal operation. Maybe it's too early to ask this. Thanks, Ray
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Old 2nd February 2013, 05:24 PM   #2685
S.A.G. is offline S.A.G.  Italy
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Default Transistor selection

I'd like to go full SMD to avoid the somewhat complex assembly of TO92 devices in the output stage. OTOH, I'd like to retain the thermal tracking feature of the PTH configuration while driving low loads.

I've been looking for dual NPN/PNP transistors in SMD packages capable of some power dissipation and the only parts that I came up with are the NXP PBSS4041SPN:

http://www.nxp.com/documents/data_sheet/PBSS4041SPN.pdf

It seems to me that those parts are designed for (static) switching rather than linear operation. They are also comparatively slower than 2N4401 / 2N4403, for instance.

Questions for the Semiconductors Gurus:

- are those parts any suitable for the output diamond buffer?
- any similar, better, parts?

Thank you.

Giorgio
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Old 2nd February 2013, 07:51 PM   #2686
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
What does that have to do with cap load drive? Put some practical numbers up there for say an RL of 600 Ohms and net gain of 20dB. An amusing conceptual circuit but not practical in many cases. Do a noise analysis for instance, or if the summing resistances are much less than RL you get all the distortion back by shoving most of your current into the correction amp.
...cap feed back to output to lower distortion... just caught me funny and I had this zanny idea - image- that it was summing and canceling distortion but another opamp in place of a cap would be more complete... thus A.Sandman's circuit. Sorry, its just the way I think sometimes. Its like a flat rock skipping across the surface of water... one point of contact quickly leads to another and who knows where it will end.

BTW- the circuit was published in Wireless World and taken to a working circuit level... into 8 Ohms. Feb 1974. It has its applications and ought be perfected (in IC's?). Or in discrete?
Oh, never mind.... carry on....

Last edited by RNMarsh; 2nd February 2013 at 07:56 PM. Reason: Out with the old, in with the new -
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Old 2nd February 2013, 08:08 PM   #2687
bcarso is offline bcarso  United States
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Quote:
Originally Posted by S.A.G. View Post
It seems to me that those parts are designed for (static) switching rather than linear operation.

Giorgio
So were the 2N4401 and 2N4403. They wound up being very good for noise if the circuit impedances are low and you send enough current through them, especially the 4403; although once people started to pursue low base spreading resistance as a primary goal, the 4403 was superseded. But we didn't use enough of those so they were discontinued. The more things change...

But what the impact of the lower gain bandwidth will be for the parts in question, and in this application, I don't know, but I'd like to play with them.
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Old 2nd February 2013, 11:54 PM   #2688
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Quote:
Originally Posted by S.A.G. View Post
I've been looking for dual NPN/PNP transistors in SMD packages capable of some power dissipation and the only parts that I came up with are the NXP PBSS4041SPN:

http://www.nxp.com/documents/data_sheet/PBSS4041SPN.pdf
Thanks for this Giorgio.

Dunno about suitability for diamond output but they sure look interesting for Lo R Lo Noise.

If you believe their Vbe (sat?) 1.05V for Ib 400mA, that means rbb should be MUCH less than 1.05V/400mA = 2R65 !

I'd have a caveat about 1/f noise but this is certainly worth investigating.

Last edited by kgrlee; 2nd February 2013 at 11:57 PM.
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Old 3rd February 2013, 06:19 PM   #2689
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Quote:
Originally Posted by RNMarsh View Post
...
BTW- the circuit was published in Wireless World and taken to a working circuit level... into 8 Ohms. Feb 1974. It has its applications and ought be perfected (in IC's?). Or in discrete?
Oh, never mind.... carry on....
As a unity gain inverter (does not work at all in follower mode) and an inverter with gain again presents a low impedance to drive, so the usefulness?
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Old 4th February 2013, 04:32 PM   #2690
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Thanks Scott! What is the latest in unity gain summing preamp (6 input) application or what opamp would you recommend. Ray
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