I'm sorry, but the amp needs a zobel - diyAudio
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Old 6th August 2004, 12:39 PM   #1
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Lightbulb I'm sorry, but the amp needs a zobel

Long time ago I tested zobels, because I had bad results with direct output and my Kimber 4TC speaker cables.
The amp was very picky with cables and speakers.
The best result I had was two 0.47 ohm/3w carbon resitors in series with the output.
I tested a resistor and cap to ground, with several values, and it didn't cure the problem.
What I didn't test was both.
I tested some days ago, several values, and I like it.
This time I'm not going into details, or this thread will degenerate into a big discussion.
Try it, listen and tell us what you think.
Note: by speaker terminals I mean on the amp.

This is what I have now, here it is:
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Old 6th August 2004, 03:05 PM   #2
Mad_K is offline Mad_K  Norway
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I prefer it without the 0,47R resistors, but the zobel is mandatory. It didn't take much listening to reveal that the chip needs a zobel at the output. Place the zobel as close to the chip as possible
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Old 6th August 2004, 03:21 PM   #3
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Quote:
Originally posted by Mad_K
I prefer it without the 0,47R resistors, but the zobel is mandatory.
I can't detect any side effect with the series resistors, at least with the cables and speakers I tested.

Quote:
Originally posted by Mad_K
Place the zobel as close to the chip as possible
I said that the zobel can be on the amp's speaker terminals because it's easier for people to test it.
Ideally it should be near the chip, but on some implementations that may not be practical.
I will put it definitively near the chip.

Thanks for your feedback.
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Old 6th August 2004, 04:01 PM   #4
Sheldon is offline Sheldon  United States
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Or use a LP filter, ala Joe Rasmussen, on the input?

Sheldon
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Old 6th August 2004, 04:04 PM   #5
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No, Sheldon, that's different, nothing to do with this...
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Old 6th August 2004, 04:19 PM   #6
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by carlosfm
No, Sheldon, that's different, nothing to do with this...
Ok, guess this is where partial knowledge is dangerous. I thought the function of the Zobel was to prevent instability of the amp due to high frequency (above audio) oscillation. If you prevent those frequencies from entering the stream, don't you circumvent the problem? Or have I got that all wrong?

thanks,
Sheldon
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Old 6th August 2004, 04:20 PM   #7
sam9 is offline sam9  United States
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I wonder if the .47 resistors are inductive. Maybe you have inadvertently added an output inductor as well.
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Old 6th August 2004, 04:28 PM   #8
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Quote:
Originally posted by sam9
I wonder if the .47 resistors are inductive. Maybe you have inadvertently added an output inductor as well.
That's why I use carbon and not bobinated resistors.
You shouldn't use bobinated resistors on the output.
For inductance and other nasties, we have the speaker cables, speaker crossovers...
The zobel makes the amp more immune to these nasties.

Sheldon, this has to be done at the output.
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Old 6th August 2004, 05:25 PM   #9
sam9 is offline sam9  United States
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Sigh! I should read more carefully.
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Old 6th August 2004, 05:46 PM   #10
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Quote:
I'm sorry, but the amp needs a zobel
Maybe, but which chip? The 1875 seems to really need it; the 3875 might need it with some combinations of speakers and cables.


Quote:
That's why I use carbon
These carbon resistors have such a pronounced 'voice' of their own that it's absolutely impossible to distinguish the contribution of the zobel and the rose tint of the carbons. Great if you like warm and cushy sound.
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