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Old 30th December 2011, 10:46 PM   #391
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Quote:
Originally Posted by SY View Post
Zero interest in that. There's plenty of guys out there (John included) who design excellent SS amps. Excellent tube amps are quite a bit rarer.
Excellent by "standard measurements", or excellent by clearness of sound? Let's go back to the topic.
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Old 30th December 2011, 10:47 PM   #392
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I can't, but Richard Heyser mentioned it in one of his earlier papers. Need a cite?
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Old 30th December 2011, 10:48 PM   #393
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Quote:
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Real delay? That's an engineering term that I'm unfamiliar with. Could you define it?
Carriers of charges have inertia.
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Old 30th December 2011, 10:56 PM   #394
jcx is offline jcx  United States
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a ill formed question - 10 Hz corner frequency is only part of the equation - gain, how much is to be used to meet Av requirement, what’s "left over" as loop gain?

today common SS audio amp numbers are near 1 MHz loop gain intercept for ~160 ns delay - where single pole compensation, conservative phase margin good separation from higher order poles (mostly output stage) is employed

audio frequency "amp delay" can be harder to pin down with high gain circuits using 2 pole compensation - formally the output can just keep accelerating with constant input error signal within the linear 2-pole gain region

"newer" decades old parts like Mosfet, Ring Emitter output Q are probably limited by common "audio" layout practice, and the package parasitics before the "ultimate" limits of ft, transit time terms of the die themselves are a hard limit


if any competent engineer understanding the issues really thought "amp delay" was a problem then why aren’t they using IXYS Linear Mosfets in RF power packaging? http://www.ixysrf.com/pdf/diodes/app...elvin_lead.pdf

Last edited by jcx; 30th December 2011 at 11:13 PM.
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Old 30th December 2011, 10:58 PM   #395
wahab is offline wahab  Algeria
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Quote:
Originally Posted by SY View Post
Propagation delay? Nanoseconds. Group delay is perhaps what you mean?

As already pointed , propagation delay in Bjts is extremely short ,
less than 10pS is a typical value and is indicative of the intrinsical
speed of the bipolar devices if they werent "infected" by parasistic
caps and resistors that are an inherent byproduct of the device geometry
and principle.

As for what is commonly understood as delay propagation,
it is the time it take for a device output to reach 90% of its
definitive value , wich is not a propagation delay but rather
a bad interpretation of the device slew rate.
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Old 30th December 2011, 10:59 PM   #396
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The chicken before the egg. Before you can LOWER the delay, you have to use FEEDBACK to FORCE the input stage to compensate. IF the input stage is NOT perfect, then it will distort, and interesting things will happen. That IS the difference between open loop and closed loop delay.
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Old 30th December 2011, 11:01 PM   #397
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Black Box with up to 10Hz, BEFORE rolling off at 6dB/octave. NO transistors, fets, tubes.
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Old 30th December 2011, 11:10 PM   #398
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Quote:
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Don't be so hard on 1968 engineering. We went to the moon in '68, you know.
But of course didn't land there until '69.

se
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Old 30th December 2011, 11:16 PM   #399
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There is a difference between the 'delay' added by a single-pole low pass filter, and the real delay added by a transmission line or other propagation mechanism. You can undo the first by inserting a complementary filter. You can't undo the second without violating causality, as you would require output to occur before input. Don't get the two confused.
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Old 30th December 2011, 11:20 PM   #400
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We went around the Moon, perhaps, in '68?
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