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Old 25th September 2013, 03:37 AM   #1
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Default What does this do?

This (image) was taken out from the Krell KSA50 clone. I have a few questions :

1) Does this improve the sound quality of any other system?
2) Or is this only for the Krell KSA50 clone?
3) What does it do?

Thanks.
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Old 25th September 2013, 04:06 AM   #2
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It is there in most amps. It prevents the power amp instability, if the load is too much capacitive. Even the speaker cable can be responsible for this.

Gajanan Phadte
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Old 25th September 2013, 05:34 AM   #3
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It's a Zobel Network, as gmphadte says above.
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Old 25th September 2013, 07:09 AM   #4
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He is asking about the R206 and L201

Gajanan Phadte
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Old 25th September 2013, 07:18 AM   #5
balerit is offline balerit  South Africa
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Quote:
Originally Posted by KatieandDad View Post
It's a Zobel Network, as gmphadte says above.
R205 and C201 is the Zobel network.
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Old 25th September 2013, 07:26 AM   #6
Mooly is offline Mooly  United Kingdom
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And no one has told him what they do yet...

L201 isolates the amplifier from capacitive loading by virtue of the rising reactance of L201 at HF. In other words it appears as a small "resistance" in series with the amplifier output at HF, and the higher the frequency the higher the "resistance".

XL (its resistance) = 2pi fL and so a typical value of 4uH would appear as a "resistance" of 2.5 ohms at 100kHz. It isolates the amplifier.

The parallel resistor "damps" any ringing that the coil would cause on squarewave testing.

R205 and C201 terminate the amplifier with a known and predictable load at HF.
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Old 25th September 2013, 07:56 AM   #7
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Thanks a lot, guys. I really appreciate your replies. But shouldn't L201 and R206 on the opposite side as well?
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Old 25th September 2013, 08:08 AM   #8
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Could it be better if they are on both sides as in the image attached?
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Old 25th September 2013, 08:17 AM   #9
Mooly is offline Mooly  United Kingdom
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That wouldn't work. As you have drawn it the effect of C201 is pretty much negated by the series L201 although the parallel 4.7 ohm would still allow C201 to provide some effect though.

You sometimes see a double network with another pair of R205 and C201 on the output side of the inductor so they appear directly across the output terminals.
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Old 25th September 2013, 08:20 AM   #10
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Quote:
Originally Posted by pmchoong View Post
Could it be better if they are on both sides as in the image attached?
No, because the coil and resistor have a reactance that will cancel the predictive loading on the amplifier at high frequencies and may cause instability.
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