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Old 11th July 2012, 02:37 AM   #341
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by jcx View Post
kinda tough when Harris was selling CFA in early '70s, unless "WAY before" was months, weeks?

Walt Jung's History chapter in his (free, online) Op Amp Applications tome is worth reading

Google turns up a 1972 ref to HA2500 second source

many cirucit topologies were implemented in potted modules, hybrid circuits before semi processes allowed fully monolithic impelementaitons
We arent on the same page.... differential inputs are not the same as [complimentary] push-pull input. Though in same family, I suppose.

I assume a patent search did not show up such prior 'art'. But never-the-less, I was doing similar work on my own and do not take any credit for the patent nor knew any of the inventors. Only talked to one of them when he called me after reading an article I wrote using closely related circuit as he was concerned that maybe he didnt have a patentable circuit. Maybe you meant it for other potential readers -- but i know Walt and read/have all his work since day one.

Last edited by RNMarsh; 11th July 2012 at 02:49 AM.
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Old 11th July 2012, 01:56 PM   #342
sonidos is offline sonidos  United States
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Yes, I always thought a differential input was absolutely necessary. This article was a jaw dropper (speaking solely for myself) because you explain how your circuit does this w/o the diff input. This and my reading of CFB op amps is starting to make much more sense now.

Full disclosure: I'm still stuck in EE101!

Last edited by sonidos; 11th July 2012 at 02:01 PM.
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Old 11th July 2012, 05:49 PM   #343
sonidos is offline sonidos  United States
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This is my 1st venture into discrete components. What is best way to increase closed loop gain? Via R8?
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Old 11th July 2012, 05:58 PM   #344
RNMarsh is offline RNMarsh  United States
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R8 could be adjusted but too much more gain and you could run into clipping the little amp. Try it first as described.
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Old 11th July 2012, 06:07 PM   #345
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Quote:
Originally Posted by RNMarsh View Post
R8 could be adjusted but too much more gain and you could run into clipping the little amp. Try it first as described.
Thanks, I've not been happy with my chip amps at 6 dB using my Senn HD580 phones, but thinking it through, 12 dB should do the trick. And I have a small scope handy to verify clipping in case I decide to tweak R8.
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Old 11th July 2012, 08:44 PM   #346
RNMarsh is offline RNMarsh  United States
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Thanks, I've not been happy with my chip amps at 6 dB using my Senn HD580 phones, but thinking it through, 12 dB should do the trick. And I have a small scope handy to verify clipping in case I decide to tweak R8.
That was my experience too. 12dB should be fine. Tell us how it sounds.
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Old 11th July 2012, 10:53 PM   #347
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Hi all, thanks for this very interesting discussion!
I've just received the MJE200/210, they are from Fairchild. I ordered 100 from each just to be safe and assure a good number of adequate complements. Fool of me! I have to say I could not have even one pair!!. All my MJE200 have Hfe in 140 to 170 margin while the MJE210 run between 210 to 225. I used a Peak Atlas DCA55 to classify them.

I was wondering if anybody else here would have pieces of these TRT to interchange (I would not like to buy 1000 or more just to get a good pair!!). Or any other possibility, I am open to other ideas.

Thanks in advance,

Javier
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Old 11th July 2012, 11:26 PM   #348
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I suspect the IC manufacturers got the idea for CFA using diamond buffers topology from Jean hiraga who published the topology back in 1983 in both BJT and Jfet versions, see Le Mostre. He called it double emitter follower. The earliest patents I could find on CFA with diamond topology dates from 1985. After Jean Hirage many amplifiers appeared using the topology, Pioneer used the most tweaked or should I say advanced form of this topolgy I ve ever seen in a power amp dating from late 1980s.
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Old 11th July 2012, 11:41 PM   #349
sonidos is offline sonidos  United States
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Originally Posted by RNMarsh View Post
Tell us how it sounds.
I'll lay out a board this weekend and go through the old etch process. It will come together in just a bit. I guarantee to put comments up.
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Old 12th July 2012, 03:36 PM   #350
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For those just skimming through the thread, jackinnj mentioned using Dale resistors. At the minimum, I want to use these for R1 and R8. But if you haven't learned yet, the particularly good ones are as follows, best one being first.

RN6xE
RN6xC
RN6xD

where x= 0 or 5. Read the datasheet for the size dimensions..they are bigger than you might think. If I'm off base folks, please correct me. Mouser has many in stock.
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