In my case, despite assurances from the 741, the video went viral. Never trust that part again.
Finite size to the universe.
It is expanding but it is not infinite. Hubble has seen the finite distance away from the center of the big bang where matter was thrown outward... to where there is no further matter to be seen. That is the end or size of the present universe. Very
, dont you think?
Update:Latest thinking I heard was that there is no end to the universe - it is infinite & expanding
It is expanding but it is not infinite. Hubble has seen the finite distance away from the center of the big bang where matter was thrown outward... to where there is no further matter to be seen. That is the end or size of the present universe. Very
, dont you think?
Last edited:
Update:
It is expanding but it is not infinite. Hubble has seen the finite distance away from the center of the big bang where matter was thrown outward... to where there is no further matter to be seen. That is the end or size of the present universe. Very
yeah, this stuff is mind blowing - even trying to conceive of our galaxy is more than I can really comprehend . . .
I'll look up the title of the documentary I saw which suggested the infinite & expanding theory - there was a logic to it . . . but I'll have to remind myself what it was !
Talking about oscillations, I had them at c. 180MHz on a cacode a few months ago (my e-Amp). I would never have seen this without my 200MHz scope. I used a 10MHz on my previous developments. Doing some work a few weeks ago, I found that it is EASY to get a follower to oscillate at 10's of MHz and my mantra now is: Always assume it does and take necessary precautions.
Trivia -
It will, perhaps expand forever, thus growing the size forever until it is infinitly large. But that isnt saying it isnt finite at any given point in time.
It will, perhaps expand forever, thus growing the size forever until it is infinitly large. But that isnt saying it isnt finite at any given point in time.
A big problem is that connecting anything to the circuit changes stuff so the oscillation and its effects often go away when you stick probes etc.
The Baxandall Papers describe the Great Guru's experience of such a problem.
This is not uncommon (??) with Golden Pinnae amplifiers. In fact when this was of great interest to me, I didn't find a single Golden Pinnae amp which would pass the tests in #29889. You are looking for "little puffballs of oscillation" which ride on part of a sine wave.
My Blind Listening Panel picked up quite a few of the bad cases and used very similar words.
We had a rule for Blind Testing new stuff. We listen FIRST. Then measure. Never the other way round.
Christophe, this stuff is load dependent. You usually don't see it on 8R loads. But you do on the #29889 tests.
Yes. You'll come across a lot of it when looking at stability with different load. A sure indication is if your 1pp zillion distortion goes wonky with about 1nF load but is OK with either less or more C.
I respectfully hope you know I know. I was able to make concurrent measurements with a scope and Agilent Analyzer. I can make you sure that once oscillations started you had to switch off the preamp to stop them.
And how was I to start the oscillations? With steep impulse to the output, in this case. For example, switching discharge when connecting signal output cable (live first as those damned RCA jacks enable) and the device was on ...
Sometimes I am very surprised how low opinion some have about abilities of others.
RFI pickup
The good news about my amp is that when connected to speakers in main listening room but with no inputs connected no amount of light switching could cause any audible noise in the speakers - may be a different story with sources connected but at least the amp itself is nicely isolated.
I'll connect sources one by one to see what is sensitive RFI
The good news about my amp is that when connected to speakers in main listening room but with no inputs connected no amount of light switching could cause any audible noise in the speakers - may be a different story with sources connected but at least the amp itself is nicely isolated.
I'll connect sources one by one to see what is sensitive RFI
This obviously depends on the precise physical nature of the switch, but I found it easy, one time when experimenting, to hold the position of one in an inbetween state; again, provoking internal sparking and lots of RFI. Not something you want to do regularly, for the health of the switch and possibly the light! But, it certainly told me that there were issues ...
Frank
Pavel, the Baxandall letters show how the Great Guru had problems with connecting stuff to investigate this very thing.
But I accept the possibility that you may have more experience & knowledge than he had. After all his experience is Jurassic, going back to the invention of RADAR, television etc. You certainly have better gear in your Agilent stuff.
My sincere apologies. It was in no way a reflection on your abilities but just a warning to others who have similar problems and may not have your skill or equipment.
My own miserable experience using gear I'm too ashamed to mention even, suggests that the type of oscillation you describe rarely occurs without eg affecting THD. (In this I beg to differ from Guru Scott experience with his evil Borbely follower.) You just have to measure the THD under the correct conditions; eg with a real speaker. My poor efforts trying to probe the circuit with cheapo 10x scope probes (with and without extra resistors) invariably affect the THD readout.
If the problem was such that the oscillation (on a scope) or THD didn't change a lot when the circuit was probed, I would consider myself lucky that day and immediately go out & place a small sum on a horse.
Problems which don't change when probed are relatively easy to solve.
Last edited:
Sorry, Bob! Another take on what happens in that TPC circuit, in this case dropping the input drive to create a output waveform well within possible real world music replay -- output waveform looks very clean, but look at what those emitter (and wrongly called collector in other post) currents are doing in the crossover region ...
Frank
Frank
Attachments
Last edited:
Richard, thank you for the explanation. This definitely makes sense, I agree.
I also agree that especially instabilities in local (nested) parts of the circuit may be easily damped (or excited) by an oscilloscope probe. In my particular case, there was a heavy buffer at the output capable to drive 50 ohm load, with 50 ohm series resistor at the output. The measurement was made at the output, behind the 50R resistor. The most interesting was that one was not able to initiate oscillations by input signal or load change, but just by RFI impulse sent to the output.
Last edited:
Or the contrary.
According to the Murphy law, measuring or observing anything change the observed object in the way that will brings-you the most trouble.
Your circuit was stable in normal condition. The oscillo's probe will trigger oscillation, and you will work to stop-it. Now, your amp, stable under measurement situation, will oscillate once closed.
There is an other situation witch tend to trigger oscillations: it is demonstration shows. May-be John can say two words about the Parasitic capacitance of the crowd ?
I wonder too why SAV laboratories are always situated in places where telluric conditions prevent any problems to appear, as your local garages.
Any square waves at high frequency to show ?
About the size of the universe, i have a big problem to imagine the universe as finite.
You imagine: you are on the latest planet, and, in a direction: "Nothing". What is Nothing ? An infinite "nothing" ?
The only thing witch can give-me an approaching feel of it, is when i look at the amount of my retirement's pension.
Last edited:
Thank you Frank for the instructive post. (*) The slope and the kinks of the waveform is a direct indication of what is going on higher up in frequency, beyond the reach of indicating instruments that us humble diyers can have in these non promising days.
Supply current of each stage, if carefully monitored and plotted against varying input signal’s amplitude and frequency –no signal included-can too provide indication of HF oscillation.
The locus . (Nyquist plot) of Aβ of an amplifier if driven high in freq is the ultimate “tool” for inspecting instability.
Having (or building) a signal source that can go to VHF is more important and within the “budget” of an amateur than buying a 500MHz scope.
Radio amateurs up to 1950-1960 could not dream of an oscilloscope, let alone a high bandwidth one.
Nevertheless, they dared to build and test their RF gear.
Technicians were successfully repairing and properly tuning multistage RF and IF complex high Z sections on radios using only a 10kOhm/V voltmeter.
Ref. Class D amps, some informed words here:
George
(*) Scott, you missed Frank’s point.
- Status
- Not open for further replies.