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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 28th November 2018, 01:49 PM   #10501
TNT is online now TNT  Sweden
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Quote:
Originally Posted by Joe Rasmussen View Post
... since F=Bli is the same under voltage and current drive, something seems to be needed: The voltage source cannot control the current,...
F=B*U/R*L

Look, it could

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Old 28th November 2018, 02:15 PM   #10502
DF96 is offline DF96  England
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Quote:
Originally Posted by Joe Rasmussen
. . .the increasing understanding that zero control of current in a voltage source will cause current chasing its own tail
Surely the definition of a voltage source is that it does not 'control' current? If you want the current to be controlled, then you don't want a voltage source.

Current drive and voltage drive are two opposite ends of a spectrum; in between is drive from a specified impedance. It happens to be the case that for most of the life of audio electronics it has been found that the best compromise is to make amplifiers to act as voltage sources and speakers to respond best to voltage drive. This despite the fact that everyone knows that it is current which actually moves the voice coil.

'Controlling' current from a voltage source is just another way of setting a specific output impedance i.e. not a voltage source.

This discussion reminds me of the issue of back-EMF, which crops up from time to time. People talk about it as though it is something wholly unconnected with impedance.
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Old 28th November 2018, 02:20 PM   #10503
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One of the recurring features of audio electronics (and radio antenna design) is that people keep thinking that a failure to grasp one or more basic points of relevant physics is in fact a deeper understanding of physics. They think they are pushing back the boundaries of knowledge, when in fact they have yet to reach the boundary and probably can't even see the boundary from where they are standing.
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Old 28th November 2018, 02:43 PM   #10504
indra1 is online now indra1  Indonesia
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Originally Posted by john curl View Post
... the UNMEASURED distortions, where there isn't any calibrated test equipment available to test it and give it a specific number. I personally define audio distortion as ANY deviation from the original signal, either by adding, subtracting, phase shifting, or any other change to the audio signal DA, PIM, and who knows what else is out there that changes the sound character of the electronics?
I am very happy that once again you want to talk about audio design. I have been pondering on issues like this for quite awhile John. Could you kindly elaborate a little bit more on those unmeasured distortions you have discovered so some of us may continue to work on? They say that it is very difficult to improve on anything without being able to verify by measurement. Perhaps some instruments already show you some sign of the problem.
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Old 28th November 2018, 03:08 PM   #10505
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Unmeasured distortions are often mentioned as a way of avoiding the known fact that many people prefer a little measurable distortion. It is postulated that these people do not actually prefer the measurable distortion, but dislike the unmeasured distortion which is allegedly made by other circuits with less measured distortion.
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Old 28th November 2018, 03:14 PM   #10506
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I would also like to see some of that "unmeasured" distortions. I am expecting our evergreens like "first cycle distortion", Hirata distortion, memory distortion and thermal distortions. As of today, we have a new one, a current distortion by poor voltage control
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Old 28th November 2018, 03:32 PM   #10507
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And they are mostly causes - not the distorsion

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Old 28th November 2018, 03:39 PM   #10508
indra1 is online now indra1  Indonesia
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Originally Posted by PMA View Post
I would also like to see some of that "unmeasured" distortions. ...
Maybe it is difficult to see them distortions, but perhaps you can hear them.
But seriously, there are some noted aspects in audio left unmeasured like the contributing factors of coupling capacitors with respect to direct coupling and interstage transformers that affect perceived difference as noted by Bud Purvine, Lynn Olson, JC Morrison and others. I quoted a post below as an example.
Quote:
Originally Posted by BudP View Post
... They have equivalent sonic characteristics though the cap has a slightly fat sound to everything, ...
... The only other difference in sound quality comes with differing loudness. When the cap passes a fortissimo from any particular instrument ,within an orchestral sound field, that instrument seems to move towards you in the sound field illusion. So, in a general sense the illusion of a sound field is always changing it's depth of field relationships with a capacitor interstage. In an IT this does not happen, at all. The same tonal characteristics and relative amplitude takes place, but the instrument in question remains in scale....
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Old 28th November 2018, 03:49 PM   #10509
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Originally Posted by indra1
But seriously, there are some noted aspects in audio left unmeasured like the contributing factors of coupling capacitors with respect to direct coupling and interstage transformers that affect perceived difference
People might like to ponder why interstage transformers were used in the past, then were replaced by coupling capacitors. There is a difference in performance, but it all points to capacitors being better (unless you intend driving the next stage into grid current).

The most perfect components we have are bits of wire, then come resistors, then capacitors, then last are wound items and active devices. Curious that there is a modern fad to maximise use of wound items.

The fact that a 'guru' has woffled in print about something does not mean that the issue is 'noted', or even that the issue exists.
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Old 28th November 2018, 03:56 PM   #10510
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I try to keep things simple for myself: if current drive or any other non-zero amp output impedance (or even an impedance profile, meaning Zout being complex and frequency dependant) gives a perceived and measured benefit for the actual driver, I use it if it is feasible to implement (single ended AB amps need only a few additional components). Some drivers benefit more than others, typically lesser quality driver seem to profit the most, and the wider their operating frequency range the more so. A nice application is active speakers with a fullrange driver.
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