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Old 4th May 2011, 01:27 PM   #1081
kubeek is offline kubeek  Czech Republic
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You can always use a DC servo, maybe with some cap to a rail to kick the amp into oscillation on startup.
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Old 4th May 2011, 03:44 PM   #1082
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In feedbeck my resistor are 10K not 1K because I like more gain, but I followed Laci's sugestion about cap in series with R7 and everything is ok. I dont have DC offset and noise but I was use 100uF
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Old 4th May 2011, 05:32 PM   #1083
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I have followed your suggestion. DC offset is OK. Noise is less without any connection at input. But when I just connected CD in but did not play any song, these is noise.Why?
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Old 4th May 2011, 05:57 PM   #1084
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Quote:
Originally Posted by opor View Post
I have followed your suggestion. DC offset is OK. Noise is less without any connection at input. But when I just connected CD in but did not play any song, these is noise.Why?
Do you use a shielded cable? Unshielded cable will pick up noise.
Look for earth loops too, because it will pick up every radioation from the board or output coil. Connect common to safety earth pole on the AC plug.
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Old 4th May 2011, 07:19 PM   #1085
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Maybe is a cable, try to short input and gnd without cable direct on pcb, you must not have any noise if everuthing is ok. If ypu have, look up at conections on input and output fets. I didnt try with 1nF on input, I try with 4.7n and 100p in paralel just like in previous desing
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Old 5th May 2011, 03:56 AM   #1086
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Default Overload protection without shunt res.

Hi to all
One good engineer from my country was recommended to me cheap and very good solution for overload protection without SHUNT resistor. He used this schmatic many times (for 30 years) and this is good because can use with any amplifier including this.

Actually its electronic fuse, very fast and stable and good because it has trim pot for setting current when amplifier will shut down.

Look at the schematic and read the word document that I atached. I belive you can understand because I use google translate from serbian to english.

What are you think?
Regards
Attached Images
File Type: gif elecfuse.gif (10.2 KB, 989 views)
Attached Files
File Type: doc Overcurent protection.doc (30.0 KB, 184 views)
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Old 5th May 2011, 11:09 AM   #1087
opor is offline opor  Thailand
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Quote:
Originally Posted by Dzony988 View Post
Maybe is a cable, try to short input and gnd without cable direct on pcb, you must not have any noise if everuthing is ok. If ypu have, look up at conections on input and output fets. I didnt try with 1nF on input, I try with 4.7n and 100p in paralel just like in previous desing
I short input to ground noise is less but still noticeable. And I use shielded input cable.So cable is not a problem.
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Old 5th May 2011, 11:09 AM   #1088
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Quote:
Originally Posted by Dzony988 View Post
Hi to all
One good engineer from my country was recommended to me cheap and very good solution for overload protection without SHUNT resistor. He used this schmatic many times (for 30 years) and this is good because can use with any amplifier including this.

Actually its electronic fuse, very fast and stable and good because it has trim pot for setting current when amplifier will shut down.

Look at the schematic and read the word document that I atached. I belive you can understand because I use google translate from serbian to english.

What are you think?
Regards
"without shunt resistor" ???
There is a 0,3 Ohm + transistor shunt in your schematic.
It will dissipate more than a simple 0,033 Ohm shunt (for 20A current sense).
So this idea is idiotic. You can do better with only a shunt and 2 transistors per side.
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Old 5th May 2011, 11:15 AM   #1089
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Quote:
Originally Posted by opor View Post
I short input to ground noise is less but still noticeable. And I use shielded input cable.So cable is not a problem.
Could you post pictures of your setup? (and about the layout too)
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Old 5th May 2011, 11:27 AM   #1090
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Click the image to open in full size.
Here is my idea to decrease shunt dissipation. Current treshold can be set by the trimpot. By using a JFET the voltage need at shunt resistor is decreased (from 0,6-0,7V, to <0,2V), so as dissipation.
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