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Old 18th January 2006, 08:08 PM   #91
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Charles, everyone should know that I stole the line amp circuit from you!
As far as the fet is concerned, people should think about shot noise generation in bipolar base-emitter junctions.
 
Old 18th January 2006, 08:14 PM   #92
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Quote:
Originally posted by john curl
As far as the fet is concerned, people should think about shot noise generation in bipolar base-emitter junctions.
I never think of shot noise junctions
Maybe that is why I sleep well at night ......
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Old 18th January 2006, 08:33 PM   #93
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Quote:
Originally posted by john curl
people should think about shot noise generation in bipolar base-emitter junctions.

Yes, since it was you who asked, we ought to have realized that.
 
Old 18th January 2006, 08:34 PM   #94
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Hi, Charles, John and others...

John would kill anyone wanting to let anyone know of his own secrets ? Just keep quiet !!! The Vendetta man is very quiet now... No 44 or 38 Special... But with some reflection, he uses full 110 V mains... or Blowtorch to let him know about ...

Frankly, your both emulation (also with Nelson Pass and some others) is a full example of what we have to do : just to overpass our own certainties, guesses, and theory basics... Just for competition and fun...Very difficult to explain as I am an European guy, but the fulll truth ! We do it all the time here, and we are NOT all natives from the same country and have NOT the same native language... But we discuss and share ideas and findings.

Charles, you introduced an interesting folded cascode path to analyze further... (Just ask John if he doesn't think so !). When you FIRST think of learning from others and NOT to criticize all things, it is much easier to achieve, as brains are very opened to newer ideas (even ludicrous ones !). Theory don't say all, or all parts and topologies would be equal... Eh, Forr... Would you comment also about sonic nasties of caps into the DC offset correction path ? Full waste of time IMO !!!

An old short story in Europe I heard 40 years ago (serious one !) : beatles can't, mathematically, fly.... But beatles don't know maths and fly... What is wrong ? Same with audio... We are NOT an the ending point of studies, but at the very beginning... Hope that anybody will help wuith beatles understanding (anyway, experiences on bugs will also help !).

So, in audio fields, all electronics rules don't act fully but the very basic ones... I have been on John's steps for years, and he always returned to this basics from different ways...

BTW, Charles, I have an equipped room for you here at home, but will be a long run from USA (and a bittcloser to Sicilia and Corsica (perhaps) close John's cousins...

All the best, guys.... Still one of the best laughs I had on this forum for months ...

BTW, I will send you both a push-pull trick to comment (sorry, other guys,... Just want NOT to be sent to Texas !)...

jbaudiophile
 
Old 18th January 2006, 11:22 PM   #95
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OK, I should make it more clear: Bipolar transistors have 3 major noise generators. The one that I am concerned about here is the shot noise generated by current flow across the base-emitter junction. IF the base-emitter junction is NOT effectively shorted at audio frequencies, then the base current shot noise will dominate and make the regulator noisy. IF you cannot effectively short circuit the base-emitter junction at audio frequencies by using large value caps from both emitter to ground and also from base to ground, then we have a problem. A fet is different. It doesn't have any significant current flow at the input, so it doesn't get noisy, IF there is not a large capacitor at the output of the 'open loop' follower regulator. Once I heard differences in electrolytic caps in my Vendetta input circuit (thanks, Peter Morcrieff for showing this to me) over 20 years ago, I had to design them out. The 0.1 polystyrene cap on the output is not doing much at audio frequencies, and it sounds good as well, for some reason.
 
Old 19th January 2006, 01:13 AM   #96
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Quote:
Originally posted by john curl
OK, I should make it more clear: Bipolar transistors have 3 major noise generators. The one that I am concerned about here is the shot noise generated by current flow across the base-emitter junction. IF the base-emitter junction is NOT effectively shorted at audio frequencies, then the base current shot noise will dominate and make the regulator noisy. IF you cannot effectively short circuit the base-emitter junction at audio frequencies by using large value caps from both emitter to ground and also from base to ground, then we have a problem. A fet is different. It doesn't have any significant current flow at the input, so it doesn't get noisy, IF there is not a large capacitor at the output of the 'open loop' follower regulator. Once I heard differences in electrolytic caps in my Vendetta input circuit (thanks, Peter Morcrieff for showing this to me) over 20 years ago, I had to design them out. The 0.1 polystyrene cap on the output is not doing much at audio frequencies, and it sounds good as well, for some reason.
John,

Thanks for the input.

Good to see this discussion get interesting.

WRT BJT shot noise in regs I think some perspective would
be in order here. The shot noise will only be a problem if
the noise current at the base has a significant impedance to
react withand cause a noise voltage. Even quite a few hundred
ohms at the base will still result in very quiet noise performance.

As such there are many ways to get a low Z base ref point
and some not using electro caps although they are obviously the
easiest solution.

One advantage of BJT regs is they have inherently lower OP Z
(before FB) than fets.

Having said all of the above, I have not directly compared an
OL fet vs BJT reg together sonically.

Cheers,

Terry
 
Old 19th January 2006, 07:11 AM   #97
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Show me Terry, with a real example.
 
Old 19th January 2006, 08:11 AM   #98
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Originally posted by lineup
At that time was not easy to find higher value film caps.
FET can be biased with higher value resistors and
these can make an effective filtering together with lower value film caps.


Originally posted by john curl
IF you cannot effectively short circuit the base-emitter junction at audio frequencies by using large value caps from both emitter to ground and also from base to ground, then we have a problem. A fet is different. It doesn't have any significant current flow at the input, so it doesn't get noisy, IF there is not a large capacitor at the output of the 'open loop' follower regulator. Once I heard differences in electrolytic caps in my Vendetta input circuit (thanks, Peter Morcrieff for showing this to me) over 20 years ago, I had to design them out. The 0.1 polystyrene cap on the output is not doing much at audio frequencies, and it sounds good as well, for some reason.
======================


What does not have a significant current flow,
does have have higher value resistors,
or am wrong?

If noone else will say it, I say it:
you were very close to the truth, lineup


today we have better film caps to use, large, higher values
and are free to use JFET or BJT nice lownoise transistors
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Old 19th January 2006, 10:14 AM   #99
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I feel more happy now, seing some fundamuntal comments about technology and topology, and feedback about these comments. Isn't part of what makes this forum intellectually rich ? Thanks.

~~~~~~~ Forr

 
Old 19th January 2006, 01:19 PM   #100
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Very interesting thread ! So if I understood well some posts here, in particular those of John Curl, Terry Demol and Lineup, taking also into account my own tests and listening on power supplies, something like a reference voltage followed by an RC filter like 1 MEG/1 uF film cap then a fet follower then a bipolar follower whose emitter output is shunted by something like 10 000uF could be a nice supply .
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