what could be the reasons for High freq roll off after 14khz - Page 2 - diyAudio
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Old 4th February 2013, 02:27 PM   #11
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but I would like to know what value of the inductance to be there as output zobel as current value is about 1uH with 10ohm 2W resistor and a .1uf with 10ohm resistor in series is shunted at the output.

I have a rolloff starting from 14khz what should be the values of the inductor so that the amp will not oscillate at higher frequencies..

or can i just eliminate the zobel as you said 98% of the amps dont have it.

what if the output is connected before the inductor? will the amp oscillate as its RLC circuit?

Last edited by rhythmsandy; 4th February 2013 at 02:32 PM.
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Old 4th February 2013, 02:36 PM   #12
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Most amplifiers that use an ouput inductor have a resistor in parallel with the inductor usually 10 ohms if your amplifier is the same the resultant impedance will never be higher than 10 ohms.

measure the amplifier frequency response with an 8 ohm resistor load. Is it flat to 20k?

Measure your amplifier frequency response with your speakers connected, use a low power level, you don't want to blow your tweeter. Is it flat? measure the voltage at the tweeter terminals? is it rising as the frequency goes from 20-20,000?

check your arithmatic XL=2*pi*F*L

=6.28 *20,000* .000018

= 2.26

in parallel with a 10 ohm resistor = 1.8 Zohms

if you made a measuring mistake with the inductor it would be much less.

Last edited by multisync; 4th February 2013 at 02:43 PM.
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Old 4th February 2013, 04:07 PM   #13
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im measuring the voltage across the output and its giving as 10mv i believe its the DC offset... but no voltage output as you have specified at the output of the speaker connectors...
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Old 4th February 2013, 04:20 PM   #14
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sure there is a rolloff atleast by listening since its major change so what is the solution now since this amp would be going for high power application in PA
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Old 4th February 2013, 04:21 PM   #15
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i have connected the speaker cable directly before the inductor it still worked fine without any problems but at moderate levels but no idea how it sounds at higher level but just have a doubt that will that blow off anything?

i dont have a cro thats a major problem..
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Old 4th February 2013, 04:22 PM   #16
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Quote:
Originally Posted by ezavalla View Post
It is a Zobel network, not a Linkwitz-Riley one


Damned, You are right.



Linkwiz-Riley we use in filters, as in active crossovers, speaker crossovers and like theese.

I am truly embarrased
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Last edited by TANDBERGEREN; 4th February 2013 at 04:24 PM.
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Old 4th February 2013, 04:23 PM   #17
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did anybody faced such prob before? whats the solution now?
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Old 4th February 2013, 04:36 PM   #18
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Waiting for an answer to what the value of the ZOBEL-networks components were.
I can't really understand such rolloff with correct values there.
One could also give the output inductor a check.

Ah, You have posted that too.
.18uH is it measured, or have you just picked one from a supplier?
Tried with 3,9Ohm in paralell?
Shuld push the roll-off even higher, but 14Khz is extremely low.
What kind of feedback is used?
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Last edited by TANDBERGEREN; 4th February 2013 at 04:41 PM.
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Old 4th February 2013, 04:44 PM   #19
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here is the schematic you can see the output stage..
Imageshack - lme49810.jpg
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Old 4th February 2013, 04:49 PM   #20
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C12 and C13 is in place, and with the correct values?

I am thinking there must be a feedback problem here, or does the R31 get hot as H***?
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