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Old 20th September 2012, 06:48 PM   #21
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so the conclusion is, while compensation networks can avoid freqvency dependent current spikes and reduce the risk of oscillation , in exchange you get less power (series resistance if Fs peak impedance is compensated too) and loss of sensitivity of speaker... not to mention the tradeoff of current spikes vs a constantly higher current, and reduction of minimal impedance since zobel is || with the voicecoil..
Best is to implent the amplifier carefully enough to be able to aviod the need of compensation networks at the output stage. Output compensation networks are a compromise.
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Old 20th September 2012, 07:17 PM   #22
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The RC network at the amplifier output is not a Zobel network like you would use for impedance linearisation. Its component values are far too small to achieve any significant impedance linearisation. It is an RF snubber. If you calculate its impedance, you will find that the loss of efficiency it introduces is far too small to be an issue.

Impedance linearisation is necessary, when the source impedance is high, i.e. on tube amps with output transformers or on class D amps with output low-pass filters. In that case the frequency response will become a scale model of the load impedance and you want a flat load impedance to achieve a flat frequency response. You do trade efficiency for sound quality. The good news is that the efficiency loss happens mostly at high frequencies, where the average power is low and the efficiency loss means very little in absolute figures.
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Old 21st September 2012, 04:57 AM   #23
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here is the link for detailed formula with explanations

IC Audio Power Amplifiers and Zobel Networks: One Size Does Not Fit All
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Old 21st September 2012, 05:18 PM   #24
AndrewT is offline AndrewT  Scotland
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Another Member referenced this same article.
That article is discussing a speaker Zobel located within the speaker.

It has nothing to do with providing a high frequency load to an amplifier that needs such for stability.

There is, in my "non designer" opinion, a fundamental flaw in the paper.
They have completely ignored amplifier output impedance, cable impedance and connector impedance by setting all source impedances to exactly ZERO OHMS at all frequencies.
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Last edited by AndrewT; 21st September 2012 at 05:20 PM.
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Old 21st September 2012, 05:48 PM   #25
DF96 is offline DF96  England
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I forget where I first saw it, but I thought the Zobel network has to work together with the output inductor. The inductor isolates the amp output from whatever is outside at RF frequencies. An inductive load could upset loop stability, so the Zobel network then imposes a resistive load at high frequencies. A Zobel with no output inductor may or may not do anything useful - it all depends on what the speaker+cable impedance looks like for RF.
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Old 21st September 2012, 08:05 PM   #26
AndrewT is offline AndrewT  Scotland
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but they completely ignore all the source impedances by setting them to exactly ZERO OHMS.
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Old 9th April 2014, 05:27 AM   #28
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Just one small addition..... if there's a LOT of rf in the location of the speaker cables and speaker, a small choke in series with the output combined with the zobel network helps significantly in keeping that rf out of the feedback; I too lean more towards the 10ohm and 0.1uF (or less) value purely on the basis of the impedance v frequency at that time constant
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