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Old 25th September 2002, 09:34 PM   #1
artnyos is offline artnyos  United States
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Default Famous Audio Designer Sighting

Did anyone else see our fellow forum fiend J. Carr inin Stereophile this month. Come back and give us some more power supply hints Mr.Carr, please.... We promise to be nice.

Art
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Old 25th September 2002, 11:25 PM   #2
jcarr is offline jcarr  United States
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Art: After reading more of the threads on this website, I have noted an overriding preference for simple designs around here.

OTOH, personally I enjoy things that are challenging enough to make me think seriously and sweat to get them to actually work, and that extends to the kinds of schematics and board layouts that I like to cook up.

But although much of my input may prove useless to this website, I really don't mind giving advice or sharing ideas where it may be warranted. So I'll probably continue hanging around, post a few things, and if the response is active, maybe I will post some more. Conversely, if the response is dead, or if there are too many responses that show a lack of basic understanding or thought, I'll likely limit my posts.

In the meantime, here's a circuit sketch for a line amp (20dB). Not too complicated, uses opamps, but not altogether uninteresting. Maybe even useful to someone.

regards, jonathan carr
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Old 25th September 2002, 11:27 PM   #3
jcarr is offline jcarr  United States
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You will have to fill in the missing parts, but it should all be fairly obvious.
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File Type: png opamplinestage01.png (3.8 KB, 822 views)
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Old 25th September 2002, 11:33 PM   #4
artnyos is offline artnyos  United States
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Default Baby you can drive my Carr

if there are too many responses that show a lack of basic understanding or thought, I'll likely limit my posts.

We will struggle to keep up. Try to be patient.

Art
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Old 25th September 2002, 11:38 PM   #5
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J Carr,

FYI, you probably already now it, but AD846 is a discontinued
product. Recommended replacements according to AD are
AD8001 and AD811, if memory doesn't fail me. I haven't
checked the datasheets, so I have no idea how compatible
they are.
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Old 26th September 2002, 01:09 AM   #6
jcarr is offline jcarr  United States
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Christer: You are right, and thanks for the correction. Oh well, it wouldn't be the first time that I have designed something using out-of-production (OOPs) components ;-).

In order to make the design that I posted work, you need external access to the internal node that drives the output buffer. AD844 is equipped with this (pin 5, same as the AD846), and I think it should work. So swap AD846 with AD844 and try it out (perhaps some fine-tuning of the time constants may be in order).

If you want to make sure that the time constants have all been trial-and-errored and optimized (so you don't have to do much debugging work yourself), I believe that the AD846 may still be available as old stock (price may be somewhat higher than when new).

regards, jonathan carr
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Old 26th September 2002, 02:51 PM   #7
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Hi Jonathan,

long time no hear.

Quote:
Originally posted by jcarr
You will have to fill in the missing parts, but it should all be fairly obvious.
Bootstrapping the internal drive signal, is it this the schematic is about ?

Have you brought this trick into your discrete Connoisseur preamps ?

regards,
Hartmut from Munich
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Old 26th September 2002, 04:01 PM   #8
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Quote:
Originally posted by jcarr
You will have to fill in the missing parts, but it should all be fairly obvious.
Jonathan,

You should have told us this was a test...!

Jan Didden
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Old 26th September 2002, 04:54 PM   #9
artnyos is offline artnyos  United States
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Default You should have told us this was a test...!

"But although much of my input may prove useless to this website, I really don't mind giving advice or sharing ideas where it may be warranted. So I'll probably continue hanging around, post a few things, and if the response is active, maybe I will post some more. Conversely, if the response is dead, or if there are too many responses that show a lack of basic understanding or thought, I'll likely limit my posts."

I think it was pretty clear that he meant it to to be exactly that.
A composite op amp with two nested feedback loops, one around compensation node a current feedback op amp. Quite a test I'd say.

"In the meantime, here's a circuit sketch for a line amp (20dB). Not too complicated, uses opamps, but not altogether uninteresting. Maybe even useful to someone."

uses opamps, but not altogether uninteresting

Well one out of four isn't to bad. The gain is actually 20.83 dB.
Man I hate to see what complicated looks like.

Gentleman start your Spice engines and warm up your 350MHz scopes!

Just a bit of fun Mr. Carr. I guess any of the good stuff that goes into a $30.000 preamp is WAY beyond mortals like us.

Art
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Old 26th September 2002, 06:57 PM   #10
jcarr is offline jcarr  United States
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Hartmut, Art: Although I don't enjoy working with opamps as components so much, many of the circuits I find immensely interesting. Some IC designers are very, very clever and talented.

And often I find it useful to try out an idea in the easiest, most painless way possible. So if I can locate an opamp that provides the necessary access nodes, it will definitely be my guinea pig (grin). Then if the idea works in practice, I can consider transferring it to a discrete implementation.

If you build and measure the posted circuit, I think you will find that the high-order distortion is _very_ much lower than either the 844 or 848 can manage on their own. The circuit can swing quite a bit of voltage, too - about 25V p-p out to 2MHz, tapering off to 10V p-p at 10MHz. The slew rate isn't bad, either, something like 300V/uS going either up or down.

Hartmut, no, I haven't gone overboard in applying this exact type of thinking to the Connoisseurs yet. The air-dielectric construction that we use is bloody hard to make, and this is both our strength and our weakness. Although I love interesting design ideas, in reality I must think very carefully about how much circuitry I introduce, what it is intended to accomplish, and whether the benefit is worth the greater complexity.

In this respect, I am no different than any DIYer. Before I can afford to get too liberal with the parts count, I need to cook up some new circuit board structural concepts that provide an acceptable level of sonic performance but won't cause too much grief in production.

Nonetheless, I always like to work on something new, and so on my next "3.1" design, in addition to a more advanced circuit construction system, I want to try a Cob-cancelling concept, push-pull self-biasing MOSFET vreg, current-sensing self-biasing JFET buffer stage, stacked/split grounding system, add another round of general topological refinements, and...and...

regards, jonathan carr
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