not so much criticizing Brad but rather the general default in this presumably "advanced analog design technique" thread that we keep hearing what single (monolithic) op amps can't do
is it really that hard to keep in mind that multiloop topologies, that you can design with monolithic op amps to make better amps
where you see the little triangle and are despairing of the needed performance - try thinking of 2 purpose chosen op amps in a multiloop
low input noise VFA up front, CFA DSL driver chip to push hard at the output
Jung devotes a few pages to them in audio driver section of his (free online) Op Amp Applications Handbook
Jerald Graeme does more in his articles, books
it really is decades old "textbook" design now
in smt the board area needn't be prohibitive
and there simply is a cost of doing better - if you need the performance then don't kvetch about paying for it - buy 2 $2 op amps if you need the performance
is it really that hard to keep in mind that multiloop topologies, that you can design with monolithic op amps to make better amps
where you see the little triangle and are despairing of the needed performance - try thinking of 2 purpose chosen op amps in a multiloop
low input noise VFA up front, CFA DSL driver chip to push hard at the output
Jung devotes a few pages to them in audio driver section of his (free online) Op Amp Applications Handbook
Jerald Graeme does more in his articles, books
it really is decades old "textbook" design now
in smt the board area needn't be prohibitive
and there simply is a cost of doing better - if you need the performance then don't kvetch about paying for it - buy 2 $2 op amps if you need the performance
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I agree---I hope I didn't imply a bias against ICs by mentioning this in this thread. There are a few areas where we lack ideal ones for certain apps, even in composite arrangements, such as for high impedance sensors, but there are some reasonable ones if the output swing needn't be too large. Some of the better JFET input devices seem to be getting discontinued. I noticed that even Linear Tech shows application circuits in which their IC op amp is prefaced with a BF862. That must have rankled
Oddly, despite having all of Graeme's stuff that I know of, I haven't seen the "plurality of networks switched to the summing node" approach anywhere. But since the literature is vast it would be easy to miss. George? Bueller?
http://www.amazon.com/Amplifier-Applications-Amps-Jerald-Graeme/dp/0071346422
really only a few drawings, few pages in Chapter 2: Gain Options> Switched-Gain Amplifiers - multiplexing isn't treated at all
really only a few drawings, few pages in Chapter 2: Gain Options> Switched-Gain Amplifiers - multiplexing isn't treated at all
not all relays are good for small signal app.... however, it should be noted that companies which try really hard to make distortion disappear, use relays. Such as in the measuring instrumentation of Audio-Precision and ShibaSoku and several others.
THx-RNMarsh
We have a bunch of TDS7xx Tektronix scopes around, all in dear need of repairing the relay controlled attenuators. The relays have increased contact resistances (to about 0.3-0.5 ohm), leading to the instruments signal path compensation failures. Sometimes exercising the relays solves the issue (someone wrote a GPIB routine to automatically switch the scope ranges back and forth), but only to come back days later.
Of course, audio applications are not exactly instrumentation, one could live with such "defective" relays forever after.
Audio Precision did a lot of work trying to find reliable relays, but even for normal use and no stupid stuff (like driving a power amp into the generator outputs and such) I believe the relays remain the biggest service issue.
Many years ago I looked at some Omron 4PDT relays for an audio demonstration switching system, and initially they seemed to be a great combination of low on resistance and good "dry" switching. But it just happened to be a very good batch, as later there were many problems, evidently with stuff plating out on the contacts.
For the Harman switcher that was never finished, I had some Hg-wetted reeds. They aren't perfect either, but at least they will switch very low-levels without going open-circuit.
I had the apartment walls lined with bookshelves, and a lot more books in banker's boxes with a listing of what was where. After many years of no inspections, a man I referred to thereafter with the name of a character in a Daniel Menaker humorous short story The Statue, a parody of South American magical realism writers like Asturias and Marquez, Generalissimo Puercofacio Mendacioso, came through and told me the unit was not zoned for storage, and I had to get rid of all the boxes and a bunch of the bookshelves. His good judgment included telling me that the entry hall was three feet wide---it is four feet wide, with three feet being a fire department requirement (and try to find that criterion anywhere).
A month later and at huge costs including lost work, I had movers put a lot of stuff in another 10' x 30' storage space, and with another 400/mo. ongoing.
It was definitely one of those times I wished I had a big cartoon lever to move and send the general down into a pit of vipers.
A lot of people supposed that I was singled out, but many people had to make changes. Although the city alleges that the inspections are regular, the actual occasion was the sale of the complex.
Having spent a bit of time with the Authority Having Jurisdiction (AHJ) the 3 foot corridor is legit. Getting rid of more bankers boxes than three is probably legit. Books on bookshelves not blocking exits should be fine. Spacing between bookshelves arranged in rows also requires 3 feet.
