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Old 22nd April 2007, 06:05 PM   #11
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Default Re: Amp oscillates with new speakers

Quote:
Originally posted by hajame
....
This is more obvious when the volume is high.
...
As volume pot is bofere an amp, then the problem is before an amp.
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Old 22nd April 2007, 06:49 PM   #12
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just out of curiosity...... what is the damping factor of the amp? since it uses global feedback i would assume it's at least 100..... you could also have a problem with the dc servo, since the dc servo is also part of the ac feedback loop. usually dc servos are in their own separate feedback loop, and it's rare that they cause problems, but if your dc servo happens to have some gain at 300 hz along with a phase inversion, you could have a low frequency instability problem. post the schematic for the dc servo.....
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Old 22nd April 2007, 11:52 PM   #13
hajame is offline hajame  Hong Kong
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Dear All,

I have read the methods you guys provided and I consider that adding network to the output is more convinient to experiment.
But I don't think there are bad caps in the power supply because the problem exists in both channels simutaneousely in playing CDs. And it has no problem with the previous speakers so I think the interation between my new speakers and the amp introduces this problem.
I am posting all the component values and the dc servo schematics for your analysis before I take the final method. Thanks a lot!
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Old 22nd April 2007, 11:57 PM   #14
hajame is offline hajame  Hong Kong
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Here is the power supply schmatics.
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Old 23rd April 2007, 12:24 AM   #15
hajame is offline hajame  Hong Kong
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The part list of the amp circuit:
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Old 23rd April 2007, 12:26 AM   #16
hajame is offline hajame  Hong Kong
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Part list of the DC servo
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Old 23rd April 2007, 01:43 AM   #17
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Do you have a zobel network at the speaker terminals????
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Old 23rd April 2007, 06:33 AM   #18
hajame is offline hajame  Hong Kong
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Quote:
Originally posted by Leolabs
Do you have a zobel network at the speaker terminals????

I am trying a zobel network of 8 ohm and 0.1uF. There seems to be effective but the 200-300 range is still a little muddy.
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Old 23rd April 2007, 03:28 PM   #19
ppa is offline ppa  Italy
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for knowing if LC network will work well it's sufficient that you connect a resistance of a few ohm in series to the loudspeaker, if the sound is cleaned up then can you connect the LC network.
Obviously consider you that one resistance in series to the loudspeaker changes its frequency response.


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Old 23rd April 2007, 05:11 PM   #20
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What value are the resistors in the power supply filter for the input circuit? That kind of front end has a pretty bad power supply rejection, all designs I have seen have used regulated power supplies for the front end... Does the frequency change if you change the value of those resistors or filter capacitors for the input stage?
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