John Curl's Blowtorch preamplifier part III

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#10,622
scott wurcer said:
This does not happen, and there are no words to describe it. Feedback does not go round and round it reaches a steady state. You keep stating that no amplifier can drive a load with nonzero phase without being "tricked" into having bad reactive current. This does not belong in a technical discussion.

You might very well run across bad amplifiers that oscillate with your cable/speaker combo, get rid of them.
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I am afraid no reasoning with this guy makes any sense. He seems not to understand even elementary circuits, not speaking about feedback. This just illustrates that audio business may be operated by anyone without even basic knowledge.
 
#10,624
PMA said:
Measurement results

No improvement in nonlinear distortion was observed for tweeters and midrange speaker. The only notable improvement was for a woofer, below 100Hz, at a closed box.

Proudove buzeni repro a zkresleni repro
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It seems those results reflect more the microphone itself than the speaker. ECM8000 and its likes are as such unsuitable for any distortion measurement, at least at such a close distance (9 cm), because of the known issue of their distortive common-source FET front stage.

With a non-distorting microphone, current drive usually shows drastic reduction in odd-order distortion products outside the bass region. Current distortion does translate very well into acoustic distortion, as it forms the dominant source of it (except for the resonance region), and gets yet magnified by the horn effect of the cone. Typical H3 and odd-IMD reductions are around 15 dB with aluminum coil formers and 30 dB with non-conductive formers.

Nonlinear distortion measurements of loudspeakers - voltage and current control

Comparative Measurements on Loudspeaker Distortion: Current vs. Voltage Control | MERILAINEN | Archives of Acoustics
 
#10,626
ETM said:
It seems those results reflect more the microphone itself than the speaker. ECM8000 and its likes are as such unsuitable for any distortion measurement, at least at such a close distance (9 cm), because of the known issue of their distortive common-source FET front stage.
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I do not agree, because I check distortion measurements by moving microphone to 50cm, 1m, for the reason you are describing. I am quite sure that the distortion was because of not very good drivers measured. One of them was Beyma T2030, which is behaving very badly. Several months ago I have made a similar set of measurements with better drivers (Seas Excel range), same microphone etc., the distortion is now only low order. I do not suspect the microphone in the measurements shown.
 
#10,628
Jakob2 said:
I don´t know if i understand correctly what you mean, but if you are looking at the definition of the resistance then you´ll see that it is based on current but not on voltage. 🙂
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OK, but I hope you would agree that with almost ideal voltage source (negligible distortion, very low output impedance) the current follows voltage divided by impedance and if impedance is nonlinear then current is distorted. I hope you are not going to support foolish and conspiracy engineering pseudo-theories, at least not in the matter that obvious like this.
 
#10,629
PMA said:
OK, but I hope you would agree that with almost ideal voltage source (negligible distortion, very low output impedance) the current follows voltage divided by impedance and if impedance is nonlinear then current is distorted. I hope you are not going to support foolish and conspiracy engineering pseudo-theories, at least not in the matter that obvious like this.
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Maybe you could try to step a bit back from being too dogmatic?
If you find some errors in my posts please refer to them and i will follow on arguments but i surely don´t plan to add a list of safeguards (against imagined supports of something) to each of my posts. 😉
 
#10,631
PMA said:
I was wondering why current could not be defined as voltage divided by resistance. I know what you meant by "definition", but I assume it irrelevant to the technical discussion about distortion in current resulting from nonlinear impedance connected to almost ideal voltage source.
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I quoted to what i wanted to respond, what else could i do?
TNT expressed mystification about the "impedes current" part and i - while admitting that i might have misinterpreted his post - pointed to the fact that the definition of resistance is based indeed on this "impedes current" property.
 
#10,634
scott wurcer said:
Please Jakob, Joe is not talking about current drive (not even a little). He is creating a nonsense about voltage mode power amps and reactive loads.
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Please Scott ( 🙂 ) but ETM and PMA did talk about current drive and i remembered a publication from the mentioned authors; in the meantime i even found it in my archive:

Mills and Hawksford. Distortion Reduction in Moving-Coil Loudspeaker Systems Using Current-Drive Technology. JAES, Volume 37, No. 3, March 1989, 129.
 
#10,638
Jakob2 said:
Please Scott ( 🙂 ) but ETM and PMA did talk about current drive and i remembered a publication from the mentioned authors; in the meantime i even found it in my archive:
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You are 100% correct but Joe is talking about the amplifier not the speaker, his examples are speaker with shunt network to make it a purely resistive load to the amplifier. The voltage amplifier is still directly connected to the speaker. This is not current drive, it is simply modifying the load seen by the amplifier.

The stuff published by his "mentor" is packed with things that are simply wrong. IME getting anyone to let go of this type of baggage after a certain length of time is frankly a waste of time.
 
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