Now arguing with AHJ's sometimes works when you can cite chapter and verse of the correct code, otherwise you are screwed.
Two tales, the local Fire Marshal visited a bunch of shops in an old neighborhood and told all of them they needed fire sprinklers. The buildings were originally mixed use buildings with a store on the first floor and apartments above. These days no one rents fourth floor walk ups and the lower floors had become additional business space. If even a few of the shops had installed fire sprinklers the old water mains could not feed them. So when my friend with the recording studio was given the ultimatum, I suggest he actually read the code book and visit the bureau office. Now the code book cost $250.00 and few ever bough one. He did, cites chapter and verse, about mixed use buildings would require fire sprinklers but not others, so the inspector went away. (His neighbors were also spared.)
Then there were the racks we shipped to site all wired for power distribution to be tied in to the junction box on top. The electrical inspector looked inside the racks and saw we had wired the AC distribution with 10 gauge wire. He made us change it to 12 gauge. No, he really didn't have a clue about the code or even where it applied. But as it was about $4,000.00 to make the change and the general rule about idiots, that was the way to go.
Now if you think you are going to get the same inspection again you might want to find out which building codes are in force and where they apply. I suspect the building code does require the hallway width, but the insurance code, which is not binding in most places, was what was being applied.
I also spoke to the guy's boss (whose name the guy mispronounced) and he said "Well, we don't like to see anything out in the room". I envisioned a 50's sitcom with the perfect wife greeting her husband near the perfect living room as he strides in saying Honey! I'm home!
I suspect they are worried about seismic code for free standing shelves in any room. In California you not only bolt racks to the floor, but often extend steel to the ceiling or roof above, as betting the floor stays down is not a good idea.
Last time I moved the help was complaining about all the books. They were most of what got moved. I used the sturdy Crown amplifier boxes to hold an amount of books that could be lifted by a human. Just under 100 boxes.
The issues with low level signals and reliability of relays have been solved. just back in the day, they were not. Silver contacts need to be regularly exercised to keep them clean and remove oxide build up. The biggest problem in Audio is in the relay in the speaker output... that seems to be always under-rated and a repair issue down the road.
But the modern day test equipment makers have found/had designed the issues away pretty much. You just need to use the same ones they use, if possible.
THx-RNMarsh
But the modern day test equipment makers have found/had designed the issues away pretty much. You just need to use the same ones they use, if possible.
THx-RNMarsh
Yes, I didn't have but one free-standing one. However the 3 foot rule, with which I was nearly compliant in the four-foot-wide entry hall, was violated as one turned the corner, as the next section of hallway was narrower. I might actually line the first hallway with shelving for CDs as they would not require that much depth.
The last move, from a industrial park office with a high bay, required about 700 banker's boxes, mostly books.
Brad,
I think there is also a minimum dimension for wheelchair access. Many buildings if you want to do any remodeling they will come in and make you completely redo all the bathrooms so a wheelchair can fit and turn in a specific radius, I once went down the road of becoming an architect. Got as far as the first year at the Southern California Institute of Architecture, SciArch, before I decided I really didn't want to do that. I designed a large model shop into one of the building I had my business at one time, got all the permits and we built the room, 1,000 sq. ft., cost $10,000. The city came in and valued the room at $50,000 and raised the taxes on the building. Guess who had to pay the taxes for the landlord after we improved his building!
I think there is also a minimum dimension for wheelchair access. Many buildings if you want to do any remodeling they will come in and make you completely redo all the bathrooms so a wheelchair can fit and turn in a specific radius, I once went down the road of becoming an architect. Got as far as the first year at the Southern California Institute of Architecture, SciArch, before I decided I really didn't want to do that. I designed a large model shop into one of the building I had my business at one time, got all the permits and we built the room, 1,000 sq. ft., cost $10,000. The city came in and valued the room at $50,000 and raised the taxes on the building. Guess who had to pay the taxes for the landlord after we improved his building!
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That wheelchair access would mean a teardown here, as there are steps everywhere including from the street to the main front door. Or maybe they would require a lift of some sort.
All it take is one complaint from someone with disabilities, ADA act, and you'll see ramps and an elevator! Sometimes reality just doesn't come into the picture, the building departments and lawyers can make a real mess of things. Depends on the city building department but if you are remodeling an old home they can make you replace all the older narrow doors and change the bathrooms, it is a real issue. I had a few years of architecture before I went to that school, so many rules and regulations. I still remember when Romex was a code violation in L.A. they would never accept anything that wasn't in a metal conduit. Now try and find a house that doesn't use that stuff and now even the water lines are plastic tubes.
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