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Bob Cordell Interview: Error Correction
Bob Cordell Interview: Error Correction
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Old 14th May 2013, 10:26 PM   #4041
jcx is offline jcx  United States
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we could start an new terminology debate here - I don't consider the Leach Super amp output to be a "true cascode" - rather a cascade/totem pole that equally splits the dynamic Vdrop - for better utilization of SOA with devices having second breakdown

I would reserve the term "cascode" for the case when one device holds the other's Vcb nearly constant
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Old 15th May 2013, 12:34 AM   #4042
Zero D is offline Zero D  United Kingdom
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Quote:
Originally Posted by Bob Cordell

VTS = Very Tough Sell.
Well, i like it & it fits the bill. Ohh that word BILL has more than 1 meaning
Quote:
I think the IRs acronym should be changed to FTC (F_ing Tax Collector).
There ya go !

Quote:
Oops, that is already taken :-)
Taken is quite appropriate too

@ Damon Hill

Hi, even though you've been diagnosed with ADD, plus you say that you're a slow learner, it hasn't prevented you with Wanting to learn more, & indeed Actually doing so I myself am far from being an expert, & don't understand a lot, & make mistakes, but i try to learn from them, & don't allow Anything/Anybody to impeed my progress, nor should you, or Anybody else. All the best for the future
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Old 15th May 2013, 08:25 AM   #4043
Edmond Stuart is offline Edmond Stuart  Netherlands
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Default It depends.....

Quote:
Originally Posted by Bob Cordell View Post
Hi Edmond,
[..]
Consider an amplifier that uses a resistively-loaded LTP input stage followed by a VAS with a preceding emitter follower (what I sloppily refer to out of convenience as a Darlington VAS). Consider that amplifier does not use Miller compensation, but rather lag compensation at the collector of the VAS. That VAS is certainly not a transimpedance stage.
[..]
Cheers,
Bob
Hi Bob,

Yes and No.
It depends whether we consider the resistive LTP load being a part of the input stage (case 1) or being a part of the 'intermediate' stage (case 2).
In case 1, it is voltage in and voltage out, thus the 'intermediate' stage is a VAS.
In case 2, it is current in and voltage out, thus the 'intermediate' stage is a TIS.

Cheers,
E.
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Old 15th May 2013, 02:12 PM   #4044
Waly is offline Waly
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Quote:
Originally Posted by Edmond Stuart View Post
It depends whether we consider the resistive LTP load being a part of the input stage (case 1) or being a part of the 'intermediate' stage (case 2).
By the same "logic" the "intermediate stage" can also be considered as a current amplifier, or even a transconductance amplifier. So it can be a VAS, TIS, TCS, or CAS. As this would cover all cases, may I suggest WAS (Whatever Amplifier Stage).
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Old 15th May 2013, 04:47 PM   #4045
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by jcx View Post
we could start an new terminology debate here - I don't consider the Leach Super amp output to be a "true cascode" - rather a cascade/totem pole that equally splits the dynamic Vdrop - for better utilization of SOA with devices having second breakdown

I would reserve the term "cascode" for the case when one device holds the other's Vcb nearly constant
I agree completely.

Cheers,
Bob
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Old 15th May 2013, 04:58 PM   #4046
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by Damon Hill View Post
Okay, I'm a slow learner. Maybe it has to do with my recently diagnosed attention deficit disorder, but it sure took a long time to soak into my thick skull. I do have an awful hard time with the learning process, and studying abstract subjects like electronics.

I'm finally cluing in on cascoded amplifiers, and somewhat on how they greatly improve on a transistor's inherently non-linear behavior (but not completely, of course on Class B non-linearity at cutoff), before negative feedback is applied. For all the decades of building and enjoying Marshall Leach's amplifier, I'd ignored his 'Super Amplifier' and its rather different Version 2 iteration simply because I was just looking at it as a much higher powered amplifier I didn't think I needed.

