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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 26th November 2012, 02:55 AM   #29921
Esperado is offline Esperado  France
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Quote:
Originally Posted by scott wurcer View Post
I agree when will people finally accept the uA741 does not work for audio and stop showing why?
Did-you had a bad experience with a 741 ?
 
Old 26th November 2012, 03:29 AM   #29922
scott wurcer is online now scott wurcer  United States
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Originally Posted by Esperado View Post
Did-you had a bad experience with a 741 ?
Didn't everyone?
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Old 26th November 2012, 04:03 AM   #29923
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
Didn't everyone?
In my case, despite assurances from the 741, the video went viral. Never trust that part again.
 
Old 26th November 2012, 05:08 AM   #29924
RNMarsh is offline RNMarsh  United States
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Default Finite size to the universe.

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Originally Posted by mikelm View Post
Latest thinking I heard was that there is no end to the universe - it is infinite & expanding
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 , dont you think?

Last edited by RNMarsh; 26th November 2012 at 05:11 AM. Reason: trivia
 
Old 26th November 2012, 05:36 AM   #29925
miklos is offline miklos  Hungary
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Originally Posted by scott wurcer View Post
This was a <100mV parasitic oscillation, I figure the FET's were so linear that it did not matter IN THIS CASE.

I think they are called reflex radios, one transistor is RF amp, oscillator, mixer, and AF amp all at the same time, what could be simpler?
Regenerative circuit - Wikipedia, the free encyclopedia
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Old 26th November 2012, 06:54 AM   #29926
mikelm is offline mikelm  England
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Quote:
Originally Posted by RNMarsh View Post
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 , dont you think?
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 !
 
Old 26th November 2012, 07:21 AM   #29927
Bonsai is offline Bonsai  Europe
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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.
 
Old 26th November 2012, 07:56 AM   #29928
RNMarsh is offline RNMarsh  United States
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Default Trivia -

Quote:
Originally Posted by mikelm View Post
I'll look up the title of the documentary I saw which suggested the infinite & expanding theory -
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.
 
Old 26th November 2012, 08:49 AM   #29929
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Quote:
Originally Posted by PMA View Post
Oh yes, I did. It was absolutely perfect! I was unable to find anything with a 100MHz analog scope ...
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.

Quote:
Originally Posted by bcarso View Post
In one of the few Abso!ute Sound articles of the day with technical details, Bascom King reviewed a big Jadis tube amp and loved the sound. He was at a loss to explain it, speculating among other things that hollow-state rectification seemed to be associated with good results from tubes. And on top of it all, when he did do some measurements he saw little puffballs of oscillation riding on square waves! Horrors!
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.

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Originally Posted by Esperado View Post
Well i can feel them, sometimes, by a strange feeling, something white in my brain i can't explain, discomfort.
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.

Quote:
... I believe we know all with a square wave on a fast scope.
If there is some oscillation at very high HF, you will see-it on the clipping level in the audio signal. Right ?
Christophe, this stuff is load dependent. You usually don't see it on 8R loads. But you do on the #29889 tests.

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Originally Posted by fas42 View Post
You won't hear the oscillations, but if the circuit is misbehaving in that fashion then the chances are that it can't be functioning as intended in the audio region; again, especially as far as the FB mechanism is concerned. It seems as if I'll have to play with LTspice, deliberately simulating non-linear behaviour in the output, to see what signal frequencies the FB area of the circuit is experiencing ...
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.
 
Old 26th November 2012, 09:09 AM   #29930
fas42 is offline fas42  Australia
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Originally Posted by jcx View Post
yes you could "prove" feedback "problems" with a toy circuit showing obvious crosover distoriton

or you could find sims with hand tweaked transistor models in the Cordell threads with 100 mA+/output Q Mosfet or bidpolar amps...
Time to take the gloves off, : Cordell's THD20 TPC amp, December 28, 2010; only one change made, load dropped from 4 to 2.5 ohms. The collector current waveforms, again, of the input differential pair ...

Frank
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