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Old 11th May 2010, 12:09 PM   #51
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Quote:
Originally Posted by vijay_meyou View Post
Hi apex,

Do you have any seperate x over ciruit for sub pre? i want to connect left + right channel to X over and output to subwoffer amp. Because DVD player sub woofer out is not comming in all DVDs. I think some AC3 DTS settings differs for different DVDs
Subwoofer filter have low cut on 30Hz, boost +4dB up to 100Hz, also have level and X-over frequency adjust from to 80-250Hz, stereo inputs from speakers and stereo inputs from line signal, output for amp... like on pics with Kelvin amp (post #31).
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Old 12th May 2010, 09:31 AM   #52
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Originally Posted by apexaudio View Post
Subwoofer filter have low cut on 30Hz, boost +4dB up to 100Hz, also have level and X-over frequency adjust from to 80-250Hz, stereo inputs from speakers and stereo inputs from line signal, output for amp... like on pics with Kelvin amp (post #31).
Hi Apex !

Thanks for your replay. your X over PCB looks small and incredable with all those controls to vary frequency. Can you post your X over Schematic and layout

Thanks
vijay
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Old 12th May 2010, 01:50 PM   #53
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So many wrong quasi NMOS output stages, look on service manuals of commercial products, there you can find some solutions for diy, before you buy 8-12 fets per channel. If you want to use NMOS outputs, for Hi-Fi single pair is enough, for PA use BJTs.
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Old 12th May 2010, 02:29 PM   #54
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Originally Posted by vijay_meyou View Post
Hi Apex !

Thanks for your replay. your X over PCB looks small and incredable with all those controls to vary frequency. Can you post your X over Schematic and layout

Thanks
vijay
I think all my PCBs looks incredable
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Old 12th May 2010, 02:49 PM   #55
maouna is offline maouna  Greece
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Try adding another diode in parallel with D1 but in the opposite direction
what is the purpose of these two opposite-parallel diodes ??
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Old 12th May 2010, 03:05 PM   #56
Eva is offline Eva  Spain
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The diodes reduce the amount of time that the output remains stuck to the rails after clipping. This is achieved by preventing the voltage across C3 from deviating too much from what it should be when the amplifier is into linear operation.

Without diodes, C3 is charged and discharged in an uncontrolled way during clipping, and the output will remain stuck to the supply rails until the voltage returns to the normal value (which takes some time).
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Old 12th May 2010, 03:27 PM   #57
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The diodes reduce the amount of time that the output remains stuck to the rails after clipping. This is achieved by preventing the voltage across C3 from deviating too much from what it should be when the amplifier is into linear operation.

Without diodes, C3 is charged and discharged in an uncontrolled way during clipping, and the output will remain stuck to the supply rails until the voltage returns to the normal value (which takes some time).
Thank's to Eva, schematics is in post #31. This is condition of overload with hard cliping (more than 10%THD), not usual home listening.
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Last edited by apexaudio; 12th May 2010 at 03:34 PM.
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Old 12th May 2010, 07:13 PM   #58
maouna is offline maouna  Greece
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and what if i dont use C3-R5??most schematics i have seen, dont have this network.

will i have to use these diodes again?
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Old 12th May 2010, 08:06 PM   #59
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Originally Posted by maouna View Post
and what if i dont use C3-R5??most schematics i have seen, dont have this network.

will i have to use these diodes again?
Don't change anything on this schematics, it just look like "most schematics" for diy, but take a better look, this is high performance amplifier, and you must use C3-R5, don't try to make it simpler, it is imposible if you want to have better amp than "most".
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Old 13th May 2010, 12:00 AM   #60
Eva is offline Eva  Spain
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C3 and R5 are part of a pole-zero compensation system.

The advantage of pole-zero compensation is higher open loop gain at mid-high frequencies, which translates into lower high-frequency distortion and lower output impedance, without any substantial degradation in stability. The usual rise in output impedance and distortion above 1khz in traditional amplifiers is moved upwards, it does not start until a higher frequency (may be as high as 20khz resulting in flat THD and constant damping factor, which makes the amplifier closer to "ideal").

Pole-zero compensation is rarely used in DIY amplifiers because it's a bit more complex than the traditional dominant pole compensation and harder to implement for people with no knowledge about feedback control loop theory (or even without an oscilloscope).
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