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Old 30th September 2012, 07:09 PM   #1391
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Chris Hornbeck View Post
A *real* opamp needs to start with a Telefunken ECC83 marked "GAP/R". The rest just follows! (Or a 6SL7 for traditionalists).

Thanks,
Chris
Or a 6C4.
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Old 30th September 2012, 07:19 PM   #1392
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Originally Posted by scott wurcer View Post
OK here is the Rush cascode version 200V/us into 600 Ohms not to shabby.
What do we assume for source impedance?
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Old 30th September 2012, 07:22 PM   #1393
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Default Dick Burwen

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Originally Posted by scott wurcer View Post
It might be interesting to offer an update since the devices specified are listed as obsolete. I found it funny that Pete also discovered Dick Burwen's work, 46 years old. I think basicly the discrete op-amp ground was well covered 40 yr. ago.
Well, didn't he design most of the Cello line? It's a favored mastering tool in many recording studios. And some of those transistors go back to the 60s. I would think that transistor manufacture has improved with getting the impurities out of the silicon sandwich in 40 years. I know they don't want to make discreet devices. Ray
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Old 30th September 2012, 07:56 PM   #1394
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I think that Tom Colangelo designed most of the Cello circuits. It is interesting to see how Mark L. tries to re-write history. Apparently, neither Tom or I am an interesting or important part in Mark's history, anymore.
Dick Burwen designed the original LMP-2, LNC-2 for Mark Levinson Audio Systems, then much later, designed the Cello equalizer. Dick Burwen has been a believer in IC's since the early 70's, almost exclusively. He DID design good discrete op amps for AD back in the '60's, but he converted over, early. In fact, that is why I was able to take over design at MLAS, for a couple of years. I designed sophisticated discrete designs, that Mark found sounded better than selected IC's at the time.
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Old 30th September 2012, 07:57 PM   #1395
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Quote:
Originally Posted by Kindhornman View Post
Scott,
Being a complete newbie here and trying to follow what I can here I'm am lost as to the feedback circuit. Where does the r6 and r12 get in the circuit?
Just connect the node labels, I am trying to make the schematics easy to read without a lot of crossing wires.
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Old 30th September 2012, 08:02 PM   #1396
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Originally Posted by bcarso View Post
What do we assume for source impedance?
I know that's an issue, but it's good to start at a baseline and work from there.
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Old 30th September 2012, 08:06 PM   #1397
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One last one for today, the fully complimentary version. If SK170/SJ74 FET's are used high source impedances are not recommended.
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Last edited by scott wurcer; 30th September 2012 at 08:09 PM.
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Old 30th September 2012, 09:45 PM   #1398
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I swear, Scott! Can't you design a SIMPLE but ELEGANT circuit? '-) Discrete devices are NOT FREE, you know.

Last edited by john curl; 30th September 2012 at 09:50 PM.
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Old 30th September 2012, 10:06 PM   #1399
RNMarsh is offline RNMarsh  United States
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I would not use 600 Ohms for a source Z. I think 100 ohms is a best fit compromise for a standard.
[ Or lower]

Last edited by RNMarsh; 30th September 2012 at 10:09 PM.
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Old 30th September 2012, 10:39 PM   #1400
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Originally Posted by scott wurcer View Post
Also as bcarso points out there might be an opportunity for power on latch-up so there might be a simple clamp needed somewhere. I don't think this is a big problem.
There's various types of latch up behaviour.

TL07x will go "bang, bang" to each rail on startup but are normally OK after that .. even on simple single supply circuits.

Far nastier is LM4562 which will latch and not let go on many simple single supply circuits.

Both have *!?@!" overload behaviour on certain HP filter circuits.

You can get round these with some extra circuit complexity but usually the best solution is to use another OPA.
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