Between Bob's book, Leach's amplifiers that employ cascoding to one degree or another, and Nelson Pass's designs, it's sunk in like a firmly applied baseball bat to my noggin. I'm surprised the practice isn't much more pervasive.

Of course, there's quite an increase in transistor parts count if cascoding is fully applied--those Krell and Pass amplifiers are >expensive<. But I coulda had a Leach Superamp by now if I'd only thought it through back in the 80s or 90s.

Forget error correction design for the moment. Any suggested reading on the subject of cascoding? I've been struggling for a long time on how to go beyond Leach's Low TIM "little" amplifier but never stumbled onto a newer design that really appealed to me, even though error correction seemed to have possibilities. Leach's amplifier worked a little >too< well, alas.

I'm going back to basics, the heart of a transistor's non-linearity. Maybe there's a downside I've not discovered about cascoding, but that's part of the learning curve, too. Time to rethink.

(For the moment and because of outright poverty, I'm having to settle for applying Thermaltrak transistors to my prototyping chassis and seeing how these faster and more linear perforated emitter devices sound and measure.)
Hi Damon,

Lots of engineers and some well-known gifted people have ADD. My son has ADD and that is how I discovered that I have it - it is often passed on through the male side. The term can be a misnomer. It does NOT mean that a person cannot focus intensely on a particular thing for an extened period when one has a reason to do so.

Cascoding can help a lot with the Early effect nonlinearity in transistors, and with the effects of nonlinear Ccb feedback capacitance, but how much cascoding brings to the table is quite dependent on the individual circuit. Cascoding is often not expensive in terms of a couple of added 10-cent transistors, if you are talking about small-signal cascode circuits. However, sometimes cascoding can carry with it a reduction in HF stability that must be watched out for in the design and layout process.

Cheers,
Bob
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Old 16th May 2013, 07:55 PM   #4047
Damon Hill is offline Damon Hill  United States
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Quote:
Originally Posted by jcx View Post
we could start an new terminology debate here - I don't consider the Leach Super amp output to be a "true cascode" - rather a cascade/totem pole that equally splits the dynamic Vdrop - for better utilization of SOA with devices having second breakdown

I would reserve the term "cascode" for the case when one device holds the other's Vcb nearly constant
I'm looking at the version 2.1 schematic, which is significantly different from the original version published in Audio. But I think I see what you mean; a voltage divider from rail to output establishes a 50% level from VAS to drivers to output 'top' transistors. The difference in version 2.x is that there are cascades(?) for each transistor rather than version 1 which really looks more like a voltage regulator to me, with all of the lower level transistors' collectors tied together.

http://users.ece.gatech.edu/mleach/superamp/circuit.pdf

In retrospect, because I hadn't been aware of the difference in designs, I ended up rather confused when I was comparing them to the Heathkit AA-1800 (and Dan Meyer's Tigersaurus uses CFP in totem pole--I built one very long ago and it seemed to work well). I'm still trying to understand the differences in Leach's implementations.

Oh well...time to haul out the curve tracer and the bench supplies, and do some basic circuits. Trying to find past threads on diyAudio that cover this subject; I know they're buried out there somewhere.

And this looks like a good one:

Cascode Output Stages

ADD has been a tremendous problem for me over the years, and I just have to muddle through as best I can.

Last edited by Damon Hill; 16th May 2013 at 08:13 PM.
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Old 17th May 2013, 11:13 AM   #4048
gootee is offline gootee  United States
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I have ADD, too. But I think of it as "AGILE FOCUS".

Some of you might also want to take the on-line test for Asperger's Syndrome, which seems to be fairly common in engineer/scientist types.

And for ADD, if your doctor hasn't had you try generic time-released dextroamphetamine, you might be suffering more than necessary.

Last edited by gootee; 17th May 2013 at 11:21 AM.
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Old 21st May 2013, 11:24 AM   #4049
gootee is offline gootee  United States
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Sorry to have interrupted. Please carry on.
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Old 3rd February 2015, 07:00 PM   #4050
mlloyd1 is offline mlloyd1  United States
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Bob Cordell Interview: Error Correction
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